MicroBiology MCQs with Answer and Explanations | Chapter 66

Answer: Anaerobic bacterial disease

Actinomycosis is a rare bacterial infection caused by Actinomyces species, which are anaerobic bacteria commonly found in the mouth, digestive tract, and female genital tract. The infection typically affects the face, neck, chest, or abdomen, and can form abscesses and sinus tracts.

The other options are incorrect:

• Aerobic bacterial disease: This refers to a disease caused by bacteria that require oxygen to survive. Actinomyces bacteria, on the other hand, are anaerobic.
• Aerobic fungal disease: This describes a disease caused by fungi that need oxygen to grow. Actinomycosis is not a fungal infection, but a bacterial one.
• Anaerobic fungal disease: While there are some anaerobic fungi, they are very rare and not known to cause actinomycosis.

Answer: The tetanospasmin component of the exotoxin act on the post-synaptic neurones and prevents impulse transmission

Tetanus toxin, produced by Clostridium tetani bacteria, binds to nerve cells and disrupts the transmission of signals between nerves and muscles. This leads to the characteristic muscle stiffness and spasms associated with tetanus.

The other options are incorrect:

• Clostridium tetani travels via the nerves to the anterior horn dells in spinal cord: While the toxin affects the spinal cord, Clostridium tetani bacteria itself doesn’t travel there directly through nerves. Spores from the bacteria enter the body through a wound and germinate in nearby tissues, releasing the toxin that reaches the spinal cord through the bloodstream.
• The patient should be given tetanus toxoid intravenously: Tetanus toxoid is a vaccine used for prevention, not treatment. Tetanus treatment typically involves tetanus immune globulin, antibiotics, and muscle relaxants. Tetanus toxoid is usually administered intramuscularly.
• Causes positive Nagler reaction: The Nagler reaction is a test used to diagnose syphilis, not tetanus. Tetanus diagnosis is based on clinical symptoms and history of potential exposure.

Answer: Does not produce any pigment

Pseudomonas aeruginosa is a type of bacteria known for producing a blue-green pigment called pyocyanin. This pigment is not the primary cause of its virulence, but it’s a characteristic feature that can aid in identification.

The other options are incorrect:

• Produces heat stable enterotoxin: Pseudomonas aeruginosa is not associated with the production of enterotoxins, which are toxins released in the intestines causing diarrhea.
• Causes Shanghai fever: Shanghai fever, also known as leptospirosis, is a bacterial disease caused by Leptospira bacteria, not Pseudomonas aeruginosa.
• Cannot be destroyed at 55 degrees Celsius for 1 hour: While some strains might exhibit higher heat tolerance, Pseudomonas aeruginosa is generally susceptible to heat and can be inactivated at temperatures around 55°C (131°F) within an hour.

Answer: All stains are highly susceptible to penicillin

Neisseria gonorrhoeae has become increasingly resistant to antibiotics, including penicillin. While penicillin was once the primary treatment for gonorrhea, many strains are now resistant, necessitating alternative antibiotic regimens.

The other options are incorrect:

• Most common cause of urethritis in males: N. gonorrhoeae is indeed a common cause of urethritis (inflammation of the urethra) in both males and females.
• Wide spread axoregnic strains cause disseminated gonococcal infection: This statement is generally true. Axoregnic strains can ascend the reproductive tract and cause disseminated gonococcal infection (DGI) with complications throughout the body.
• Found exclusively in human beings: N. gonorrhoeae is a human-specific pathogen, meaning it primarily infects humans and doesn’t have a known animal reservoir.

Answer: Ziehl-Neelsen stain

Ziehl-Neelsen stain, also known as acid-fast stain, is the most effective staining method for visualizing Mycobacterium tuberculosis. This staining method utilizes a carbol-fuchsin dye, which penetrates the thick lipid-rich cell wall of mycobacteria, making them resistant to decolorization with acid-alcohol, and thus appear as bright red or pink against a blue background under the microscope.

The other options are incorrect:

• Gram’s stain: This is a common stain used to differentiate between gram-positive and gram-negative bacteria. Mycobacterium tuberculosis wouldn’t be easily visualized with Gram’s stain due to its unique cell wall composition.
• H & E stain (Hematoxylin and Eosin stain): This stain is commonly used in tissue biopsies to visualize general tissue structures. While it might show inflammatory cells associated with tuberculosis infection, it wouldn’t definitively identify Mycobacterium tuberculosis itself.
• PAS stain (Periodic Acid-Schiff stain): This stain is used to identify carbohydrates present in certain structures like fungi and some bacteria. While Mycobacterium tuberculosis has a complex cell wall, PAS stain wouldn’t be the optimal choice for definitive diagnosis.

Answer: Clostridium tetani

Clostridium tetani is the bacteria responsible for tetanus. Tetanus is a severe and potentially fatal disease characterized by muscle stiffness and spasms. This is caused by a potent neurotoxin produced by C. tetani called tetanospasmin. Tetanospasmin blocks the release of neurotransmitters essential for muscle relaxation, leading to the characteristic symptoms of tetanus.

The other options are incorrect:

• Pseudomonas: While some Pseudomonas species produce toxins, they are not known for potent exotoxins compared to C. tetani.
• Shigella: Shigella bacteria produce toxins called Shiga toxins, which cause diarrhea and inflammation in the intestines. Shiga toxins are potent, but their effects are localized to the gut compared to the widespread neurological effects of tetanospasmin.
• Klebsiella: Klebsiella can produce various toxins, but they are generally not considered as potent as tetanospasmin. The severity of Klebsiella infections depends on various factors, not just toxin production.

Answer: Borrelia vincenti

Fusospirochetosis is an infection caused by a synergistic relationship between two types of bacteria: fusiform bacteria and spirochetes. While several spirochete species can be involved, Borrelia vincentii is the most commonly associated one with fusospirochetosis.

The other options are incorrect:

• Treponema pallidum: This spirochete is the causative agent of syphilis, a sexually transmitted disease. It’s not typically linked to fusospirochetosis.
• Treponjema pertenue: This is another treponema species responsible for yaws, a tropical skin disease. It’s not associated with fusospirochetosis.
• Borrelia burgdorferi: This spirochete causes Lyme disease, which is transmitted by ticks. While Borrelia species can be broadly categorized, B. burgdorferi is not the primary culprit in fusospirochetosis.

Answer: Streptococcus sanguis

Streptococcus sanguinis is a commensal bacterium commonly found in the oral cavity and is considered beneficial to the host. It competes with pathogenic bacteria for attachment sites on teeth and oral tissues, thus playing a protective role in oral health. Additionally, S. sanguinis produces hydrogen peroxide, which can inhibit the growth of other bacteria.

The other options are incorrect:

• Porphyromonas gingivalis: This bacterium is a known pathogen associated with gum disease (periodontitis). It contributes to inflammation and breakdown of gum tissue.
• Treponema denticola: Similar to P. gingivalis, Treponema denticola is another harmful bacterium involved in gum disease progression.
• Spirochetes: While not all spirochetes are detrimental, some, like the ones mentioned in the incorrect options (Treponema denticola and Borrelia vincentii), can be pathogenic. Streptococcus sanguis, on the other hand, can be a beneficial part of the oral microbiome when present in a healthy balance.

Answer: Legionella

Legionella is a genus of Gram-negative bacteria that are known to cause Legionnaires’ disease, a severe form of pneumonia, as well as Pontiac fever, a milder flu-like illness. Legionella bacteria grow on selective media such as charcoal yeast extract medium, which is used to culture Legionella species from clinical samples.

The other options are incorrect:

• H. influenza: While H. influenza can cause respiratory infections, it typically doesn’t grow on BCYE medium.
• Moraxella catarrhalis: This bacterium can sometimes cause respiratory infections, but it also doesn’t grow well on BCYE medium.
• Burkholderia cepacia: This bacterium is an opportunistic pathogen that can cause infections in immunocompromised individuals. However, it doesn’t grow on BCYE medium and wouldn’t be the likely culprit based on the patient’s symptoms and the growth medium used in the culture.

Answer: Shigella sonnei

Shigella sonnei is an enteric organism that is anaerogenic, meaning it does not produce gas from carbohydrate fermentation, and non-motile, lacking flagella for movement. It is a causative agent of bacillary dysentery (shigellosis), typically associated with symptoms such as bloody diarrhea, fever, and abdominal cramps

The other options are incorrect:

• Salmonella typhi: This bacterium, responsible for typhoid fever, is facultatively anaerobic, meaning it can survive and grow with or without oxygen. It is also motile.
• Proteus mirabilis: This is a motile, facultatively anaerobic bacterium commonly associated with urinary tract infections. It can be differentiated from Shigella sonnei by its ability to swarm on agar plates and ferment lactose.
• Klebsiella pneumoniae: This is a motile, facultatively anaerobic bacterium that can cause various infections, including pneumonia and urinary tract infections.

Answer: Bartonella henselae

Cat-scratch disease, also known as cat-scratch fever, is caused by the bacterium Bartonella henselae. This bacterium is transmitted to humans through scratches or bites from infected cats, particularly kittens.

The other options are incorrect:

• Chlamydia trachomatis: This bacterium is the causative agent of trachoma, an eye infection, and doesn’t cause cat-scratch disease.
• Donovania granulomatis: This bacterium causes Donovanosis, a sexually transmitted infection with skin lesions, and is not linked to cat-scratch disease.
• Hemophilus ducreyi: This bacterium causes chancroid, a sexually transmitted infection with ulcers, and is not involved in cat-scratch disease.

Answer: Group A steptococci

Erysipelas is a bacterial skin infection caused by Group A Streptococcus (Streptococcus pyogenes), a bacterium commonly found on the skin and in the throat. It typically affects the superficial layers of the skin, resulting in characteristic symptoms such as redness, swelling, warmth, and pain.

The other options are incorrect:

• Group B staphylococci: While group B Streptococcus (Strep B) can cause various infections, particularly in newborns and pregnant women, it’s not the usual culprit behind erysipelas.
• Gonococci: Neisseria gonorrhoeae, also known as gonococci, is a bacterium responsible for gonorrhea, a sexually transmitted disease. It doesn’t cause erysipelas.
• Pneumococci: Streptococcus pneumoniae, or pneumococci, can cause pneumonia, meningitis, and other infections but isn’t typically associated with erysipelas.

Answer: Pseudomonas aerogenosa

Pseudomonas aeruginosa is an obligate aerobe, meaning it requires oxygen to survive and grow. It utilizes oxygen in its metabolic processes for energy production.

The other options are incorrect:

• E. coli (Escherichia coli): E. coli is a facultative anaerobe. It can grow in both aerobic (with oxygen) and anaerobic (without oxygen) environments, depending on the availability of oxygen.
• Proteus: Proteus species, like Proteus mirabilis, are also facultative anaerobes, able to adapt their metabolism based on oxygen presence.
• Corynebacterium diphtheriae (causing diphtheria): This bacterium is another facultative anaerobe, capable of both aerobic and anaerobic respiration.

Answer: Enterotoxin F

Staphylococcal toxic shock syndrome (STSS) is a rare but serious condition caused by the release of toxins produced by certain strains of Staphylococcus aureus bacteria. Enterotoxin F (SEF) is one of the toxins produced by Staphylococcus aureus that is associated with toxic shock syndrome.

The other options are incorrect:

• Enterotoxin A: Enterotoxin A (SEA) is another toxin produced by Staphylococcus aureus, but it is more commonly associated with staphylococcal food poisoning rather than toxic shock syndrome. Therefore, this option is incorrect.
• Enterotoxin B: Enterotoxin B (SEB) is a superantigen produced by Staphylococcus aureus and can contribute to toxic shock syndrome-like symptoms, but it is not typically associated with Staphylococcal toxic shock syndrome (STSS). Therefore, this option is incorrect.
• Enterotoxin D: Enterotoxin D (SED) is produced by some strains of Staphylococcus aureus and can contribute to various staphylococcal infections, but it is not typically associated with Staphylococcal toxic shock syndrome (STSS). Therefore, this option is incorrect

Answer: B.Cereus

Bacillus cereus is a bacterium commonly found in soil and food. It produces heat-resistant spores that can survive cooking and cause food poisoning if contaminated food is not properly stored or reheated. Symptoms of B. cereus food poisoning typically include abdominal pain, vomiting, and diarrhea, which can occur within a few hours after consuming contaminated food.

The other options are incorrect:

• Staphylococcus aureus: Staphylococcus aureus can also cause food poisoning, characterized by symptoms such as nausea, vomiting, abdominal cramps, and diarrhea. However, symptoms usually develop within a few hours after consuming contaminated food, similar to Bacillus cereus
• Salmonella: Salmonella is a bacterium commonly associated with foodborne illness. While it can cause symptoms such as abdominal pain and vomiting, the onset of symptoms typically occurs within 6 to 72 hours after consuming contaminated food, which does not align with the scenario described.
• Clostridium botulinum: Clostridium botulinum produces a potent neurotoxin that causes botulism, a severe and potentially life-threatening illness. However, symptoms of botulism typically develop within 12 to 36 hours after consuming contaminated food, not within 6 hours as described in the scenario.

Answer: Proteus

The Weil-Felix test is a historical serological test used to diagnose rickettsial infections. However, it is not very specific and has largely been replaced by more accurate methods. The test relies on the presence of cross-reactive antigens between Rickettsia bacteria, the cause of rickettsial infections, and certain strains of Proteus bacteria.

The other options are incorrect:

• E. coli: Escherichia coli doesn’t share the specific antigens necessary for the Weil-Felix reaction.
• Haemophilus: Similar to E. coli, Haemophilus species don’t possess the cross-reactive antigens required for the Weil-Felix test.
• Staphylococcus: Staphylococcus bacteria also lack the specific antigens needed for the Weil-Felix reaction.

Answer: Bordet Gengou medium

This is a specialized charcoal-containing medium specifically designed for the cultivation of Bordetella pertussis, the causative agent of whooping cough. It provides the necessary nutrients and factors required for the growth of this fastidious bacterium.

The other options are incorrect:

• Wilson Blair medium: This medium is used for motility testing of various bacteria and wouldn’t be suitable for the primary isolation of Bordetella pertussis.
• Bile broth: While some bile broths can be used for enrichment of certain bacteria, they wouldn’t be ideal for primary isolation of Bordetella pertussis, which is sensitive to bile salts.
• Robertson cooked meat medium: This medium is used for the cultivation of anaerobic bacteria and wouldn’t be appropriate for Bordetella pertussis, which is an aerobic bacterium.

Answer: Gram positive bacteria

Teichoic acids are a major component of the cell wall in most Gram-positive bacteria. They are polymers of glycerol phosphate or ribitol phosphate linked by phosphodiester bonds. Teichoic acids contribute to the overall structure and rigidity of the Gram-positive cell wall, helping it resist osmotic pressure and the action of certain antibiotics.

The other options are incorrect:

• Gram-negative bacteria: The cell wall of Gram-negative bacteria has a different structure and doesn’t contain teichoic acids. Their cell wall is composed mainly of peptidoglycan and an outer membrane with lipopolysaccharides (LPS).
• Yeast: Yeast cell walls are primarily made of glucans, mannan, and chitin, which are different from teichoic acids.
• Protozoa: Protozoa are single-celled eukaryotes and don’t have cell walls in the same way that bacteria do. Their outer covering may be composed of various materials depending on the specific protozoa.

Answer: Rabbit testis only

Pathogenic treponemes, such as Treponema pallidum (causing syphilis), are notoriously difficult to cultivate in vitro (outside a living host). They have specific growth requirements that haven’t been fully replicated in artificial media.

The other options are incorrect:

• Tissue culture: While some bacteria can be grown in tissue culture systems, current methods haven’t been successful for maintaining and propagating pathogenic treponemes in this way.
• Chick embryos: Chick embryos have been used historically for cultivating some pathogens, but they are not suitable for pathogenic treponemes.
• Artificial media: Despite ongoing research, artificial media formulations haven’t yet been able to consistently support the growth of pathogenic treponemes for extended periods.

Answer: Spirochaete

Borrelia vincentii is a type of bacteria belonging to the genus Borrelia. This genus is characterized by its members being spiral-shaped bacteria, known as spirochetes.

The other options are incorrect:

• Mycoplasma: Mycoplasma are the smallest self-replicating cells and lack a cell wall.
• Mycobacteria: Mycobacteria are known for their waxy cell wall and are responsible for diseases like tuberculosis.
• Chlamydia: Chlamydia are obligate intracellular bacteria, meaning they can only survive and replicate inside host cells.

Answer: Francisella spp

Francisella species are Gram-negative coccobacilli that are oxidase positive. They are known to cause zoonotic infections, particularly tularemia, which can affect various animals, including humans. Francisella tularensis is the causative agent of tularemia.

The other options are incorrect:

• Pasteurella spp.: While some Pasteurella species are oxidase-positive, they are less commonly associated with PUO in humans compared to Francisella tularensis.
• Bartonella spp.: Bartonella species are typically associated with different clinical presentations, like cat-scratch disease, and wouldn’t be the most likely culprit in this scenario.
• Brucella spp.: Brucella species are also Gram-negative but are usually oxidase-negative. Brucellosis, the disease they cause, can cause PUO, but the veterinary profession wouldn’t be the highest risk group compared to Francisella.

Answer: Bile solubility

Pneumococcus (Streptococcus pneumoniae) can be differentiated from other streptococci by its susceptibility to bile. Pneumococci are bile soluble, meaning they lyse in the presence of bile salts, while most other streptococci are bile resistant.

The other options are incorrect:

• Type of hemolysis: Both pneumococcus and other streptococci may exhibit alpha or beta hemolysis on blood agar plates, making hemolysis type an unreliable method for differentiation.
• Gram staining: Both pneumococcus and other streptococci are Gram-positive cocci, and their Gram staining characteristics are similar.
• Growth characteristics: While pneumococcus may have specific growth characteristics, these characteristics alone are not sufficient for differentiation from other streptococci.

Answer: Cell wall carbohydrate

Streptococcal classification primarily relies on the Lancefield grouping system, which differentiates streptococci based on the presence and type of specific carbohydrates in their cell wall. This system uses the capital letters A through V (excluding I and J) to designate different serological groups.

The other options are incorrect:

• M Protein: M protein is a virulence factor present on the surface of some group A streptococci (GAS). While it can be used for further characterization within a specific group, it’s not the primary basis for classification across all streptococci.
• Cultural characteristics: Although growth characteristics like hemolysis patterns on blood agar can be helpful for initial identification, they are not the most definitive method for classification across all Streptococcus species.
• Bile Solubility: Bile solubility can be a characteristic used to differentiate between certain enterococcal and non-enterococcal streptococci. However, it wouldn’t be sufficient for classifying all streptococcal species.

Answer: Foot paid on nine branded armadilo

Leprosy bacilli, Mycobacterium leprae, are notoriously difficult to cultivate in vitro (outside a living host). However, the nine-banded armadillo (Dasypus novemcinctus) is a unique animal model that can be susceptible to leprosy infection and allows for the growth of M. leprae.

The other options are incorrect:

• Tail of guinea pig: Guinea pigs are not natural hosts for M. leprae and wouldn’t be suitable for cultivation.
• Testes of albino rats: Similar to guinea pigs, albino rats are not susceptible to leprosy, and their testes wouldn’t support the growth of M. leprae.
• Testes of guinea pig: As mentioned earlier, guinea pigs are not appropriate hosts for M. leprae cultivation.

Answer: Auramine-Rhodamine stain

Auramine-Rhodamine stain is a fluorescent staining technique used for the rapid detection of acid-fast bacilli (AFB) in sputum samples. It is more sensitive than traditional Ziehl-Neelsen stain and allows for the quick identification of Mycobacterium tuberculosis, the bacterium that causes tuberculosis (TB), under a fluorescence microscope.

The other options are incorrect:

• Ziel-Neelsen stain: This is the traditional method for identifying acid-fast bacilli but takes longer than Auramine-Rhodamine stain.
• Kin Young stain: This stain is used for identifying different types of malaria parasites and wouldn’t be suitable for diagnosing TB.
• Giemsa stain: Giemsa stain is commonly used for visualizing various blood cells and might not be specific enough for detecting Mycobacterium tuberculosis.

Answer: M. tuberculosis

Mycobacterium tuberculosis is the causative agent of tuberculosis (TB), which is a highly prevalent bacterial infection in tropical countries. TB is transmitted through the air when an infected person coughs or sneezes, making it a significant public health concern in regions with densely populated areas and limited access to healthcare resources.

The other options are incorrect:

• M. leprae: Leprosy caused by M. leprae has a worldwide presence but is less common than tuberculosis, especially in tropical regions.
• M. avium intracellulare (MAI): MAI can cause infections, but they are less frequent compared to M. tuberculosis, particularly in tropical areas.
• Kansasii: Mycobacterium kansasii can cause pulmonary infections, but it’s less prevalent than M. tuberculosis, especially in tropical settings.

Answer: Lecithinase

The opacity observed around colonies of Clostridium perfringens is caused by the enzyme lecithinase. This enzyme breaks down lecithin, a phospholipid found in egg yolk, which is often present in the media used to culture C. perfringens.

The other options are incorrect:

• Theta toxin: Theta toxin is one of several toxins produced by C. perfringens, but it’s not directly responsible for the opacity around colonies.
• Desmolase: Desmolases are a category of enzymes that can break down various molecules. While C. perfringens might produce some desmolases, lecithinase is the specific enzyme causing the opacity in this case.
• Cytokinin: Cytokinins are plant hormones and wouldn’t be produced by a bacterium like C. perfringens.

Answer: Clostridium welchii

Clostridium perfringens, historically referred to as Clostridium welchii, is the primary causative organism for gas gangrene. This bacterium produces potent toxins that break down tissues and generate gas, leading to the characteristic symptoms of gas gangrene.

The other options are incorrect:

• Clostridium tetani: Clostridium tetani is responsible for tetanus, a different disease characterized by muscle stiffness and spasms. While both are Clostridium species, they cause distinct illnesses.
• Escherichia coli (E. coli): E. coli is a common inhabitant of the intestines and can cause various gastrointestinal issues, but it’s not associated with gas gangrene.
• Streptococcus faecalis: Streptococcus faecalis is a Gram-positive coccus that can cause various infections, including urinary tract infections and endocarditis. It wouldn’t be the culprit behind gas gangrene.

Answer: All of the above

Rickettsiae are a group of obligate intracellular bacteria, meaning they can only survive and multiply inside the living cells of a host organism. Here’s why all the listed options are true for rickettsiae:

• Multiply within living cell: As obligate intracellular bacteria, rickettsiae lack the machinery to survive and reproduce on their own. They invade host cells, typically endothelial cells lining blood vessels, and replicate within the host cell cytoplasm.
• Transmitted by arthropod vectors: Rickettsiae are transmitted to humans through the bites of infected arthropods like ticks, lice, mites, and fleas. These arthropods serve as vectors, carrying and transmitting the bacteria between animal reservoirs and humans.
• Respond to tetracycline therapy: Tetracycline antibiotics are a mainstay treatment for rickettsial infections. 

Answer: All of the above

A VDRL (Venereal Disease Research Laboratory) test is a non-specific test used to detect antibodies against certain lipids (fatty molecules) present in the blood. While it’s commonly used for syphilis screening, a positive VDRL result can also occur in various other conditions

• Yaws: This bacterial infection caused by Treponema pallidum subspecies pertenue can cause skin lesions and bone deformities. It can lead to a false-positive VDRL test due to the presence of similar antibodies.
• Lepromatous leprosy: This severe form of leprosy caused by Mycobacterium leprae can also lead to a false-positive VDRL test, although the mechanism isn’t fully understood.
• Malaria: Malaria, a parasitic infection caused by Plasmodium species, can sometimes trigger a false-positive VDRL result due to non-specific immune system activation.

Answer: Both third & fourth

Syphilis is typically diagnosed through a combination of tests. The VDRL test is a screening test that detects antibodies to Treponema pallidum, the bacterium that causes syphilis. However, false-positive results can occur. The TPHA test is a confirmatory test that detects specific antibodies to T. pallidum and is more specific than the VDRL test.

The other options are incorrect:

• TPI test (Treponema pallidum immobilization test): The TPI test is an older serological test for syphilis that is less commonly used today. It is not the primary diagnostic investigation for syphilis.
• VDRL test: While the VDRL test is indeed used in the diagnosis of syphilis, it is not the sole diagnostic investigation.
• TPHA test: The TPHA test is a confirmatory test for syphilis but is not typically used alone for diagnosis.

Answer: Staphylococcus epidermis

Prosthetic valve endocarditis occurring within 60 days of surgery is typically caused by coagulase-negative staphylococci, particularly Staphylococcus epidermidis. These organisms are common contaminants of the surgical site and can colonize prosthetic materials, leading to infection.

The other options are incorrect:

• Streptococcus Viridans: Streptococcus viridans can cause subacute infective endocarditis, but it is less commonly associated with prosthetic valve endocarditis, particularly within the first 60 days of surgery.
• Staphylococcus aureus: Staphylococcus aureus is a common cause of acute infective endocarditis, but it is less commonly associated with prosthetic valve endocarditis within the first 60 days of surgery.
• Fungus: While fungal infections can cause prosthetic valve endocarditis, they are less common than bacterial infections, particularly within the first 60 days of surgery.

Answer: Second & Third

Several transport media can be used for stool samples suspected of containing Vibrio cholerae, the bacterium causing cholera.

• Cary Blair Medium: This is a widely used and recommended transport medium for cholera. It contains alkaline peptone broth, which neutralizes stomach acids and promotes the survival of V. cholerae. Additionally, it includes sodium thiosulfate to neutralize chlorine, which might be present in some water sources and could harm the bacteria.
• Venkatraman – Ramakrishnan Medium: This is another effective transport medium for V. cholerae. It utilizes a similar principle of having an alkaline peptone broth base and also incorporates ingredients like glycerol to help preserve the bacteria during transport.

The other options are incorrect:

• Tellurite Medium: While tellurite medium is used for some bacteria, it’s not typically the preferred choice for transporting V. cholerae. Tellurite can inhibit the growth of some strains of V. cholerae.

Answer: All of the above

All the listed bacteria (Bacteroides fragilis, Fusobacterium nucleatum, and Peptostreptococcus anaerobius) are indeed non-spore forming anaerobic bacteria that play a significant role in various disease processes.

• Bacteroides fragilis: This Gram-negative, obligate anaerobic bacterium is a major component of the gut microbiota. However, it can also cause opportunistic infections, particularly intra-abdominal abscesses and surgical site infections.
• Fusobacterium nucleatum: This Gram-negative anaerobic bacterium is part of the oral microbiome. While it can be present as commensal flora, it’s also implicated in periodontal diseases and some systemic infections.
• Peptostreptococcus anaerobius: This Gram-positive anaerobic coccus is another inhabitant of the human microbiome, particularly the gut and oral cavity.

Answer: Streptococcus viridians

Subacute bacterial endocarditis is typically caused by bacteria that are part of the normal flora of the mouth and upper respiratory tract, such as Streptococcus viridans. These bacteria can enter the bloodstream during dental procedures or other activities that disrupt the mucosal barrier, leading to colonization of damaged heart valves and the development of endocarditis.

The other options are incorrect:

• Haemolytic streptococci: Haemolytic streptococci, particularly group A and group B streptococci, are more commonly associated with acute bacterial endocarditis rather than subacute bacterial endocarditis.
• Staphylococcus aureus: Staphylococcus aureus is a common cause of acute bacterial endocarditis but is less commonly associated with subacute bacterial endocarditis.
• Nisseria: Neisseria species, particularly Neisseria gonorrhoeae and Neisseria meningitidis, are not typically associated with endocarditis.

Answer: Tryptophan

Salmonella bacteria, like many other microorganisms, require specific nutrients for growth. Tryptophan is one such essential growth factor required by Salmonella species for their metabolic processes and proliferation.

The other options are incorrect:

• Niacin: Niacin (vitamin B3) is not a growth factor specifically required by Salmonella bacteria. While it is essential for various metabolic processes in humans and other organisms, it is not a primary requirement for Salmonella growth.
• B-12: Vitamin B12 (cobalamin) is not a growth factor specifically needed by Salmonella bacteria. While it is essential for various biological functions, particularly in mammals, it is not directly involved in Salmonella growth.
• Citrate: Citrate is not a growth factor needed by Salmonella bacteria. While some bacteria can utilize citrate as a carbon source, it is not considered an essential growth factor for Salmonella.

Answer: Escherichia coli

Escherichia coli (E. coli) is the most common cause of urinary tract infections (UTIs), accounting for approximately 80-85% of cases. E. coli normally inhabits the intestines but can migrate to the urinary tract, leading to infections, particularly in females due to their shorter urethra.

The other options are incorrect:

• Neisseria gonorrhoeae: Neisseria gonorrhoeae is a bacterium responsible for gonorrhea, a sexually transmitted infection. While it can infect the genitourinary tract, it is less frequently associated with urinary tract infections compared to E. coli.
• T-strain mycoplasma: Mycoplasma genitalium, often referred to as the T-strain mycoplasma, can cause urethritis and other genitourinary tract infections, but it is not as commonly associated with urinary tract infections as E. coli.
• Streptococcus faecalis (Enterococcus faecalis): Streptococcus faecalis is a bacterium commonly found in the gastrointestinal tract and is associated with certain infections, but it is not the primary organism associated with urinary tract infections.

Answer: Prevent their phagocytosis

Phagocytosis is a process where immune cells, such as macrophages, engulf and destroy foreign particles, including bacteria. The capsule can act as a shield, making it harder for phagocytes to recognize and engulf the bacteria.

The other options are incorrect:

• Spore formation: Spore formation is a different process used by some bacteria to survive harsh environmental conditions. Spores are dormant stages that are highly resistant to heat, desiccation, and disinfectants. They are not typically associated with preventing phagocytosis.
• Decreased virulence: While encapsulation might have some indirect effects on virulence (disease-causing ability), it’s not the primary purpose. Some encapsulated bacteria can still be quite virulent.
• Oxygen effect: The oxygen effect refers to the increased susceptibility of certain bacteria to oxygen. Encapsulation might offer some protection from the oxygen effect, but it’s not the main benefit for most bacteria.

Answer: Pili

Pili are short, hair-like protein structures found on many bacteria. They act like tiny hooks that allow bacteria to attach to surfaces, including other cells, which is crucial for colonization and infection.

The other options are incorrect:

• Capsule: Capsules are thicker external layers made of polysaccharides. They can help protect bacteria from desiccation and phagocytosis but are not specifically involved in attachment.
• Flagella: Flagella are long, whip-like structures that bacteria use for movement, not attachment.
• Mesosomes: Mesosomes are infoldings of the plasma membrane inside the bacterial cell. They are not external structures and are not involved in attachment.

Answer: increase in invasiveness

Capsules are structures external to the bacterial cell wall that are composed of polysaccharides or other materials. Capsules play a significant role in bacterial virulence by enhancing resistance to phagocytosis and promoting adherence to host cells and tissues. Loss of capsule can lead to increased invasiveness as the bacteria may more readily penetrate tissues and evade host immune responses.

Incorrect Options:

• Decrease in virulence: Capsules are important virulence factors for many pathogenic bacteria. Loss of capsule typically results in decreased virulence as the bacteria become more susceptible to phagocytosis and less able to adhere to host cells and tissues.
• Loss of infectivity: Capsules contribute to the infectivity of many bacterial pathogens by promoting adherence to host cells and tissues. Loss of capsule would likely lead to a decrease in infectivity rather than an increase.
• Inability to spread through tissue: Capsules facilitate bacterial adherence to host tissues and may also contribute to the ability of bacteria to spread through tissues. Loss of capsule would not necessarily result in an inability to spread through tissue.

Answer: Gas gangrene

Nagler’s reaction is a rapid test used to diagnose infections caused by Clostridium perfringens, a bacterium associated with gas gangrene. This test detects the presence of alpha toxin, a key virulence factor produced by C. perfringens, which contributes to gas production and tissue damage in gas gangrene.

The other options are incorrect:

• Malaria: Malaria is a parasitic disease transmitted by mosquitoes, not a bacterial infection.
• Whooping cough: Whooping cough, also known as pertussis, is caused by the bacterium Bordetella pertussis. While a different type of diagnostic test is used for this bacterial infection, Nagler’s reaction is specific to C. perfringens.
• Wool sorter’s disease: Wool sorter’s disease is another term for anthrax, caused by Bacillus anthracis. Similar to whooping cough, Nagler’s reaction is not used for diagnosing anthrax.

Answer: Auramine and Rhodamine

A combination of Auramine and Rhodamine dyes is commonly used in the fluorescent microscopy technique for detecting Mycobacterium tuberculosis, the bacteria that cause tuberculosis. These dyes bind to the mycolic acids in the cell wall of the bacteria, causing them to fluoresce a bright yellow or orange color under a UV microscope.

The other options are incorrect:

• Acridine orange: While Acridine orange is a fluorescent dye used in various biological applications, it’s not commonly used for detecting Mycobacterium tuberculosis.
• Thioglavin: Thioglavin is another fluorescent dye, but it has applications in other areas like DNA staining and isn’t typically used for diagnosing tuberculosis.
• Congo red: Congo red is a histological stain used for different purposes, not for detecting bacteria in general and not specifically for Mycobacterium tuberculosis.

Answer: Anaerobic, gram positive, non-acid fast bacteria.

Actinomycosis is a chronic bacterial infection primarily caused by Actinomyces species, which are anaerobic, gram-positive, filamentous bacteria. These bacteria typically form branching filaments resembling fungal hyphae and can cause localized or disseminated infections in humans, commonly involving the head, neck, thorax, and abdomen.

The other options are incorrect:

• Fungus: Actinomycosis is a bacterial infection, not a fungal one. Fungal infections are caused by organisms like molds and yeasts.
• Acid fast, non-motile bacillus: While some bacteria share some of these characteristics, like Mycobacterium tuberculosis being acid-fast, they are not the cause of Actinomycosis. Acid-fast bacteria have a unique cell wall structure that retains specific stains.
• Retrovirus: Retroviruses are a type of virus that uses RNA as its genetic material. They are not involved in bacterial infections like Actinomycosis.

Answer: Able to grow in the presence of absence of oxygen

Facultative anaerobic bacteria have the metabolic flexibility to grow in environments with or without oxygen. In the presence of oxygen, they can perform aerobic respiration, utilizing oxygen as the terminal electron acceptor. In the absence of oxygen, they can switch to fermentation or anaerobic respiration, utilizing alternative electron acceptors or pathways.

The other options are incorrect:

• Unable to grow in the presence of oxygen: This describes obligate anaerobes, bacteria that are harmed or even killed by oxygen.
• Unable to grow in the absence of oxygen: This describes obligate aerobes, bacteria that require oxygen for survival and cannot ferment.
• Able to grow in the presence of carbon dioxide: While some bacteria can utilize carbon dioxide for growth, this characteristic doesn’t define facultative anaerobes. Many types of bacteria can use carbon dioxide, regardless of their oxygen requirement.

Answer: Alpha hymolytic streptococci (S. viridans)

Alpha hemolytic streptococci, specifically Streptococcus viridans, are a common inhabitant of the throat and tonsils in humans. They are part of the normal flora, meaning they reside in these areas without causing harm under normal circumstances.

The other options are incorrect:

• Staphylococci: While Staphylococci can also be found in the throat and nasal passages, they are less prevalent than alpha hemolytic streptococci.
• Beta hemolytic streptococci: These are a more virulent type of streptococci known to cause strep throat and other infections. They are not typically part of the normal flora.
• Pneumococci: Pneumococci (Streptococcus pneumoniae) can colonize the throat but are less common than alpha hemolytic streptococci. They are also associated with respiratory infections like pneumonia.

Answer: Elaboration of an enzyme that destroy penicillin

Many strains of Staphylococcus aureus have developed resistance to penicillin, a commonly used antibiotic. This resistance is primarily due to the elaboration of an enzyme called beta-lactamase. This enzyme breaks down the beta-lactam ring structure, a crucial component of penicillin and other related antibiotics, rendering them ineffective against the bacteria.

The other options are incorrect:

• Pleomorphism: Pleomorphism refers to the ability of some bacteria to change shape. While some resistant strains might exhibit pleomorphism, it’s not the primary mechanism of resistance in S. aureus.
• Penicillin analogue production: This is not a common resistance strategy for S. aureus. Bacteria typically don’t produce molecules that directly mimic antibiotics.
• Lack of nucleic acid in the cell wall: Staphylococcus aureus, like all bacteria, has nucleic acids (DNA and/or RNA) in its cytoplasm, not the cell wall. Lack of nucleic acids wouldn’t be a factor in antibiotic resistance.

Answer: Salmonella

Salmonella spp. are a major group of intestinal pathogens that are non-lactose fermenters. This means they cannot ferment lactose, a sugar commonly found in milk products. When grown on a culture medium containing lactose, like MacConkey agar, they will not produce acid and therefore won’t change the color of the media.

The other options are incorrect:

• Klebsiella: Klebsiella are typically lactose fermenters. They can ferment lactose and will appear as red colonies on MacConkey agar.
• Escherichia coli (E. coli): Most strains of E. coli are lactose fermenters. However, a small percentage are non-lactose fermenters. While some non-lactose fermenting E. coli can cause intestinal disease, Salmonella is a more common culprit.
• Paracolons: Paracolons is a historical term sometimes used for a group of lactose-fermenting bacteria related to E. coli. They are not typically considered major intestinal pathogens.

Answer: Bacteroides

Bacteroides are obligate anaerobes, meaning they require an oxygen-free environment for growth and survival. They are a common part of the gut microbiome and play a role in digestion but can also be opportunistic pathogens when introduced to other tissues.

The other options are incorrect:

• E. coli (Escherichia coli): E. coli is a facultative anaerobe. It can grow with or without oxygen, depending on the environment.
• Pseudomonas: Most Pseudomonas species are aerobic, meaning they require oxygen for growth.
• Klebsiella: Klebsiella is another facultative anaerobe, able to grow in both aerobic and anaerobic conditions.

Answer: Staphylococcus

Staphylococcus bacteria are known for forming grape-bunch shaped colonies when grown on culture plates. This characteristic appearance is due to the way they divide and remain attached after cell division.

The other options are incorrect:

• Streptococcus: Streptococcus bacteria typically form chains or pairs when they grow, resulting in round or oval colonies, not grape-bunch shaped.
• E. coli (Escherichia coli): E. coli colonies tend to be round, flat, and smooth on culture plates.
• Gonococci: Neisseria gonorrhoeae (gonococci) form mostly coffee bean-shaped pairs, leading to irregular or opaque colonies, not grape-bunch shaped.

Answer: Coagulase

Coagulase is an enzyme produced by some strains of Staphylococcus, particularly Staphylococcus aureus. This enzyme plays a crucial role in the pathogenesis of staphylococcal infections by converting fibrinogen, a soluble blood protein, into fibrin. Fibrin is a key component of blood clots, and its formation helps to localize the infection and evade the immune system.

The other options are incorrect:

• Lysozyme: Lysozyme is an enzyme with antibacterial properties found in tears, saliva, and other bodily fluids. It breaks down bacterial cell walls, so it would actually work against staphylococcal growth and not clot formation.
• Fibrinolysin: Fibrinolysin is an enzyme that breaks down fibrin clots. While some bacteria produce fibrinolysin, it wouldn’t be beneficial for staphylococci to dissolve the clot they are trying to form to localize the infection.
• S protein: S protein is a protein on the surface of Staphylococcus aureus that binds to various host factors, including clotting factors. While it plays a role in staphylococcal virulence, it’s not an enzyme and doesn’t directly induce clot formation.