MicroBiology MCQs with Answer and Explanations | Chapter 67

Answer: Clostridium tetani

Clostridium tetani is the bacterium responsible for causing tetanus, a condition characterized by muscle stiffness and spasms. It produces a potent exotoxin called tetanospasmin, which affects the nervous system.

The other options are incorrect:

• Pseudomonas: This bacterium can cause various infections, including pneumonia, wound infections, and urinary tract infections. However, it is not associated with tetanus.
• Shigella: This bacterium causes shigellosis, a type of diarrheal illness. It does not produce the toxin responsible for tetanus.
• Klebsiella: This bacterium can cause pneumonia, bloodstream infections, and wound infections. It is not known to produce the toxin that causes tetanus.

Answer: Syphilis

The Wassermann test is an antibody test specifically designed to detect syphilis infection. It identifies the body’s immune response to the bacteria Treponema pallidum, the causative agent of syphilis.

The other options are incorrect:

• Gonorrhea: This sexually transmitted disease is caused by the bacteria Neisseria gonorrhoeae. While there are diagnostic tests for gonorrhea, the Wassermann test is not one of them.
• TB (Tuberculosis): This bacterial infection primarily affects the lungs. Diagnosis of TB involves different tests like chest X-rays, sputum analysis, and specific blood tests. The Wassermann test is not used for TB diagnosis.
• Typhoid: This bacterial illness caused by Salmonella typhi is diagnosed through stool cultures and blood tests that identify the specific bacteria. The Wassermann test is not used for typhoid diagnosis.

Answer: in the absence of oxygen

Anaerobic bacteria are those that can live and grow in environments with little to no oxygen. They have adapted metabolic pathways that don’t require oxygen as the final electron acceptor in energy production.

The other options are incorrect:

• in the presence of oxygen: This describes aerobic bacteria, which thrive in environments with oxygen and use it in their metabolism for energy production.
• in the presence of nitrogen: While nitrogen is an abundant element essential for many biological processes, it’s not directly related to bacterial growth based on oxygen availability.
• differential media: This refers to a type of culture medium used in microbiology to distinguish between different types of bacteria based on their specific characteristics. It’s not a growth requirement for anaerobic bacteria.

Answer: It is a unique flexible plastic structure

While the bacterial cell wall does have some flexibility to allow for growth and division, it’s not considered a plastic-like material. It provides a rigid structure for the cell but maintains some elasticity.

The other options are incorrect:

• It consists of a mixed polymer called peptidoglycan: This is true. Peptidoglycan, a mesh-like structure of sugars and amino acids, is the main component of the bacterial cell wall.
• It is the structure principally responsible for the reaction of gram staining: This is true. The gram stain differentiates bacteria based on the structure of their cell wall, with gram-positive bacteria having a thicker peptidoglycan layer.
• It contains D-isomers of amino acids: This is true. Peptidoglycan contains unusual amino acids, and most of them are in the D-isomer form, which is different from the L-isomers typically found in proteins.

Answer: Spirochetes

Necrotizing ulcerative gingivitis (ANUG) is associated with a complex bacterial community. Studies have shown that spirochetes, particularly Treponema species, are often the first to invade healthy gum tissue in ANUG. Their motility allows them to penetrate deeper into the tissues before other bacteria take hold.

The other options are incorrect:

• Cocci: While cocci (spherical bacteria) can be present in ANUG, they are not typically the initial invaders.
• Bacteriophages: These are viruses that infect bacteria, not bacteria themselves. They wouldn’t be the first organisms found in healthy tissues.
• Filamentous rods: Some filamentous rods like Fusobacterium species can be involved in ANUG, but they are not usually the first to colonize healthy tissue. They often thrive in the necrotic (dead) tissue created by other bacteria.

Answer: Fimbria

Fimbriae (also called pili) are hair-like appendages on the surface of many bacteria. They play a crucial role in bacterial attachment to host cells or other surfaces. Fimbriae have specific receptors that can bind to complementary molecules on the target surface, allowing the bacteria to adhere and establish itself.

The other options are incorrect:

• Capsule: While capsules are sugary layers surrounding some bacteria, their primary function is protection from the environment and phagocytosis (being eaten by immune cells). They don’t directly contribute to attachment.
• Flagella: Flagella are whip-like structures used for bacterial motility, allowing them to move towards nutrients or away from harmful substances. They are not directly involved in attachment.

Answer: All of the above

Typhoid fever, if left untreated, can lead to various serious complications, including.

• Hemorrhage: The bacteria can damage blood vessels, increasing the risk of internal bleeding in the intestines.
• Perforation: Severe inflammation and ulceration in the intestines can lead to a hole (perforation) forming in the intestinal wall. This is a life-threatening complication that requires immediate surgery.
• Osteomyelitis: In rare cases, the bacteria can spread through the bloodstream and infect bones, causing osteomyelitis (bone infection).

Answer: All of the above

In the initial stages of typhoid fever, Salmonella Typhi, the causative bacteria, can be present in various bodily fluids.

• Feces: During the first week of illness, stool cultures have a high chance (around 85-90%) of detecting Salmonella Typhi.
• Urine: While less common than stool samples, Salmonella Typhi can sometimes be present in the urine, especially during the first week of infection.
• Blood: Blood cultures are another approach for detecting Salmonella Typhi, particularly in the first week. However, they may be less sensitive than stool cultures.

Answer: Drum stick

Clostridium tetani is a rod-shaped bacterium with a characteristic bulge at one end, giving it a resemblance to a drumstick under the microscope, especially after staining. This terminal bulge is caused by the presence of a spore, a dormant and highly resistant form that the bacteria can form under unfavorable conditions.

The other options are incorrect:

• Bunch of grapes: This describes the appearance of some bacteria that grow in clusters, like Staphylococcus aureus.
• Chain of beads: This describes the appearance of some bacteria that grow in long chains, like Streptococcus pyogenes.
• Safety pin: This doesn’t typically resemble the shape of Clostridium tetani.

Answer: Dark ground microscope

Leptospira bacteria are very thin and difficult to see under a brightfield microscope, the most common type. A dark ground microscope uses a special illumination technique that allows visualization of unstained, transparent structures like Leptospira by creating a bright background against which the bacteria appear as bright, thin spirals.

The other options are incorrect:

• Scanning electron microscope (SEM): While SEM can provide high-resolution images of a bacteria’s surface, it’s not typically used for routine diagnostic screening of live bacteria in fluids like urine.
• Inverted microscope: This type of microscope is commonly used for cell cultures but doesn’t offer the specific illumination needed to visualize Leptospira effectively.
• Electron microscope: While electron microscopes can provide incredibly detailed images, they are expensive and not commonly used for routine diagnostic purposes due to the complex sample preparation required.

Answer: None of the above

Why none of the listed options fulfill all of Koch’s postulates:

• Treponema pallidum: This bacterium is strongly associated with syphilis, but it’s difficult to cultivate in the lab, making it challenging to fulfill the isolation and reintroduction steps of Koch’s postulates.
• Mycobacterium leprae: Similar to T. pallidum, this bacterium is the causative agent of leprosy but has difficulty growing in artificial culture, hindering complete fulfillment of Koch’s postulates.
• N. gonorrhoeae: This bacterium causes gonorrhea, and it can be grown in culture. However, fulfilling the Koch’s postulate of causing the disease in a healthy animal is often not ethical or practical for human pathogens.

Answer: Buccae

Black-pigmented anaerobes, also known as black-pigmented gram-negative anaerobes (BPGNAs), include genera such as Tannerella, Porphyromonas, and Prevotella. These bacteria produce black pigments due to the presence of iron sulfide in their membranes. However, “Buccae” is not typically classified as a black-pigmented anaerobe.

The other options are incorrect:

• Tannerella: Tannerella is a genus of black-pigmented anaerobes known for its role in periodontal disease. It produces black pigments and is often found in subgingival plaque.
• Porphyromonas: Porphyromonas is another genus of black-pigmented anaerobic bacteria commonly associated with periodontal diseases. It also produces black pigments due to the presence of iron sulfide.
• Prevotella: Prevotella is a genus of anaerobic bacteria that includes some black-pigmented species. It is commonly found in various human body sites, including the oral cavity, respiratory tract, and gastrointestinal tract.

Answer: Presence of antibodies in serum in diagnostic of the disease

While the presence of antibodies in serum indicates exposure to Bordetella pertussis, it doesn’t necessarily confirm an active infection. People can have antibodies from past vaccination or a previous infection. A definitive diagnosis requires other tests like a bacterial culture.

The other options are incorrect:

• Most common cause is B. Petrussis: Bordetella pertussis is indeed the most common cause of whooping cough.
• It may occur in children and young adults after vaccination: Whooping cough can occur even after vaccination, especially as immunity wanes over time. Vaccination is crucial for reducing the severity and preventing complications.
• Bacteria culture from nasopharyngeal swab is the definitive diagnosis: A nasopharyngeal swab culture is the gold standard test for diagnosing whooping cough. It directly detects the presence of Bordetella pertussis bacteria.

Answer: Infection is mostly due to endogenous source

Infections caused by Pseudomonas are commonly acquired from exogenous sources rather than endogenous sources. Endogenous sources refer to pathogens that are normally present in or on the body and cause infection due to factors such as weakened immunity, while exogenous sources involve acquiring the pathogen from the external environment.

The other options are incorrect:

• Strict aerobes: Pseudomonas species are strict aerobes, meaning they require oxygen for growth and metabolism.
• Can grow in disinfectants in hospitals: Pseudomonas species are known for their resistance to disinfectants and antiseptics commonly used in hospitals, making them a concern for nosocomial infections.
• Most common organism in burn patients: Pseudomonas aeruginosa is a common cause of infections in burn patients due to its ability to thrive in moist environments and its intrinsic resistance to many antibiotics.

Answer: Prognosis

The lepromin skin test is not a diagnostic tool for leprosy. It helps determine the type of leprosy a person has (e.g., tuberculoid or lepromatous) and can offer some insight into the prognosis (disease course).

The other options are incorrect:

• Diagnosis: While the test result can be suggestive, a definitive diagnosis of leprosy relies on a combination of clinical presentation, skin biopsy, and bacterial culture.
• Treatment plan: The lepromin test result doesn’t directly influence the treatment plan. Treatment decisions are based on the leprosy type and severity.
• Epidemiology: The lepromin test isn’t used for epidemiological studies (tracking disease spread in populations). Epidemiological studies rely on case reporting and public health surveillance.

Answer: Onset of IgM in 2 days

While symptoms of leptospirosis can appear within a few days, the detectable presence of IgM antibodies (indicating a recent infection) typically takes longer to develop, usually around a week or more after exposure.

The other options are incorrect:

• Faeces & urine of rodents is the cause: Rodents, along with other animals like dogs and farm animals, can shed Leptospira bacteria in their urine and sometimes feces, contaminating water and soil. This contaminated environment is the source of infection for humans.
• Incubation period is 10 days: The incubation period for leptospirosis is typically between 2 and 4 weeks, with some cases ranging from 10 days to a month.
• It is sensitive to penicillin: Leptospirosis is effectively treated with antibiotics, including penicillin and other antibiotics like doxycycline.

Answer: Cardiac valves

The group A carbohydrate of Streptococcus pyogenes, also known as Lancefield group A antigen, cross-reacts with human cardiac valves. This molecular mimicry can lead to autoimmune reactions, causing rheumatic heart disease, particularly affecting the heart valves.

The other options are incorrect:

• Synovial fluid: Streptococcus pyogenes infection does not typically cross-react with human synovial fluid. Rheumatic fever, which results from an immune response to group A streptococcal infection, primarily affects the heart, joints, skin, and central nervous system.
• Myocardium: While rheumatic fever can cause myocarditis (inflammation of the myocardium), the cross-reactivity of Streptococcus pyogenes with human tissues primarily affects the heart valves, leading to rheumatic heart disease.
• Vascular intima: Streptococcus pyogenes infection does not commonly cross-react with the vascular intima. Rheumatic fever primarily affects connective tissues, particularly those of the heart valves, joints, and skin, due to molecular mimicry between streptococcal antigens and human tissues.

Answer: Clostridium welchii

Clostridium welchii, also known as Clostridium perfringens, is the most frequently encountered species in gas gangrene, also known as clostridial myonecrosis. This bacterium produces toxins that cause tissue destruction and gas formation within affected tissues.

The other options are incorrect:

• Clostridium botulinum: This species causes botulism, a different and serious illness affecting the nervous system.
• Clostridium tetani: Tetanus is another distinct condition caused by Clostridium tetani. It primarily affects the nervous system, leading to muscle stiffness and spasms.
• Clostridium difficile: This bacterium is known for causing pseudomembranous colitis, an inflammation of the colon.

Answer: Cardiolipin

The reagin test, such as the Venereal Disease Research Laboratory (VDRL) test, uses cardiolipin as an antigen. This phospholipid is not specific to Treponema pallidum (the syphilis bacteria), but it reacts with antibodies produced by the body in response to the infection.

The other options are incorrect:

• Plasminogen: This is a blood protein involved in clot breakdown, not related to the reagin test.
• Palmityl lecithin: While a phospholipid, it’s not specifically used in the reagin test.
• Serine: This is an amino acid, not a phospholipid, and doesn’t play a role in the reagin test.

Answer: Haemagglutination test

Fimbriae are hair-like appendages on the surface of bacteria that facilitate adhesion to host cells or surfaces. The presence of fimbriae can be demonstrated by performing a haemagglutination test, where the bacteria are mixed with red blood cells. If fimbriae are present, they will agglutinate (clump together) the red blood cells.

The other options are incorrect:

• Culture: Bacterial cultures grow the bacteria but wouldn’t reveal details like fimbriae.
• Gram stain: This staining technique differentiates bacteria based on cell wall composition but wouldn’t show fine structures like fimbriae.
• Biochemical reaction: Biochemical tests identify specific metabolic pathways of bacteria and wouldn’t provide information on fimbriae presence.

Answer: Transduction

Transduction is the process where a bacteriophage (phage) transfers bacterial genetic material from one bacterium to another. The phage acts as a carrier, injecting the bacterial DNA from a donor cell into a recipient cell.

The other options are incorrect:

• Translation: Translation is the process where cellular machinery converts the genetic code in mRNA (messenger RNA) into proteins. It doesn’t involve transfer of genetic material between bacteria.
• Lysogeny: This is a specific type of transduction where the phage DNA integrates into the host bacterial chromosome and replicates along with it. However, lysogeny itself isn’t the mechanism of transfer, but rather a consequence of transduction.
• Conjugation: Conjugation is a different mechanism where bacteria directly connect and transfer a plasmid (a small circular DNA molecule) between them. It doesn’t involve a phage as a carrier.

Answer: Group B

Group B streptococci, also known as Streptococcus agalactiae, typically exhibit a positive reaction in the cAMP (cyclic AMP) test. This test involves streaking the organism alongside a streak of a β-hemolytic strain of Staphylococcus aureus on a blood agar plate. The presence of a zone of increased hemolysis due to enhanced β-hemolysin production by S. aureus in the presence of cAMP produced by Group B streptococci indicates a positive result.

The other options are incorrect:

• Group A: Group A streptococci, or Streptococcus pyogenes, do not typically show a positive cAMP reaction. They are known for their β-hemolytic activity on blood agar but do not produce the required cAMP for a positive reaction.
• Group C: Group C streptococci are a diverse group of streptococci, including several species such as Streptococcus equi and Streptococcus equisimilis. They do not typically exhibit a positive cAMP reaction.
• Group D: Group D streptococci include various species, such as Enterococcus faecalis and Enterococcus faecium. They are not known for showing a positive cAMP reaction.

Answer: Pertussis

The cough plate method is a diagnostic tool historically used to identify Bordetella pertussis, the bacteria causing whooping cough (pertussis). It involves collecting respiratory droplets coughed onto a culture plate.

The other options are incorrect:

• Y. pestis: Yersinia pestis is the causative agent of plague and wouldn’t be effectively diagnosed using a cough plate.
• Mycoplasma: Mycoplasma are a type of bacteria that lack a cell wall and wouldn’t grow well on the standard media used in cough plates.
• M. Tuberculosis: Mycobacterium tuberculosis, the bacteria causing tuberculosis, primarily infects the lungs but isn’t efficiently captured by a cough plate. Sputum culture is the preferred method for diagnosing tuberculosis.

Answer: Bacterial fimbriae

Negative staining is a quick and simple technique used to visualize structures with low electron density (appear light) against a dark background (dense stain). Fimbriae, being hair-like and thin bacterial appendages, have low electron density and are well-suited for visualization with negative staining.

The other options are incorrect:

• Bacterial spore: Spores have a thick and dense outer coat, making them readily visible with various staining methods, not requiring the contrasting effect of negative staining.
• Bacterial Flagella: Flagella can sometimes be visualized with negative staining, but other techniques like transmission electron microscopy (TEM) with a metal coating might offer clearer visualization due to their structure.
• Bacterial capsule: Capsules, being composed of sugary or polysaccharide material, might have lower electron density, but dedicated stains like India ink are often preferred for highlighting capsules.

Answer: Fusiform bacilli

Borrelia vincentii is always associated with fusiform bacilli, which are elongated, spindle-shaped bacteria. These bacteria are often found in association with Borrelia vincentii in cases of acute necrotizing ulcerative gingivitis (ANUG), also known as Vincent’s angina.

The other options are incorrect:

• Spirochaetes: Spirochaetes are a distinct group of spiral-shaped bacteria, to which Borrelia species belong. However, Borrelia vincentii is specifically associated with fusiform bacilli rather than spirochaetes.
• Treponema vincenti: There is no bacterium named Treponema vincenti. Borrelia vincentii is associated with fusiform bacilli, not Treponema species. Treponema species are indeed spirochaetes, but they are not associated with Borrelia vincentii.
• None of the above: This option is incorrect because Borrelia vincentii is indeed associated with fusiform bacilli. Therefore, “None of the above” is not the correct answer in this context.

Answer: Streptococcus pyogenes

Streptococcus pyogenes, also known as Group A Strep, is an extracellular pathogen. It doesn’t typically survive or replicate inside host cells. It primarily targets the throat and skin, causing infections like strep throat and impetigo.

The other options are incorrect:

• Neisseria meningitidis: This bacterium can survive and replicate within the lining of the brain and spinal cord, causing meningitis.
• Salmonella typhi: This specific Salmonella species can invade and live inside intestinal epithelial cells, leading to typhoid fever.
• Legionella pneumophila: This bacterium replicates within macrophages (immune cells) in the lungs, causing Legionnaires’ disease.

Answer: Parotitis

Chlamydia is not typically associated with parotitis, which is inflammation of the parotid glands (salivary glands near the cheeks). Parotitis is more commonly caused by viruses like mumps virus.

The other options are incorrect:

• Trachoma: Chlamydia trachomatis can cause trachoma, an eye infection leading to blindness in severe cases.
• Non-gonococcal urethritis: Chlamydia is a major cause of nongonococcal urethritis, a sexually transmitted infection (STI) of the urethra.
• Pneumonia: Chlamydia pneumoniae can cause pneumonia, particularly walking pneumonia.

Answer: Polysaccharide C antigen

Lancefield’s classification of β-hemolytic streptococci is based on the presence of specific carbohydrate antigens in the bacterial cell wall, particularly the polysaccharide C antigen. This classification system categorizes these streptococci into different groups (Groups A, B, C, D, etc.) based on their antigenic properties.

The other options are incorrect:

• M Protein: The M protein is a virulence factor found on the surface of Group A streptococci (Streptococcus pyogenes). It is not used in Lancefield’s classification.
• Type of lipid in cell membrane: The type of lipid in the cell membrane is not used in Lancefield’s classification. This classification is based on antigenic properties rather than lipid composition.
• Physiological properties: Lancefield’s classification is primarily based on antigenic properties, particularly the presence of specific carbohydrate antigens in the bacterial cell wall, rather than physiological properties.

Answer: Through breast milk

Leprosy bacilli, also known as Mycobacterium leprae, are not typically transmitted through breast milk. The primary routes of transmission for leprosy include prolonged close contact with an untreated individual with lepromatous or multibacillary leprosy, primarily through respiratory droplets from the nose and mouth of infected individuals.

The other options are incorrect:

• Discharge from nasal mucosa: Mycobacterium leprae can be transmitted through respiratory droplets released from the nasal mucosa of infected individuals, particularly during prolonged close contact.
• From open sore: Leprosy can be transmitted through direct contact with open sores or lesions of an infected individual, particularly in cases of untreated lepromatous or multibacillary leprosy.
• Through intact skin: Transmission of leprosy through intact skin is possible, particularly in cases of prolonged close contact with an untreated individual with lepromatous or multibacillary leprosy, although it is less efficient compared to transmission through respiratory droplets or open sores.

Answer: Lecithinase

Nagler’s reaction is a laboratory test used to detect the presence of lecithinase enzyme, particularly produced by Clostridium perfringens. Lecithinase hydrolyzes lecithin (a phospholipid) in egg yolk, causing precipitation or opalescence in the medium, which is a positive reaction indicating the presence of the enzyme.

The other options are incorrect:

• Coagulase: Coagulase is an enzyme produced by some strains of Staphylococcus aureus, which causes the coagulation of plasma or blood. Nagler’s reaction does not detect coagulase.
• Hyaluronidase: Hyaluronidase is an enzyme produced by certain bacteria, including Streptococcus and Staphylococcus species, which hydrolyzes hyaluronic acid, a component of connective tissue. Nagler’s reaction does not detect hyaluronidase.
• None of the above: This option is incorrect because Nagler’s reaction specifically detects lecithinase activity, as described in the correct answer. Therefore, “None of the above” is not the correct answer in this context.

Answer: Cl. tetani

The drumstick appearance is a characteristic morphological feature observed in the spores of Clostridium tetani. When Clostridium tetani forms spores, the vegetative cell enlarges at one end, giving it a resemblance to a drumstick.

The other options are incorrect:

• Cl. tetanomorphum: While this is a synonym for Clostridium tetani, it doesn’t directly refer to the drumstick morphology.
• Cl. sphenoids: This is not a recognized species within the Clostridium genus. There’s no documented association of drumstick morphology with any other Clostridium species.
• All of the above: Only Clostridium tetani exhibits the drumstick appearance during spore formation.

Answer: C. burnetti

Q fever is caused by the bacterium Coxiella burnetii. It’s an obligate intracellular bacterium, meaning it can only replicate inside the host cells.

The other options are incorrect:

• Rickettsia tsutsugamushi: This bacterium causes scrub typhus, a different infectious disease transmitted by mites.
• R. prowozekii: This bacterium is responsible for epidemic typhus, transmitted through lice.
• R. quintana: This rickettsial species causes trench fever, historically associated with crowded wartime conditions.

Answer: Gram positive bacteria

Actinomycetes are a group of gram-positive bacteria with some unique characteristics. They are often mistaken for fungi due to their filamentous growth patterns, but they have a distinct cell wall structure characteristic of gram-positive bacteria.

The other options are incorrect:

• Gram negative bacteria: Actinomycetes lack the outer lipopolysaccharide membrane typical of gram-negative bacteria.
• Fungus: Fungi are eukaryotic organisms with a cell wall composed of chitin, distinct from the peptidoglycan cell wall of gram-positive bacteria.
• A yeast-like form: While some actinomycetes can exhibit a yeast-like morphology in certain conditions, their overall classification falls under gram-positive bacteria.

Answer: All of the above

The VDRL (Venereal Disease Research Laboratory) test is:

• Non-specific: It detects antibodies produced by the body in response to syphilis infection, but these antibodies can also be present in other infections or autoimmune conditions.
• Slide flocculation test: It uses a slide agglutination technique to observe clumping (flocculation) of particles if antibodies against syphilis are present.
• Best followed by a confirmatory test: While a positive VDRL suggests a possible syphilis infection, it’s not definitive. A confirmatory test like the Treponema pallidum microhemagglutination assay (MHA-TP) is needed for diagnosis.

Answer: Scarlet fever

Scarlet fever is caused by Streptococcus pyogenes bacteria, not Staphylococcus. Staphylococcus aureus, a common type of staph bacteria, can cause various infections, including osteomyelitis (bone infection), abscesses (collections of pus), and pneumonia (lung infection).

The other options are incorrect:

• Osteomyelitis: Staphylococcus aureus can cause bone infections.
• Abscess: Staphylococcus aureus is a common cause of abscess formation.
• Pneumonia: Staphylococcus aureus can cause pneumonia, especially hospital-acquired pneumonia.

Answer: Koch

Robert Koch, a German physician, is credited with discovering Vibrio cholerae in 1883. His work helped solidify the germ theory of disease.

The other options are incorrect:

• Medintoff: This name is not associated with the discovery of Vibrio cholerae.
• John Snow: While John Snow made significant contributions to our understanding of cholera transmission through his epidemiological studies in 1854, he did not discover the causative bacteria.
• Virchow: Rudolf Virchow was a prominent pathologist who made significant contributions to cellular pathology but is not credited with discovering Vibrio cholerae.

Answer: Pili

Pili are hair-like structures on the surface of Neisseria gonorrhoeae (gonococcus) that play a crucial role in its virulence. These pili help the bacteria attach to host cells, resist phagocytosis by immune cells, and facilitate bacterial movement within the host.

The other options are incorrect:

• Cell Membrane: While the cell membrane plays a general role in protecting the bacteria and regulating cellular processes, it’s not a specific virulence factor for gonococcal infections.
• Intracellular Location: Neisseria gonorrhoeae is an extracellular bacterium, meaning it lives outside the host cells.
• Cytolytic enzymes: While some bacteria use cytolytic enzymes to damage host cells, this is not a primary virulence factor for gonococcus.

Answer: Loefflers serum slope

Loeffler’s serum slope is a specialized culture medium enriched with horse serum that provides optimal growth conditions for Corynebacterium diphtheriae. It allows for rapid growth (visible in 6-8 hours) and characteristic morphology of C. diphtheriae colonies, aiding in diagnosis of diphtheria.

The other options are incorrect:

• McConkey Agar: This medium is selective for lactose-fermenting and lactose-non-fermenting bacteria and is not suitable for C. diphtheriae, which doesn’t ferment lactose.
• Sabouraud Dextrose Agar (SDA): This medium is commonly used for cultivating fungi and some yeasts, not bacteria like C. diphtheriae.
• Löwenstein-Jensen Medium: This medium is selective for Mycobacterium tuberculosis, the causative agent of tuberculosis, and not for C. diphtheriae.

Answer: Bacillus anthracis

Bacillus anthracis, the causative agent of anthrax, exhibits a characteristic “beaded” or “hairy” appearance in Gram-stained smears prepared from culture films. This appearance is due to the arrangement of the bacteria in long chains with gaps between individual cells

The other options are incorrect:

• Brucella species: Brucella species, which cause brucellosis, typically appear as small, coccobacilli (rod-shaped bacteria resembling cocci) in smears and don’t exhibit the beaded pattern.
• Bordetella pertussis: Bordetella pertussis, responsible for whooping cough, appears as coccobacilli in smears and lacks the distinct beaded morphology.
• Clostridium weichii: Clostridium weichii, a causative agent of botulism, usually appears as large rods in smears, not the beaded chains seen with Bacillus anthracis.

Answer: Typhoid

The Widal test, although no longer widely used due to limitations in accuracy, was historically employed to diagnose typhoid fever. It detects antibodies against Salmonella Typhi bacteria in a patient’s blood.

The other options are incorrect:

• Plague: Plague is caused by Yersinia pestis bacteria, and a different diagnostic approach is used to identify it.
• Leprosy: Leprosy is caused by Mycobacterium leprae, and specific tests like skin smears or biopsies are used for diagnosis.
• Pemphgoid: Pemphgoid is an autoimmune blistering skin disease, not a bacterial infection. Diagnosis involves skin biopsy and immunofluorescence testing.

Answer: Refractile granules

All the other terms (metachromatic granules, Babes Ernst granules, and volutin granules) refer to the same structures in Corynebacterium diphtheriae. These are refractile granules composed of polyphosphate, appearing dark blue or purple under specific stains like Albert’s stain.

The other options are incorrect:

• Metachromatic granules: This term describes the staining property of the granules, which appear a different color (blue) compared to the surrounding structures (purple) when stained with certain dyes.
• Babes Ernst granules: This is another name for the same polyphosphate granules in C. diphtheriae.
• Voluntin granules: Yet another synonym for the metachromatic or Babes Ernst granules.

Answer: Strep. Mutans

Streptococcus mutans, a bacterium commonly associated with dental caries (cavities), is known for its ability to produce extracellular polysaccharides. These polysaccharides help form the biofilm on tooth surfaces, which contributes to plaque formation and caries development.

The other options are incorrect:

• Strep. pyogenes: Streptococcus pyogenes, a major cause of strep throat and other infections, does not typically produce significant amounts of extracellular polysaccharides.
• Peptostreptococcus: Peptostreptococcus species are anaerobic bacteria and generally don’t produce substantial extracellular polysaccharides.
• Enterococcus: While some Enterococcus species can produce limited amounts of extracellular polysaccharides, it’s not a defining characteristic of the genus compared to Strep. mutans.

Answer: Detection of coagulase

Coagulase is an enzyme produced by some Staphylococcus species, particularly Staphylococcus aureus, a major virulent pathogen. Coagulase converts fibrinogen in blood plasma to fibrin, a key step in clot formation. Detecting coagulase helps differentiate highly virulent S. aureus from other less virulent staphylococci.

The other options are incorrect:

• Mannitol fermentation: While some staphylococci, including S. aureus, can ferment mannitol, this test alone isn’t sufficient to determine virulence. Other staphylococci can also ferment mannitol.
• Hemolysis of sheep erythrocytes: This test assesses a bacterium’s ability to lyse (break down) red blood cells. While S. aureus often exhibits beta-hemolysis (complete hemolysis), other staphylococci can also show hemolysis patterns, and hemolysis alone doesn’t directly correlate with virulence.
• The catalase test: This test detects the presence of the catalase enzyme, which breaks down hydrogen peroxide. Most staphylococci are catalase-positive, and this test doesn’t differentiate virulence.

Answer: Having either DNA or RNA

Bacteria typically possess both DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) as part of their genetic material. This distinction is not true because bacteria possess both DNA and RNA.

The other options are incorrect:

• Unicellular: Bacteria are unicellular organisms, meaning they are made up of a single cell. They do not have complex structures like multicellular organisms.
• Free living: Many bacteria are free-living organisms, meaning they are not dependent on a host organism for survival. They can exist and reproduce independently in various environments, such as soil, water, and the human body.
• Cell wall containing muramic acid: The cell wall of most bacteria contains peptidoglycan, a unique macromolecule composed of alternating sugar units and peptides. Peptidoglycan contains a component called muramic acid, which is characteristic of bacterial cell walls and provides structural support.

Answer: All of the above

Salmonella Typhi, the causative agent of typhoid fever, can be isolated from various clinical specimens depending on the stage of the infection.

• Feaces: During the acute phase of typhoid fever, when patients experience diarrhea, Salmonella Typhi can be shed in the stool, allowing isolation from fecal samples.
• Blood: In the early stages of typhoid fever, bacteria can be present in the bloodstream. Blood cultures can be helpful for diagnosis during this time.
• Urine: While less common than feces or blood, Salmonella Typhi can be present in the urine, particularly during the later stages of the illness or in carriers who don’t exhibit typical symptoms.

Answer: 37 degrees

Mycobacterium species, including Mycobacterium tuberculosis (the causative agent of tuberculosis), are typically cultivated at 37°C (98.6°F). This temperature mimics the human body temperature, which provides optimal conditions for their growth in the laboratory.

The other options are incorrect:

• 2 degrees and 0 degrees: These temperatures are too cold for Mycobacterium growth. They are closer to the freezing point of water, which can inhibit bacterial growth or kill the bacteria.
• 27 degrees: While some Mycobacterium species might tolerate slightly lower temperatures, 27°C is generally considered on the cooler end for optimal growth. 37°C provides a more favorable environment for most Mycobacteria.

Answer: Both of the above

The silver impregnation method of staining, also known as the silver staining technique, is particularly useful for demonstrating spirochetes. Spirochetes are spiral-shaped bacteria with a unique structure that makes them difficult to visualize using conventional staining methods. Silver staining allows for the visualization of the spiral morphology of spirochetes, aiding in their identification under the microscope.

Answer: Red color

During the Gram staining procedure, Gram-negative bacteria typically stain red or pink. This occurs because the crystal violet-iodine complex is washed out of the thin peptidoglycan layer of Gram-negative bacteria by the alcohol decolorizer.

The other options are incorrect:

• Blue color: This is the color of Gram-positive bacteria, not Gram-negative.
• Green: This color is not typically used in Gram staining.
• Colorless: Completely colorless bacteria would be difficult to see under a microscope. While some bacteria may stain faintly, they would not be entirely colorless.

Answer: Gall Bladder

Typhoid fever is caused by the bacteria Salmonella Typhi. In chronic carriers, who don’t show symptoms but can still spread the bacteria, Salmonella Typhi can reside in various organs. The gall bladder, with its bile-rich environment, provides a favorable niche for the bacteria to persist.

The other options are incorrect:

• Spleen: While Salmonella Typhi can be present in the spleen during acute infection, it’s less common in chronic carriers.
• Liver: Similar to the spleen, the liver can be involved during acute infection but is less frequent in carriers.
• Salivary gland: Salivary glands are not a typical reservoir for Salmonella Typhi.

Answer: Beta phage

Diphtheria is caused by the bacterium Corynebacterium diphtheriae, which becomes pathogenic only when infected with a specific bacteriophage known as the beta phage. The beta phage carries the gene encoding for the diphtheria toxin, which is responsible for the characteristic symptoms of diphtheria, such as the formation of pseudomembranes in the throat and systemic toxicity.

The other options are incorrect:

• Alpha phage: There is no bacteriophage known as the alpha phage associated with diphtheria. The disease is specifically linked to the beta phage.
• Lambda K12: Lambda and K12 are specific types of bacteriophages, but they are not associated with diphtheria. Lambda phage is commonly used in molecular biology research, and K12 is a laboratory strain of Escherichia coli.
• Delta Phage: There is no bacteriophage known as the delta phage associated with diphtheria. The disease is specifically linked to the beta phage.