MicroBiology MCQs with Answer and Explanations | Chapter 74

Answer: Penicillium chrysogenum

Penicillium chrysogenum (previously known as Penicillium notatum) is the primary fungal strain used for large-scale penicillin production. This specific strain has been optimized through mutation and selection for high penicillin yield.

The other options are incorrect:

• P-notatum: While historically, Penicillium notatum was the original strain used by Alexander Fleming to discover penicillin, it has largely been replaced by the higher-yielding Penicillium chrysogenum for industrial production.
• Streptomyces Aureus: Streptomyces Aureus is a type of bacteria, not a fungus. It’s known for producing various antibiotics but not penicillin.
• Saccharomyces sps: Saccharomyces species are yeasts, not filamentous fungi like Penicillium. They are commonly used for fermentation processes like bread making and beer production, not antibiotic production.

Answer: Efficacy of a disinfectant

The phenol coefficient is a historical method for comparing the effectiveness of a disinfectant against a standard disinfectant, phenol. A higher phenol coefficient indicates a disinfectant is more effective at killing microorganisms compared to phenol at a similar concentration.

The other options are incorrect:

• Dilution of a disinfectant: Phenol coefficient doesn’t directly tell you the recommended dilution for a disinfectant. It’s a relative measure of effectiveness, not a specific use concentration.
• Quality of a disinfectant: While efficacy is a quality, the phenol coefficient only considers germ-killing power, not other factors like safety or shelf life.
• Purity of a disinfectant: Phenol coefficient doesn’t tell you about the purity of a disinfectant. It focuses on how well it works against microbes compared to phenol, not its chemical composition.

Answer: 20o C

Psychrophilic bacteria, also known as cryophiles, thrive in cold environments. Their ideal growth temperatures are typically around 0°C to 15°C, and they can even survive and reproduce at subzero temperatures. 20°C is still on the cooler side but is within the tolerable range for some psychrophiles.

The other options are incorrect:

• 50-60°C: This is way too hot for psychrophilic bacteria. Most wouldn’t survive at such high temperatures. They are adapted to cold environments and their enzymes wouldn’t function correctly at these high temperatures.
• 20-40°C: While some psychrophiles might tolerate this range, it’s on the warmer end of their spectrum. They would likely grow slower or not at all compared to ideal cold conditions.
• 90°C: This is extremely hot and unsuitable for any psychrophilic bacteria.

Answer: Rickettsia prowazeki

Dark-ground microscopy is a useful tool for visualizing unstained, transparent microorganisms. It’s particularly helpful for observing bacteria like Treponema pallidum (syphilis), Borrelia recurrentis (relapsing fever), and Leptospira biflexa (leptospirosis) because they are too thin and lack sufficient contrast for bright-field microscopy.

The other options are incorrect:

• Treponema pallidum: This bacterium is a classic example requiring dark-ground microscopy due to its helical shape and minimal intrinsic contrast.
• Borrelia recurrentis: Similar to Treponema pallidum, Borrelia is a thin, helical bacterium poorly visible under bright-field microscopy. Dark-ground microscopy is the preferred method for visualization.
• Leptospira biflexa: This slender, spiral-shaped bacterium also benefits from dark-ground microscopy for clear visualization due to its low intrinsic contrast.

Answer: Streptococcus pyogenes

Streptococcus pyogenes, also known as group A streptococcus, is a species of bacteria sometimes referred to as “flesh-eating bacteria” because it can cause necrotizing fasciitis, a serious infection that rapidly destroys skin and tissues.

The other options are incorrect:

• Enterococcus faecium: Enterococcus faecium is a type of enterococcus bacteria commonly found in the intestines. While it can cause some infections, it’s not associated with necrotizing fasciitis.
• Streptococcus mucilagenosus: Streptococcus mucilagenosus is a species found in the mouth and throat. It’s not typically linked to severe invasive infections like necrotizing fasciitis.
• Streptococcus sanguis: Streptococcus sanguis is another species found in the mouth and throat. It’s more commonly associated with minor infections like strep throat and rarely causes serious invasive diseases.

Answer: Pour plate method

The pour plate method is a standard technique for counting bacteria in liquid samples, not air. It involves mixing a diluted sample with agar media and pouring it into petri dishes.

The other options are incorrect:

• Settle plate: This is a common method for air sampling. Microbes from the air settle onto an agar plate exposed for a specific time, allowing for colony growth and enumeration.
• Slit sampler: This device uses a moving air stream to draw microbes onto an agar surface, enabling their collection and subsequent analysis.
• Air centrifuge: This method utilizes a centrifuge to concentrate airborne microorganisms onto a collection plate or filter for further analysis.

Answer: Leptospira

Noguchi’s medium is a specific type of enriched culture media designed for the isolation and growth of Leptospira bacteria. It provides the necessary nutrients and environment for these fastidious organisms to thrive.

The other options are incorrect:

• Borrelia: While Borrelia and Leptospira are both spiral-shaped bacteria, they have different growth requirements. Borrelia typically needs specialized media like Barbour-Stoenner (BSK) medium.
• Brucella: Brucella bacteria have different nutritional needs and are usually cultured on media enriched with blood or serum, such as tryptic soy agar (TSA) with added sheep or horse blood.
• Francisella: Francisella bacteria also have distinct growth preferences. They are often cultured on media containing blood or charcoal, such as Thayer-Martin (TM) agar.

Answer: Superoxide dismutase and catalase

Superoxide dismutase and catalase are enzymes produced by obligate aerobes to break down toxic reactive oxygen species such as superoxides (O2-) and hydrogen peroxide (H2O2). Superoxide dismutase converts superoxide radicals into oxygen and hydrogen peroxide, while catalase further breaks down hydrogen peroxide into water and oxygen.

The other options are incorrect:

• Thermonuclease: Thermonuclease is an enzyme that breaks down nucleic acids at high temperatures. It’s not directly involved in dealing with superoxides or hydrogen peroxide produced during respiration.
• Phosphatase: Phosphatase is an enzyme that hydrolyzes phosphate groups from various molecules. It’s not relevant to the breakdown of superoxides or hydrogen peroxide in obligate aerobes.
• Luciferase: Luciferase is an enzyme involved in bioluminescence, the production of light in certain organisms. It has no role in the detoxification pathway of obligate aerobes.

Answer: Limulus Amoebocyte Lysate(LAL)

Limulus Amoebocyte Lysate (LAL) is a traditional diagnostic test used for detecting endotoxins from Gram-negative bacteria. It is derived from the blood cells of the horseshoe crab Limulus polyphemus and has been in use since the 1970s.

The other options are incorrect:

• Mass Spectrometry Immuno Assay: Mass Spectrometry Immuno Assay is a recent diagnostic technique that combines mass spectrometry with immunoassay methods for the detection and quantification of biomolecules such as proteins and peptides.
• Matrix Assisted Laser Desorption/Ionisation (MALDI): MALDI is a modern diagnostic method used for the rapid identification of microorganisms, particularly bacteria and fungi, based on their unique mass spectra obtained from the analysis of microbial biomolecules such as proteins and peptides.
• Chemiluminescence Immuno Assay: Chemiluminescence Immuno Assay is a contemporary diagnostic technique that utilizes chemiluminescent reactions to detect antigens or antibodies in clinical samples, providing high sensitivity and specificity in diagnosis.

Answer: Mycobacterium avium

Among the listed Mycobacterium species, only Mycobacterium avium is known to be able to infect and multiply inside protozoa, specifically macrophages. These macrophages are white blood cells that normally engulf and destroy bacteria. However, M. avium has mechanisms to survive and even replicate within the macrophage.

The other options are incorrect:

• Mycobacterium bovis: This bacterium primarily infects mammals, including humans, and causes bovine tuberculosis. It is not known to infect and multiply inside protozoa.
• Mycobacterium xenopi: Similar to M. bovis, M. xenopi can cause infections in humans and animals but does not typically establish itself within protozoa.
• Mycobacterium simiae: This species is known to cause opportunistic infections in immunocompromised individuals, but it does not target protozoa for growth.

Answer: Microsporum canis

Microsporum canis is the species known for having characteristic two-celled macroconidia (large, asexual spores). These macroconidia are typically spindle-shaped, thick-walled, and often have a terminal knob. M. canis is a zoophilic fungus commonly causing ringworm in humans and animals.

The other options are incorrect:

• Microsporum gypseum: This species produces macroconidia with multiple septa (divisions) and a variable number of cells, typically exceeding two.
• Microsporum audouinii: Similar to M. gypseum, M. audouinii has macroconidia with multiple septa and generally more than two cells.
• Microsporum nanum: M. nanum also produces multicellular macroconidia, usually with more than two compartments within the spores.

Answer: C. albicans

Candida albicans is the species known to produce “pseudo-germ tubes.” These are elongated bud scars or outgrowths that resemble germ tubes, but they lack the characteristic true germ tube structure. A germ tube test is a rapid method for presumptive identification of C. albicans, but the presence of true germ tubes is a stronger indicator.

The other options are incorrect:

• C. dubliniensis: While C. dubliniensis can produce true germ tubes under specific conditions, it typically does not form pseudo-germ tubes like C. albicans.
• C. tropicalis: Candida tropicalis does not typically produce germ tubes or pseudo-germ tubes.
• C. krusei: Similar to C. tropicalis, C. krusei is not known for forming germ tubes or pseudo-germ tubes.

Answer: Cladosporium

Cladosporium species are filamentous fungi that typically do not form sclerotic bodies. They reproduce primarily through asexual spores called conidia.

The other options are incorrect:

• Exophiala: Some Exophiala species, particularly E. dermatitidis and E. jeanselmei, are known to produce sclerotic bodies in culture and tissues. These structures help them survive harsh environmental conditions.
• Phialophora: Phialophora species, like Phialophora verrucosa, can form sclerotia (plural of sclerotic bodies) as a dormant survival strategy.
• Fonsecaea: Fonsecaea pedrosoi, the main agent of chromoblastomycosis, is known for producing dark, thick-walled sclerotic bodies in infected tissues.

Answer: Trichophyton mentagrophytes

The hair perforation test is used to differentiate between certain dermatophyte species. Among the listed options, only Trichophyton mentagrophytes typically produces a positive hair perforation test.

The other options are incorrect:

• Positive Hair Perforation Test: In this test, fungal isolates are incubated with hair strands. If the fungus is T. mentagrophytes, it will degrade the hair structure, causing localized areas of pitting and erosion observable under a microscope after several weeks.
• Negative Results: Other dermatophytes like T. tonsurans, T. schoenleinii, and T. verrucosum are unlikely to show significant hair degradation in this test.

Answer: Actinomadura

Actinomadura belongs to a group of bacteria called Actinomycetes. Eumycotic mycetoma is a fungal infection, while Actinomycetes are not fungi. The other listed options (Pseudoallescheria boydii, Exophiala jeanselmei, Acremonium kifience) are all fungal species known to cause eumycotic mycetoma.

The other options are incorrect:

• Pseudoallescheria boydii: This fungus can cause eumycotic mycetoma, particularly in tropical and subtropical regions.
• Exophiala jeanselmei: This black yeast-like fungus is another agent of eumycotic mycetoma.
• Acremonium kifience: This fungus is a known cause of eumycetoma, often affecting the foot.

Answer: Aspergillus spp

Aspergillus species are characterized by septate hyphae that branch dichotomously, meaning they divide into two equal branches. This branching pattern is a key feature used in the identification of Aspergillus species.

The other options are incorrect:

• Rhizopus spp.: Rhizopus species, including Rhizopus oryzae, typically have non-septate (aseptate) hyphae and sporangiophores that branch irregularly rather than dichotomously.
• Mucor spp.: Mucor species, such as Mucor circinelloides, typically have non-septate (aseptate) hyphae and sporangiophores that branch irregularly rather than dichotomously.
• Absidia spp.: Absidia species, like Mucor species, typically have non-septate (aseptate) hyphae and sporangiophores that branch irregularly rather than dichotomously.

Answer: Pneumocystis jeroveci

Pneumocystis jiroveci is a fungus. While it was previously classified as a protozoan, recent scientific understanding based on nucleic acid analysis confirms its fungal nature.

The other options are incorrect:

• Cryptosporidium parvum: This is a protozoan parasite commonly transmitted through contaminated water or food.
• Eikenella corrodens: This is a gram-negative bacterium often found in the mouth and can be associated with human bites.
• Ehrlichia chaffeensis: This is a bacterium belonging to the Rickettsiales order. It’s transmitted by ticks and can cause ehrlichiosis, a tick-borne disease.

Answer: Aspergillus nidulans

Hülle cells are characteristic structures produced by certain species within the Aspergillus genus, and Aspergillus nidulans is a well-known fungus that exhibits this feature. These cells are often found surrounding the cleistothecia (sexual spore-containing structures) in A. nidulans.

The other options are incorrect:

• Aspergillus fumigatus: While A. fumigatus is a medically important fungus, it doesn’t typically produce Hülle cells.
• Aspergillus terreus: Similar to A. fumigatus, Hülle cell formation is not a characteristic feature of A. terreus.
• Aspergillus flavus: A. flavus also doesn’t typically produce Hülle cells.

Answer: Viral etiology

Viral meningitis is often characterized by a normal glucose level in the cerebrospinal fluid (C.S.F.), unlike bacterial or fungal meningitis, which typically present with decreased glucose levels. Mycobacterial meningitis, caused by organisms like Mycobacterium tuberculosis, can also lead to decreased glucose levels in the C.S.F.

The other options are incorrect:

• Bacterial etiology: Low CSF glucose is more likely with bacterial meningitis.
• Mycobacterial etiology: Similar to bacterial meningitis, mycobacterial infections can also cause low CSF glucose.
• Fungal etiology: CSF glucose levels in fungal meningitis can vary, but a normal level might be less indicative compared to viral meningitis.

Answer: It is sensitive to Novobiocin

Staphylococcus saprophyticus is resistant to Novobiocin. This characteristic is used to differentiate it from other coagulase-negative staphylococci, which are typically sensitive to Novobiocin.

The other options are incorrect:

• Commonly causes UTI in young, sexually active, young females: This statement is true. Staphylococcus saprophyticus is a common cause of urinary tract infections (UTIs), particularly in young, sexually active females.
• It is coagulase negative: This statement is false. Staphylococcus saprophyticus is coagulase-positive, unlike most other coagulase-negative staphylococci.
• It is modified oxidase test negative: This statement is false. Staphylococcus saprophyticus is oxidase-positive, not negative.

Answer: Cell wall M protein

Griffith’s serotyping classifies beta-hemolytic streptococci based on the specific variations in their M protein. This protein is located on the bacterial cell wall and plays a role in virulence (disease-causing ability). By detecting different M protein types using specific antibodies, scientists can differentiate between various strains of beta-hemolytic streptococci.

The other options are incorrect:

• Cell wall carbohydrate C antigen: While Lancefield grouping, another classification method for streptococci, relies on cell wall carbohydrates, Griffith’s serotyping specifically focuses on M protein.
• Cell wall peptidoglycan: Peptidoglycan is a structural component found in most bacterial cell walls, but it doesn’t provide enough variation for specific strain differentiation.
• Cell wall murein: Murein is another term for peptidoglycan and has the same limitations for serotyping.

Answer: It produces a potential endotoxin

Bacillus anthracis produces an exotoxin, not an endotoxin. The exotoxin produced by B. anthracis is composed of three proteins: protective antigen, lethal factor, and edema factor, which play a crucial role in the pathogenesis of anthrax.

The other options are incorrect:

• It produces Medusa head colony: This statement is true. Bacillus anthracis colonies on agar plates exhibit a characteristic appearance resembling a “Medusa head” due to their irregular, filamentous projections.
• It gives positive M’Fadyean’s reaction: This statement is true. M’Fadyean’s reaction is a method used to stain the capsule of Bacillus anthracis, resulting in a positive reaction.
• It is used as an agent of bioterrorism: Unfortunately, this statement is true. Bacillus anthracis has been used as a biological weapon due to its ability to form highly resistant spores and cause severe disease in humans and animals.

Answer: B. stearothermophilus

Spores of B. stearothermophilus are highly resistant to heat, making them ideal for use in biological indicators within autoclaves. These indicators are used to verify the effectiveness of the sterilization process by ensuring it can kill even highly resistant organisms.

The other options are incorrect:

• B. megaterium: While some strains of B. megaterium can form spores, they are not as heat-resistant as B. stearothermophilus and wouldn’t be suitable for autoclave validation.
• B. thuringiensis: This species is known for producing insecticidal proteins and wouldn’t be used for sterilization purposes.
• B. anthracis: B. anthracis spores are highly dangerous due to their potential use in bioterrorism. They wouldn’t be introduced into an autoclave for safety reasons.

Answer: C. tetani

C. tetani is known for producing subterminal endospores. These endospores are located off-center, closer to one end of the bacterial cell.

The other options are incorrect:

• C. tertium: While some strains of C. tertium can form spores, the location isn’t typically subterminal.
• C. septicum: The spore location in C. septicum is usually terminal, meaning it’s positioned at the very end of the cell.
• C. ramosum: Information on spore location for C. ramosum is less readily available, but it’s not known for having subterminal spores.

Answer: C. perfringens

A reverse CAMP test is used to identify C. perfringens. In this test, the synergy between a CAMP factor produced by Group B Streptococcus (usually S. agalactiae) and alpha toxin from C. perfringens leads to a characteristic “arrowhead” or “bow tie” shaped zone of hemolysis on a blood agar plate.

The other options are incorrect:

• C. tetani: C. tetani doesn’t produce the necessary alpha toxin for a positive reverse CAMP test.
• C. difficile: C. difficile doesn’t produce the required factors for a positive reverse CAMP test.
• C. novyi: While some strains of C. novyi may produce hemolytic toxins, they typically wouldn’t interact with the CAMP factor in a way that yields a positive reverse CAMP test.

Answer: Klebsiella granulomatis

Klebsiella granulomatis is the bacterium responsible for granuloma inguinale, a sexually transmitted infection (STI) that causes ulcers on the genitals.

The other options are incorrect:

• Chlamydia trachomatis: This bacterium is the leading cause of chlamydia, another STI, but it doesn’t cause granuloma inguinale.
• Mycoplasma hominis: This mycoplasma species can be associated with pelvic inflammatory disease but isn’t the cause of granuloma inguinale.
• Klebsiella rhinoscleromatis: This Klebsiella species causes rhinoscleroma, a chronic upper respiratory tract infection, and isn’t linked to granuloma inguinale.

Answer: Throat swab

The human throat naturally harbors a variety of anaerobic bacteria as part of the normal flora. Culturing a throat swab for anaerobes would likely yield a mix of these normal inhabitants, making it difficult to identify any specific pathogens that might be present.

The other options are incorrect:

• Blood: While blood cultures are typically performed aerobically, anaerobic cultures can be necessary in some situations to detect certain bacteria that may not grow well in oxygenated environments.
• Culdocentesis aspirate: This fluid aspirated from the pouch behind the uterus can harbor anaerobic bacteria involved in pelvic inflammatory disease and requires anaerobic culture for proper diagnosis.
• Peritoneal fluid: Similar to culdocentesis fluid, the peritoneal cavity (abdominal cavity lining) can be infected with anaerobic bacteria, necessitating anaerobic cultures for accurate diagnosis.

Answer: N-Acetyl-L-cysteine

N-Acetyl-L-cysteine is not a constituent of bacterial cell walls. It is a derivative of the amino acid cysteine and is sometimes used in microbiology laboratories to break down mucus and other substances that can interfere with the isolation and identification of bacteria.

The other options are incorrect:

• N-acetyl muramic acid (NAM): As mentioned earlier, NAM is a crucial component of peptidoglycan.
• N-acetyl glucosamine (NAG): Similar to NAM, NAG is another essential building block of peptidoglycan.
• Teichoic acid: While not present in all bacteria, teichoic acids are found in some bacterial cell walls and contribute to their overall structure and function.

Answer: Candida albicans

Non-specific urethritis (NSU) is typically caused by bacteria or other microorganisms. While Candida albicans is a fungus, not a bacterium, it’s not a common culprit in NSU. NSU is primarily a sexually transmitted infection, and Candida infections are usually not transmitted sexually.

The other options are incorrect:

• Ureplasma urealyticum: This bacterium is a known cause of NSU, particularly in men.
• Gardnerella vaginalis: This bacterium can contribute to bacterial vaginosis, which can sometimes be confused with NSU in women.
• Actinobacillus hominis: This is a less common cause of NSU, but it can still be a contributing factor.

Answer: Candle jar

A candle jar is not suitable for culturing anaerobic organisms because it doesn’t create a completely oxygen-free environment. While the burning candle consumes oxygen, it also produces carbon dioxide, which can create an environment that’s microaerophilic (with low oxygen levels) but not entirely anaerobic (completely oxygen-free).

The other options are incorrect:

• Gas-Pak: A Gas-Pak system creates an anaerobic environment by using a chemical packet that absorbs oxygen and releases carbon dioxide and hydrogen. This method is commonly used for anaerobic culture.
• McIntosh & Fildes jar: This jar uses a combination of chemicals and evacuation techniques to remove oxygen and create an anaerobic environment for culturing bacteria.
• Thioglycollate broth: This type of broth contains a reducing agent (often sodium thioglycolate) that scavenges oxygen throughout the entire depth of the broth, making it suitable for culturing both aerobic and anaerobic bacteria at different depths depending on their oxygen preference.

Answer: It ferments Sorbitol sugar in the medium

EHEC strains are typically sorbitol-negative. This means they cannot ferment sorbitol, a sugar alcohol, and this characteristic is used in laboratory tests to differentiate EHEC from other E. coli strains.

The other options are incorrect:

• The most common serotype is O157:H7: This is true. O157:H7 is the most common serotype associated with EHEC outbreaks.
• It can cause Hemolytic Uremic Syndrome (HUS): EHEC infection can lead to HUS, a serious complication affecting the kidneys, blood cells, and circulatory system.
• It produces toxin which is toxic to HeLa cell lines: EHEC produces Shiga toxin, a potent cytotoxin that can damage various cell lines, including HeLa cells.

Answer: S. bongori & S. enterica

The genus Salmonella is divided into two main species:

• S. bongori: This species is typically associated with cold-blooded animals like reptiles.
• S. enterica: This species is further divided into six subspecies, and it includes most of the serotypes that cause salmonellosis in humans and warm-blooded animals.

The other options are incorrect:

• S. enterica & S. arizonae: S. arizonae is no longer considered a separate species within Salmonella. It’s now classified as a subspecies within S. enterica, specifically S. enterica subsp. arizonae.
• S. arizonae & S. enteritidis: Similar to S. arizonae, S. enteritidis is not a separate species. It belongs to S. enterica subsp. enterica, the same subspecies as S. typhi.
• S. bongori & S. typhi: While both are classified within Salmonella, S. typhi is a serotype within S. enterica subsp. enterica, not a separate species.

Answer: String of pearls appearance

The Gram stained smear of Vibrios in mucus flakes of a stool specimen often resembles a “string of pearls” appearance. This characteristic morphology is due to the arrangement of the bacteria, which appear as curved or comma-shaped rods lined up in a chain-like fashion.

The other options are incorrect:

• School of fish appearance: While this term might be used more generally for large numbers of similarly shaped bacteria, “string of pearls” is more specific to the arrangement and staining pattern seen with Vibrios.
• Fish in stream appearance: Similar to the above, this description is less specific than “string of pearls.”
• Sea-gul appearance: This term is not typically used to describe the appearance of bacteria in a Gram stain.

Answer: Hemophilus aegyptius

Hemophilus aegyptius is the bacterial organism identified as the cause of Brazilian Purpuric Fever (BPF). This recently discovered disease is characterized by symptoms like conjunctivitis and hemorrhagic manifestations.

The other options are incorrect:

• Hemophilus hemolyticus: While this species can cause respiratory infections, it’s not linked to BPF.
• Hemophilus aphrophilus: This bacterium is primarily found in the oral cavity and doesn’t cause BPF.
• Hemophilus parainfluenzae: This species is associated with respiratory illnesses but not BPF.

Answer: Staph.aureus

Staphylococcus aureus is not typically a gelatin liquefier. While some strains may exhibit weak gelatinase activity, it’s not a reliable characteristic for identification.

The other options are incorrect:

• Morganella morganii: This bacterium possesses the enzyme gelatinase and can liquefy gelatin.
• Bacillus subtilis: B. subtilis is a well-known gelatin liquefier. It produces a strong extracellular gelatinase that breaks down gelatin.
• Proteus vulgaris: Proteus vulgaris also has gelatinase activity and can liquefy gelatin, often with a characteristic spreading pattern.

Answer: Obligate parasite

An obligate parasite depends entirely on a host organism to survive and complete its life cycle. It cannot live or reproduce outside of a host.

The other options are incorrect:

• Facultative parasite: A facultative parasite can live both with and without a host. It may have a free-living stage in its life cycle but can also parasitize a host for some or all of its life.
• Hyperparasite: A hyperparasite is a parasite that parasitizes another parasite. It can be either obligate or facultative in its relationship with the primary host.
• Pathogenic parasite: A pathogenic parasite is any parasite that causes harm or disease to its host. This term doesn’t specify the dependence on the host for survival.

Answer: M.africanum

Mycobacterium tuberculosis complex (MTBC): This group of closely related bacteria causes tuberculosis (TB) in humans and animals. M. africanum is one of the confirmed members of this complex.

The other options are incorrect:

• M. ulcerans: This bacterium causes Buruli ulcer, a chronic skin disease. While it’s a Mycobacterium species, it’s not part of the MTBC.
• M. gordonae: This is a non-pathogenic Mycobacterium species, meaning it doesn’t cause disease in humans.
• M. kansasii: This Mycobacterium species can cause pulmonary infections similar to TB, but it’s not considered part of the MTBC. It belongs to a group called non-tuberculous mycobacteria (NTM).

Answer: M.ulcerans

M. ulcerans: This specific Mycobacterium species produces a toxin called mycolactone, which is responsible for causing the characteristic necrotic lesions (tissue death) associated with Buruli ulcer.

The other options are incorrect:

• M. avium intracellulare (MAI): This is a type of Mycobacterium that can cause opportunistic infections in immunocompromised individuals, but it isn’t linked to Buruli ulcer.
• M. xenopi: Similar to MAI, M. xenopi is another Mycobacterium species known to cause opportunistic infections, but not Buruli ulcer.
• M. malmoense: This Mycobacterium species is rarely associated with human infections and isn’t known to cause Buruli ulcer.

Answer: Their cell wall contains diaminopimelic acid

Mycoplasma: These are the smallest known free-living organisms and lack a cell wall. Diaminopimelic acid is a component found in the cell walls of some bacteria, but not in Mycoplasma.

The other options are incorrect:

• They belong to the class Mollicutes: This is true. Mycoplasma is indeed classified within the Mollicutes class, known for lacking cell walls.
• They require sterols for their growth: Mycoplasma species often require cholesterol or other sterols from their host for membrane stability and growth.
• Their colonies have “Fried egg” appearance: This is a characteristic feature of some Mycoplasma colonies when grown on culture plates. They appear with a fried-egg morphology, with a central, darker, and denser core surrounded by a flattened, translucent periphery.

Answer: Ixodides tick and Tularemia

These hard-bodied ticks are known vectors (transmitters) for several diseases. The other three options (Babesiosis, Lyme disease, Endemic relapsing fever) are all transmitted by Ixodides ticks.

The other options are incorrect:

• Ixodides tick and Babesiosis: Babesia is a parasite transmitted by Ixodes ticks, causing a malaria-like illness.
• Ixodides tick and Lyme disease: The bacterium Borrelia burgdorferi, which causes Lyme disease, is transmitted through the bite of Ixodes ticks.
• Ixodides tick and Endemic relapsing fever: Borrelia spirochetes, different from the one causing Lyme disease, are transmitted by Ixodes ticks and cause Endemic relapsing fever.

Answer: These are strictly aerobic gram positive branching filaments

Actinomyces are anaerobic or facultatively anaerobic, gram-positive branching filaments. They are not strictly aerobic.

The other options are incorrect:

• They produce sulphur granules: Actinomyces species can indeed produce sulfur granules in tissues, particularly in chronic infections.
• They cause Actinomycetoma: Actinomycetoma is a chronic bacterial infection of the skin and soft tissue caused by Actinomycetes, including some species of Actinomyces.
• They are Non acid fast: Actinomyces are indeed non-acid-fast bacteria, meaning they do not retain the stain when treated with acid-alcohol during staining procedures like the Ziehl-Neelsen stain for acid-fast organisms.

Answer: Legionella pneumophila

This bacterium thrives in warm, stagnant water environments like cooling towers and air conditioning systems. It can be aerosolized through these systems and inhaled, causing Legionnaires’ disease, a type of pneumonia.

The other options are incorrect:

• Methicillin resistant Staph aureus (MRSA): While MRSA is a major hospital-acquired infection, it’s primarily spread through direct contact with infected individuals or contaminated surfaces, not through air conditioning systems.
• Mycobacterium scrofulaceum: This bacterium can cause skin and lymph node infections but isn’t typically associated with hospital-acquired infections via air conditioning systems.
• Aeromonas hydrophila: This bacterium is more commonly associated with waterborne infections and is not a typical culprit in hospital-acquired infections spread through air conditioning.

Answer: Active efflux of antibiotic

Bacteria can develop resistance to tetracyclines through the mechanism of active efflux, where specialized proteins pump the antibiotic out of the bacterial cell, reducing its concentration inside the cell and thus its effectiveness.

The other options are incorrect:

• Altered target enzymes: This mechanism involves modifying the target site of the antibiotic, reducing its binding affinity. It is more commonly associated with resistance to other classes of antibiotics, such as beta-lactams.
• Poor transport across membrane: This refers to reduced uptake of the antibiotic into the bacterial cell, which is not a common mechanism of tetracycline resistance.
• Altered ribosomal targets: Tetracyclines exert their antibacterial effect by binding to the bacterial ribosome and inhibiting protein synthesis. Altering the ribosomal target would make the bacteria susceptible, not resistant, to tetracyclines.

Answer: 1-2 X 10 8 cfu/ml

A 0.5 McFarland turbidity standard corresponds to a bacterial concentration in the range of 1 x 10^8 to 5 x 10^8 colony-forming units per milliliter (CFU/mL). Matching a bacterial suspension to this standard indicates that the bacterial concentration falls within this range.

The other options are incorrect:

• 0.5-1 X 10^5 cfu/ml: This value is too low. A 0.5 McFarland standard is designed to represent a higher bacterial density.
• 2-3 X 10^8 cfu/ml: While within the possible range for some variations of the McFarland standard, typically a 0.5 standard targets the lower end (1-2 x 10^8 cfu/ml).
• 1-2 X 10^5 cfu/ml (mentioned twice): As explained above, this value is too low to correspond to a 0.5 McFarland turbidity standard.

Answer: B.anthracis

This bacterium is the causative agent of anthrax, a primarily zoonotic disease. While it can cause gastrointestinal issues in some cases, bloody diarrhea is not a typical symptom. Anthrax infection usually occurs through inhalation of spores, ingestion of contaminated food, or skin contact with infected animals or their products.

The other options are incorrect:

• Shigella dysenteriae: This bacterium causes shigellosis, characterized by bloody diarrhea, abdominal cramps, fever, and vomiting.
• Campylobacter fetus: This species can cause campylobacteriosis, leading to bloody diarrhea, abdominal pain, fever, and nausea.
• Clostridium difficile: This bacterium is a common cause of hospital-acquired diarrhea, often with blood and mucus in the stool. It disrupts the gut microbiome and produces toxins that damage the intestinal lining.

Answer: Acute rheumatic fever

Acute rheumatic fever is a post-streptococcal sequelae, occurring as a complication of untreated or inadequately treated Streptococcal infections, particularly group A Streptococcus. It often follows streptococcal pharyngitis and can lead to various symptoms, including fever, joint pain, and inflammation of the heart.

The other options are incorrect:

• Cellulitis: Cellulitis is a bacterial skin infection commonly caused by Staphylococcus aureus or Streptococcus pyogenes, but it is not typically considered a post-streptococcal sequelae.
• Pharyngitis: While streptococcal pharyngitis (strep throat) is caused by group A Streptococcus bacteria, it is the precursor to acute rheumatic fever, not a post-streptococcal sequelae itself.
• Impetigo: Impetigo is a superficial bacterial skin infection often caused by Staphylococcus aureus or Streptococcus pyogenes. It is not considered a post-streptococcal sequelae.

Answer: Widal test

The Widal test is a serological test used for the diagnosis of typhoid fever. It detects antibodies against Salmonella typhi, the causative agent of typhoid fever, in the patient’s serum.

The other options are incorrect:

• Blood culture: While blood culture can also be used for diagnosing typhoid fever by isolating the causative bacterium, Salmonella typhi, from the patient’s blood, it is not a specific diagnostic test like the Widal test.
• Dick Test: The Dick test is used to determine a person’s susceptibility to diphtheria by injecting a small amount of diphtheria toxin into the skin. It is not used for the diagnosis of typhoid fever.
• Schick Test: The Schick test is used to determine a person’s susceptibility to diphtheria by testing for immunity to diphtheria toxin. It is not used for the diagnosis of typhoid fever.

Answer: Shick test

This is the specific diagnostic test used to assess susceptibility to diphtheria, not to diagnose an active infection. It injects a small amount of diphtheria toxin under the skin. If the person has no immunity (antibodies) to diphtheria toxin, an inflammatory reaction develops at the injection site within 24-48 hours.

The other options are incorrect:

• Blood culture: While blood cultures can be used in some severe diphtheria cases to identify Corynebacterium diphtheriae bacteria, the Shick test is the primary tool to assess susceptibility.
• Dick Test: This test is used to diagnose scarlet fever, not diphtheria. It detects the presence of toxins produced by Streptococcus pyogenes bacteria.
• Widal test: This test is used for typhoid fever, not diphtheria, and detects antibodies against Salmonella Typhi bacteria.

Answer: Mantoux test

The Mantoux test, also known as the tuberculin skin test, is a diagnostic test used for tuberculosis (TB). It involves injecting a small amount of purified protein derivative (PPD) tuberculin into the skin. A positive reaction, characterized by induration at the injection site, indicates exposure to the TB bacteria.

The other options are incorrect:

• Dick Test: This test is used to diagnose scarlet fever, not TB. It detects the presence of toxins produced by Streptococcus pyogenes bacteria.
• Shick test: This test is used to assess susceptibility to diphtheria, not TB.
• Widal test: This test is used for typhoid fever, not TB, and detects antibodies against Salmonella Typhi bacteria.

Answer: Dick Test

The Dick test is a specific diagnostic tool used to confirm scarlet fever, caused by Streptococcus pyogenes bacteria. It injects a small amount of a toxin produced by these bacteria (scarlet fever toxin) under the skin. If the person has scarlet fever, they will have developed antibodies against the toxin. An injection of the toxin in such a case will not cause a local inflammatory reaction because the antibodies will neutralize the toxin.

The other options are incorrect:

• Mantoux test: This test is used for TB, not scarlet fever.
• Shick test: This test is used to assess susceptibility to diphtheria, not scarlet fever.
• Widal test: This test is used for typhoid fever, not scarlet fever, and detects antibodies against Salmonella Typhi bacteria.