Bacteriology — MCQs

Bacteriology Indian Medical PG Practice Questions and MCQs

Question 2351: Kanagawa's phenomenon is seen in ?

A. Vibrio parahaemolyticus (Correct Answer)
B. Proteus mirabilis
C. Pseudomonas aeruginosa
D. Shigella sonnei

Explanation: ***Vibrio parahaemolyticus*** - The **Kanagawa phenomenon** refers to the production of a **thermostable direct hemolysin (TDH)** by *Vibrio parahaemolyticus*. - This hemolysin is associated with gastroenteritis caused by contaminated seafood, leading to **beta-hemolysis** on Wagatsuma agar. *Pseudomonas aeruginosa* - This bacterium is known for producing various toxins and enzymes, but the **Kanagawa phenomenon** specifically relates to hemolysin production by *Vibrio parahaemolyticus*, not *Pseudomonas aeruginosa*. - *P. aeruginosa* is often associated with **opportunistic infections** in immunocompromised patients, burn victims, and individuals with cystic fibrosis. *Shigella sonnei* - *Shigella sonnei* is a common cause of **bacterial dysentery** (shigellosis) and does not exhibit the Kanagawa phenomenon. - Its pathogenicity is primarily due to its ability to invade and replicate within colonic epithelial cells and produce **Shiga toxin**. *Proteus mirabilis* - *Proteus mirabilis* is a common cause of **urinary tract infections** and is characterized by its **swarming motility** on agar. - It does not produce the specific hemolysin associated with the Kanagawa phenomenon.

Question 2352: Subterminal spores are seen in which of the following organisms?

A. Clostridium perfringens (Correct Answer)
B. Clostridium tetani
C. Clostridium tertium
D. None of the options

Explanation: ***Clostridium perfringens*** - This bacterium is known for producing **subterminal spores**, meaning the spores are located near, but not at, the end of the cell. - *C. perfringens* is a common cause of **gas gangrene** and food poisoning, often forming spores under adverse environmental conditions. *Clostridium tetani* - *C. tetani* produces **terminal spores**, which are found directly at one end of the bacterial cell. - These terminal spores give the organism a characteristic **"drumstick" or "tennis racket" appearance**. *Clostridium tertium* - Similar to *Clostridium tetani*, *C. tertium* is also known to produce **terminal spores**. - Its spores are typically located at the extreme end of the cell. *None of the options* - This option is incorrect because *Clostridium perfringens* specifically fits the description of producing subterminal spores. - The other *Clostridium* species listed, *C. tetani* and *C. tertium*, produce terminal spores, not subterminal.

Question 2353: Primary mode of transmission of Listeria monocytogenes is:

A. Ingestion (Correct Answer)
B. Inhalation
C. Skin inoculation
D. None of the options

Explanation: ***Ingestion*** - *Listeria monocytogenes* is primarily transmitted through the **consumption of contaminated food**, making **ingestion** the main route. - This bacterium can adapt well to cold temperatures and grow in refrigerated foods, such as **deli meats**, **soft cheeses**, and **unpasteurized milk**. *Inhalation* - While possible in specific occupational settings (e.g., slaughterhouse workers exposed to aerosols), **inhalation** is not the primary mode of transmission for the general population. - Respiratory infections with *Listeria* are rare and typically occur secondary to severe systemic infection. *Skin inoculation* - **Skin inoculation** is an uncommon route of transmission for *Listeria monocytogenes* and is not considered a primary mode of spread. - It could theoretically occur through direct contact with infected animal tissues, but this is a rare event. *None of the options* - This option is incorrect because **ingestion** is a well-established and primary mode of transmission for *Listeria monocytogenes*. - The other options are either rare or not the main way this pathogen is acquired by humans.

Question 2354: Which of the following statements is true about Campylobacter jejuni?

A. Obligate aerobe
B. Oxidase negative
C. Grows at 42°C (Correct Answer)
D. Non-motile

Explanation: ***Grows at 42°C*** - *Campylobacter jejuni* is thermophilic, meaning it **prefers and grows optimally at warmer temperatures**, specifically around 42°C. - This characteristic is often exploited in selective culture media used for its isolation from clinical samples. *Obligate aerobe* - *Campylobacter jejuni* is not an obligate aerobe, but rather a **microaerophilic** organism, meaning it requires a reduced oxygen atmosphere (typically 5-10% oxygen) for growth. - Obligate aerobes require normal atmospheric oxygen levels (around 21%) to survive and grow. *Oxidase negative* - *Campylobacter jejuni* is **oxidase-positive**, an important diagnostic characteristic that helps differentiate it from other enteric bacteria. - The oxidase test detects the presence of cytochrome c oxidase, an enzyme involved in the electron transport chain. *Non-motile* - *Campylobacter jejuni* is highly **motile** due to its **single polar flagellum**, which contributes to its ability to colonize and invade the intestinal mucosa. - Motility is a key virulence factor, allowing the bacterium to move through the viscous mucosal layer.

Question 2355: In which part of Mycoplasma are sterols found?

A. Cell wall of Rickettsia
B. Cell membrane of Rickettsia
C. Cell wall of Mycoplasma
D. Cell membrane of Mycoplasma (Correct Answer)

Explanation: ***Cell membrane of Mycoplasma*** - **Mycoplasma** species are unique among bacteria because they lack a **cell wall**. - Instead, their **cell membrane** contains **sterols**, which are acquired from the host, providing stability and strength to the membrane. *Cell wall of Rickettsia* - **Rickettsia** are obligate intracellular bacteria that possess a typical **gram-negative cell wall**, but it does not contain **sterols**. - **Sterols** are generally not found in bacterial cell walls, and most bacteria cannot synthesize them. *Cell membrane of Rickettsia* - **Rickettsia** have a typical bacterial **cell membrane** that lacks **sterols**. - **Sterols** are primarily components of eukaryotic cell membranes, with **Mycoplasma** being a notable exception among bacteria. *Cell wall of Mycoplasma* - **Mycoplasma** species are characterized by the complete **absence of a cell wall**, which makes them resistant to many common antibiotics that target cell wall synthesis. - Therefore, **sterols** cannot be found in their cell wall, as it does not exist.

Question 2356: Which strain of E. coli is primarily associated with hemolytic uremic syndrome?

A. Enteropathogenic
B. Enterotoxigenic
C. Enteroinvasive
D. Enterohemorrhagic (Correct Answer)

Explanation: ***Enterohemorrhagic*** - **Enterohemorrhagic E. coli (EHEC)**, particularly the O157:H7 serotype, produces **Shiga toxins** (Stx1 and Stx2). - These toxins damage endothelial cells in the kidneys, leading to **hemolytic uremic syndrome (HUS)**, characterized by hemolytic anemia, thrombocytopenia, and acute kidney injury. *Enteropathogenic* - **Enteropathogenic E. coli (EPEC)** causes **diarrhea** in infants by attaching to intestinal cells and effacing microvilli, leading to malabsorption. - It does not produce Shiga toxins and is not associated with HUS. *Enterotoxigenic* - **Enterotoxigenic E. coli (ETEC)** is a common cause of **traveler's diarrhea**, producing **heat-labile (LT)** and **heat-stable (ST)** toxins. - These toxins stimulate fluid and electrolyte secretion in the small intestine, but do not cause HUS. *Enteroinvasive* - **Enteroinvasive E. coli (EIEC)** invades and destroys the colonic epithelium, causing **dysentery** with fever and bloody stools. - It is similar to Shigella in its pathogenic mechanism but is not associated with the development of HUS.

Question 2357: Which of the following bacteria can cause enteric fever?

A. Salmonella paratyphi A
B. Salmonella paratyphi B
C. Salmonella typhi
D. All of the above (Correct Answer)

Explanation: ***All of the above*** - **Enteric fever** (typhoid fever and paratyphoid fever) is a systemic infection caused by specific serotypes of *Salmonella enterica*. - *Salmonella typhi*, *Salmonella paratyphi A*, and *Salmonella paratyphi B* are all known to cause different forms of enteric fever. *Salmonella typhi* - This is the primary causative agent of **typhoid fever**, the most severe form of enteric fever. - It is responsible for the classic presentation of prolonged fever, headache, abdominal pain, and rose spots rash. *Salmonella paratyphi A* - This serotype is a well-established cause of **paratyphoid fever**, which is clinically similar to typhoid but often milder. - It specifically refers to infections caused by *Salmonella enterica* serovar Paratyphi A. *Salmonella paratyphi B* - Similar to *Salmonella paratyphi A*, this serotype also causes **paratyphoid fever**. - Infections by *Salmonella enterica* serovar Paratyphi B represent another cause of enteric fever with clinical presentation similar to but milder than typhoid.

Question 2358: Double zone of hemolysis is seen in ?

A. Streptococcus pyogenes
B. Clostridium perfringens (Correct Answer)
C. Corynebacterium diphtheriae
D. Staphylococcus aureus

Explanation: ***Clostridium perfringens*** - **Double zone of hemolysis** is a classic characteristic seen when *Clostridium perfringens* is grown on **blood agar**. - This is due to the synergistic action of two different toxins: the inner zone of complete hemolysis (**beta-hemolysis**) is caused by **alpha-toxin** (lecithinase), and the outer, less complete zone is caused by **theta-toxin**. *Staphylococcus aureus* - *Staphylococcus aureus* typically exhibits a **single zone of beta-hemolysis** (complete hemolysis) on blood agar, not a double zone. - It produces various hemolysins, but their combined effect does not result in the distinct double-zone phenomenon. *Streptococcus pyogenes* - *Streptococcus pyogenes* is known for producing **clear, complete beta-hemolysis** on blood agar due to the action of streptolysin O and S. - It does not produce a double zone of hemolysis; the zone of clearing is uniform around the colonies. *Corynebacterium diphtheriae* - *Corynebacterium diphtheriae* is generally **non-hemolytic** or shows **alpha-hemolysis** (partial hemolysis), which appears as a green discoloration around the colonies. - It is commonly identified by its growth on selective media like tellurite agar, where it forms black colonies.

Question 2359: On which medium is the earliest growth of diphtheria detected?

A. Potassium tellurite medium with iron
B. MacConkey agar
C. Dorset egg medium
D. Loeffler serum slope (Correct Answer)

Explanation: ***Loeffler serum slope*** - This medium provides rapid early growth of *Corynebacterium diphtheriae*, facilitating quick diagnosis. - It enhances the **pleomorphism** and typical **metachromatic granules** (Babes-Ernst bodies) of diphtheria bacilli, making them observable within **6-8 hours**. *Potassium tellurite medium with iron* - This medium is **selective** for *Corynebacterium diphtheriae* and differentiates it from other bacteria. - While useful for isolation, the earliest growth and colonial morphology are observed later, providing a result in **18-24 hours**. *MacConkey agar* - This is a **selective and differential medium** primarily used for **Gram-negative bacteria**, particularly enteric bacilli. - *Corynebacterium diphtheriae* is a **Gram-positive bacterium** and would not grow well or at all on this medium. *Dorset egg medium* - This is a solid medium used for the **transport and cultivation of various bacteria**, including some mycobacteria. - It is not specifically optimized for the rapid or earliest growth of *Corynebacterium diphtheriae* compared to Loeffler's serum slope.

Question 2360: Frisch bacillus affects most commonly

A. Nose (Correct Answer)
B. Mouth
C. Eye
D. Ear

Explanation: ***Nose*** - *Klebsiella rhinoscleromatis*, also known as Frisch bacillus, is the causative agent of **rhinoscleroma**, a chronic granulomatous disease. - This bacterium primarily affects the **nasal mucosa** and upper respiratory tract, leading to progressive inflammation and nodule formation. *Mouth* - While *Klebsiella* species can be found in the oral cavity as commensals, *Klebsiella rhinoscleromatis* does not typically cause primary disease predominantly affecting the mouth. - Other infections of the mouth are more commonly linked to different bacterial or fungal pathogens. *Eye* - Ocular involvement in conditions caused by Frisch bacillus is **rare** and usually secondary to extensive spread from the primary nasal sites, not a direct primary infection. - The eye has its own specific set of infectious agents that commonly cause primary ocular pathology. *Ear* - Infection of the ear by Frisch bacillus is **not a common or primary manifestation** of rhinoscleroma. - Ear infections are typically caused by bacteria like *Streptococcus pneumoniae* or *Haemophilus influenzae*, especially in otitis media.

Practice by Chapter

Staphylococci

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Streptococci and Enterococci

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Neisseria and Moraxella

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Corynebacterium and Listeria

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Bacillus and Clostridium

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Enterobacteriaceae

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Vibrio, Aeromonas, and Plesiomonas

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Pseudomonas and Related Bacteria

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Haemophilus and HACEK Group

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Bordetella and Brucella

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Mycobacteria

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Spirochetes

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