Bacteriology — MCQs

Bacteriology Indian Medical PG Practice Questions and MCQs

Question 2371: Which organism is the most common cause of acute bacterial prostatitis?

A. Enterococcus
B. Streptococcus viridans
C. Peptostreptococcus
D. E.coli (Correct Answer)

Explanation: ***E.coli*** - **E.coli** is the most common cause of **acute bacterial prostatitis**, accounting for a significant majority of cases. - It is a **gram-negative rod** commonly found in the gastrointestinal tract and can ascend into the urinary tract and prostate. *Enterococcus* - While **Enterococcus species** can cause urinary tract infections and, less commonly, prostatitis, they are a distant second to E.coli in frequency. - They are **gram-positive cocci** and are often associated with catheter-associated infections or healthcare-acquired infections. *Streptococcus viridans* - **Streptococcus viridans** group bacteria are typically commensals of the oral cavity and are more known for causing **endocarditis** or dental infections. - They are not a common cause of acute bacterial prostatitis. *Peptostreptococcus* - **Peptostreptococcus** is a genus of **anaerobic gram-positive cocci** commonly found in the normal flora of the mouth, gastrointestinal tract, and vagina. - They are typically involved in **polymicrobial anaerobic infections** but are not a primary or common cause of acute bacterial prostatitis.

Question 2372: Which of the following vectors is known to transmit a disease that can be identified by the presence of spirochetes under dark-field microscopy?

A. Anopheles
B. Ixodes scapularis ticks (Correct Answer)
C. Louse
D. Rat flea

Explanation: ***Ixodes scapularis ticks*** - *Ixodes scapularis* ticks are the primary vectors for **Lyme disease**, caused by the spirochete *Borrelia burgdorferi*. - **Spirochetes** can be identified in tissue samples or cultures using **dark-field microscopy** or silver staining techniques. - Direct visualization from patient samples is uncommon; diagnosis typically relies on serology and clinical presentation. *Louse* - Lice (e.g., *Pediculus humanus corporis*) transmit **relapsing fever** (*Borrelia recurrentis*) and epidemic typhus (*Rickettsia prowazekii*). - *Borrelia recurrentis* spirochetes are readily visible in **peripheral blood smears** using Wright or Giemsa stain during febrile episodes. - While this is also a spirochete disease, the question specifically refers to dark-field microscopy, which is classically associated with Lyme disease spirochete identification. *Anopheles* - The *Anopheles* mosquito is the vector for **malaria**, caused by *Plasmodium* parasites, not spirochetes. - Malaria is diagnosed by identifying ring forms, trophozoites, and schizonts within red blood cells on blood smears. *Rat flea* - The rat flea (*Xenopsylla cheopis*) is the primary vector for **bubonic plague** (*Yersinia pestis*) and murine typhus (*Rickettsia typhi*). - *Yersinia pestis* is a gram-negative coccobacillus, not a spirochete.

Question 2373: Which anaerobic organism is known to cause multiple abscesses with discharging sinuses and demonstrates sulfur granules in pus?

A. Nocardia asteroides
B. Salmonella enterica
C. Francisella tularensis
D. Actinomyces (Correct Answer)

Explanation: ***Actinomyces*** - *Actinomyces* species are classic causes of **actinomycosis**, characterized by chronic, suppurative infections with **multiple abscesses**, draining sinuses, and the presence of **sulfur granules** in pus. - They are **anaerobic or microaerophilic gram-positive bacteria** that are part of the normal flora of the mouth and gastrointestinal tract, causing infection when mucosal barriers are disrupted. *Nocardia asteroides* - *Nocardia asteroides* causes **nocardiosis**, which can also present with abscesses, but it is an **aerobic bacterium** and typically does not produce sulfur granules. - Nocardial infections often involve the lungs, skin, or central nervous system, particularly in **immunocompromised individuals**. *Salmonella enterica* - *Salmonella enterica* is a facultative anaerobic Gram-negative bacterium known for causing **gastroenteritis**, typhoid fever, and bacteremia. - It is not associated with the formation of multiple abscesses with draining sinuses or sulfur granules. *Francisella tularensis* - *Francisella tularensis* causes **tularemia**, a zoonotic disease characterized by ulceroglandular lesions, fever, and lymphadenopathy. - It does not typically cause multiple abscesses with draining sinuses or produce sulfur granules.

Question 2374: Which microorganism is the most common cause of pyogenic osteomyelitis?

A. S. aureus (Correct Answer)
B. Streptococcus spp.
C. Corynebacterium spp.
D. Neisseria gonorrhoeae (gonococcus)

Explanation: ***Staph aureus*** - **_Staphylococcus aureus_** is the most frequent cause of **pyogenic osteomyelitis** across all age groups and routes of infection. - Its ability to adhere to bone, form biofilms, and produce toxins contributes to its prevalence in bone infections. *Streptococcus spp.* - While various **_Streptococcus_** species can cause infections, they are less common causes of pyogenic osteomyelitis compared to **_Staphylococcus aureus_**. - **Group A _Streptococcus_** can cause severe invasive infections but rarely involves primary bone infection. *Corynebacterium spp.* - **_Corynebacterium_** species, particularly **_Corynebacterium striatum_**, are increasingly recognized as opportunistic pathogens, especially in immunocompromised individuals or those with foreign bodies. - However, they are not the most common cause of osteomyelitis in the general population. *Neisseria gonorrhoeae (gonococcus)* - **_Neisseria gonorrhoeae_** can cause **disseminated gonococcal infection (DGI)**, which may include joint involvement (**septic arthritis**). - While it can lead to bone pain and swelling, it primarily affects joints and is a less common cause of direct **pyogenic osteomyelitis** than **_S. aureus_**.

Question 2375: Granulomatosis infantiseptica is caused by:

A. Pseudomonas
B. Chlamydia trachomatis
C. Group D streptococci
D. Listeria (Correct Answer)

Explanation: ***Listeria*** - **Granulomatosis infantiseptica** is a severe manifestation of congenital **listeriosis**, caused by *Listeria monocytogenes*. - This condition is characterized by widespread **granulomas** and **microabscesses** in various organs of the infected newborn. *Pseudomonas* - *Pseudomonas aeruginosa* is a common cause of healthcare-associated infections but is not typically associated with **granulomatosis infantiseptica**. - It can cause severe infections in immunocompromised individuals, including **pneumonia**, **sepsis**, and wound infections. *Chlamydia trachomatis* - *Chlamydia trachomatis* is a common cause of **conjunctivitis** and **pneumonia** in neonates, acquired during passage through the birth canal. - It does not cause **granulomatosis infantiseptica**. *Group D streptococci* - While Group D streptococci (e.g., *Enterococcus faecalis*) can cause neonatal infections like **sepsis** and **meningitis**, they are not the causative agents of **granulomatosis infantiseptica**. - This condition is specifically linked to **Listeria**.

Question 2376: All are true about anaerobic infections except:

A. Specimen for UTI is suprapubic aspiration
B. They are found normally on skin and GIT
C. Exudates and swabs are ideal for culture (Correct Answer)
D. Most infections are endogenous

Explanation: ***Exudates and swabs are ideal for culture.*** - **Swabs exposed to air** are generally **not ideal** for anaerobic culture because oxygen exposure can kill obligate anaerobes, leading to false-negative results. - Optimal anaerobic specimen collection requires techniques that **minimize oxygen exposure**, such as aspirates or tissue biopsies placed in anaerobic transport media. *Most infections are endogenous* - Anaerobic infections commonly arise from **one's own commensal flora**, which becomes pathogenic under specific conditions like tissue damage or impaired blood supply. - These bacteria are part of the normal microbiota of various body sites, including the gastrointestinal tract, oral cavity, and skin. *Specimen for UTI is suprapubic aspiration* - For **suspected anaerobic urinary tract infections (UTIs)**, suprapubic aspiration is considered the gold standard for specimen collection. - This method bypasses potential contamination from urethral flora and ensures a sterile, oxygen-free sample for accurate anaerobic culture. *They are found normally on skin and GIT* - **Anaerobic bacteria** are a significant component of the normal flora of the **skin and gastrointestinal tract (GIT)**, as well as the oral cavity and genitourinary tract. - Their presence in these sites is crucial for maintaining normal physiological functions and preventing the overgrowth of pathogens.

Question 2377: Which of the following statements about anthrax toxin is false?

A. Increase cAMP
B. Has three components
C. Coded by plasmid
D. Inhibits protein synthesis (Correct Answer)

Explanation: ***Inhibits protein synthesis*** - Anthrax toxin, specifically the **lethal factor (LF)**, is a **zinc-dependent metalloprotease** that cleaves and inactivates **mitogen-activated protein kinase kinase (MAPKKs)**, leading to cell death, not directly inhibiting protein synthesis. - The **edema factor (EF)** component of the toxin is an **adenylate cyclase** that increases **intracellular cyclic AMP (cAMP)**, which also does not directly inhibit protein synthesis. *Has three components* - Anthrax toxin is indeed composed of three distinct proteins: **protective antigen (PA)**, **edema factor (EF)**, and **lethal factor (LF)**. - PA is necessary for EF and LF to enter host cells, while EF causes edema and LF is responsible for cytotoxicity. *Increase cAMP* - The **edema factor (EF)** component of anthrax toxin is a **calmodulin-dependent adenylate cyclase**. - Once inside the cell, EF converts **ATP to cyclic AMP (cAMP)**, leading to increased intracellular cAMP levels, which disrupts water homeostasis and causes edema. *Coded by plasmid* - The genes encoding the anthrax toxin components (PA, EF, and LF) are located on a large plasmid known as **pXO1**. - This plasmid, along with another plasmid (pXO2) carrying genes for the capsule, is crucial for the full virulence of *Bacillus anthracis*.

Question 2378: Draughtsman colonies are seen with:

A. Anthrax
B. Pertussis
C. Pneumococci (Correct Answer)
D. Yersinia

Explanation: ***Pneumococci*** - **Draughtsman colonies** (or **draughtsman-like colonies**) are a characteristic morphological feature observed when *Streptococcus pneumoniae* (pneumococci) grows on certain agar media, such as blood agar. - This appearance is due to the **central umbilication or depression** of the colony caused by autolytic enzymes that break down the bacterial cells in the center as the colony matures. *Anthrax* - Colonies of *Bacillus anthracis* are typically described as **"Medusa head" colonies**, characterized by swirling projections at the periphery. - They are generally **non-hemolytic** on blood agar, distinguishing them from other *Bacillus* species. *Pertussis* - *Bordetella pertussis* colonies are characteristic on **Bordet-Gengou agar**, appearing as small, glistening, pearl-like, or "mercury droplet" colonies. - This distinct morphology is crucial for its identification in laboratory cultures. *Yersinia* - *Yersinia pestis* (which causes plague) colonies on blood agar at 28°C often show a **"fried egg" appearance** over several days, with a dark center and lighter periphery. - Other *Yersinia* species like *Y. enterocolitica* can show a **bull's-eye pattern** on CIN (Cefsulodin-Irgasan-Novobiocin) agar.

Question 2379: Bartonella quintana causes:

A. Trench fever (Correct Answer)
B. Scrub typhus
C. Epidemic typhus
D. Endemic typhus

Explanation: ***Trench fever*** - **Bartonella quintana** is the causative agent of **trench fever**, a louse-borne disease historically common during wartime. - Symptoms include **recurrent fevers**, headache, bone pain (especially in the shins), and rash. *Scrub typhus* - Scrub typhus is caused by **Orientia tsutsugamushi**, a rickettsial bacterium, not Bartonella. - It is transmitted by **chiggers** and characterized by a rash, fever, and eschar at the bite site. *Epidemic typhus* - Epidemic typhus is caused by **Rickettsia prowazekii** and is also louse-borne. - It presents with sudden high fever, severe headache, and a maculopapular rash that spares the face, palms, and soles. *Endemic typhus* - Endemic typhus (murine typhus) is caused by **Rickettsia typhi** and is transmitted by **rat fleas**. - Its symptoms are generally milder than epidemic typhus, including fever, headache, and a truncal rash.

Question 2380: Which of the following statements is NOT true about the El Tor biotype of Vibrio cholerae?

A. VP (+)
B. Lower mortality
C. Reduced environmental persistence (Correct Answer)
D. Hemolysis negative

Explanation: ***Reduced environmental persistence*** - The **El Tor biotype** of *Vibrio cholerae* is known for its **increased environmental persistence** compared to the classical biotype, making this statement NOT true. - El Tor survives longer in water sources due to its hardiness and ability to form biofilms, which contributes to its pandemic potential and makes outbreaks harder to control. *VP (+)* - The El Tor biotype is **Voges-Proskauer (VP) positive**, which is a key biochemical characteristic used to differentiate it from the classical biotype (VP negative). - This is a TRUE statement about El Tor. *Lower mortality* - The El Tor biotype causes **milder disease with lower mortality rates** compared to the classical biotype. - While individual cases may be less severe, the higher infectivity and asymptomatic carriage of El Tor contribute to its widespread transmission - this is a TRUE statement. *Hemolysis negative* - The El Tor biotype is **hemolysis positive** (produces beta-hemolysis on sheep blood agar), which is another key differentiating feature from the classical biotype (hemolysis negative). - This makes the statement "hemolysis negative" NOT true about El Tor.

Practice by Chapter

Staphylococci

Practice Questions

Streptococci and Enterococci

Practice Questions

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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