Bacteriology Practice Questions

Q: Which of the following is a true statement regarding Enterobacteriaceae?

All members are oxidase negative. ***All members are oxidase negative*** - This is the **definitive and universally true** statement for all Enterobacteriaceae, with **no exceptions**. - The **negative oxidase test** is a key defining characteristic that distinguishes Enterobacteriaceae from other Gram-negative bacteria such as *Pseudomonas*. - This enzymatic characteristic is crucial for basic laboratory identification and is **consistently used as a primary screening test** for this family. *Glucose is fermented by most members of the family* - While the fermentation of glucose is indeed a characteristic of Enterobacteriaceae, the statement is **imprecise** because it says "most" when in fact **ALL members** ferment glucose. - The use of "most" makes this statement technically less accurate than the oxidase-negative statement, which correctly uses "all." *Motility in Enterobacteriaceae is via peritrichous flagella* - This statement is **incomplete and potentially misleading** because **not all members are motile**. - While motile members do have **peritrichous flagella** (distributed over the entire cell surface), important members like *Klebsiella* species are **non-motile**. - The statement implies universal motility, which is incorrect. *Nitrate reduction positive* - While all Enterobacteriaceae do reduce nitrates to nitrites, this statement **lacks specificity** compared to the oxidase test. - The oxidase-negative characteristic is more **diagnostically distinctive** and is the **primary screening test** used to differentiate Enterobacteriaceae from other Gram-negative bacteria. - Nitrate reduction is confirmatory but not as definitive for initial identification.

Q: Which of the following organisms is an obligate intracellular bacterium that commonly causes sexually transmitted infections?

Chlamydia. ***Chlamydia*** - **Chlamydia trachomatis** is a classic example of an **obligate intracellular bacterium** that is a leading cause of sexually transmitted infections (STIs). - It has a unique biphasic developmental cycle, alternating between an infectious **elementary body** and a replicative **reticulate body** within host cells. *Rickettsia* - **Rickettsia** species are also **obligate intracellular bacteria** but are primarily transmitted via **arthropod vectors** (e.g., ticks, fleas, lice), causing diseases like **Rocky Mountain spotted fever** and **typhus**. - They are not typically associated with **sexually transmitted infections** in humans. *Mycoplasma* - **Mycoplasma** species are bacteria characterized by the **absence of a cell wall**, but they are generally **extracellular** or **intracellular but not obligate**. - While some *Mycoplasma* species can cause STIs (e.g., *Mycoplasma genitalium*), they do not fit the description of an **obligate intracellular bacterium** in the same way *Chlamydia* does (which requires host cell machinery for energy production). *Prion* - A **prion** is an **infectious protein particle** that lacks genetic material (DNA or RNA) and causes transmissible spongiform encephalopathies (TSEs), such as **Creutzfeldt-Jakob disease**. - It is not a bacterium and is not associated with **sexually transmitted infections**.

Q: A 26-year-old male patient presented with a granulomatous penile ulcer. On Wright Giemsa staining, tiny organisms of 2 microns are seen engulfed by macrophages. What is the causative organism?

Donovanosis (Calymmatobacterium granulomatis). ***Donovanosis (Calymmatobacterium granulomatis)*** - The presence of **granulomatous penile ulcers** and characteristic **Donovan bodies** (2-micron organisms engulfed by macrophages on Wright-Giemsa stain) are pathognomonic for donovanosis. - This condition is caused by *Calymmatobacterium granulomatis* (now reclassified as *Klebsiella granulomatis*). *Lymphogranuloma venereum (LGV)* - While LGV also causes genital ulcers and lymphadenopathy, the causative agent is *Chlamydia trachomatis* serovars L1, L2, or L3, and it does not present with **Donovan bodies** in macrophages. - Histologically, LGV often shows **stellate abscesses** in lymph nodes, not intracellular organisms in a granulomatous ulcer. *Gonorrhea (Neisseria gonorrhoeae)* - Gonorrhea typically presents as **urethritis** with purulent discharge in males or cervicitis in females, not commonly as a granulomatous penile ulcer. - Microscopic examination would show **Gram-negative intracellular diplococci** within neutrophils, not macrophage-engulfed organisms like Donovan bodies. *Syphilis (Treponema pallidum)* - Primary syphilis manifests as a **painless chancre**, which is typically a clean-based, indurated ulcer, not usually granulomatous. - Diagnosis is made by **darkfield microscopy** to visualize spirochetes or serological tests (e.g., RPR, VDRL, FTA-ABS), not by finding intracellular organisms on Wright-Giemsa stain.

Q: Causative agent of trench fever is which of the following?

Bartonella quintana. ***Bartonella Quintana*** - **Bartonella quintana** is the bacterium responsible for causing **trench fever**, a disease historically prevalent during wartime in crowded and unsanitary conditions. - It is transmitted by the **human body louse** (*Pediculus humanus corporis*), which acts as a vector for the bacteria. *Coxiella burnetii* - **Coxiella burnetii** is the causative agent of **Q fever**, a zoonotic disease typically transmitted to humans through contact with infected animals or their products. - Its clinical presentation often includes acute fever, pneumonia, and hepatitis, which differs from the characteristic relapsing fever of trench fever. *R. tsutsugamushi* - **R. tsutsugamushi** (also known as *Orientia tsutsugamushi*) causes **scrub typhus**, a mite-borne disease common in rural areas of Asia and Australia. - The disease is characterized by a distinctive eschar, lymphadenopathy, and maculopapular rash, which are not typical features of trench fever. *R. prowazekii* - **R. prowazekii** is the bacterium responsible for **epidemic typhus** (louse-borne typhus), which shares the human body louse as a vector with trench fever. - However, epidemic typhus presents with a sustained high fever, rash that spreads centrifugally, and severe systemic symptoms, differentiating it from the relapsing fever patterns of trench fever.

Q: Which of the following structures is least likely to be affected by gonococcus?

Testis. ***Testis*** - The **testis** itself is relatively protected from direct gonococcal infection and is thus least likely to be primarily affected. - While epididymitis can occur due to gonococcus, orchitis (inflammation of the testis) without epididymitis is rare and generally caused by other pathogens like mumps virus. *Urethra* - The **urethra** is the most common site of initial gonococcal infection in males, leading to **urethritis** [1]. - Symptoms often include dysuria and purulent discharge [1]. *Prostate* - The **prostate** can be affected by ascending gonococcal infection from the urethra, leading to **prostatitis**. - This typically presents with pelvic pain, dysuria, and fever. *Seminal vesicle* - The **seminal vesicles** can also be involved in ascending gonococcal infections, often alongside epididymitis or prostatitis. - Inflammation can contribute to pain and reproductive complications.

Q: A 30-year-old male patient has a large, spreading, and exuberant ulcer with bright red granulation tissue over the glans penis, with no lymphadenopathy. What is the most likely causative organism?

Klebsiella granulomatis. ***Klebsiella granulomatis*** - This organism causes **donovanosis (granuloma inguinale)**, characterized by exuberant, beefy-red **granulation tissue** and ulcers, often on the genitalia. - The absence of **lymphadenopathy** is a key feature differentiating it from other venereal ulcers, as the infection remains largely localized. - Previously known as *Calymmatobacterium granulomatis*, the organism was reclassified as Klebsiella granulomatis in 1999. *Treponema pallidum* - Causes **syphilis**, which typically presents as a **chancre**—a firm, painless ulcer with an indurated base and clean borders, often accompanied by regional **lymphadenopathy**. - The ulcer in this case is described as large, spreading, and exuberant with bright red granulation tissue, which is not characteristic of a syphilitic chancre. *Herpes simplex virus type 1* - HSV-1 can cause genital herpes, but it typically presents as **multiple, painful vesicular lesions** that may progress to shallow ulcers. - The description of a single, large, spreading, and exuberant ulcer with bright red granulation tissue does not fit the typical presentation of herpetic lesions. *Herpes simplex virus type 2* - HSV-2 is the most common cause of **genital herpes**, manifesting as **painful vesicles** and subsequent shallow ulcers, often recurrent. - This presentation would involve vesicular lesions and pain, which are not described, and the ulcer type is inconsistent with classic HSV-2 lesions.

Q: Which of the following statements about Enterohemorrhagic E. coli (EHEC) is false?

Ferments sorbitol. ***Ferments sorbitol*** - Most **EHEC** strains, particularly O157:H7, are **unable to ferment sorbitol**, a characteristic used in laboratory identification. - This inability to ferment sorbitol helps differentiate EHEC from most other *E. coli* strains which typically ferment sorbitol. - Sorbitol-MacConkey (SMAC) agar is used for selective identification of EHEC O157:H7. *Causes HUS* - **EHEC** is a major cause of **hemolytic uremic syndrome (HUS)**, especially in children, due to its production of Shiga toxins. - HUS is characterized by **hemolytic anemia**, **thrombocytopenia**, and **acute kidney injury**. *Elaborates shiga like exotoxin* - **EHEC** produces potent **Shiga-like toxins (Stx1 and Stx2)**, also known as Verotoxins, which are responsible for its virulence. - These toxins damage endothelial cells, particularly in the gastrointestinal tract and kidneys, leading to symptoms like **hemorrhagic colitis** and **HUS**. *Does not invade intestinal epithelium* - **EHEC** causes disease primarily through **toxin production and adherence**, not through invasive infection of host cells. - Unlike *Shigella* or enteroinvasive *E. coli* (EIEC), EHEC remains extracellular and does not invade the intestinal mucosa. - The Sereny test, which assesses bacterial invasiveness, is **negative** for EHEC.

Q: Most common organism in acute osteomyelitis is

Staphylococcus aureus. ***Staphylococcus aureus*** - **_Staphylococcus aureus_** is the most common causative organism in cases of **acute osteomyelitis** across all age groups and is the primary pathogen isolated in most osteomyelitis cases. - Its ability to adhere to bone, form **biofilms**, and produce various virulence factors contributes to its dominance in bone infections. *Salmonella* - **_Salmonella_** species are a common cause of osteomyelitis, particularly in patients with **sickle cell disease** due to their impaired splenic function. - While significant in specific populations, it is not the most common cause of osteomyelitis in the general population. *Pseudomonas aeruginosa* - **_Pseudomonas aeruginosa_** is frequently associated with osteomyelitis in patients with a history of **intravenous drug use**, **puncture wounds** (particularly through athletic shoes), healthcare-associated infections, or those with compromised immunity. - It is an important pathogen in these specific contexts but not generally the most common cause. *Streptococcus pneumoniae* - **_Streptococcus pneumoniae_** can cause osteomyelitis, especially in **neonates** and **young children**, and in individuals with **immunosuppression**. - However, it is not as prevalent as **_Staphylococcus aureus_** as the overall leading cause of acute osteomyelitis.

Q: Which organism is most commonly associated with causing bacterial meningitis in adults?

Streptococcus pneumoniae (Pneumococcus). ***Streptococcus pneumoniae (Pneumococcus)*** - *Streptococcus pneumoniae* is the most common bacterial cause of **meningitis** in adults and children worldwide. - It often follows a primary infection like **otitis media**, sinusitis, or pneumonia. *Staphylococcus aureus* - While *S. aureus* can certainly cause meningitis, it is more commonly associated with **post-neurosurgical**, **post-traumatic**, or **hematogenous meningitis** from distant foci. - It is not the most frequent cause of community-acquired meningitis in the general population. *Streptococcus agalactiae (Group B Strep)* - *Streptococcus agalactiae* is a leading cause of **neonatal meningitis** (in newborns). - It is an important pathogen in infants but much less common in older children and adults. *Mycoplasma pneumoniae* - *Mycoplasma pneumoniae* is primarily known for causing **atypical pneumonia** and tracheobronchitis. - While neurological complications can occur, such as encephalitis or Guillain-Barré syndrome, it is a very rare cause of meningitis itself.

Q: What is the primary use of the lepromin test in leprosy?

Assessment of cell-mediated immunity. ***Assessment of cell-mediated immunity*** - The lepromin test primarily measures the host's **cell-mediated immune response** to *Mycobacterium leprae* antigens. - A positive reaction indicates a strong CMI, typically seen in **tuberculoid leprosy**, while a negative reaction suggests absent or suppressed CMI, as in **lepromatous leprosy**. *Diagnosis of leprosy* - The lepromin test is **not used for diagnosing active leprosy**, as it does not distinguish between current infection, past exposure, or vaccination. - Diagnosis relies on clinical signs, **acid-fast bacilli** in smears, and histopathology. *Epidemiological studies* - While it can provide insights into population immune profiles, it's **not the primary tool for epidemiological surveillance** or prevalence estimation, which often uses clinical examination. - Its utility in epidemiology is limited by its inability to identify active cases or recent infections. *Determining treatment efficacy* - The lepromin test remains positive for a long time after effective treatment and thus **cannot be used to monitor treatment response** or cure. - Treatment efficacy is assessed by clinical improvement and reduction in bacterial load.

Question 1

Which of the following is a true statement regarding Enterobacteriaceae?

Accepted Answer

All members are oxidase negative

Answer

Glucose is fermented by most members of the family

Answer

Motility in Enterobacteriaceae is via peritrichous flagella

Answer

Nitrate reduction positive

Question 2

Which of the following organisms is an obligate intracellular bacterium that commonly causes sexually transmitted infections?

Accepted Answer

Chlamydia

Answer

Mycoplasma

Answer

Rickettsia

Answer

Prion

Question 3

A 26-year-old male patient presented with a granulomatous penile ulcer. On Wright Giemsa staining, tiny organisms of 2 microns are seen engulfed by macrophages. What is the causative organism?

Accepted Answer

Donovanosis (Calymmatobacterium granulomatis)

Answer

Lymphogranuloma venereum (LGV)

Answer

Gonorrhea (Neisseria gonorrhoeae)

Answer

Syphilis (Treponema pallidum)

Question 4

Causative agent of trench fever is which of the following?

Accepted Answer

Bartonella quintana

Answer

Coxiella burnetii

Answer

R. tsutsugamushi

Answer

R. prowazekii

Question 5

Which of the following structures is least likely to be affected by gonococcus?

Accepted Answer

Testis

Answer

Seminal vesicle

Answer

Urethra

Answer

Prostate

Question 6

A 30-year-old male patient has a large, spreading, and exuberant ulcer with bright red granulation tissue over the glans penis, with no lymphadenopathy. What is the most likely causative organism?

Accepted Answer

Klebsiella granulomatis

Answer

Treponema pallidum

Answer

Herpes simplex virus type 1

Answer

Herpes simplex virus type 2

Question 7

Which of the following statements about Enterohemorrhagic E. coli (EHEC) is false?

Accepted Answer

Ferments sorbitol

Answer

Causes HUS

Answer

Elaborates shiga like exotoxin

Answer

Does not invade intestinal epithelium

Question 8

Most common organism in acute osteomyelitis is

Accepted Answer

Staphylococcus aureus

Answer

Salmonella

Answer

Pseudomonas aeruginosa

Answer

Streptococcus pneumoniae

Question 9

Which organism is most commonly associated with causing bacterial meningitis in adults?

Accepted Answer

Streptococcus pneumoniae (Pneumococcus)

Answer

Streptococcus agalactiae (Group B Strep)

Answer

Staphylococcus aureus

Answer

Mycoplasma pneumoniae

Question 10

What is the primary use of the lepromin test in leprosy?

Accepted Answer

Assessment of cell-mediated immunity

Answer

Diagnosis of leprosy

Answer

Epidemiological studies

Answer

Determining treatment efficacy

Bacteriology — MCQs

Bacteriology — MCQs

On this page

Practice by Chapter

Want unlimited practice?