Bacteriology Practice Questions

Q: Treatment of sexual partners is required for all sexually transmitted infections except:

Gardnerella vaginalis. **Explanation:** The core concept behind this question is distinguishing between a **Sexually Transmitted Infection (STI)** and a **Dysbiosis (Imbalance of normal flora)**. **1. Why Gardnerella vaginalis is the correct answer:** *Gardnerella vaginalis* is the primary organism associated with **Bacterial Vaginosis (BV)**. BV is not classified as a traditional STI; rather, it is a clinical syndrome resulting from the replacement of normal hydrogen peroxide-producing *Lactobacilli* with an overgrowth of anaerobic bacteria. Multiple randomized controlled trials have demonstrated that treating the male sexual partner **does not prevent recurrence** in the woman or improve cure rates. Therefore, partner notification and treatment are not recommended. **2. Analysis of Incorrect Options:** * **Trichomonas vaginalis (C):** This is a protozoan STI. Partners are often asymptomatic reservoirs. Failure to treat partners leads to high rates of "ping-pong" reinfection. * **Chlamydia trachomatis (D) & Mycoplasma genitalium (B):** These are obligate or facultative intracellular bacteria that cause urethritis and cervicitis. They are strictly transmitted through sexual contact. Partner treatment is mandatory to prevent reinfection and complications like Pelvic Inflammatory Disease (PID). **3. NEET-PG High-Yield Pearls:** * **Amsel’s Criteria for BV (3 out of 4):** 1. Thin, homogenous discharge; 2. Vaginal pH >4.5; 3. Positive Whiff test (10% KOH); 4. **Clue cells** on microscopy (most specific). * **Nugent Scoring:** The gold standard for diagnosing BV (based on Gram stain morphotypes). * **Drug of Choice:** Metronidazole (Oral or Gel) is the treatment of choice for BV, regardless of pregnancy status (though some prefer oral in pregnancy). * **Note:** While BV is not an STI, it is more common in sexually active individuals and is a risk factor for acquiring other STIs like HIV.

Q: What is the most common cause of acute urinary tract infection?

Escherichia coli. **Explanation:** **Escherichia coli (Option A)** is the most common cause of acute urinary tract infection (UTI) in both community and hospital settings, accounting for approximately **70–90%** of cases. The primary medical concept behind its dominance is its specialized virulence factors, specifically **P-pili (pyelonephritis-associated pili)** and **Type 1 fimbriae**, which allow the bacteria to adhere to the uroepithelium and resist being flushed out by urine flow. **Analysis of Incorrect Options:** * **Klebsiella (Option B):** While a common cause of healthcare-associated (nosocomial) UTIs and infections in patients with urinary catheters or structural abnormalities, it ranks significantly lower than *E. coli* in overall incidence. * **Streptococcus faecalis (Enterococcus) (Option C):** This is a Gram-positive coccus typically associated with UTIs in elderly men (often related to prostate issues) or hospitalized patients with indwelling catheters. * **Staphylococcus saprophyticus (Option D):** This is the **second most common cause** of acute UTIs in young, sexually active females (often referred to as "Honeymoon Cystitis"). However, it still accounts for only 5–15% of cases, making *E. coli* the statistically superior answer. **High-Yield Clinical Pearls for NEET-PG:** * **Most common overall:** *E. coli*. * **Second most common in young females:** *S. saprophyticus* (Novobiocin resistant). * **Common in catheterized patients:** *Proteus mirabilis* (associated with staghorn calculi due to urease production) and *Pseudomonas*. * **Diagnostic Gold Standard:** Significant bacteriuria is defined as **≥10⁵ CFU/mL** (Kass concept). * **Culture Media:** *E. coli* produces flat, dark pink colonies on **MacConkey agar** (Lactose Fermenter) and a classic **metallic sheen** on EMB agar.

Q: All the following statements about Vibrio cholerae O139 are true, except:

It produces O1 Lipopolysaccharide.. **Explanation:** The correct answer is **D (It produces O1 Lipopolysaccharide)**. This statement is false because *Vibrio cholerae* O139 is defined by its unique surface antigen. Unlike the O1 strain, O139 has lost the genes for O1 lipopolysaccharide (LPS) biosynthesis and replaced them with a large insert of DNA that encodes the **O139-specific polysaccharide capsule** and a different LPS structure. This antigenic shift is why the O139 strain can cause epidemics even in populations with pre-existing immunity to the O1 strain. **Analysis of other options:** * **A is true:** The clinical presentation of O139 is identical to O1 El Tor, characterized by "rice-water stools" and rapid dehydration. Both strains utilize the same **cholera toxin (CT)** mechanism. * **B is true:** *V. cholerae* O139 (also known as the **Bengal strain**) was first identified during an outbreak in **Chennai (Madras)** in October 1992, subsequently spreading across the Indian subcontinent. * **C is true:** Epidemiologically, O139 behaves like the El Tor biotype; it is hardy, survives well in the environment, and has a high ratio of asymptomatic carriers to clinical cases. **High-Yield Clinical Pearls for NEET-PG:** * **Serogroups:** Only O1 and O139 cause epidemic/pandemic cholera. Non-O1/Non-O139 strains usually cause sporadic gastroenteritis. * **Capsule:** O139 is the **only** cholera strain that possesses a prominent polysaccharide capsule, which aids in its virulence. * **Pandemic Status:** While O139 caused a massive epidemic in the 1990s (often called the "8th pandemic candidate"), the current ongoing 7th pandemic is still officially attributed to *V. cholerae* O1 El Tor. * **Diagnosis:** O139 does not agglutinate with O1 antiserum. It requires specific O139 antiserum for identification.

Q: Which is a venereal form of treponemal infection?

Yaws. **Explanation:** The question asks for the **venereal** (sexually transmitted) form of treponemal infection. However, there appears to be a discrepancy in the provided key: **Syphilis** is the only venereal treponematosis, while Yaws, Pinta, and Endemic Syphilis are **non-venereal** (endemic) treponematoses. **1. Why Syphilis is the correct conceptual answer:** Treponemal diseases are caused by the genus *Treponema*. They are divided into two categories based on transmission: * **Venereal Treponematosis:** Caused by *Treponema pallidum* subspecies *pallidum*. It is transmitted primarily through sexual contact or congenitally. * **Non-Venereal (Endemic) Treponematoses:** These are diseases of childhood, transmitted via direct skin-to-skin contact or fomites, usually in areas of poor hygiene. **2. Analysis of Options:** * **Syphilis (Option C):** The only venereal form. It presents in stages (Primary, Secondary, Latent, Tertiary). * **Yaws (Options A & D):** Caused by *T. pallidum* ssp. *pertenue*. It is a **non-venereal** infection affecting skin and bones, common in humid tropical climates. * **Pinta (Option B):** Caused by *T. carateum*. It is a **non-venereal** infection limited strictly to the skin, found in Central and South America. **High-Yield Clinical Pearls for NEET-PG:** * **Causative Organisms:** * Venereal Syphilis: *T. pallidum pallidum* * Endemic Syphilis (Bejel): *T. pallidum endemicum* * Yaws: *T. pallidum pertenue* * Pinta: *T. carateum* * **Eradication:** India was declared free of Yaws in 2016 (the first country to be declared free of a non-venereal treponematosis). * **Treatment:** A single dose of **Azithromycin** (30 mg/kg) is now the preferred treatment for Yaws (Morgans Strategy), replacing Benzathine Penicillin. * **Diagnosis:** All treponemes are morphologically identical and serologically indistinguishable (all give positive VDRL/FTA-ABS).

Q: A man presents to a dermatologist with a severe mucocutaneous rash involving most of his body, including his palms and soles. He reports a recent sexual encounter with a prostitute in Southeast Asia several months prior. Which of the following is the most likely causative agent of this rash?

Treponema pallidum. The clinical presentation describes a classic case of **Secondary Syphilis**, caused by the spirochete ***Treponema pallidum***. ### **Explanation of the Correct Answer** Secondary syphilis typically manifests 2–10 weeks after the primary chancre heals. It is characterized by a generalized, non-pruritic, maculopapular rash. A hallmark feature for NEET-PG is the involvement of the **palms and soles**, which is rare in other viral exanthems. The history of a high-risk sexual encounter several months prior aligns with the incubation period and progression from primary to secondary syphilis. ### **Why Other Options are Incorrect** * **Herpes Simplex I & II (A & B):** These typically present with localized, painful vesicles on an erythematous base (cold sores or genital herpes). While they can cause disseminated disease in immunocompromised states, they do not present as a generalized mucocutaneous rash involving the palms and soles. * **HIV (C):** Acute Retroviral Syndrome can cause a morbilliform rash and fever, but it usually occurs 2–4 weeks after exposure and is transient. While HIV is a risk factor, the specific distribution (palms/soles) and timing point more specifically to syphilis. ### **High-Yield Clinical Pearls for NEET-PG** * **"The Great Mimicker":** Syphilis is known for its diverse presentations. * **Palmar/Plantar Rash Differential:** Syphilis, Rocky Mountain Spotted Fever, Hand-Foot-Mouth Disease, and Erythema Multiforme. * **Condyloma Lata:** Flat, moist, highly infectious lesions in intertriginous areas (Secondary Syphilis). * **Diagnosis:** Screening with non-treponemal tests (VDRL/RPR) and confirmation with treponemal tests (FTA-ABS/TPHA). * **Treatment:** Benzathine Penicillin G (2.4 million units IM) is the drug of choice.

Q: What is the causative organism of acute salpingitis?

Chlamydia. **Explanation:** Acute salpingitis is a key component of Pelvic Inflammatory Disease (PID). While PID is often polymicrobial, **Chlamydia trachomatis** is recognized as the most common causative organism worldwide, particularly in the subacute and chronic presentations that lead to tubal factor infertility. * **Why Chlamydia is Correct:** *Chlamydia trachomatis* is an obligate intracellular bacterium that frequently causes asymptomatic or "silent" salpingitis. It is the leading cause of tubal damage and ectopic pregnancy due to its ability to cause significant endosalpingeal destruction despite mild clinical symptoms. * **Why Neisseria is Incorrect:** *Neisseria gonorrhoeae* was historically considered the primary cause. While it causes a more "acute" and clinically florid presentation (high fever, severe pain, and purulent discharge), epidemiological data now shows Chlamydia has a higher overall prevalence in PID cases. * **Why Streptococcus & Ureaplasma are Incorrect:** *Streptococcus* (Group B) and *Ureaplasma urealyticum* are part of the vaginal flora and can be isolated in polymicrobial PID, but they are rarely the primary or most common initiators of acute salpingitis. **High-Yield Clinical Pearls for NEET-PG:** * **Gold Standard Diagnosis:** Laparoscopy (shows hyperemic, edematous tubes with purulent exudate). * **Most Common Route of Infection:** Ascending infection from the lower genital tract. * **Fitz-Hugh-Curtis Syndrome:** A complication of salpingitis (usually Chlamydial) involving peri-hepatitis and "violin-string" adhesions between the liver capsule and parietal peritoneum. * **Treatment:** Must cover both *Chlamydia* and *Neisseria* (e.g., Ceftriaxone plus Doxycycline).

Q: Toxins are implicated as the major pathogenic mechanism in all of the following bacterial diarrheas except?

Vibrio parahemolyticus. ### Explanation The pathogenesis of bacterial diarrhea is generally classified into two mechanisms: **Toxin-mediated** (secretory) and **Invasive** (inflammatory). **Why Vibrio parahaemolyticus is the correct answer:** While *Vibrio parahaemolyticus* produces a thermostable direct hemolysin (TDH or Kanagawa phenomenon), its primary pathogenic mechanism is **direct mucosal invasion** and destruction of intestinal epithelial cells. It causes an inflammatory diarrhea (often with blood and mucus) rather than a purely toxin-driven secretory process. **Analysis of Incorrect Options:** * **Vibrio cholerae:** The prototype of toxin-mediated diarrhea. It produces **Cholera Toxin (Choleragen)**, which increases cAMP levels, leading to massive secretion of water and electrolytes (Rice water stools) without mucosal invasion. * **Shigella sp:** Although *Shigella* is invasive, it produces the potent **Shiga Toxin (Stx)**. The question asks where toxins are the *major* mechanism; in Shigellosis, the toxin is a critical virulence factor responsible for cell death, microvascular damage, and potential HUS. * **Staphylococcus aureus:** Causes food poisoning via the ingestion of **Pre-formed Enterotoxins** (Type A-E). The bacteria do not need to colonize the gut; the toxin alone triggers the emetic center and diarrhea. **NEET-PG High-Yield Pearls:** * **Kanagawa Phenomenon:** Refers to the β-hemolysis produced by *V. parahaemolyticus* on High Salt Blood Agar (Wagatsuma Agar); it correlates with pathogenicity. * **Mechanism of Cholera Toxin:** ADP-ribosylation of Gs protein → Persistent activation of Adenylate Cyclase → ↑ cAMP. * **Pre-formed toxins:** *S. aureus* and *Bacillus cereus* (emetic type) are the fastest causes of food poisoning (incubation 1–6 hours). * **Invasive organisms:** *Salmonella*, *Shigella*, *Campylobacter*, and *EIEC* typically present with fever and fecal leucocytes.

Q: Which of the following statements about Campylobacter is false?

Campylobacter is a spore-forming bacterium.. **Explanation:** The correct answer is **C** because **Campylobacter species are non-spore-forming**, Gram-negative, curved or spiral-shaped bacilli. In medical microbiology, spore formation is a characteristic primarily reserved for specific Gram-positive rods, such as *Bacillus* and *Clostridium* species. **Analysis of Options:** * **Option A & B (Correct statements):** *Campylobacter jejuni* is a major zoonotic pathogen. The primary reservoir is the gastrointestinal tract of wild and domestic animals, especially **poultry**. Human infection typically occurs via the fecal-oral route through the consumption of **undercooked meat**, contaminated milk, or water. * **Option D (Correct statement):** *Campylobacter* is a leading **enteric pathogen** worldwide. It is a common cause of bacterial gastroenteritis, characterized by inflammatory, often bloody diarrhea (dysentery), fever, and abdominal cramps. **High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** Described as "seagull-wing" shaped appearance. * **Motility:** Exhibits characteristic **"darting motility"** via a single polar flagellum. * **Culture Requirements:** It is **microaerophilic** (requires 5% $O_2$) and **thermophilic**, growing best at **42°C** on selective media like **Skirrow’s medium** or **Preston agar**. * **Complications:** It is the most common antecedent infection associated with **Guillain-Barré Syndrome (GBS)** due to molecular mimicry between bacterial lipooligosaccharides and human gangliosides. It is also linked to Reactive Arthritis.

Q: Which of the following statements is not true about Vibrio cholerae?

It cannot survive in an extracellular environment.. **Explanation:** The correct answer is **D**, as the statement is false. *Vibrio cholerae* is a facultative intracellular pathogen, but it is primarily known for its ability to survive and multiply extensively in **extracellular environments**, particularly in brackish water and estuarine ecosystems. It often attaches to the chitinous shells of copepods (zooplankton) for survival outside the human host. **Analysis of Options:** * **Option A (Non-halophilic):** This is true. Unlike most other *Vibrio* species (like *V. parahaemolyticus*) which are halophilic (salt-loving) and require high NaCl concentrations, *V. cholerae* is non-halophilic and can grow in media with 0% NaCl, though it tolerates low salt concentrations (up to 3%). * **Option B (Simple media):** This is true. *V. cholerae* is not fastidious. It grows well on routine laboratory media like Nutrient Agar and MacConkey Agar (forming colorless colonies). * **Option C (Man is the only natural host):** This is true. While the bacteria persist in water bodies, there is no known animal reservoir; humans are the only natural hosts affected by the clinical disease. **High-Yield NEET-PG Pearls:** * **Morphology:** Gram-negative, comma-shaped (vibrion) rods with a single polar flagellum showing **"darting motility."** * **Selective Media:** **TCBS** (Thiosulfate Citrate Bile salts Sucrose) agar is the gold standard, where it produces **yellow colonies** due to sucrose fermentation. * **Enrichment Media:** Alkaline Peptone Water (APW) and Monsur’s Taurocholate Tellurite Peptone Water. * **Biochemical Key:** It is **Oxidase positive** (distinguishes it from Enterobacteriaceae) and grows at a high pH (alkaline pH 8.2–9.0).

Question 1

Treatment of sexual partners is required for all sexually transmitted infections except:

Accepted Answer

Gardnerella vaginalis

Answer

Mycoplasma genitalium

Answer

Trichomonas vaginalis

Answer

Chlamydia trachomatis

Question 2

What is the most common cause of acute urinary tract infection?

Accepted Answer

Escherichia coli

Answer

Klebsiella

Answer

Streptococcus faecalis

Answer

Staphylococcus saprophyticus

Question 3

All the following statements about Vibrio cholerae O139 are true, except:

Accepted Answer

It produces O1 Lipopolysaccharide.

Answer

Clinical manifestations are similar to the O1 El Tor strain.

Answer

It was first discovered in Chennai.

Answer

It is epidemiologically indistinguishable from the O1 El Tor strain.

Question 4

Which is a venereal form of treponemal infection?

Accepted Answer

Yaws

Answer

Pinta

Answer

Syphilis

Question 5

A man presents to a dermatologist with a severe mucocutaneous rash involving most of his body, including his palms and soles. He reports a recent sexual encounter with a prostitute in Southeast Asia several months prior. Which of the following is the most likely causative agent of this rash?

Accepted Answer

Treponema pallidum

Answer

Herpes simplex I

Answer

Herpes simplex II

Answer

HIV

Question 6

What is the causative organism of acute salpingitis?

Accepted Answer

Chlamydia

Answer

Streptococcus

Answer

Neisseria

Answer

Ureaplasma

Question 7

Toxins are implicated as the major pathogenic mechanism in all of the following bacterial diarrheas except?

Accepted Answer

Vibrio parahemolyticus

Answer

Vibrio cholerae

Answer

Shigella sp

Answer

Staphylococcus aureus

Question 8

Which of the following statements about Campylobacter is false?

Accepted Answer

Campylobacter is a spore-forming bacterium.

Answer

Uncooked meat can be a source of infection.

Answer

Poultry is a common source of infection.

Answer

Campylobacter is an enteric pathogen.

Question 9

All the following are false regarding C. diphtheriae toxin EXCEPT:

Accepted Answer

Toxin production depends on optimum concentration of iron

Answer

It is an endotoxin

Answer

It acts by activating adenyl cyclase

Answer

Schick Test demonstrates circulating toxin

Question 10

Which of the following statements is not true about Vibrio cholerae?

Accepted Answer

It cannot survive in an extracellular environment.

Answer

It is non-halophilic.

Answer

It grows on simple media.

Answer

Man is the only natural host.

Bacteriology — MCQs

Bacteriology — MCQs

On this page

Practice by Chapter

Want unlimited practice?