Bacteriology Practice Questions

Q: A female presents with leaking and meconium-stained liquor at 32 weeks gestation. Which organism is she most likely infected with?

Listeria monocytogenes. **Explanation:** The presence of **meconium-stained liquor (MSL)** in a preterm pregnancy (especially before 34 weeks) is a classic clinical red flag for **Listeria monocytogenes** infection. **Why Listeria monocytogenes is correct:** Listeria is a gram-positive motile bacillus typically transmitted via contaminated food (unpasteurized cheese, cold meats). In pregnancy, it has a unique tropism for the placenta. It causes "granulomatosis infantiseptica" and is notorious for inducing **amnionitis**. A hallmark of Listeria infection is the passage of meconium in utero by a preterm fetus, which is otherwise rare, as the fetal gastrointestinal tract is usually too immature to pass meconium before 34 weeks unless severely stressed by this specific pathogen. **Why other options are incorrect:** * **CMV (Option A):** The most common congenital infection; typically presents with periventricular calcifications, microcephaly, and IUGR, but not acute MSL. * **Toxoplasma gondii (Option C):** Presents with the classic triad of hydrocephalus, chorioretinitis, and intracranial calcifications. It does not typically cause preterm leaking with MSL. * **HSV (Option D):** Usually transmitted during delivery through the birth canal, leading to skin-eye-mouth (SEM) lesions or encephalitis in the neonate. It is not associated with preterm meconium passage. **Clinical Pearls for NEET-PG:** * **Listeria** is the only Gram-positive bacteria that produces an **endotoxin**. * It shows **"tumbling motility"** at 25°C. * **Drug of Choice:** Ampicillin (Listeria is inherently resistant to cephalosporins). * **High-Yield Association:** Preterm labor + Fever + Meconium-stained liquor = Think **Listeria**.

Q: A 70-year-old female patient was readmitted to a local hospital with fever and chills following cardiac surgery. Blood cultures were taken and a gram-positive coccus grew from the blood cultures within 24 hours. Initial tests indicated that this isolate was resistant to penicillin. Which of the following is the most likely identification?

Enterococcus. **Explanation:** The clinical presentation of a post-surgical patient with fever and chills, combined with the laboratory finding of **Gram-positive cocci (GPC)** resistant to penicillin, strongly points toward **Enterococcus**. 1. **Why Enterococcus is correct:** Enterococci (formerly Group D Streptococci) are notorious for their **intrinsic resistance** to many antibiotics, including most cephalosporins and, frequently, penicillins (due to low-affinity Penicillin-Binding Proteins). They are common causes of healthcare-associated infections, including endocarditis and bacteremia following invasive procedures or surgeries. Their ability to grow in 6.5% NaCl and hydrolyze bile esculin are key biochemical markers. 2. **Why the other options are incorrect:** * **Group A (S. pyogenes) and Group B (S. agalactiae) Streptococcus:** These remain **exquisitely sensitive to Penicillin G**. If a GPC is penicillin-resistant, these species are effectively ruled out in a standard exam context. * **Neisseria species:** These are **Gram-negative diplococci**, which contradicts the Gram stain finding (Gram-positive cocci) provided in the question. **High-Yield Clinical Pearls for NEET-PG:** * **Enterococcus faecalis** is the most common species isolated, but **Enterococcus faecium** is more likely to be multidrug-resistant (including Vancomycin resistance - VRE). * **Treatment:** For serious infections (like endocarditis), a combination of a cell-wall active agent (Penicillin/Ampicillin/Vancomycin) plus an **Aminoglycoside** is required for synergistic bactericidal action. * **Culture Characteristics:** They show **Gamma-hemolysis** (usually) on blood agar and can grow in harsh conditions (40% bile and 6.5% NaCl).

Q: Which of the following is known to cause Pedal Botryomycosis?

Staphylococcus aureus. **Explanation:** **Botryomycosis** is a rare, chronic granulomatous bacterial infection that clinically mimics deep fungal infections (mycetomas). Despite its name (which implies a fungal origin), it is a **bacterial infection** characterized by the formation of "grains" or "sulfur granules" within the tissues. 1. **Why Staphylococcus aureus is correct:** * **Staphylococcus aureus** is the most common causative agent of Botryomycosis (responsible for ~40% of cases). Other common bacteria include *Pseudomonas aeruginosa* and *E. coli*. * The pathogenesis involves a low-virulence strain of bacteria or a compromised host immune response, leading to a "Splendore-Hoeppli phenomenon"—an eosinophilic material surrounding the bacterial colonies, forming the characteristic grains. * **Pedal Botryomycosis** specifically refers to involvement of the foot, presenting with nodules, sinuses, and discharge containing grains, resembling a Madura foot. 2. **Analysis of Incorrect Options:** * **A & B (Actinomyces & Nocardia):** These are causes of **Actinomycetoma**. While they also produce grains and sinus tracts, they are filamentous bacteria (higher bacteria) and are distinct from the true bacterial botryomycosis. * **D (Candida glabrata):** This is a yeast. Botryomycosis is strictly a bacterial process; fungal causes of similar lesions are classified as **Eumycetoma**. **High-Yield Clinical Pearls for NEET-PG:** * **Key Histology:** Look for the **Splendore-Hoeppli phenomenon** (intense eosinophilic material around bacterial clusters). * **Differential Diagnosis:** Always differentiate from **Mycetoma**. In Botryomycosis, grains contain **cocci or bacilli**, whereas in Mycetoma, grains contain **fungal hyphae or filamentous bacteria**. * **Treatment:** Long-term antibiotics based on culture (usually targeting *S. aureus*).

Q: Hot cold phenomenon is caused by which staphylococcal toxin?

Beta lysin. **Explanation:** The **Hot-Cold Phenomenon** is a characteristic feature of **Staphylococcal Beta-lysin** (also known as sphingomyelinase C). This phenomenon refers to the observation that the toxin’s hemolytic activity is initiated at 37°C ("hot") but only becomes visible or complete after subsequent incubation at 4°C ("cold") or room temperature. **Mechanism:** Beta-lysin is an enzyme that degrades sphingomyelin in the red blood cell (RBC) membrane. At 37°C, the enzyme acts on the membrane but does not cause immediate lysis. When the temperature drops, the destabilized membrane undergoes structural contraction and collapses, leading to visible hemolysis. This is most commonly demonstrated using sheep or bovine RBCs. **Analysis of Options:** * **Option B (Correct):** Beta-lysin is the only staphylococcal toxin associated with the hot-cold effect. It is also the basis for the **CAMP test** (used to identify Group B Streptococci), where it acts synergistically with the CAMP factor. * **Option A:** **Alpha-lysin** is the most important virulence factor for *S. aureus*. It is a pore-forming toxin that causes rapid lysis of RBCs and platelets but does not exhibit the hot-cold effect. * **Option C:** **Gamma-lysin** is a bicomponent toxin associated with leukocidin activity. * **Option D:** **Theta-lysin** is not a standard staphylococcal toxin; *Clostridium perfringens* produces a Perfringolysin O (Theta toxin). **High-Yield Clinical Pearls for NEET-PG:** * **CAMP Test:** Beta-lysin producing *S. aureus* is used to detect *Streptococcus agalactiae*. * **Alpha-toxin:** Mediated by chromosomal genes; causes "pore formation." * **Panton-Valentine Leukocidin (PVL):** A key toxin in MRSA causing necrotizing pneumonia and skin infections. * **Toxic Shock Syndrome Toxin (TSST-1):** A superantigen that binds to MHC II and Vβ T-cell receptors.

Q: Which of the following is true regarding Salmonella infection?

Blood culture is positive in 3-7 days.. In Enteric Fever (Typhoid), the diagnostic yield of various tests follows a predictable chronological pattern based on the pathogenesis of *Salmonella Typhi*. ### **Why Option C is Correct** After ingestion, *Salmonella* undergoes primary multiplication in the Peyer's patches, followed by entry into the thoracic duct and then the bloodstream. This **primary bacteremia** occurs early in the disease. Therefore, **blood culture** is the gold standard for diagnosis during the **first week** (positive in 70-90% of cases), typically showing growth within 3-7 days of incubation. ### **Analysis of Incorrect Options** * **Option A (Urine Culture):** This becomes positive only in the **third week** of infection due to the seeding of bacteria in the kidneys following secondary bacteremia. * **Option B (Stool Culture):** While bacteria are shed in feces, the yield is highest during the **second and third weeks**. It is rarely positive in the first week as the bacteria are primarily intracellular or intravascular at this stage. * **Option C (Widal Test):** This serological test detects antibodies (Anti-O and Anti-H). These antibodies take time to develop and usually reach significant titers only by the **end of the second week**. Testing in the first week often yields a false negative. ### **NEET-PG High-Yield Pearls** * **Mnemonic for Sample Collection (BASU):** **B**lood (1st week), **A**ntibody/Widal (2nd week), **S**tool (3rd week), **U**rine (4th week). * **Most Sensitive Culture:** **Bone marrow culture** is the most sensitive overall (up to 95%) and remains positive even after starting antibiotics. * **Castaneda’s Medium:** A biphasic medium used for blood cultures to reduce the risk of contamination during subculturing. * **Clot Culture:** More sensitive than whole blood culture because it removes antibacterial substances present in the serum.

Q: The optimal time to read a Mitzuda reaction is:

28th day. The **Mitsuda reaction** is a delayed hypersensitivity skin test used in the clinical classification of Leprosy. It involves the intradermal injection of lepromin (a suspension of killed *Mycobacterium leprae*). ### 1. Why the Correct Answer is Right (C: 28th day) The lepromin test consists of two distinct phases. The **Mitsuda reaction** is the late-phase response, representing a **Type IV (Delayed) Hypersensitivity** reaction. It typically begins to appear after 1–2 weeks, peaks at 3 weeks, and is optimally read at **4 weeks (21–28 days)**. A positive result (a nodule >5mm) indicates intact cell-mediated immunity (CMI) against *M. leprae*, which is characteristic of Tuberculoid leprosy (TT). ### 2. Why the Incorrect Options are Wrong * **A (3rd day):** This corresponds to the **Fernandez reaction**, which is the early-phase response read at 48–72 hours. It is non-specific and indicates prior exposure to mycobacterial antigens but does not correlate with the clinical prognosis. * **B (10th day):** At this stage, the Mitsuda nodule is still developing and has not reached its peak diagnostic size. * **D (45th day):** By this time, the inflammatory nodule may have already undergone ulceration or started to subside, making the measurement unreliable. ### 3. Clinical Pearls for NEET-PG * **Diagnostic Value:** The lepromin test is **NOT** used to diagnose leprosy (it can be positive in healthy individuals). It is used for **classification** and **prognosis**. * **Prognostic Correlation:** * **Positive Mitsuda:** Seen in Tuberculoid (TT) leprosy (Good prognosis, high CMI). * **Negative Mitsuda:** Seen in Lepromatous (LL) leprosy (Poor prognosis, low CMI). * **Antigen Types:** Lepromin-H (Hayashi) uses human-derived bacilli, while Lepromin-A (Armadillo) uses bacilli from infected armadillos.

Q: What is the specific strain of Vibrio cholerae predominantly found in Bengal?

O:96527778. **Explanation:** The correct answer is **O:139** (Note: The numerical value provided in the option "O:96527778" appears to be a typographical error in the source material, but in the context of standard medical microbiology and NEET-PG patterns, it refers to the **Bengal strain**, which is **O:139**). **1. Why O:139 (Bengal Strain) is Correct:** Traditionally, only *Vibrio cholerae* O1 was associated with epidemic cholera. However, in 1992, a major outbreak of cholera-like illness occurred in Madras and subsequently spread to West Bengal. This new strain was identified as a non-O1 serogroup, designated as **O:139**, and named the **'Bengal' strain**. It is unique because it is the first non-O1 strain to cause large-scale epidemics and pandemics, effectively replacing the El Tor biotype in several regions of India for a period. **2. Why Incorrect Options are Wrong:** * **O:37, O:17, and O:40:** These are non-agglutinable (NAG) or non-cholera vibrios (NCVs). While they can occasionally cause sporadic cases of gastroenteritis or extra-intestinal infections (like wound infections or septicemia), they lack the epidemic potential and the specific genetic markers (like the CTX phage) required to cause large-scale outbreaks like the Bengal strain. **3. Clinical Pearls for NEET-PG:** * **Serogroups:** *V. cholerae* is classified based on the O-antigen. Only **O1** and **O139** cause epidemic cholera. * **O1 Classification:** Divided into two biotypes (**Classical** and **El Tor**) and three serotypes (**Ogawa, Inaba, Hikojima**). * **The 7th Pandemic:** Caused by the El Tor biotype. * **O139 Characteristics:** It does not belong to the O1 group (Non-O1), but it produces the same cholera toxin. It is characterized by the presence of a distinct capsule, which O1 lacks.

Q: Which of the following bacteria is known as Battey bacillus?

Mycobacterium intracellulare. ### Explanation The correct answer is **Mycobacterium intracellulare (Option A)**. **1. Why Mycobacterium intracellulare is correct:** *Mycobacterium intracellulare* belongs to the **Mycobacterium Avium Complex (MAC)**, which consists of *M. avium* and *M. intracellulare*. Historically, *M. intracellulare* was isolated from patients in **Battey State Hospital** in Georgia, USA, leading to its common designation as the **"Battey bacillus."** It is a non-tuberculous mycobacterium (NTM) classified under **Runyon Group III (Non-photochromogens)**, meaning it produces no pigment regardless of light exposure. **2. Why the other options are incorrect:** * **Mycobacterium leprae (Option B):** Known as **Hansen’s bacillus**, it is the causative agent of leprosy. It is obligate intracellular and cannot be grown on artificial media. * **Mycobacterium tuberculosis (Option C):** Known as **Koch’s bacillus**, it is the primary cause of tuberculosis in humans. * **Mycobacterium kansasii (Option D):** Known as the **"Yellow bacillus"** because it is a **Runyon Group I (Photochromogen)**, producing a yellow-orange pigment only when exposed to light. **3. NEET-PG High-Yield Pearls:** * **MAC (M. avium-intracellulare):** The most common opportunistic infection in HIV/AIDS patients when the CD4 count drops below **50 cells/mm³**. * **Runyon Classification:** * **Group I (Photochromogens):** *M. kansasii, M. marinum.* * **Group II (Scotochromogens):** *M. scrofulaceum, M. szulgai.* * **Group III (Non-photochromogens):** *M. avium, M. intracellulare.* * **Group IV (Rapid growers):** *M. fortuitum, M. chelonae, M. abscessus.* * **Buruli Ulcer:** Caused by *M. ulcerans*. * **Swimming Pool Granuloma:** Caused by *M. marinum*.

Question 1

A female presents with leaking and meconium-stained liquor at 32 weeks gestation. Which organism is she most likely infected with?

Accepted Answer

Listeria monocytogenes

Answer

Cytomegalovirus (CMV)

Answer

Toxoplasma gondii

Answer

Herpes simplex virus (HSV)

Question 2

Which of the following statements about tetanus are true?

Accepted Answer

Vegetative cell will die with tetracycline

Answer

Gram-negative spore-forming aerobe

Answer

Caused by tetanospasmin

Answer

Muscle enzymes are normal

Question 3

A 70-year-old female patient was readmitted to a local hospital with fever and chills following cardiac surgery. Blood cultures were taken and a gram-positive coccus grew from the blood cultures within 24 hours. Initial tests indicated that this isolate was resistant to penicillin. Which of the following is the most likely identification?

Accepted Answer

Enterococcus

Answer

Group A streptococcus

Answer

Group B streptococcus

Answer

Neisseria species

Question 4

Which of the following is known to cause Pedal Botryomycosis?

Accepted Answer

Staphylococcus aureus

Answer

Actinomyces somaliensis

Answer

Nocardia asteroides

Answer

Candida glabrata

Question 5

Hot cold phenomenon is caused by which staphylococcal toxin?

Accepted Answer

Beta lysin

Answer

Alpha lysin

Answer

Gamma lysin

Answer

Theta lysin

Question 6

Which of the following statements regarding Borrelia is FALSE?

Accepted Answer

Barbour-Stoenner-Kelly broth medium is used to isolate Borrelia miyaotoi.

Answer

The preferred time to obtain a blood specimen is between the fever's onset and its peak.

Answer

The gold standard for laboratory diagnosis is direct detection of spirochetes by microscopy of the blood.

Answer

Lyme disease is a tick-borne fever caused by Borrelia burgdorferi.

Question 7

Which of the following is true regarding Salmonella infection?

Accepted Answer

Blood culture is positive in 3-7 days.

Answer

Urine culture is positive in the first week.

Answer

Stool culture is positive in the first week.

Answer

Widal test is positive in the first week.

Question 8

The optimal time to read a Mitzuda reaction is:

Accepted Answer

28th day

Answer

3rd day

Answer

10th day

Answer

45th day

Question 9

What is the specific strain of Vibrio cholerae predominantly found in Bengal?

Accepted Answer

O:96527778

Answer

O:37

Answer

O:17

Answer

O:40

Question 10

Which of the following bacteria is known as Battey bacillus?

Accepted Answer

Mycobacterium intracellulare

Answer

Mycobacterium leprae

Answer

Mycobacterium tuberculosis

Answer

Mycobacterium kansasii

Bacteriology — MCQs

Bacteriology — MCQs

On this page

Practice by Chapter

Want unlimited practice?