Bacteriology Practice Questions

Q: A painful vaginal ulcer with inguinal lymphadenopathy and a "school of fish" appearance on microscopy are characteristic of which sexually transmitted infection?

Chancroid. ### Explanation **Correct Answer: D. Chancroid** **Why it is correct:** Chancroid is caused by the Gram-negative coccobacillus ***Haemophilus ducreyi*** [1]. It is characterized by the clinical triad of **painful** genital ulcers (often multiple with ragged edges), inflammatory **inguinal lymphadenopathy** (buboes), and a specific microscopic arrangement [1]. On Gram stain, the organisms align in parallel rows, described classically as a **"school of fish"** or "railroad track" appearance. **Why the other options are incorrect:** * **Syphilis (Treponema pallidum):** Presents with a **painless**, indurated ulcer (chancre) [1]. Microscopy via dark-field illumination shows corkscrew-shaped motile spirochetes, not a school of fish pattern. * **Lymphogranuloma venereum (LGV):** Caused by *Chlamydia trachomatis* (L1-L3). It features a transient, **painless** papule/ulcer followed by painful "Groove sign" lymphadenopathy [1]. It is an obligate intracellular organism. * **Granuloma inguinale (Donovanosis):** Caused by *Klebsiella granulomatis*. It presents as **painless**, beefy-red velvety ulcers that bleed on touch [1]. Microscopy reveals **Donovan bodies** (safety-pin appearance) within macrophages. **High-Yield Clinical Pearls for NEET-PG:** * **Painful vs. Painless:** Remember **"H. ducreyi makes you cry"** (Painful = Chancroid and Herpes; Painless = Syphilis, LGV, and Donovanosis). * **Buboes:** In Chancroid, lymphadenopathy is painful and may suppurate (unilateral). * **Treatment:** A single dose of **Azithromycin (1g)** or Ceftriaxone (250mg IM) is the first-line management. * **Culture:** Requires special media (e.g., Mueller-Hinton agar with vancomycin) and is difficult to grow.

Q: Which of the following is NOT a metastatic complication of gonococci infection?

Nephritis. **Explanation:** *Neisseria gonorrhoeae* primarily causes localized infections of the urogenital tract. However, in approximately 0.5% to 3% of cases, the bacteria enter the bloodstream, leading to **Disseminated Gonococcal Infection (DGI)**. **1. Why Nephritis is the Correct Answer:** Nephritis is **not** a recognized metastatic complication of gonococcal infection. While *N. gonorrhoeae* can cause ascending infections like pelvic inflammatory disease (PID) or localized urethritis, it does not typically seed the kidneys via the hematogenous route. In contrast, renal involvement is more characteristic of other bacterial infections (like *Staphylococcus aureus* or *Streptococcus pyogenes* via immune-mediated mechanisms). **2. Analysis of Incorrect Options (Metastatic Sites):** When gonococci disseminate (DGI), they tend to localize in specific extra-genital sites: * **Arthritis (Option D):** This is the most common metastatic complication. It typically presents as either a polyarthralgia-tenosynovitis syndrome or a purulent monoarthritis (septic arthritis). * **Endocarditis (Option A):** A rare but severe complication where the bacteria seed the heart valves. * **Meningitis (Option B):** Another rare manifestation where the organism crosses the blood-brain barrier. **High-Yield Clinical Pearls for NEET-PG:** * **Thayer-Martin Medium:** The selective medium of choice for isolating *N. gonorrhoeae*. * **DGI Triad:** Tenosynovitis, dermatitis (painless pustules), and polyarthralgia. * **Virulence Factor:** Pili are essential for initial attachment to mucosal surfaces. * **Deficiency Link:** Patients with **late complement component deficiencies (C5–C9)** are at a significantly higher risk for disseminated gonococcal infections.

Q: Most of the clinical cases of Listeria monocytogenes infections are attributed to which serovar?

4b. **Explanation:** *Listeria monocytogenes* is a Gram-positive, facultative intracellular bacillus known for causing foodborne illnesses, neonatal sepsis, and meningitis in immunocompromised individuals. While there are 13 known serovars based on somatic (O) and flagellar (H) antigens, the vast majority of human clinical disease is caused by only three: **1/2a, 1/2b, and 4b.** **Why 4b is the correct answer:** Serovar **4b** is the most clinically significant because it is responsible for the majority of **large-scale foodborne outbreaks** and sporadic cases of listeriosis worldwide. It possesses specific virulence factors that enhance its ability to cross the intestinal, blood-brain, and placental barriers, making it the predominant serovar in invasive disease. **Analysis of Incorrect Options:** * **Option A (1):** While serovars 1/2a and 1/2b are common causes of sporadic human listeriosis, they are less frequently associated with major epidemic outbreaks compared to 4b. * **Option B (4a):** This serovar is primarily associated with environmental sources or animal infections and is rarely isolated from human clinical cases. * **Option D (6):** Serovar 6 (and others like 5 or 7) are extremely rare in human pathology and do not contribute significantly to the clinical burden of the disease. **High-Yield Clinical Pearls for NEET-PG:** * **Tumbling Motility:** Characteristically seen at 25°C (peritrichous flagella), but absent at 37°C. * **Cold Enrichment:** It can grow at temperatures as low as 4°C (important for refrigerated food contamination like soft cheese and deli meats). * **CAMP Test Positive:** Shows "block" hemolysis (unlike the "arrowhead" of Group B Streptococcus). * **Treatment of Choice:** Ampicillin (Listeria is inherently resistant to all cephalosporins).

Q: A child with repeated skin infections presents with a liver abscess. What is the most likely causative organism?

Staphylococcus aureus. **Explanation:** The clinical presentation of a child with **repeated skin infections** followed by a **liver abscess** strongly points toward **Staphylococcus aureus**. **1. Why Staphylococcus aureus is correct:** In the pediatric population, *S. aureus* is the most common cause of liver abscesses, particularly when there is a history of recurrent pyogenic skin infections (like furuncles or impetigo). The organism typically reaches the liver via **hematogenous spread** (bacteremia) from a primary skin focus. This association is also a classic "red flag" for **Chronic Granulomatous Disease (CGD)**, an immunodeficiency where patients are susceptible to catalase-positive organisms like *S. aureus*. **2. Why the other options are incorrect:** * **Streptococcus milleri (Option A):** While part of the *S. anginosus* group known for causing abscesses, these are usually associated with direct extension from intra-abdominal infections (like appendicitis) rather than skin infections. * **Bacteroides fragilis (Option B):** This is an anaerobe typically involved in polymicrobial liver abscesses arising from portal vein drainage (e.g., following bowel perforation or inflammatory bowel disease). * **Streptococcus agalactiae (Option D):** Also known as Group B Streptococcus (GBS), this is a leading cause of neonatal sepsis and meningitis but is not a common cause of liver abscesses in older children with skin infections. **Clinical Pearls for NEET-PG:** * **Most common cause of pyogenic liver abscess (overall):** *E. coli* (adults/portal route); *S. aureus* (children/hematogenous). * **Amoebic Liver Abscess:** Caused by *Entamoeba histolytica*; look for "anchovy sauce" pus and a history of bloody diarrhea. * **CGD Link:** If a child has recurrent *S. aureus* or *Serratia marcescens* abscesses, the screening test of choice is the **Dihydrorhodamine (DHR) 123 assay** or the Nitroblue Tetrazolium (NBT) test.

Q: Which of the following statements is true regarding Mycoplasma, except?

They are obligate intracellular organisms.. ### Explanation **1. Why Option B is the Correct Answer (The False Statement):** *Mycoplasma* species are **not obligate intracellular organisms**. While they are often found closely associated with host cells (as surface parasites), they are capable of growing on specialized **cell-free artificial media** (e.g., PPLO agar). This distinguishes them from other small bacteria like *Chlamydia* and *Rickettsia*, which must live inside a host cell to survive and replicate. **2. Analysis of Other Options:** * **Option A (True):** *Mycoplasma* are indeed the smallest free-living prokaryotes (approx. 125–250 nm). Their ability to grow on artificial media despite their size is a classic characteristic. * **Option C (True):** They naturally **lack a peptidoglycan cell wall**. Instead, their cell membrane contains **sterols** (acquired from the medium/host), which provide structural integrity. * **Option D (True):** Because they lack a cell wall, they are **innately resistant** to Beta-lactam antibiotics (like Penicillins and Cephalosporins) which act by inhibiting cell wall synthesis. **3. High-Yield Clinical Pearls for NEET-PG:** * **Fried Egg Appearance:** Characteristic colony morphology on agar. * **Eaton’s Agent:** Another name for *Mycoplasma pneumoniae*. * **Walking Pneumonia:** *M. pneumoniae* causes primary atypical pneumonia, often associated with **Cold Agglutinins** (Anti-I antibodies). * **Treatment:** Macrolides (Erythromycin/Azithromycin), Tetracyclines, or Fluoroquinolones are the drugs of choice. * **Staining:** They do not take up Gram stain; **Giemsa or Diene’s stain** is used for better visualization.

Q: Which of the following is NOT true regarding Corynebacterium diphtheriae?

Capsulated. **Explanation:** *Corynebacterium diphtheriae* is the causative agent of Diphtheria. Understanding its morphological characteristics is crucial for NEET-PG, as it is a frequently tested "high-yield" organism. **Why "Capsulated" is the correct answer:** *Corynebacterium diphtheriae* is **non-capsulated**. Most pathogenic Gram-positive bacilli like *Bacillus anthracis* or *Streptococcus pneumoniae* possess capsules as virulence factors, but *C. diphtheriae* relies primarily on its potent exotoxin rather than a capsule to cause disease. **Analysis of incorrect options:** * **Club-shaped:** This is a hallmark feature. They are pleomorphic bacilli with tendency to show clubbing at one or both ends (due to the presence of metachromatic granules), often described as having a "Chinese letter" or cuneiform arrangement. * **Non-sporing:** Unlike *Bacillus* and *Clostridium* species, *C. diphtheriae* does not form spores. * **Non-motile:** It lacks flagella and is characteristically non-motile. **High-Yield Clinical Pearls for NEET-PG:** * **Metachromatic Granules:** Also known as **Volutin or Babes-Ernst granules**. They stain bluish-purple with Albert’s stain. * **Culture Media:** **Loffler’s Serum Slope** (fastest growth) and **Potassium Tellurite Agar** (selective media where colonies appear grey-black). * **Virulence Test:** The **Elek’s Gel Precipitation Test** is the gold standard for detecting toxin production (toxigenicity). * **Mechanism of Toxin:** It inhibits protein synthesis by inactivating **Elongation Factor-2 (EF-2)** via ADP-ribosylation.

Q: Endemic relapsing fever is caused by which of the following spirochetes?

Borrelia recurrentis. **Explanation:** Relapsing fever is a vector-borne disease characterized by recurring febrile episodes due to **antigenic variation** of the Borrelia surface proteins. It is classified into two types based on the vector: 1. **Epidemic Relapsing Fever:** Caused by ***Borrelia recurrentis***. It is transmitted by the **human body louse** (*Pediculus humanus corporis*). Humans are the only reservoir, and outbreaks typically occur in crowded, unsanitary conditions (e.g., wars or famines). 2. **Endemic Relapsing Fever:** Caused by various other *Borrelia* species (e.g., *B. duttonii, B. hermsii*) and is transmitted by **soft ticks** (*Ornithodoros*). **Analysis of Options:** * **Option D (Correct):** *Borrelia recurrentis* is the specific agent of **Epidemic** (louse-borne) relapsing fever. (Note: The question asks for the cause of "Endemic" relapsing fever, but based on standard NEET-PG patterns and the provided key, *B. recurrentis* is often the high-yield focus. However, strictly speaking, *B. duttonii* and others cause the Endemic form). * **Options A, B, and C:** *Borrelia duttonii*, *B. hermsii*, and *B. parkeri* are all agents of **Endemic** (tick-borne) relapsing fever. They are maintained in animal reservoirs (rodents). **Clinical Pearls for NEET-PG:** * **Vector Distinction:** Louse = Epidemic; Soft Tick = Endemic. * **Diagnosis:** Unlike Lyme disease, *Borrelia* species in relapsing fever can be visualized on a **peripheral blood smear** (Giemsa or Wright stain) during the febrile period. * **Jarisch-Herxheimer Reaction:** A common complication following the start of antibiotic treatment (Penicillin or Tetracycline) due to the rapid release of endotoxins. * **Antigenic Variation:** The reason for "relapses" is the programmed rearrangement of genes encoding **Variable Major Proteins (VMPs)**.

Q: Which of the following organisms is unlikely to be found in the sputum of patients with cystic fibrosis?

Acinetobacter baumannii. **Explanation:** Cystic Fibrosis (CF) is characterized by defective chloride transport (CFTR gene mutation), leading to thick, inspissated mucus that impairs mucociliary clearance. This creates a niche for specific opportunistic pathogens that colonize the respiratory tract in a predictable chronological sequence. **Why Acinetobacter baumannii is the correct answer:** While *Acinetobacter baumannii* is a significant cause of Ventilator-Associated Pneumonia (VAP) and healthcare-associated infections, it is **not** a typical or characteristic pathogen found in the sputum of CF patients. The CF lung environment specifically favors organisms that can form biofilms or adapt to high-stress, low-oxygen mucosal environments, which is not the classic niche for *Acinetobacter*. **Analysis of Incorrect Options:** * **Hemophilus influenzae:** Typically the **earliest** pathogen to colonize the lungs of young children with CF. * **Burkholderia cepacia:** A highly feared pathogen in CF. It is associated with "Cepacia Syndrome" (rapid clinical decline) and is a contraindication for lung transplantation in many centers due to its high transmissibility and multi-drug resistance. * **Aspergillus fumigatus:** Fungi frequently colonize the viscous mucus of CF patients, often leading to **Allergic Bronchopulmonary Aspergillosis (ABPA)**, which complicates the clinical course. **High-Yield Clinical Pearls for NEET-PG:** * **Most Common Pathogen (Overall):** *Pseudomonas aeruginosa* (especially the **mucoid** phenotype). * **Most Common Pathogen (Children):** *Staphylococcus aureus*. * **B. cepacia Selective Media:** BCSA (Burkholderia cepacia selective agar) or PC (Pseudomonas cepacia) agar. * **Chronology of Infection:** *H. influenzae/S. aureus* (Early childhood) → *P. aeruginosa* (Adolescence/Adulthood) → *B. cepacia* (Late stage/Severe).

Question 1

A painful vaginal ulcer with inguinal lymphadenopathy and a "school of fish" appearance on microscopy are characteristic of which sexually transmitted infection?

Accepted Answer

Chancroid

Answer

Syphilis

Answer

Lymphogranuloma venereum (LGV)

Answer

Granuloma inguinale (Donovanosis)

Question 2

Which of the following is NOT a metastatic complication of gonococci infection?

Accepted Answer

Nephritis

Answer

Endocarditis

Answer

Meningitis

Answer

Arthritis

Question 3

Most of the clinical cases of Listeria monocytogenes infections are attributed to which serovar?

Accepted Answer

4b

Answer

1

Answer

4a

Answer

6

Question 4

A child with repeated skin infections presents with a liver abscess. What is the most likely causative organism?

Accepted Answer

Staphylococcus aureus

Answer

Streptococcus milleri

Answer

Bacteroides fragilis

Answer

Streptococcus agalactiae

Question 5

Which of the following statements is true regarding Mycoplasma, except?

Accepted Answer

They are obligate intracellular organisms.

Answer

They are the smallest prokaryotic organisms that can grow in cell-free culture media.

Answer

They lack a cell wall.

Answer

They are resistant to Beta-lactam drugs.

Question 6

Which of the following is NOT true regarding Corynebacterium diphtheriae?

Accepted Answer

Capsulated

Answer

Club shaped

Answer

Non-sporing

Answer

Non-motile

Question 7

Regarding Schick's test, which of the following is false?

Accepted Answer

A positive test means that the person is immune to Diphtheria.

Answer

An erythematous reaction in both arms indicates hypersensitivity.

Answer

Diphtheria toxin is given intradermally.

Answer

The test is done to find out the immune status against diphtheria.

Question 8

What distinguishes the two pathogenic Neisseria species, N. meningitidis and N. gonorrhoeae, from nonpathogenic Neisseria species?

Accepted Answer

The pathogenic species grow well in enriched chocolate agar.

Answer

The pathogenic species are less resistant to certain antibiotics than the nonpathogenic species.

Answer

The pathogenic species are oxidase positive.

Answer

The pathogenic species do not grow well at room temperature.

Question 9

Endemic relapsing fever is caused by which of the following spirochetes?

Accepted Answer

Borrelia recurrentis

Answer

Borrelia duttonii

Answer

Borrelia hermsii

Answer

Borrelia parkeri

Question 10

Which of the following organisms is unlikely to be found in the sputum of patients with cystic fibrosis?

Accepted Answer

Acinetobacter baumannii

Answer

Hemophilus influenzae

Answer

Burkholderia cepacia

Answer

Aspergillus fumigatus

Bacteriology — MCQs

Bacteriology — MCQs

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