Bacteriology Practice Questions

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).

Q: A patient presents with fever for 3 weeks. On examination, splenomegaly is observed. Ultrasonography reveals a hypoechoic shadow in the spleen near the hilum. Gram-negative bacilli are isolated on blood culture. Which of the following is the most likely causative organism?

Salmonella. **Explanation:** The clinical presentation of prolonged fever (3 weeks) and splenomegaly, combined with the isolation of **Gram-negative bacilli** from blood culture, is classic for **Enteric Fever (Typhoid)** caused by *Salmonella Typhi* or *Paratyphi*. 1. **Why Salmonella is correct:** *Salmonella* is a Gram-negative, motile bacillus. During the first and second weeks of infection, it causes bacteremia (positive blood cultures). A known complication of enteric fever is the formation of **splenic abscesses** or focal lesions, which appear as hypoechoic shadows on ultrasonography. Splenomegaly is a hallmark physical finding in the second week of the disease. 2. **Why other options are incorrect:** * **Cytomegalovirus (CMV):** While it causes fever and splenomegaly (mononucleosis-like syndrome), CMV is a virus and would not grow as Gram-negative bacilli on blood culture. * **Toxoplasmosis:** Caused by the protozoan *Toxoplasma gondii*, it typically presents with lymphadenopathy. It does not present as Gram-negative bacilli. * **Lymphoma virus (EBV/HTLV):** These are viruses associated with malignancy or infectious mononucleosis. They do not produce bacterial growth on standard culture media. **High-Yield Clinical Pearls for NEET-PG:** * **Culture Sensitivity:** Blood culture is most sensitive in the **1st week** (90%), while Stool culture is most sensitive in the **3rd week**. * **Widal Test:** Becomes positive only after the **2nd week** (detects antibodies against O and H antigens). * **Pathognomonic sign:** Rose spots on the abdomen (seen in the 2nd week). * **Complications:** Intestinal perforation and hemorrhage typically occur in the **3rd week** due to necrosis of Peyer's patches.

Q: Which of the following statements about tetanus is FALSE?

Tetanolysin is responsible for the clinical symptoms.. **Explanation:** The correct answer is **B**, as **Tetanospasmin**, not tetanolysin, is the potent neurotoxin responsible for the clinical manifestations of tetanus. **1. Why Option B is False (The Medical Concept):** *Clostridium tetani* produces two distinct exotoxins: * **Tetanospasmin:** A powerful neurotoxin that blocks the release of inhibitory neurotransmitters (GABA and Glycine) from Renshaw cells in the spinal cord. This leads to unchecked muscular spasms, the hallmark of the disease. * **Tetanolysin:** An oxygen-labile hemolysin that causes local tissue destruction and creates an anaerobic environment favorable for the bacteria, but it has **no known role** in causing the systemic clinical symptoms of tetanus. **2. Analysis of Other Options:** * **Option A:** Correct statement. Tetanospasmin is the primary virulence factor causing trismus (lockjaw), risus sardonicus, and opisthotonus. * **Option C:** Correct statement. Active immunization with Tetanus Toxoid (TT/Td) is the most effective preventive strategy. It induces protective antitoxin levels (>0.01 IU/mL). * **Option D:** Correct statement. Tetanus neonatorum is often called **"8th day disease"** because symptoms typically appear between the 3rd and 14th day after birth (most commonly around the 8th day) due to umbilical cord infection. **Clinical Pearls for NEET-PG:** * **Incubation Period:** Usually 6–10 days. The shorter the incubation period, the worse the prognosis. * **Elimination Goal:** Maternal and Neonatal Tetanus (MNT) elimination is defined as <1 case per 1,000 live births in every district. India achieved this in 2015. * **Autonomic Dysfunction:** A major cause of death in modern intensive care settings. * **Management:** Includes wound debridement, Metronidazole (preferred over Penicillin), and Human Tetanus Immunoglobulin (HTIG).

Q: A seven-year-old boy presented with high-grade fever, headache, disorientation, and projectile vomiting. Examination revealed neck rigidity and a positive Kernig's sign. Lumbar puncture was performed. Gram staining of the cerebrospinal fluid (CSF) showed Gram-negative cocci. What is the most likely cause of this infection?

Neisseria meningitidis. ### Explanation **Correct Answer: B. Neisseria meningitidis** The clinical presentation of high-grade fever, projectile vomiting, neck rigidity, and a positive Kernig’s sign is classic for **acute bacterial meningitis**. The definitive clue lies in the CSF Gram stain: **Gram-negative cocci**. *Neisseria meningitidis* (Meningococcus) is the only organism among the options that fits this morphological description (typically appearing as Gram-negative bean-shaped diplococci). It is a leading cause of meningitis in children and young adults, often occurring in outbreaks. **Analysis of Incorrect Options:** * **A. Escherichia coli:** While a common cause of neonatal meningitis (0–3 months), it is a **Gram-negative bacilli** (rod), not a coccus. * **C. Haemophilus influenzae:** This is a **Gram-negative coccobacillus**. While it was a leading cause of childhood meningitis, its incidence has significantly decreased due to the Hib vaccine. * **D. Streptococcus pneumoniae:** This is the most common cause of sporadic meningitis in adults and children. However, it is a **Gram-positive coccus** (typically lancet-shaped diplococci). **High-Yield Clinical Pearls for NEET-PG:** * **Age-wise Etiology:** * *Neonates:* Group B Streptococcus, *E. coli*, *Listeria monocytogenes*. * *Children/Adults:* *S. pneumoniae*, *N. meningitidis*. * **CSF Findings in Bacterial Meningitis:** Increased opening pressure, high protein, low glucose (<40 mg/dL), and marked neutrophilic pleocytosis. * **Waterhouse-Friderichsen Syndrome:** A severe complication of meningococcemia characterized by adrenal hemorrhage and shock. * **Culture:** *N. meningitidis* grows best on **Thayer-Martin medium** or Chocolate agar in a 5–10% $CO_2$ environment.

Question 1

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 2

Which of the following is NOT true regarding Corynebacterium diphtheriae?

Accepted Answer

Capsulated

Answer

Club shaped

Answer

Non-sporing

Answer

Non-motile

Question 3

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 4

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 5

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 6

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

Question 7

A patient presents with fever for 3 weeks. On examination, splenomegaly is observed. Ultrasonography reveals a hypoechoic shadow in the spleen near the hilum. Gram-negative bacilli are isolated on blood culture. Which of the following is the most likely causative organism?

Accepted Answer

Salmonella

Answer

Cytomegalovirus

Answer

Toxoplasmosis

Answer

Lymphoma virus

Question 8

Which of the following statements about tetanus is FALSE?

Accepted Answer

Tetanolysin is responsible for the clinical symptoms.

Answer

Tetanospasmin is responsible for the clinical symptoms.

Answer

It is best prevented by active immunization with tetanus toxoid.

Answer

Tetanus neonatorum is also known as "8th day disease".

Question 9

A seven-year-old boy presented with high-grade fever, headache, disorientation, and projectile vomiting. Examination revealed neck rigidity and a positive Kernig's sign. Lumbar puncture was performed. Gram staining of the cerebrospinal fluid (CSF) showed Gram-negative cocci. What is the most likely cause of this infection?

Accepted Answer

Neisseria meningitidis

Answer

Escherichia coli

Answer

Haemophilus influenzae

Answer

Streptococcus pneumoniae

Question 10

A 40-year-old man presents with a nonproductive cough, malaise, sinusitis, and sore throat. His chest x-ray reveals patchy infiltrates in the upper right lung without consolidation. He denies recent exposure to new pets. Sputum Gram-stain shows poorly staining Gram-negative rods. Laboratory cultures on standard media are unsuccessful, but the organism grows in tissue culture. What bacterium is most likely causing this infection?

Accepted Answer

Chlamydophila pneumoniae

Answer

Chlamydia trachomatis

Answer

Chlamydophila psittaci

Answer

Mycoplasma pneumoniae

Bacteriology — MCQs

Bacteriology — MCQs

On this page

Practice by Chapter

Want unlimited practice?