Bacteriology Practice Questions

Q: Scotochromogens are:

Mycobacterium Gordonae. **Explanation:** The classification of Non-Tuberculous Mycobacteria (NTM) is based on the **Runyon Classification**, which categorizes species according to their growth rate and pigment production in response to light. **1. Why Mycobacterium gordonae is correct:** * **Scotochromogens (Runyon Group II):** These organisms produce pigment (usually yellow-orange) regardless of whether they are grown in the dark or light. * *M. gordonae* (the "tap water bacillus") is the classic example of a Scotochromogen. It is generally non-pathogenic and often encountered as a laboratory contaminant. **2. Why the other options are incorrect:** * **Mycobacterium marinum (Option B):** This is a **Photochromogen (Runyon Group I)**. These organisms are non-pigmented when grown in the dark but produce a photo-activated yellow-orange pigment after exposure to light. * **Mycobacterium intracellulare & Mycobacterium avium (Options C & D):** These belong to the **Mycobacterium Avium Complex (MAC)**, which are **Non-chromogens (Runyon Group III)**. They produce little to no pigment regardless of light exposure and appear as buff-colored colonies. **High-Yield Clinical Pearls for NEET-PG:** * **Runyon Group I (Photochromogens):** *M. kansasii, M. marinum* (causes "Swimming pool granuloma"). * **Runyon Group II (Scotochromogens):** *M. gordonae, M. scrofulaceum* (causes cervical lymphadenitis in children). * **Runyon Group III (Non-chromogens):** *M. avium, M. intracellulare* (common in HIV/AIDS patients). * **Runyon Group IV (Rapid Growers):** Growth occurs within 7 days. Examples include *M. fortuitum, M. chelonae, M. abscessus*. * **Mnemonic:** **P**hoto-**S**coto-**N**on-**R**apid (**P**lease **S**ay **N**o **R**unyon).

Q: Which of the following statements is FALSE regarding actinomycetes?

Penicillin is used in treatment for 6 weeks. **Explanation:** The correct answer is **D** because the statement regarding the duration of treatment is incorrect. While **Penicillin G** is indeed the drug of choice for Actinomycosis, the treatment duration is significantly longer than 6 weeks. Due to the tendency of the infection to cause dense fibrosis and abscess formation, antibiotics must be administered for **6 to 12 months** to prevent relapse. **Analysis of other options:** * **Option A (Non-acid fast):** Most species of *Actinomyces* (e.g., *A. israelii*) are non-acid fast. This distinguishes them from *Nocardia*, which is weakly acid-fast. * **Option B (Most common site):** The **cervicofacial** region ("lumpy jaw") is the most common clinical presentation (approx. 50-60%), usually following dental trauma or poor oral hygiene. * **Option C (Obligate anaerobe):** *Actinomyces* are typically strict anaerobes or microaerophilic, unlike *Nocardia*, which is an obligate aerobe. **High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** They are Gram-positive, branching filamentous bacteria (not fungi, despite the name). * **Sulfur Granules:** A pathognomonic finding in pus/tissue; these are yellowish colonies of bacteria, not actual sulfur. * **Ray Fungus Appearance:** On microscopy, crushed granules show a "sun-ray" appearance (central mycelium with peripheral clubs). * **IUD Association:** *Actinomyces* is a known cause of pelvic inflammatory disease (PID) in women using intrauterine devices. * **Differential:** Always differentiate from *Nocardia* (Aerobic, Acid-fast, treated with Cotrimoxazole).

Q: A positive Schick test indicates that a person is?

Susceptible to diphtheria. ### Explanation The **Schick test** is a classic skin test used to determine the immune status of an individual against *Corynebacterium diphtheriae*. It works on the principle of **toxin-antitoxin neutralization**. **Why Option C is Correct:** A person is considered **susceptible** if they lack circulating antitoxin (antibodies) against the diphtheria toxin. In the test, 0.1 ml of purified diphtheria toxin is injected intradermally into one forearm (test) and inactivated toxin into the other (control). If the person lacks immunity, the toxin remains active and causes a localized inflammatory reaction (erythema and swelling) at the injection site within 4–7 days. This is a **Positive Result**, indicating susceptibility. **Why Other Options are Incorrect:** * **Option A:** If a person is **immune**, their circulating antitoxin neutralizes the injected toxin, resulting in no skin reaction (Negative Result). * **Option B:** Hypersensitivity is detected by a **Pseudo-reaction**, where both the test and control arms show a reaction that disappears rapidly (within 48 hours). This indicates an allergy to the bacterial proteins, not susceptibility to the toxin. * **Option D:** A carrier state is identified through throat or nasal swabs and culture (e.g., on Löffler's serum slope), not by the Schick test, which only measures humoral immunity. ### NEET-PG High-Yield Pearls: * **Positive Reaction:** Erythema (10–50 mm) reaching peak at 4–7 days. Indicates **Susceptibility**. * **Negative Reaction:** No reaction on either arm. Indicates **Immunity**. * **Combined Reaction:** Both arms show reaction, but the test arm reaction is larger and lasts longer. Indicates both **Susceptibility and Hypersensitivity**. * **Current Status:** The Schick test is largely obsolete in clinical practice due to the widespread use of the DPT/Pentavalent vaccine, but it remains a frequent topic in competitive exams.

Q: Which of the following organisms is most commonly responsible for Sudden Infant Death Syndrome (SIDS), particularly after honey consumption by the infant?

Clostridium botulinum. **Explanation:** **Clostridium botulinum** is the correct answer because it is the causative agent of **Infant Botulism**. In infants under 12 months, the intestinal flora is not fully developed, allowing ingested *C. botulinum* spores to germinate, colonize the gut, and release a potent neurotoxin. **Honey** is a well-known environmental reservoir for these spores. The toxin inhibits acetylcholine release at the neuromuscular junction, leading to "Floppy Baby Syndrome" (descending paralysis). In severe cases, it causes sudden respiratory failure, which is a recognized, preventable cause of **Sudden Infant Death Syndrome (SIDS)**. **Analysis of Incorrect Options:** * **Staphylococcus aureus:** While a common cause of skin infections and food poisoning (via preformed enterotoxin), it is not linked to honey consumption or the specific pathogenesis of SIDS. * **E. coli:** Primarily associated with neonatal sepsis, meningitis, or gastroenteritis, but not with the toxidrome leading to SIDS following honey ingestion. * **Clostridium perfringens:** Causes gas gangrene and food poisoning in adults; it does not colonize the infant gut to cause the paralytic syndrome seen in botulism. **Clinical Pearls for NEET-PG:** * **Age Group:** Most common between **2 to 6 months**. * **Classic Presentation:** Constipation (earliest sign), followed by weak cry, poor suck reflex, loss of head control, and generalized hypotonia (**"Floppy Baby"**). * **Diagnosis:** Identification of spores or toxin in the **stool** (not the serum, as toxin levels are often too low to detect). * **Management:** Treatment is with **Botulism Immune Globulin Intravenous (BIG-IV)**. Avoid honey in all infants <1 year of age.

Q: What is the most likely organism causing epididymitis in a 30-year-old man?

Chlamydia. **Explanation:** The etiology of epididymitis is primarily determined by the patient's age and sexual history. In men **under 35 years of age**, the condition is most commonly caused by sexually transmitted infections (STIs). **1. Why Chlamydia is Correct:** *Chlamydia trachomatis* is the most frequent cause of epididymitis in sexually active men aged <35 years [1]. It typically presents with a gradual onset of scrotal pain, swelling, and may be associated with urethritis [1]. While *Neisseria gonorrhoeae* is also a common cause in this demographic, epidemiological studies consistently show *Chlamydia* as the leading pathogen [1]. **2. Why the other options are incorrect:** * **E. coli (Option A):** This is the most common cause of epididymitis in men **over 35 years** or in children. In these groups, the infection is usually associated with urinary tract infections (UTIs), bladder outlet obstruction (e.g., BPH), or recent urological instrumentation. * **Gonococci (Option B):** *Neisseria gonorrhoeae* is a major cause of STI-related epididymitis in young men, but it ranks second to *Chlamydia* [1]. Gonococcal infection often presents with more acute symptoms and a purulent urethral discharge [1]. * **Ureaplasma ureolyticum (Option D):** While *Ureaplasma* can cause non-gonococcal urethritis, it is a much rarer cause of epididymitis compared to *Chlamydia* [1]. **Clinical Pearls for NEET-PG:** * **Age *Gonorrhea*). Treatment: Ceftriaxone (IM) + Doxycycline (Oral). * **Age >35 years:** Think Enteric organisms (*E. coli*, *Klebsiella*, *Pseudomonas*). Treatment: Fluoroquinolones (e.g., Levofloxacin). * **Prehn’s Sign:** Elevation of the scrotum relieves pain in epididymitis (Positive Prehn's), helping differentiate it from **Testicular Torsion** (Negative Prehn's), which is a surgical emergency.

Question 1

Scotochromogens are:

Accepted Answer

Mycobacterium Gordonae

Answer

Mycobacterium Marinum

Answer

Mycobacterium Intracellulare

Answer

Mycobacterium avium

Question 2

Which of the following statements is FALSE regarding actinomycetes?

Accepted Answer

Penicillin is used in treatment for 6 weeks

Answer

Non-acid fast

Answer

Most common site is cervico-facial

Answer

Obligate anaerobe

Question 3

Which causative organism of a sexually transmitted disease has a safety pin appearance?

Accepted Answer

Syphilis

Answer

Lymphogranuloma venereum (LGV)

Answer

Chancroid

Answer

Genital herpes

Question 4

Gas gangrene is caused by which of the following bacteria?

Accepted Answer

Clostridium sporogenes

Answer

Clostridium histolyticum

Answer

Clostridium novyi

Answer

Clostridium septicum

Question 5

What reaction is due to lysis of bacterial cell wall and necrotic cell products?

Accepted Answer

Jarisch-Herxheimer reaction

Answer

Arthus reaction

Answer

Serum sickness

Answer

Infectious mononucleosis-ampicillin reaction

Question 6

A positive Schick test indicates that a person is?

Accepted Answer

Susceptible to diphtheria

Answer

Immune to diphtheria

Answer

Hypersensitive to diphtheria

Answer

Carrier of diphtheria

Question 7

A 57-year-old man with a history of cardiac valvular prosthesis implanted 5 years ago presents with several weeks of weakness, fatigue, and intermittent fever. Blood cultures grew gram-positive cocci. Laboratory tests revealed that the organisms failed to ferment mannitol and their growth was inhibited by novobiocin. What is the most likely infectious agent?

Accepted Answer

Staphylococcus epidermidis

Answer

Staphylococcus aureus

Answer

Staphylococcus saprophyticus

Answer

Streptococcus viridans

Question 8

The causative organism can be best isolated in which of the following conditions?

Accepted Answer

Tampons in toxic shock syndrome

Answer

Rheumatic valvulitis

Answer

CSF in tetanus

Answer

Diptheritic myocarditis

Question 9

Which of the following organisms is most commonly responsible for Sudden Infant Death Syndrome (SIDS), particularly after honey consumption by the infant?

Accepted Answer

Clostridium botulinum

Answer

Staphylococcus aureus

Answer

E. coli

Answer

Clostridium perfringens

Question 10

What is the most likely organism causing epididymitis in a 30-year-old man?

Accepted Answer

Chlamydia

Answer

E. coli

Answer

Gonococci

Answer

Ureaplasma ureolyticum

Bacteriology — MCQs

Bacteriology — MCQs

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