NEET-PG 2021 - Microbiology Practice Questions

Q: A group of people ate patty late at night and experienced bouts of vomiting early in the morning. What is the most likely cause?

Staphylococcus aureus. ***Staphylococcus aureus*** - This scenario describes classic **Staphylococcal food poisoning** with rapid onset of vomiting (4-8 hours after ingestion). - *S. aureus* produces preformed **heat-stable enterotoxins** in contaminated foods left at room temperature, particularly **meat products, pastries, and cream-filled items**. - Clinical hallmark: **Prominent vomiting** with minimal diarrhea and rapid resolution (24 hours). - The timing (late night eating → early morning vomiting) and food item (patty) make this the **definitive diagnosis**. *Escherichia coli* - Most pathogenic *E. coli* strains (ETEC, EHEC, EPEC) have **longer incubation periods** (1-3 days). - Typically presents with **diarrhea as the predominant symptom**, not isolated vomiting. - The rapid onset of symptoms excludes direct bacterial infection and indicates preformed toxin ingestion. *Lactobacillus* - These are **probiotic bacteria** and part of normal human flora (gut, vagina, mouth). - Not pathogenic and not associated with food poisoning. - Used therapeutically to prevent antibiotic-associated diarrhea. *Bacillus cereus* - While *B. cereus* has an emetic form with rapid onset (1-5 hours), it is **classically associated with reheated fried rice** and starchy foods, not meat products. - The emetic toxin (cereulide) is produced in improperly stored rice, not patties. - The food item (patty) clearly points to *S. aureus* rather than *B. cereus*.

Q: A pregnant woman, whose niece contracted varicella while living in the same house, tested negative for serum antibodies to varicella. What does this result indicate?

She is susceptible to chickenpox. ***She is susceptible to chickenpox*** - A negative test for serum antibodies to varicella indicates a **lack of protective immunity** to the varicella-zoster virus (VZV). - This woman has not previously been infected with VZV or vaccinated, making her **susceptible to primary infection (chickenpox)** upon exposure. *She is susceptible to zoster* - **Zoster (shingles)** is caused by the **reactivation of latent VZV** in individuals who have previously had chickenpox. - Since she tested negative for antibodies, she has not had chickenpox and thus **cannot harbor latent VZV** to reactivate. *She is immune to zoster* - Immunity to zoster implies that she has had chickenpox and subsequently developed a robust immune response to prevent viral reactivation. - A negative antibody test directly contradicts this, as it signifies no prior exposure or immune response. *She is immune to chicken pox* - Immunity to chickenpox is established by the presence of **varicella antibodies**, which are absent in this case. - A negative antibody result means she is **not immune** and is therefore at risk of contracting chickenpox if exposed.

Q: A male patient presents with white discharge from the urethra, as shown in the image. What is the most probable causative organism?

Neisseria gonorrhoeae. ***Neisseria gonorrhoeae*** - Among the given options, *Neisseria gonorrhoeae* is the **most probable causative organism** for **urethral discharge** in males. - Gonorrhea is a common sexually transmitted infection (STI) presenting with **purulent urethritis**, typically with thick, yellow-green discharge, though appearance can vary. - **Clinical note:** While classic gonococcal discharge is purulent and yellow-green, the clinical presentation can vary. None of the other organisms listed cause urethritis with discharge. *Haemophilus ducreyi* - This bacterium causes **chancroid**, a sexually transmitted infection characterized by **painful genital ulcers (chancres)** and **inguinal lymphadenopathy**, not urethral discharge. - Presents with ulcerative lesions, not discharge. *Klebsiella granulomatis* - This organism is responsible for **donovanosis** (granuloma inguinale), which manifests as **painless, progressive ulcerative lesions** on the genitals. - It does not cause urethral discharge; presents with beefy red granulomatous lesions. *Treponema pallidum* - This spirochete causes **syphilis**, which presents with **painless chancres** in the primary stage, **maculopapular rash** in the secondary stage, and gummas or neurological symptoms in later stages. - Urethral discharge is not a typical symptom of syphilis; primary lesions are ulcerative.

Q: A hair perforation test was performed on a yeast isolate, and the result was positive. Which of the following organisms is associated with a positive hair perforation test?

Candida albicans. ***Candida albicans*** - The **hair perforation test** is a classic diagnostic test specifically used to identify *Candida albicans*, which characteristically produces **conical projections** when incubated with sterilized blonde hair in water at room temperature. - This test has historically been used as a simple, rapid method for **presumptive identification** of *C. albicans* from other Candida species, indicating the organism's ability to produce **keratinolytic enzymes**. *Candida tropicalis* - *Candida tropicalis* gives a **negative hair perforation test** and does not produce the characteristic hair perforations seen with *C. albicans*. - While it can form **pseudohyphae** and true hyphae, it can be differentiated from *C. albicans* using this test among others. *Candida glabrata* - *Candida glabrata* does **NOT** produce a positive hair perforation test and typically remains in **yeast form**. - It is distinguished from other Candida species by its **smaller cell size** and inability to form germ tubes or hair perforations. *Candida parapsilosis* - *Candida parapsilosis* also gives a **negative hair perforation test** and does not produce hair perforations. - This species can form **pseudohyphae** but the hair perforation test helps distinguish it from *C. albicans*.

Question 1

A group of people ate patty late at night and experienced bouts of vomiting early in the morning. What is the most likely cause?

Accepted Answer

Staphylococcus aureus

Answer

Escherichia coli

Answer

Lactobacillus

Answer

Bacillus cereus

Question 2

A pregnant woman, whose niece contracted varicella while living in the same house, tested negative for serum antibodies to varicella. What does this result indicate?

Accepted Answer

She is susceptible to chickenpox

Answer

She is susceptible to zoster

Answer

She is immune to zoster

Answer

She is immune to chicken pox

Question 3

A male patient presents with white discharge from the urethra, as shown in the image. What is the most probable causative organism?

Accepted Answer

Neisseria gonorrhoeae

Answer

Haemophilus ducreyi

Answer

Klebsiella granulomatis

Answer

Treponema pallidum

Question 4

A hair perforation test was performed on a yeast isolate, and the result was positive. Which of the following organisms is associated with a positive hair perforation test?

Accepted Answer

Candida albicans

Answer

Candida tropicalis

Answer

Candida glabrata

Answer

Candida parapsilosis

NEET-PG 2021 — Microbiology