NEET-PG 2020 - Microbiology Practice Questions

Q: Identify the following bacterium from the image.

Neisseria meningitidis. ***Neisseria meningitidis*** - The image displays **Gram-negative diplococci** (pink/red, paired cocci) predominantly located **intracellularly within neutrophils**, which is characteristic of *Neisseria meningitidis* in cerebrospinal fluid or blood smears. - The morphology and intracellular presence in phagocytes, combined with the **clinical context suggesting systemic/CNS infection**, strongly indicate **meningococcal infection**. *Neisseria cinerea* - While also a **Gram-negative coccus**, *Neisseria cinerea* is a **commensal organism** of the upper respiratory tract. - It rarely causes invasive disease and is **not pathogenic**, making it incompatible with the clinical presentation suggested by this image. *Neisseria gonorrhoeae* - *Neisseria gonorrhoeae* also appears as **Gram-negative diplococci within neutrophils**, with nearly identical microscopic morphology to *N. meningitidis*. - However, *N. gonorrhoeae* causes **genitourinary infections** (urethritis, cervicitis) and occasionally disseminated gonococcal infection, but **not meningitis**. - The clinical context (CSF or blood smear suggesting systemic/meningeal infection) distinguishes this as *N. meningitidis*. *Neisseria polysaccharea* - *Neisseria polysaccharea* is a **commensal species** of the upper respiratory tract. - It is **non-pathogenic** and does not cause invasive infections or present with the clinical picture suggested by this image.

Q: Nosocomial infections are diagnosed after how many hours of hospitalization / admission?

48 hours. ***48 hours*** - Nosocomial infections, also known as **hospital-acquired infections (HAIs)**, are defined as infections that develop at least **48 hours** after hospital admission. - This time frame helps differentiate infections acquired in the hospital setting from those the patient was incubating upon admission. *96 hours* - A 96-hour threshold is **too long** for the standard definition of a nosocomial infection. - Infections emerging after this extended period would almost certainly be considered hospital-acquired, but the conventional diagnostic window is shorter. *72 hours* - While 72 hours might capture many HAIs, it is **not the universally accepted or most common cutoff** for defining a nosocomial infection. - The 48-hour mark is more widely used for epidemiological and diagnostic purposes. *24 hours* - Infections diagnosed within **24 hours** of admission are typically considered to have been present or incubating **prior to hospitalization**. - This short timeframe is generally insufficient to classify an infection as hospital-acquired.

Q: Urethritis in males is not caused by:

H. ducreyi. ***H. ducreyi*** - *Haemophilus ducreyi* is the causative agent of **chancroid**, a sexually transmitted infection characterized by **genital ulcers** [1] with painful regional lymphadenopathy. - It does not typically cause urethritis as its primary site of infection is the **skin and mucous membranes** of the external genitalia, forming ulcers rather than urethral inflammation. *Chlamydia* - **Chlamydia trachomatis** is a common cause of **non-gonococcal urethritis** in males [1]. - It often presents with **dysuria**, **urethral discharge**, and sometimes can be asymptomatic [1]. *Gonococcus* - **Neisseria gonorrhoeae** (gonococcus) is a well-known cause of urethritis, often referred to as **gonococcal urethritis** [1]. - It typically causes a **purulent urethral discharge** and **dysuria** [1]. *Trichomonas* - **Trichomonas vaginalis** can cause **urethritis** in males [1], although it is less common than in females. - Males may experience **dysuria**, **urethral discharge**, or can be asymptomatic carriers.

Q: Which of the following is a Category A bioterrorism agent?

Bacillus anthracis. ***Bacillus anthracis*** - **_Bacillus anthracis_** (causing anthrax) is a classic example of a **Category A bioterrorism agent** due to its high mortality, ease of dissemination, and potential for major public health impact. - Category A agents are considered the **highest priority** because they pose a significant risk to national security. *Brucella* - **_Brucella_** species are classified as **Category B bioterrorism agents**. - They are moderately easy to disseminate and can cause moderate morbidity but generally have a **low mortality rate**. *Nipah virus* - **Nipah virus** is categorized as a **Category C bioterrorism agent**. - These are emerging pathogens that could be engineered for mass dissemination in the future, but their current risk is lower than Category A or B. *Coxiella* - **_Coxiella burnetii_** (causing Q fever) is classified as a **Category B bioterrorism agent**. - It is relatively easy to disseminate and can cause high morbidity but has a **low mortality rate**.

Q: Superantigen is produced by which of the following?

Streptococcus pyogenes. ***Streptococcus pyogenes*** - *Streptococcus pyogenes* produces **superantigens** such as **streptococcal pyrogenic exotoxins (SPE-A, SPE-B, SPE-C)**. - These superantigens cause massive non-specific T-cell activation, leading to **toxic shock syndrome** and **scarlet fever**. - Superantigens bypass normal antigen processing by directly binding MHC class II molecules to T-cell receptors. *Clostridium perfringens* - *Clostridium perfringens* primarily produces **alpha-toxin** (phospholipase C) and other toxins causing **gas gangrene** and **food poisoning**. - It does not produce superantigens. *Vibrio cholerae* - *Vibrio cholerae* produces **cholera toxin**, an **enterotoxin** that causes massive fluid secretion in the intestine, leading to profuse watery diarrhea. - Cholera toxin is not a superantigen; it acts by activating adenylate cyclase through ADP-ribosylation. *Staphylococcus epidermidis* - *Staphylococcus epidermidis* is a common skin commensal that can cause infections related to **medical devices** and **biofilm formation**. - Unlike *Staphylococcus aureus* (which produces TSST-1 and enterotoxins), *S. epidermidis* does not produce superantigens.

Q: A 29 year old male was brought to ED with complaints of nausea, vomiting and abdominal cramps 3-4 hours after eating meat at dinner. What is the likely cause of this condition?

Staphylococcus aureus. ***Staphylococcus aureus*** - The rapid onset of symptoms (3-4 hours) after eating meat, characterized by **nausea**, **vomiting**, and **abdominal cramps**, is highly suggestive of preformed toxin-mediated food poisoning, with **Staphylococcus aureus** being a common culprit. - *S. aureus* produces heat-stable enterotoxins that, when ingested, cause prompt gastrointestinal symptoms due to their direct irritant effect on the gut. *Clostridium perfringens* - This bacterium typically causes food poisoning with an incubation period of **8-16 hours** and symptoms primarily include **abdominal cramps** and **diarrhea**, with vomiting being less common. - Symptoms arise from toxins produced *in vivo* after spore ingestion, not preformed toxins, which leads to a longer incubation time. *Clostridium botulinum* - While *Clostridium botulinum* produces a potent neurotoxin, its food poisoning primarily manifests as **neurological symptoms** (e.g., flaccid paralysis, diplopia, dysphagia), not acute gastrointestinal upset like vomiting and cramps. - The incubation period is typically **12-36 hours**, longer than the reported 3-4 hours, and it is usually associated with improperly canned foods. *Salmonella Enteritidis* - *Salmonella* infections usually have a longer incubation period of **6 hours to 6 days**, and while they can cause nausea, vomiting, cramps, and diarrhea, the rapid onset in this case makes *S. aureus* more likely. - Infection typically leads to **inflammatory gastroenteritis**, sometimes with fever, which is not mentioned as a prominent symptom here.

Q: A 12 year old boy presents with vomiting within 3 hours of consumption of food at a party. What is the likely causative organism responsible for the symptoms?

Staphylococcus aureus. ***Staphylococcus aureus*** - **Vomiting occurring within 1-6 hours of food consumption** is highly characteristic of preformed toxin ingestion, commonly associated with *S. aureus*. - *S. aureus* produces **heat-stable enterotoxins** that cause rapid onset nausea, vomiting, and abdominal cramps. *Clostridium perfringens* - This bacterium typically causes symptoms like **abdominal cramps and diarrhea**, with vomiting being less common. - The onset of illness from *C. perfringens* is usually **8-16 hours** after consumption, which is longer than the 3-hour window in this case. *Clostridium botulinum* - *C. botulinum* causes **botulism**, a neuroparalytic illness, which may include nausea and vomiting in its early stages but is primarily characterized by **flaccid paralysis**. - Symptoms usually appear **12-36 hours** after exposure, which is much longer than the presentation described. *Salmonella* - **Salmonellosis** typically has an incubation period of **6-72 hours**, with symptoms including diarrhea, fever, and abdominal cramps; vomiting may occur but is not as immediate or predominant as with *S. aureus* toxin. - The illness is caused by bacterial colonization and invasion, not preformed toxins, leading to a longer onset compared to the 3-hour presentation.

Q: A 35-year-old HIV positive patient comes with intractable diarrhea, crampy abdominal pain and vomiting. Biopsy of small intestine was taken which shows oocysts <10 µm as given below. What is the appropriate diagnosis?

Cryptosporidium parvum. ***Cryptosporidium parvum*** - The classic presentation in an **HIV-positive** patient with **intractable diarrhea**, **abdominal pain**, and identifying **acid-fast oocysts <10 µm** in a small intestine biopsy strongly indicates *Cryptosporidium parvum*. - This parasite is a common cause of **severe diarrheal illness** in immunocompromised individuals. *Giardia lamblia* - While *Giardia lamblia* causes **diarrhea** and **abdominal cramps**, its cysts are larger (10-14 µm) and typically pear-shaped trophozoites are seen, not small acid-fast oocysts. - It usually causes **malabsorption** and **steatorrhea**, and is not typically associated with intractable diarrhea in HIV patients to the same extent as *Cryptosporidium*. *CMV* - **Cytomegalovirus (CMV)** can cause **colitis** or **enteritis** in immunocompromised patients, leading to diarrhea and abdominal pain. - However, diagnosis involves identifying **intranuclear inclusions** (cytomegalic cells) on biopsy, not small cysts or oocysts. *Isospora belli* - *Isospora belli* is another coccidian parasite causing diarrhea in HIV patients, but its oocysts are **larger (20-30 µm)** and **ellipsoidal**, differentiating them from the smaller, round oocysts of *Cryptosporidium*. - Like *Cryptosporidium*, its oocysts are also **acid-fast**, but size and shape are key distinguishing features.

Q: Which of the following is most likely to be acquired by traumatic inoculation?

Sporothrix schenckii. ***Sporothrix schenckii*** - **Sporothrix schenckii** causes **sporotrichosis** (rose gardener's disease), which is classically acquired through **traumatic inoculation** via thorns, splinters, or plant material contaminated with the fungus. - This dimorphic fungus exists in soil and vegetation, and the mode of transmission is characteristically associated with **gardeners, farmers, and florists** who experience penetrating injuries during their work. - Presents as lymphocutaneous infection with nodular lesions along lymphatic channels. *Histoplasma capsulatum* - Causes histoplasmosis and is endemic to certain regions (Ohio and Mississippi River valleys). - Primarily acquired through **inhalation of microconidia** from soil contaminated with bird or bat droppings, not through traumatic inoculation. - Presents as pulmonary infection in most cases. *Coccidioides immitis* - Causes coccidioidomycosis (Valley Fever) and is found in arid regions of southwestern United States. - Acquired through **inhalation of airborne arthroconidia** from disturbed soil, not through traumatic inoculation. - While rare cases of primary cutaneous infection can occur, inhalation remains the typical route. *Aspergillus fumigatus* - Ubiquitous environmental mold associated with decaying organic matter. - Primarily causes disease through **inhalation of conidia**, leading to allergic reactions, aspergilloma, or invasive aspergillosis in immunocompromised patients. - Not typically associated with traumatic inoculation as the primary mode of infection.

Q: Which of the following doesn't cause urethritis in males?

H. Ducreyi. ***H. Ducreyi*** - *Haemophilus ducreyi* is the causative agent of **chancroid**, a sexually transmitted infection characterized by painful **genital ulcers** and **lymphadenopathy**. - It does not primarily cause **urethritis**, which is inflammation of the urethra. *Trichomonas vaginalis* - **Trichomonas vaginalis** is a protozoan parasite that commonly causes **trichomoniasis**, a sexually transmitted infection. - In males, it can lead to **urethritis** with symptoms such as dysuria and urethral discharge. *Chlamydia trachomatis* - **Chlamydia trachomatis** is a very common bacterial cause of **urethritis** in males, often presenting with a **mucopurulent discharge** and dysuria. - It is frequently asymptomatic, making it a significant cause of undiagnosed sexually transmitted infections. *N. gonorrhoeae* - **Neisseria gonorrhoeae** is the bacterium responsible for **gonorrhea**, a well-known cause of **purulent urethritis** in males. - Symptoms typically include a profuse, **purulent urethral discharge** and painful urination.

Question 1

Identify the following bacterium from the image.

Accepted Answer

Neisseria meningitidis

Answer

Neisseria cinerea

Answer

Neisseria gonorrhoeae

Answer

Neisseria polysaccharea

Question 2

Nosocomial infections are diagnosed after how many hours of hospitalization / admission?

Accepted Answer

48 hours

Answer

96 hours

Answer

72 hours

Answer

24 hours

Question 3

Urethritis in males is not caused by:

Accepted Answer

H. ducreyi

Answer

Chlamydia

Answer

Gonococcus

Answer

Trichomonas

Question 4

Which of the following is a Category A bioterrorism agent?

Accepted Answer

Bacillus anthracis

Answer

Brucella

Answer

Nipah virus

Answer

Coxiella

Question 5

Superantigen is produced by which of the following?

Accepted Answer

Streptococcus pyogenes

Answer

Clostridium perfringens

Answer

Vibrio cholerae

Answer

Staphylococcus epidermidis

Question 6

A 29 year old male was brought to ED with complaints of nausea, vomiting and abdominal cramps 3-4 hours after eating meat at dinner. What is the likely cause of this condition?

Accepted Answer

Staphylococcus aureus

Answer

Clostridium perfringens

Answer

Clostridium botulinum

Answer

Salmonella Enteritidis

Question 7

A 12 year old boy presents with vomiting within 3 hours of consumption of food at a party. What is the likely causative organism responsible for the symptoms?

Accepted Answer

Staphylococcus aureus

Answer

Clostridium perfringens

Answer

Clostridium botulinum

Answer

Salmonella

Question 8

A 35-year-old HIV positive patient comes with intractable diarrhea, crampy abdominal pain and vomiting. Biopsy of small intestine was taken which shows oocysts <10 µm as given below. What is the appropriate diagnosis?

Accepted Answer

Cryptosporidium parvum

Answer

Giardia lamblia

Answer

CMV

Answer

Isospora belli

Question 9

Which of the following is most likely to be acquired by traumatic inoculation?

Accepted Answer

Sporothrix schenckii

Answer

Coccidioides immitis

Answer

Histoplasma capsulatum

Answer

Aspergillus fumigatus

Question 10

Which of the following doesn't cause urethritis in males?

Accepted Answer

H. Ducreyi

Answer

Trichomonas vaginalis

Answer

Chlamydia trachomatis

Answer

N. gonorrhoeae

NEET-PG 2020 — Microbiology