NEET-PG 2013 - Microbiology Practice Questions

Q: The most common cause of meningitis in children aged 5 yrs is-

S. pneumoniae. ***S. pneumoniae*** - **_Streptococcus pneumoniae_** (Pneumococcus) is the **most common cause of bacterial meningitis** in children aged 5 years and older, as well as in adults. - Widespread vaccination has reduced its incidence but it remains a significant pathogen. *H. influenzae* - **_Haemophilus influenzae_ type b (Hib)** was a major cause of meningitis in young children, but its incidence has **drastically decreased** due to the routine **Hib vaccine**. - Without vaccination, it would still be a significant cause in this age group, but with high vaccine coverage, it is less common than _S. pneumoniae_. *Staphylococcus* - **_Staphylococcus aureus_** and other staphylococcal species are **less common causes of meningitis** in otherwise healthy children. - They are more typically associated with meningitis following **neurosurgery**, trauma, or in immunocompromised patients. *E.coli* - **_Escherichia coli_** is a common cause of **neonatal meningitis** (in infants less than 3 months old), often acquired during passage through the birth canal. - It is **rarely a cause of meningitis** in children aged 5 years.

Q: Empyema thoracis is most commonly caused by which organism

Streptococcus pneumoniae. ***Streptococcus pneumoniae*** - This is the **most common cause of empyema thoracis**, accounting for **40-70% of all cases** in most published series - It is the leading cause of **community-acquired pneumonia** that progresses to parapneumonic effusion and empyema - The pneumococcal infection leads to **inflammatory exudation** into the pleural space, which can progress through exudative, fibrinopurulent, and organizing phases to form frank empyema - Remains the most frequent causative organism across all age groups in community-acquired empyema *Staphylococcus aureus* - An important but **less common cause** of empyema, accounting for approximately 10-20% of cases - More frequently seen in **specific clinical contexts**: post-influenza pneumonia, hospital-acquired infections, hematogenous spread, and pediatric empyema - Causes **severe, necrotizing infections** with abscess formation and is associated with higher morbidity - While clinically significant, it is **not the most common** overall cause *Pseudomonas* - *Pseudomonas aeruginosa* is primarily associated with **nosocomial empyema** in hospitalized patients - Risk factors include **ventilator-associated pneumonia**, immunosuppression, and **cystic fibrosis** - Accounts for a small percentage of empyema cases overall *Mycobacterium* - *Mycobacterium tuberculosis* causes **tuberculous empyema**, a chronic condition with characteristic **thick pleural fluid** and caseous material - Important in regions with high TB prevalence but represents a distinct entity from acute bacterial empyema - Not a common cause of acute pyogenic empyema in most settings

Q: A young sexually active female presents with intense pruritus and watery discharge. What is the most likely causative organism?

Trichomonas vaginalis. ***Trichomonas vaginalis*** - **Trichomoniasis** presents with **intense vulvovaginal pruritus** and **profuse discharge** that can range from watery to **frothy, yellow-green** in appearance, often with a **strawberry cervix**. - It is a **sexually transmitted infection (STI)** caused by a **flagellated protozoan** with vaginal **pH >4.5** and is treated with **metronidazole**. *Chlamydia trachomatis* - Often causes **asymptomatic infections** or **mucopurulent cervical discharge** with **dysuria** and **post-coital bleeding**, but typically **no intense pruritus**. - It is a **bacterial STI** that primarily causes **cervicitis** and **pelvic inflammatory disease**, not the characteristic intense itching described. *Candida albicans* - Causes **severe vulvovaginal pruritus** but with a **thick, white, curd-like discharge** rather than watery discharge, and is **not sexually transmitted**. - Known as **vulvovaginal candidiasis** or yeast infection, caused by fungal overgrowth, often precipitated by **antibiotics** or **immunosuppression**. *Gardnerella vaginalis* - Associated with **bacterial vaginosis**, presenting with **thin, grayish-white discharge** and **fishy odor** (especially after intercourse), but **minimal pruritus**. - Caused by **vaginal flora imbalance** with loss of **lactobacilli** and overgrowth of anaerobic bacteria, not primarily an STI.

Q: Which organism causes puerperal sepsis?

Group A beta hemolytic streptococci. ***Group A beta hemolytic streptococci*** - **Group A Streptococcus (GAS)**, specifically *Streptococcus pyogenes*, is the **classic and most important cause of puerperal sepsis** (puerperal fever). - Historically, GAS was responsible for devastating epidemics of puerperal fever in maternity wards before the introduction of antiseptic practices by Ignaz Semmelweis. - GAS causes severe, rapidly progressive postpartum infections with **high morbidity and mortality** if untreated. - Clinically presents with fever, severe uterine tenderness, and can progress to **toxic shock syndrome** and septicemia. *Group B beta hemolytic streptococci* - **Group B Streptococcus (GBS)**, *Streptococcus agalactiae*, can cause postpartum endometritis and maternal infections. - However, GBS is **more commonly associated with neonatal sepsis** rather than being the primary cause of classic puerperal sepsis. - While it can colonize the genital tract and cause infection, it is not the historical or most severe cause of puerperal fever. *CMV* - **Cytomegalovirus (CMV)** is a viral infection that causes congenital infections when transmitted in utero. - It is not a bacterial cause of **puerperal sepsis**, which is primarily a bacterial postpartum infection. *Toxoplasma gondii* - **Toxoplasma gondii** is a parasite causing toxoplasmosis, which can lead to congenital abnormalities. - It is not associated with **puerperal sepsis**, which is a bacterial infection of the postpartum period.

Q: Dermatophytes affect -

Keratin. ***Keratin*** - **Dermatophytes** are a group of fungi that have a unique ability to digest **keratin**, a protein found in **skin, hair, and nails**. - This characteristic allows them to colonize and thrive in these superficial tissues, causing infections like **tinea corporis** (ringworm) or **tinea pedis** (athlete's foot). *Dermis of skin* - The **dermis** is the layer of skin beneath the epidermis, rich in **collagen, elastin, blood vessels, and nerves**. - Dermatophytes do not typically invade the dermis; their infections are generally limited to the **stratum corneum** and other keratinized structures. *Stratum spongiosum* - **Stratum spongiosum** is a term sometimes used to describe an edematous (swollen) epidermis, often seen in **eczema** and **dermatitis**. - Dermatophytes do not target this specific architectural change in the epidermis but rather feed on the keratin present in the more superficial layers. *Stratum basal* - The **stratum basale** (also called stratum germinativum) is the deepest layer of the **epidermis**, responsible for cell division and producing new skin cells. - Dermatophytes primarily infect the **dead keratinized cells** of the stratum corneum rather than the metabolically active cells of the stratum basale.

Q: Rash is absent in ?

Q. fever. ***Q. fever*** - Q fever, caused by **Coxiella burnetii**, is characterized by **flu-like symptoms**, pneumonia, and hepatitis, but **does not typically present with a rash**. - This differentiates it from other rickettsial infections that commonly involve skin manifestations. *Endemic typhus* - Endemic (murine) typhus, caused by **Rickettsia typhi**, is transmitted by **fleas** and commonly presents with a **maculopapular rash** on the trunk and extremities [2]. - The rash usually appears several days after fever onset [2]. *Epidemic typhus* - Epidemic typhus, caused by **Rickettsia prowazekii** and transmitted by the **human body louse**, classically presents with a **centrifugal rash** that spares the face, palms, and soles [2]. - The rash typically starts on the trunk and spreads outwards [2]. *Scrub typhus* - Scrub typhus, caused by **Orientia tsutsugamushi**, is transmitted by **chiggers** and often features an **eschar** (a necrotic lesion at the bite site) along with a **maculopapular rash** [1]. - The rash may be transient or absent in some cases, but an eschar is a highly characteristic finding [1].

Q: SA 14-14-2 vaccine is an example of which type of vaccine?

Live attenuated vaccine. ***Live attenuated vaccine*** - The **SA 14-14-2 vaccine** is a **live attenuated Japanese Encephalitis (JE) vaccine** developed through serial passage and attenuation of the wild-type SA 14 strain. - The designation "14-14-2" refers to the specific **attenuated strain** after multiple passages, not to an inactivation process. - This vaccine uses **weakened (attenuated) virus** that can replicate minimally, providing robust and long-lasting immunity similar to natural infection. - It is widely used in **China, India, and other Asian countries** in national immunization programs. *Inactivated vaccine* - While there is also an **inactivated version** of the SA 14-14-2 strain (vero cell-derived inactivated JE vaccine), the term "SA 14-14-2 vaccine" by itself typically refers to the **live attenuated formulation**. - Inactivated vaccines contain killed viral particles that cannot replicate. *Toxoid vaccine* - **Toxoid vaccines** are based on inactivated bacterial toxins (toxoids), not viral antigens. - Examples include vaccines for **tetanus** and **diphtheria**, which target toxins produced by bacteria. - This type does not apply to viral vaccines like Japanese Encephalitis. *Subunit vaccine* - **Subunit vaccines** contain only specific purified antigenic components (proteins, polysaccharides) rather than whole organisms. - Examples include **Hepatitis B vaccine** (HBsAg) and **HPV vaccine**. - The SA 14-14-2 vaccine uses the whole attenuated virus, not subunits.

Q: The difference between contamination and infection is that in infection

Infectious agent is in the body of human. ***Infectious agent is in the body of human*** - **Infection** implies that microorganisms have successfully **invaded the host tissues** and are replicating within the body, potentially causing a host response or disease. - The presence of the pathogen *inside* the body, beyond just surface adherence, is the defining characteristic of infection. *Arthropods on the body surface* - This describes an **infestation** (e.g., lice, mites), where the arthropods are physically present on the body surface but may not have *invaded* tissues in the same way bacteria or viruses do during an infection. - While some arthropods can transmit infectious agents, their mere presence on the surface is not synonymous with an internal infection. *Infectious agent is on body surface or on non-human objects* - This scenario describes **contamination**, where microorganisms are present on surfaces (either human skin or inanimate objects) but have not yet penetrated or established themselves within host tissues. - Contamination is a potential precursor to infection but is not an infection itself. *Infectious agents on clothes* - This is a clear example of **fomite contamination**, where infectious agents are present on inanimate objects like clothing. - The microorganisms are external to the body and are not causing an infection in the person wearing the clothes unless they are transferred and subsequently invade the host.

Question 1

The most common cause of meningitis in children aged 5 yrs is-

Accepted Answer

S. pneumoniae

Answer

Staphylococcus

Answer

E.coli

Answer

H. influenzae

Question 2

Empyema thoracis is most commonly caused by which organism

Accepted Answer

Streptococcus pneumoniae

Answer

Pseudomonas

Answer

Staphylococcus aureus

Answer

Mycobacterium

Question 3

A young sexually active female presents with intense pruritus and watery discharge. What is the most likely causative organism?

Accepted Answer

Trichomonas vaginalis

Answer

Chlamydia trachomatis

Answer

Candida albicans

Answer

Gardnerella vaginalis

Question 4

Which organism causes puerperal sepsis?

Accepted Answer

Group A beta hemolytic streptococci

Answer

CMV

Answer

Toxoplasma gondii

Answer

Group B beta hemolytic streptococci

Question 5

Dermatophytes affect -

Accepted Answer

Keratin

Answer

Dermis of skin

Answer

Stratum spongiosum

Answer

Stratum basale

Question 6

Rash is absent in ?

Accepted Answer

Q. fever

Answer

Endemic typhus

Answer

Epidemic typhus

Answer

Scrub typhus

Question 7

SA 14-14-2 vaccine is an example of which type of vaccine?

Accepted Answer

Live attenuated vaccine

Answer

Toxoid vaccine

Answer

Inactivated vaccine

Answer

Subunit vaccine

Question 8

The difference between contamination and infection is that in infection

Accepted Answer

Infectious agent is in the body of human

Answer

Infectious agent is on body surface (arthropods)

Answer

Infectious agent is on body surface or on non-human objects

Answer

Infectious agent is on clothes

NEET-PG 2013 — Microbiology