Bacteriology Practice Questions

Q: Causative organism of rheumatic fever is:

Group A Streptococci. ***Group A Streptococci*** - **Rheumatic fever** is a serious inflammatory complication that can develop after an untreated or inadequately treated infection of the throat with **streptococcus pyogenes**, which is also known as **Group A Streptococcus (GAS)**. - The immune response to GAS infection mistakenly attacks the body's own tissues, particularly the heart, joints, brain, and skin. *Group B Streptococci* - **Group B Streptococcus (GBS)** is primarily known for causing serious infections in **newborns** (e.g., sepsis, meningitis) and can cause infections in pregnant women. - It is not associated with the development of rheumatic fever. *Group D Streptococci* - **Group D Streptococci** encompasses species such as *Enterococcus faecalis* and *Streptococcus gallolyticus* (formerly *Streptococcus bovis*). - These are typically associated with **urinary tract infections**, **endocarditis**, and **colorectal cancer** (in the case of *S. gallolyticus*), not rheumatic fever. *Staphylococci* - **Staphylococci**, such as *Staphylococcus aureus*, cause a wide range of infections including **skin infections**, **pneumonia**, **sepsis**, and **toxic shock syndrome**. - They are not the causative agents of rheumatic fever; this condition is specifically linked to streptococcal infections.

Q: What is the etiological agent for buruli ulcer which usually occurs in the tropics?

Mycobacterium ulcerans. ***Mycobacterium ulcerans*** - **Buruli ulcer** (also known as Bairnsdale ulcer or Daintree ulcer) is caused by infection with **Mycobacterium ulcerans**. - This bacterium produces a toxin called **mycolactone**, which destroys tissue and suppresses the immune system, leading to characteristic skin lesions. *Mycobacterium fortuitum* - *Mycobacterium fortuitum* is a **rapidly growing mycobacterium** that can cause skin and soft tissue infections, especially after trauma or surgery. - However, it is not the etiologic agent for **Buruli ulcer**, which is associated with a specific slow-growing mycobacterium. *Mycobacterium marinum* - *Mycobacterium marinum* is known to cause **"fish tank granuloma"** or "swimming pool granuloma," an infection acquired from contaminated water, typically presenting as skin lesions on extremities. - While it is a **nontuberculous mycobacterium** with environmental reservoirs, it is not responsible for **Buruli ulcer**. *Mycobacterium kansasii* - *Mycobacterium kansasii* is a **nontuberculous mycobacterium** primarily associated with pulmonary disease, resembling tuberculosis, particularly in individuals with compromised immune systems. - It is not the causative agent of **Buruli ulcer**, which has distinct clinical and epidemiological characteristics.

Q: Vibrio parahaemolyticus is seen in which of the following if undercooked?

Shellfish. ***Shellfish*** - **Vibrio parahaemolyticus** is a common cause of **foodborne gastroenteritis** associated with consumption of raw or undercooked **shellfish**, including both mollusks and crustaceans. - This halophilic bacterium thrives in **warm coastal and estuarine waters** and colonizes various marine shellfish. - Most commonly isolated from **oysters, clams, mussels** (bivalve mollusks that concentrate bacteria through filter feeding), but also found in **shrimp, prawns, and crabs**. - **Shellfish** is the most comprehensive and correct answer as it encompasses all these seafood types. *Prawn* - Prawns (a type of shellfish/crustacean) can indeed harbor **Vibrio parahaemolyticus** and are a recognized source of infection. - However, this answer is **too specific** when a broader category (shellfish) is available. - While medically accurate, "Shellfish" is the better answer as it includes prawns and all other affected seafood. *Crab* - Crabs (also shellfish/crustaceans) can carry **Vibrio parahaemolyticus**, especially in warm coastal waters. - Like prawns, this is **too specific** when the broader category "Shellfish" encompasses crabs. - Multiple outbreaks have been linked to crab consumption, but "Shellfish" remains the more complete answer. *Fish* - While **cross-contamination** can occur, finfish are **less commonly** the primary source of *V. parahaemolyticus* infection compared to shellfish. - The bacterium preferentially colonizes shellfish rather than finfish. - Fish is therefore the least associated option among the choices given.

Q: All of the following organisms are known to survive intracellularly except

Neisseria meningitidis. ***Neisseria meningitidis*** - While *Neisseria meningitidis* can be found in the **phagosomes of neutrophils** in infected individuals, it is not considered a classic intracellular pathogen that replicates significantly or survives for extended periods within host cells. - Its primary mechanism of pathogenesis involves replication extracellularly and the production of a capsule to evade phagocytosis. *Legionella pneumophila* - *Legionella pneumophila* is a **facultative intracellular pathogen** known to replicate within **macrophages** and **amoebae** in aquatic environments. - Its ability to survive and multiply inside host cells is crucial for its virulence and persistence. *Streptococcus pyogenes* - *Streptococcus pyogenes* (Group A Streptococcus) can **invade and survive within non-phagocytic cells** such as epithelial cells, which may contribute to persistent infections and immune evasion. - This intracellular survival mechanism can make it more challenging for antibiotics and the immune system to eradicate the bacteria. *Salmonella Typhi* - *Salmonella Typhi* is a well-known **intracellular pathogen** that survives and replicates within **macrophages and other phagocytic cells** in the host. - This intracellular lifestyle allows it to evade immune surveillance and disseminate throughout the body, leading to systemic infections like typhoid fever.

Q: Most common serotype of Listeria causing infections:

1/2a. ***1/2a*** - **Listeria monocytogenes serotype 1/2a** is one of the three major serotypes (1/2a, 1/2b, and 4b) responsible for the vast majority of human listeriosis cases. - **Serotype 1/2a** is the most frequently isolated serotype from food sources and is commonly associated with sporadic cases of invasive listeriosis. - Together with serotypes 1/2b and 4b, serotype 1/2a accounts for over 95% of clinical isolates worldwide. - While serotype 4b is more commonly associated with epidemic outbreaks and severe disease, **1/2a predominates in sporadic cases** and environmental/food contamination. *1/2c* - **Serotype 1/2c** is a relatively uncommon serotype in human listeriosis. - It accounts for a small minority of clinical cases compared to the major serotypes. - This serotype is less frequently isolated from both food products and clinical specimens. *1/3b* - **Serotype 1/3b** is a rare serotype of Listeria monocytogenes in human infections. - It represents a very small fraction of clinical isolates and is not considered a major pathogenic serotype. - This serotype is infrequently encountered in outbreak investigations. *1/3a* - **Serotype 1/3a** is another uncommon serotype with minimal clinical significance. - It accounts for a negligible proportion of human listeriosis cases. - This serotype is rarely isolated from clinical specimens or implicated in disease.

Q: Legionella causes:

Pontiac fever. ***Pontiac fever*** - **Pontiac fever** is a self-limiting, **flu-like illness** caused by *Legionella* species, without pneumonia. - Symptoms include fever, chills, headache, and myalgia, typically lasting 2-5 days. *Myocarditis* - While rare, **myocarditis** is not a primary or common manifestation of *Legionella* infection. - *Legionella* is primarily known for causing respiratory and, sometimes, gastrointestinal symptoms. [1] *Diarrhea* - **Diarrhea** can occur in some cases of severe *Legionella* infection, particularly **Legionnaires' disease**. - However, it is not a hallmark or exclusive symptom, and *Legionella* causes a broader spectrum of illness. *All of the options* - While *Legionella* can cause some extrapulmonary symptoms, **myocarditis** is exceedingly rare and not a characteristic feature. - **Pontiac fever** is a distinct, non-pneumonic illness caused by *Legionella*, making this option partially correct but not wholly accurate regarding the full spectrum of manifestations.

Q: Incubation period of Lymphogranuloma venereum is:

10-30 days. ***10-30 days*** - The incubation period for **Lymphogranuloma venereum (LGV)**, caused by specific serovars of *Chlamydia trachomatis*, typically ranges from **10 to 30 days**. - This period aligns with the presentation of the primary lesion, often a transient, painless papule or ulcer. *60-90 days* - An incubation period of **60-90 days** is excessively long for the primary stage of LGV. - Such an extended period is more typical for diseases with a very slow progression or long latency, not the initial manifestation of LGV. *5-7 days* - While some sexually transmitted infections (STIs) have an incubation period of **5-7 days**, this is too short for LGV. - This shorter timeframe is more characteristic of diseases like **genital herpes** or **chancroid**. *1-5 days* - An incubation period of **1-5 days** is very short and not consistent with LGV. - This rapid onset suggests infections like **gonorrhea** or early stages of some bacterial infections.

Q: Which of the following bacterial organisms does not cause invasive diarrhea?

Bacillus cereus. ***Bacillus cereus*** - *Bacillus cereus* typically causes **food poisoning** through the production of **exotoxins**, leading to either emetic (vomiting) or diarrheal syndromes. - Its pathogenic mechanism does not involve invasion of the intestinal mucosa, differentiating it from causes of invasive diarrhea. *Shigella* - **Shigella** species are well-known causes of **bacillary dysentery**, characterized by invasive diarrhea with bloody and mucous stools. - They invade the **colonic epithelial cells**, leading to inflammation, ulceration, and destruction of the mucosa. *Campylobacter jejuni* - **Campylobacter jejuni** is a leading cause of **bacterial gastroenteritis**, often resulting in invasive diarrhea. - It invades and damages the **intestinal epithelial cells**, particularly in the jejunum, ileum, and colon, causing inflammation and bloody stools. *Aeromonas sp* - **Aeromonas species** are recognized as opportunistic pathogens that can cause **gastroenteritis**, including invasive diarrheal disease. - They are capable of invading the intestinal mucosa and producing enterotoxins, contributing to symptoms of dysentery.

Q: Not true about gas gangrene:

Cl perfringens produce heat-labile spores. ***Cl perfringens produce heat-labile spores*** - *Clostridium perfringens* spores are, in fact, **heat-resistant**, allowing them to survive harsh conditions and subsequently germinate into vegetative cells causing infection. - This heat resistance is a crucial factor in food poisoning outbreaks and wound infections, as spores can survive cooking temperatures. *Metronidazole is the drug of choice* - While metronidazole can be used as an adjunct, **penicillin G** is generally the primary antibiotic of choice for gas gangrene, often in combination with other agents like clindamycin. - **Surgical debridement** and **hyperbaric oxygen therapy** are also critical components of treatment, as antibiotics alone are often insufficient. *Most common cause is Cl perfringens* - **_Clostridium perfringens_** is indeed the most frequent cause of gas gangrene (clostridial myonecrosis), accounting for approximately 80-95% of cases. - This bacterium produces potent **exotoxins** that cause rapid tissue destruction and gas formation, leading to the characteristic symptoms. *Extensive necrosis of muscles* - Gas gangrene is characterized by **rapid and extensive necrosis of muscle tissue**, which is caused by the potent toxins produced by clostridial species, particularly alpha-toxin. - This muscle destruction leads to systemic toxicity, pain, and the production of gas within the tissues.

Q: Regarding yaws, all are true except -

Sexually transmitted. ***Sexually transmitted*** - Yaws is typically transmitted through **direct skin-to-skin contact** with an infected person, especially in tropical and subtropical regions [1]. - It is **not considered a sexually transmitted infection (STI)**, differentiating it from syphilis which is caused by a related spirochete [1]. *Drug of choice is penicillin* - **Penicillin** is the highly effective and standard treatment for yaws, usually a single dose of intramuscular benzathine penicillin. - Its efficacy makes it a cornerstone of eradication efforts for this disease [1]. *Caused by T. pertenue* - Yaws is caused by **_Treponema pallidum_ subspecies _pertenue_**, a spirochete closely related to the causative agent of syphilis. - This bacterial infection leads to chronic skin, bone, and cartilage lesions [1]. *Cross-reactive antibodies with syphilis* - Due to the close genetic relationship between **_T. pallidum_ subsp. _pertenue_** (yaws) and **_T. pallidum_ subsp. _pallidum_** (syphilis), immunological tests for syphilis often show positive results in individuals with yaws. - This cross-reactivity means that standard **nontreponemal** and **treponemal tests** for syphilis cannot differentiate between the two infections without clinical context [1].

Question 1

Causative organism of rheumatic fever is:

Accepted Answer

Group A Streptococci

Answer

Group B Streptococci

Answer

Group D Streptococci

Answer

Staphylococci

Question 2

What is the etiological agent for buruli ulcer which usually occurs in the tropics?

Accepted Answer

Mycobacterium ulcerans

Answer

Mycobacterium fortuitum

Answer

Mycobacterium marinum

Answer

Mycobacterium kansasii

Question 3

Vibrio parahaemolyticus is seen in which of the following if undercooked?

Accepted Answer

Shellfish

Answer

Prawn

Answer

Crab

Answer

Fish

Question 4

All of the following organisms are known to survive intracellularly except

Accepted Answer

Neisseria meningitidis

Answer

Legionella pneumophila

Answer

Streptococcus pyogenes

Answer

Salmonella Typhi

Question 5

Most common serotype of Listeria causing infections:

Accepted Answer

1/2a

Answer

1/2c

Answer

1/3b

Answer

1/3a

Question 6

Legionella causes:

Accepted Answer

Pontiac fever

Answer

Myocarditis

Answer

Diarrhea

Answer

All of the options

Question 7

Incubation period of Lymphogranuloma venereum is:

Accepted Answer

10-30 days

Answer

60-90 days

Answer

5-7 days

Answer

1-5 days

Question 8

Which of the following bacterial organisms does not cause invasive diarrhea?

Accepted Answer

Bacillus cereus

Answer

Shigella

Answer

Campylobacter jejuni

Answer

Aeromonas sp

Question 9

Not true about gas gangrene:

Accepted Answer

Cl perfringens produce heat-labile spores

Answer

Metronidazole is the drug of choice

Answer

Most common cause is Cl perfringens

Answer

Extensive necrosis of muscles

Question 10

Regarding yaws, all are true except -

Accepted Answer

Sexually transmitted

Answer

Drug of choice is penicillin

Answer

Caused by T. pertenue

Answer

Cross-reactive antibodies with syphilis

Bacteriology — MCQs

Bacteriology — MCQs

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