Bacteriology Practice Questions

Q: A patient with colorectal cancer develops septicemia complicated by endocarditis. You would expect the blood cultures to grow?

Streptococcus bovis. ***Streptococcus bovis*** - **Streptococcus bovis** (now often referred to as *Streptococcus gallolyticus subsp. gallolyticus*) is strongly associated with **colorectal cancer** and can cause **bacteremia** and **infective endocarditis**. - Its presence in blood cultures, particularly in cases of endocarditis, should prompt a workup for underlying colorectal malignancy. *Streptococcus agalactiae* - This organism, also known as **Group B Streptococcus (GBS)**, is a common cause of **neonatal sepsis** and meningitis, and can cause infections in immunocompromised adults, but it does not have a specific association with colorectal cancer. - While it can cause endocarditis, it is not the most likely causative agent in a patient with colorectal cancer. *Streptococcus pyogenes* - **Streptococcus pyogenes** (Group A Streptococcus or **GAS**) is known for causing **pharyngitis** ("strep throat"), **scarlet fever**, **rheumatic fever**, and **necrotizing fasciitis**. - It is not typically associated with chronic conditions like colorectal cancer or with endocarditis in this specific context. *Streptococcus pneumoniae* - **Streptococcus pneumoniae** is a leading cause of **pneumonia**, **otitis media**, **meningitis**, and **sepsis**, particularly in young children and the elderly. - While it can cause endocarditis, there is no direct link between *S. pneumoniae* infection and underlying colorectal cancer.

Q: Carrion's disease is caused by:

Bartonella bacilliformis. ***Bartonella bacilliformis*** - **Carrion's disease**, also known as **Bartonellosis**, is exclusively caused by the bacterium **Bartonella bacilliformis**. - This disease manifests in two distinct stages: an acute phase (**Oroya fever**) characterized by severe anemia, and a chronic eruptive phase (**verruga peruana**) with skin lesions. *Bartonella henselae* - This bacterium is primarily responsible for **Cat-scratch disease** and can also cause **bacillary angiomatosis**, endocarditis, and trench fever-like syndrome. - It is typically transmitted to humans through scratches or bites from infected cats. *Bartonella quintana* - This species is the causative agent of **trench fever**, a louse-borne illness, and can also lead to **bacillary angiomatosis**. - Trench fever is characterized by recurrent fevers, headache, body aches, and sometimes a rash. *Bartonella washoensis* - **Bartonella washoensis** is a less common species primarily associated with **myocarditis** and endocarditis in humans. - Infections with this bacterium are often linked to exposure to rodents, particularly ground squirrels.

Q: A child after consuming food in a party complains of diarrhea within 1-5 hours. The diagnosis is:

S. aureus. ***S. aureus*** - **_Staphylococcus aureus_** food poisoning has a rapid onset (**1-6 hours**) because symptoms are caused by preformed **exotoxins** ingested with contaminated food, not by bacterial growth in the host. - Common sources include foods handled extensively and left at **room temperature**, allowing the bacteria to multiply and produce heat-stable toxins. *Clostridium perfringens* - **_Clostridium perfringens_** food poisoning typically has a longer incubation period (**6-24 hours**), as symptoms are caused by toxins produced by bacteria replicating in the host intestine. - It often results from eating large quantities of contaminated meat or poultry that has been improperly cooked or stored. *Streptococcus* - **_Streptococcus_** species are not primary causes of acute **foodborne diarrheal illness** with such a rapid onset. - While some strains can cause infections, their role in common food poisoning with preformed toxins is negligible compared to _S. aureus_. *Clostridium botulinum* - **_Clostridium botulinum_** causes **botulism**, a severe neuroparalytic illness, not primarily diarrhea, and typically has a longer incubation period (**12-36 hours**). - Symptoms are due to neurotoxins affecting the nervous system, leading to **flaccid paralysis**, not acute gastroenteritis.

Q: Subdural empyema is most commonly caused by:

Streptococcus pneumoniae. ***Streptococcus pneumoniae*** - **_Streptococcus species_**, including **_S. pneumoniae_**, aerobic and anaerobic streptococci, and S. milleri group, are the **most common causative organisms** of **subdural empyema**, accounting for **60-70% of cases**. - **Subdural empyema** most frequently arises from **paranasal sinusitis** (50-80% of cases) or **otitis media/mastoiditis**, infections typically caused by **streptococcal species**. - The polymicrobial nature of sinus and ear infections explains why **streptococci** predominate in subdural empyema. *Staphylococcus aureus* - **_Staphylococcus aureus_** is an important cause of **subdural empyema**, particularly in **post-neurosurgical cases** and following **penetrating head trauma**. - It accounts for approximately **10-20% of cases** but is **not the most common** overall pathogen. - When subdural empyema follows **surgery** or **direct inoculation**, S. aureus becomes more likely than in community-acquired cases. *H. influenzae* - **_Haemophilus influenzae_** was historically significant before widespread **Hib vaccination**. - Currently uncommon as a cause of **subdural empyema**, especially in vaccinated populations. - May still be seen in unvaccinated individuals or those with underlying immunodeficiency. *E. coli* - **_E. coli_** is a rare cause of **subdural empyema** in adults. - More relevant in **neonatal meningitis** and infections in **immunocompromised hosts**. - Gram-negative bacilli are generally uncommon in subdural empyema compared to gram-positive cocci.

Q: Which of the following statements about El Tor and Classical Vibrio is true?

El Tor has a higher carrier rate. ***El Tor has a higher carrier rate*** - **El Tor biotype Vibrio cholerae** is associated with a **higher carrier rate** and a greater proportion of asymptomatic infections compared to the Classical biotype. - This characteristic contributes to the **greater epidemic potential** and widespread dissemination of El Tor strains. *Classical is associated with more carriers* - The **Classical biotype** generally produces a more severe clinical disease but is associated with a **lower proportion of asymptomatic carriers**. - This means that individuals infected with Classical *Vibrio cholerae* are more likely to develop obvious symptoms, thus reducing the number of silent carriers. *All of the options* - This option is incorrect because only one of the presented statements regarding carrier rates and severity is factually accurate when comparing El Tor and Classical *Vibrio cholerae*. - The characteristics of each biotype pertaining to carrier rates and disease severity are distinct and not universally true for all statements. *El Tor is more severe* - **El Tor biotype infections** are typically **less severe** clinically, often presenting with milder symptoms or asymptomatic carriage, compared to Classical biotype infections. - The **Classical biotype** is historically associated with more cases of **severe, dehydrating cholera**, leading to rapid fluid loss and high mortality if untreated.

Q: True about tetanus are all EXCEPT?

Requires oxygen. ***Requires oxygen*** - *Clostridium tetani*, the bacteria causing tetanus, is an **anaerobic bacterium**, meaning it cannot grow in the presence of oxygen. - The spores germinate and produce toxins in **anaerobic conditions**, typically in deep, contaminated wounds. *Spread along the nerves* - The toxin produced by *Clostridium tetani* (tetanospasmin) travels via the **peripheral motor nerves** and then to the central nervous system. - This **retrograde axonal transport** is how the neurotoxin reaches the spinal cord and brainstem to exert its effects. *Incubation period is variable* - The incubation period for tetanus can vary significantly, typically ranging from **3 to 21 days**, but can be longer or shorter. - Shorter incubation periods are often associated with more severe disease and wounds closer to the central nervous system. *Tetanus bacilli cannot spread through blood* - The disease is caused by the **toxins** produced by the bacteria at the wound site, not by the systemic spread of the bacteria itself. - While the toxin is transported, primarily neuronally, the **bacterial cells do not spread** throughout the body via the bloodstream.

Q: Levinthal-Coles-Lillie bodies are seen in:

Psittacosis. ***Psittacosis*** - **Levinthal-Coles-Lillie (LCL) bodies** are characteristic cytoplasmic inclusions found in cells infected with *Chlamydophila psittaci*, the causative agent of **psittacosis**. - These bodies represent aggregations of elementary and reticulate bodies within the host cell cytoplasm, visible on microscopy. *Chicken pox* - Chickenpox, caused by the **varicella-zoster virus**, is characterized by **Cowdry type A intranuclear inclusions**, not LCL bodies [1]. - These inclusions are typically seen in skin lesions and are indicative of herpesvirus infections [1]. *LGV* - **Lymphogranuloma venereum (LGV)** is caused by specific serovars of *Chlamydia trachomatis* and is characterized by **chlamydial inclusions**. - While *Chlamydia* species form inclusions, they are not specifically termed LCL bodies, which are unique to *Chlamydophila psittaci*. *Kala-Azar* - **Kala-Azar (visceral leishmaniasis)** is caused by **Leishmania donovani** parasites. - Diagnostic features include the presence of **amastigotes** within macrophages in various tissues, not LCL bodies. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, pp. 366-367.

Q: True for tetanus is:

Due to exotoxin. ***Due to exotoxin*** - Tetanus is caused by **neurotoxins** (exotoxins) produced by *Clostridium tetani*, primarily **tetanospasmin**. - These exotoxins block the release of inhibitory neurotransmitters, leading to **muscle spasms** and rigidity. *Due to endotoxin* - **Endotoxins** are components of the outer membrane of gram-negative bacteria, released upon bacterial lysis. - *Clostridium tetani* is a **gram-positive bacterium** and does not produce endotoxins. *Both of the options* - This option is incorrect because tetanus is specifically caused by **exotoxins**, not endotoxins. - The pathophysiology of tetanus is solely linked to the neurotoxic effects of **tetanospasmin**. *None of the options* - This option is incorrect because tetanus is indeed caused by an **exotoxin**. - The primary mechanism of disease is the action of **tetanospasmin** produced by the bacteria.

Q: Acute mesenteric lymphadenitis is caused by?

Yersinia. ***Yersinia*** - **_Yersinia enterocolitica_** and **_Yersinia pseudotuberculosis_** are common causative agents of acute mesenteric lymphadenitis, primarily transmitted via contaminated food or water. - Infection leads to inflammation of the **lymph nodes in the mesentery**, mimicking acute appendicitis with abdominal pain and fever. *Alpha Hemolytic streptococci* - While various streptococcal species can cause infections, **alpha-hemolytic streptococci** (e.g., *Streptococcus viridans*) are typically associated with conditions like **bacterial endocarditis** or dental infections, not primary mesenteric lymphadenitis. - They are part of the normal flora of the **oral cavity** and upper respiratory tract. *E. Coli* - **_Escherichia coli_** is a common cause of **urinary tract infections**, food poisoning, and sepsis, but it is not a primary cause of acute mesenteric lymphadenitis. - Though some strains can cause intestinal inflammation, it rarely specifically targets mesenteric lymph nodes to cause acute mesenteric lymphadenitis rather than other forms of GI infection. *Hemophilus influenza* - **_Haemophilus influenzae_** is known for causing respiratory tract infections like **otitis media**, sinusitis, and historically, meningitis and epiglottitis (before widespread vaccination). - It is not a typical pathogen associated with infections leading to **mesenteric lymphadenitis**.

Q: Which of the following is NOT true regarding Chlamydia trachomatis?

Susceptible to penicillin. ***Susceptible to penicillin*** - This statement is **not true** because *Chlamydia trachomatis* lack **peptidoglycan** in their cell walls, making them intrinsically resistant to penicillins and other beta-lactam antibiotics. - They are typically treated with **macrolides** (e.g., azithromycin) or **tetracyclines** (e.g., doxycycline) which interfere with bacterial protein synthesis. *Cause infertility* - This is a **true** statement; *Chlamydia trachomatis* infection can lead to **pelvic inflammatory disease (PID)** in women, causing scarring of the fallopian tubes and subsequent infertility or ectopic pregnancy. - In men, it can cause **epididymitis**, which may also impair fertility. *Gram negative* - This is a **true** statement; *Chlamydia trachomatis* are obligate **intracellular bacteria** that stain Gram-negative due to the structure of their outer membrane, although they have a unique cell wall composition. - Due to their intracellular nature and lack of traditional peptidoglycan synthesis, they do not stain distinctly with Gram stain in a manner similar to typical Gram-negative bacteria, but are still classified as Gram-negative. *Transmitted sexually* - This is a **true** statement; *Chlamydia trachomatis* is primarily transmitted through **sexual contact**, making it one of the most common sexually transmitted infections (STIs) worldwide. - It can infect the **genital tract**, rectum, and pharynx, and can also be transmitted from mother to newborn during childbirth.

Question 1

A patient with colorectal cancer develops septicemia complicated by endocarditis. You would expect the blood cultures to grow?

Accepted Answer

Streptococcus bovis

Answer

Streptococcus agalactiae

Answer

Streptococcus pyogenes

Answer

Streptococcus pneumoniae

Question 2

Carrion's disease is caused by:

Accepted Answer

Bartonella bacilliformis

Answer

Bartonella henselae

Answer

Bartonella quintana

Answer

Bartonella washoensis

Question 3

A child after consuming food in a party complains of diarrhea within 1-5 hours. The diagnosis is:

Accepted Answer

S. aureus

Answer

Clostridium perfringens

Answer

Streptococcus

Answer

Clostridium botulinum

Question 4

Subdural empyema is most commonly caused by:

Accepted Answer

Streptococcus pneumoniae

Answer

Staphylococcus aureus

Answer

H. influenzae

Answer

E. coli

Question 5

Which of the following statements about El Tor and Classical Vibrio is true?

Accepted Answer

El Tor has a higher carrier rate

Answer

Classical is associated with more carriers

Answer

All of the options

Answer

El Tor is more severe

Question 6

True about tetanus are all EXCEPT?

Accepted Answer

Requires oxygen

Answer

Spread along the nerves

Answer

Incubation period is variable

Answer

Tetanus bacilli cannot spread through blood

Question 7

Levinthal-Coles-Lillie bodies are seen in:

Accepted Answer

Psittacosis

Answer

Chicken pox

Answer

LGV

Answer

Kala-Azar

Question 8

True for tetanus is:

Accepted Answer

Due to exotoxin

Answer

Due to endotoxin

Answer

Both of the options

Answer

None of the options

Question 9

Acute mesenteric lymphadenitis is caused by?

Accepted Answer

Yersinia

Answer

Alpha Hemolytic streptococci

Answer

E. Coli

Answer

Haemophilus influenzae

Question 10

Which of the following is NOT true regarding Chlamydia trachomatis?

Accepted Answer

Susceptible to penicillin

Answer

Cause infertility

Answer

Gram negative

Answer

Transmitted sexually

Bacteriology — MCQs

Bacteriology — MCQs

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