Bacteriology Practice Questions

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.

Q: A 19 year old college student presents to the student health clinic complaining of weakness, malaise, and a chronic cough. He has a fever of 100 degrees F and a dry cough; no sputum can be obtained for laboratory analysis, so a bronchial lavage is performed and the washings are submitted to the laboratory. The laboratory reports that the organism is "slow-growing." Serodiagnosis reveals Strep MG agglutinins in the patient's serum. Which of the following organisms is the most likely cause of this student's illness?

Mycoplasma pneumoniae. ***Mycoplasma pneumoniae*** - The combination of **weakness**, **malaise**, **dry cough**, and low-grade fever in a young adult is classic for **atypical pneumonia**, often caused by *Mycoplasma pneumoniae*. - The organism being "slow-growing" and the presence of **Strep MG agglutinins** (cold agglutinins, commonly associated with *M. pneumoniae* infections) further point to this diagnosis. *Respiratory syncytial virus* - RSV is a common cause of **bronchiolitis and pneumonia** in infants and young children, less so in healthy young adults. - While it can cause respiratory symptoms, the presence of **Strep MG agglutinins** is not characteristic of RSV infection. *Klebsiella pneumoniae* - *Klebsiella pneumoniae* typically causes **severe, necrotizing pneumonia**, often in older, immunocompromised, or alcoholic individuals [1]. - It presents with a **productive cough** (currant jelly sputum) and rapid onset, not the atypical, slow-growing pattern described [1]. *Parainfluenza virus* - Parainfluenza viruses are common causes of **croup** (laryngotracheobronchitis) in children and can cause respiratory infections in adults. - However, they do not produce **Strep MG agglutinins**, and the "slow-growing" description in a bronchial lavage is not typical for a viral pathogen.

Q: True about chlamydia

McCoy cells for isolation. ***McCoy cells for isolation*** - *Chlamydia trachomatis* are **obligate intracellular bacteria** and require cell culture for laboratory isolation and propagation. - **Cycloheximide-treated McCoy cells** are the gold standard cell line for isolation of *Chlamydia trachomatis*, though other cell lines like HeLa and HEp-2 cells can also be used. - This characteristic makes their cultivation more challenging compared to extracellular bacteria, necessitating the use of viable host cells. *Extracellular bacteria* - This statement is incorrect because *Chlamydia trachomatis* is an **obligate intracellular bacterium**, meaning it can only replicate and survive within the host cell. - Unlike extracellular bacteria, it cannot be cultured on standard bacterial growth media. *Penicillin is drug of choice* - **Penicillin** is ineffective against *Chlamydia* because these bacteria lack a **peptidoglycan cell wall**, which is the primary target of penicillin. - The drugs of choice for *Chlamydia* infections are typically **macrolides** (e.g., azithromycin) or **tetracyclines** (e.g., doxycycline). *Gram positive* - Though *Chlamydia* has a cell wall, its structure is unique and lacks **peptidoglycan**, which prevents it from staining robustly with the Gram stain. - While it has characteristics of both Gram-negative and Gram-positive bacteria, it is generally considered **Gram-negative** due to its outer membrane, but often described as Gram-variable or not typically Gram-stainable.

Q: True about Legionella pneumonia is -

Can be isolated from lung biopsy. ***Can be isolated from lung biopsy*** - **Legionella pneumophila** is a fastidious bacterium that can be difficult to grow on routine culture media and microscopic examination of sputum may not always reveal the organism. - In cases of severe or persistent pneumonia where a definitive diagnosis is needed, **lung biopsy** provides tissue that can be stained (e.g., with direct fluorescent antibody stain) or cultured on specialized media (like buffered charcoal yeast extract agar) for isolation of *Legionella*. *Sputum shows polymorphonuclear leukocytes with organism* - While **polymorphonuclear leukocytes (PMNs)** are typically present in sputum from bacterial pneumonia, *Legionella* is an **intracellular pathogen** and often difficult to visualize on Gram stain due to its poor staining characteristics. - The absence of readily visible organisms in sputum Gram stain despite abundant leukocytes is a classic clue for **Legionella pneumonia**. *Acid fast* - **Legionella pneumophila** is **not acid-fast**; acid-fast staining is characteristic of mycobacteria (e.g., *Mycobacterium tuberculosis*). - Special stains like **Dieterle silver stain** or **direct fluorescent antibody (DFA) stain** are used to visualize *Legionella* in tissue or samples. *Gram positive* - **Legionella pneumophila** is a **Gram-negative bacterium**, although it stains poorly with standard Gram stain. - It is typically a **rod-shaped bacterium** that requires specialized culture conditions.

Q: A 34-year-old woman is seen in the emergency department. About 5 hours previously, she began to have nausea, vomiting, abdominal cramps, and diarrhea. She then developed double vision, which prompted her to ask her husband to bring her to the emergency department. When she is asked to go into the examining room, she stumbles. When she tries to answer questions, her voice sounds odd and she seems to mumble. Physical examination demonstrates a dry mouth, drooping eyelids, markedly diminished pupillary light reflex, a flaccid facial expression, and difficulty in opening her mouth. Within an hour, her condition has markedly deteriorated. She can no longer stand and is intubated because of difficulty breathing. Which of the following microbial species is MOST likely to have caused her condition?

Clostridium botulinum. ***Clostridium botulinum*** - The rapid onset of **nausea, vomiting, abdominal cramps, and diarrhea** followed by neurological symptoms like **double vision, stumbling, slurred speech (dysarthria), dry mouth, drooping eyelids (ptosis), diminished pupillary light reflex, and progressive muscle weakness** (leading to inability to stand and respiratory failure) is characteristic of **botulism**. - **Botulinum toxin**, produced by *Clostridium botulinum*, is a potent neurotoxin that inhibits acetylcholine release at the neuromuscular junction, causing a **flaccid paralysis** that can rapidly progress to respiratory paralysis. *Clostridium ramosum* - This species is an infrequent cause of **bacteremia and localized infections**, particularly in immunocompromised individuals. - It does not typically produce neurotoxins that lead to the rapid onset of severe neurological symptoms and flaccid paralysis seen in the patient. *Clostridium perfringens* - *Clostridium perfringens* is a common cause of **food poisoning** (characterized by nausea, vomiting, and diarrhea) and **gas gangrene**. - While it causes gastrointestinal symptoms, it does not produce neurotoxins that result in oculomotor dysfunction, dysphagia, or widespread flaccid paralysis. *Clostridium septicum* - *Clostridium septicum* is primarily associated with **gas gangrene** and **severe systemic infections**, often in patients with underlying malignancies. - It does not cause the specific neurological symptoms, particularly the descending flaccid paralysis, observed in this clinical presentation.

Question 1

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 2

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 3

Levinthal-Coles-Lillie bodies are seen in:

Accepted Answer

Psittacosis

Answer

Chicken pox

Answer

LGV

Answer

Kala-Azar

Question 4

True for tetanus is:

Accepted Answer

Due to exotoxin

Answer

Due to endotoxin

Answer

Both of the options

Answer

None of the options

Question 5

Acute mesenteric lymphadenitis is caused by?

Accepted Answer

Yersinia

Answer

Alpha Hemolytic streptococci

Answer

E. Coli

Answer

Haemophilus influenzae

Question 6

Which of the following is NOT true regarding Chlamydia trachomatis?

Accepted Answer

Susceptible to penicillin

Answer

Cause infertility

Answer

Gram negative

Answer

Transmitted sexually

Question 7

A 19 year old college student presents to the student health clinic complaining of weakness, malaise, and a chronic cough. He has a fever of 100 degrees F and a dry cough; no sputum can be obtained for laboratory analysis, so a bronchial lavage is performed and the washings are submitted to the laboratory. The laboratory reports that the organism is "slow-growing." Serodiagnosis reveals Strep MG agglutinins in the patient's serum. Which of the following organisms is the most likely cause of this student's illness?

Accepted Answer

Mycoplasma pneumoniae

Answer

Respiratory syncytial virus

Answer

Klebsiella pneumoniae

Answer

Parainfluenza virus

Question 8

True about chlamydia

Accepted Answer

McCoy cells for isolation

Answer

Extracellular bacteria

Answer

Penicillin is drug of choice

Answer

Gram positive

Question 9

True about Legionella pneumonia is -

Accepted Answer

Can be isolated from lung biopsy

Answer

Sputum shows polymorphonuclear leukocytes with organism

Answer

Acid fast

Answer

Gram positive

Question 10

A 34-year-old woman is seen in the emergency department. About 5 hours previously, she began to have nausea, vomiting, abdominal cramps, and diarrhea. She then developed double vision, which prompted her to ask her husband to bring her to the emergency department. When she is asked to go into the examining room, she stumbles. When she tries to answer questions, her voice sounds odd and she seems to mumble. Physical examination demonstrates a dry mouth, drooping eyelids, markedly diminished pupillary light reflex, a flaccid facial expression, and difficulty in opening her mouth. Within an hour, her condition has markedly deteriorated. She can no longer stand and is intubated because of difficulty breathing. Which of the following microbial species is MOST likely to have caused her condition?

Accepted Answer

Clostridium botulinum

Answer

Clostridium ramosum

Answer

Clostridium perfringens

Answer

Clostridium septicum

Bacteriology — MCQs

Bacteriology — MCQs

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