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: Which of the following is the first step in Gram staining?

Crystal violet. ***Crystal violet*** - **Crystal violet** is the **primary stain** used in Gram staining, coloring all bacterial cells purple. - It works by penetrating the **peptidoglycan layer** of both Gram-positive and Gram-negative bacteria. *Mordant- iodine treatment* - The **iodine solution** acts as a **mordant**, forming a crystal violet-iodine complex within the cell. - This step occurs *after* the primary staining with crystal violet to help retain the stain. *Alcohol wash* - The **alcohol wash** is a **decolorizing agent** applied *after* the mordant step. - It removes the crystal violet-iodine complex from Gram-negative bacteria but not from Gram-positive cells. *Safranin* - **Safranin** is the **counterstain** used in Gram staining, applied *last*. - It stains the decolorized Gram-negative cells **pink or red** to make them visible under the microscope.

Q: "Endemic" typhus is caused by:

Rickettsia mooseri. ***Rickettsia mooseri (Rickettsia typhi)*** - **Endemic (murine) typhus** is caused by *Rickettsia typhi*, also known as *Rickettsia mooseri*. - This form of typhus is typically transmitted to humans through contact with **feces of infected rat fleas** (*Xenopsylla cheopis*). - Clinical features include fever, headache, and maculopapular rash. *Coxiella burnetii* - *Coxiella burnetii* is the causative agent of **Q fever**, which presents differently from typhus. - Q fever is primarily transmitted by inhaling **aerosols from infected animals**, particularly livestock (cattle, sheep, goats). - It does not cause endemic typhus. *Ehrlichia chafeensis* - *Ehrlichia chafeensis* causes **human monocytic ehrlichiosis** (HME), a tick-borne disease. - This condition is characterized by fever, headache, and myalgia, but it is distinct from typhus. - Transmitted by the **lone star tick** (*Amblyomma americanum*), not by fleas. *Rickettsia prowazekii* - *Rickettsia prowazekii* causes **epidemic (louse-borne) typhus**, which is a distinct form of typhus. - Epidemic typhus is transmitted by the **human body louse** (*Pediculus humanus corporis*). - Historically associated with overcrowded, unsanitary conditions, war, and famine.

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: Which of the following bacteria is classified as facultative anaerobe?

Escherichia. ***Escherichia*** - *Escherichia coli* (E. coli) is a classic example of a **facultative anaerobe**, meaning it can grow in the presence or absence of oxygen. - It uses **aerobic respiration** when oxygen is available and switches to **fermentation** or **anaerobic respiration** in an anaerobic environment. *Bacteroides* - *Bacteroides* species are **obligate anaerobes**, meaning they can only survive and grow in the **complete absence of oxygen**. - They are a major component of the normal human gut flora and are sensitive to oxygen exposure. *Pseudomonas* - *Pseudomonas* species, such as *Pseudomonas aeruginosa*, are **obligate aerobes**, requiring **oxygen for growth and metabolism**. - They possess enzymes like cytochrome oxidase and catalase, which are essential for aerobic respiration. *Clostridium* - *Clostridium* species, like *Clostridium tetani* and *Clostridium perfringens*, are **obligate anaerobes**. - They lack the enzymes (e.g., superoxide dismutase, catalase) necessary to detoxify reactive oxygen species, making oxygen lethal to them.

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.

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

Which of the following is the first step in Gram staining?

Accepted Answer

Crystal violet

Answer

Mordant- iodine treatment

Answer

Alcohol wash

Answer

Safranin

Question 4

"Endemic" typhus is caused by:

Accepted Answer

Rickettsia mooseri

Answer

Coxiella burnetii

Answer

Ehrlichia chafeensis

Answer

Rickettsia prowazekii

Question 5

True for tetanus is:

Accepted Answer

Due to exotoxin

Answer

Due to endotoxin

Answer

Both of the options

Answer

None of the options

Question 6

Acute mesenteric lymphadenitis is caused by?

Accepted Answer

Yersinia

Answer

Alpha Hemolytic streptococci

Answer

E. Coli

Answer

Haemophilus influenzae

Question 7

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 8

Which of the following bacteria is classified as facultative anaerobe?

Accepted Answer

Escherichia

Answer

Bacteroides

Answer

Pseudomonas

Answer

Clostridium

Question 9

True about chlamydia

Accepted Answer

McCoy cells for isolation

Answer

Extracellular bacteria

Answer

Penicillin is drug of choice

Answer

Gram positive

Question 10

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

Bacteriology — MCQs

Bacteriology — MCQs

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