Bacteriology Practice Questions

Q: Which of the following statements about anthrax toxin is false?

Inhibits protein synthesis. ***Inhibits protein synthesis*** - Anthrax toxin, specifically the **lethal factor (LF)**, is a **zinc-dependent metalloprotease** that cleaves and inactivates **mitogen-activated protein kinase kinase (MAPKKs)**, leading to cell death, not directly inhibiting protein synthesis. - The **edema factor (EF)** component of the toxin is an **adenylate cyclase** that increases **intracellular cyclic AMP (cAMP)**, which also does not directly inhibit protein synthesis. *Has three components* - Anthrax toxin is indeed composed of three distinct proteins: **protective antigen (PA)**, **edema factor (EF)**, and **lethal factor (LF)**. - PA is necessary for EF and LF to enter host cells, while EF causes edema and LF is responsible for cytotoxicity. *Increase cAMP* - The **edema factor (EF)** component of anthrax toxin is a **calmodulin-dependent adenylate cyclase**. - Once inside the cell, EF converts **ATP to cyclic AMP (cAMP)**, leading to increased intracellular cAMP levels, which disrupts water homeostasis and causes edema. *Coded by plasmid* - The genes encoding the anthrax toxin components (PA, EF, and LF) are located on a large plasmid known as **pXO1**. - This plasmid, along with another plasmid (pXO2) carrying genes for the capsule, is crucial for the full virulence of *Bacillus anthracis*.

Q: Draughtsman colonies are seen with:

Pneumococci. ***Pneumococci*** - **Draughtsman colonies** (or **draughtsman-like colonies**) are a characteristic morphological feature observed when *Streptococcus pneumoniae* (pneumococci) grows on certain agar media, such as blood agar. - This appearance is due to the **central umbilication or depression** of the colony caused by autolytic enzymes that break down the bacterial cells in the center as the colony matures. *Anthrax* - Colonies of *Bacillus anthracis* are typically described as **"Medusa head" colonies**, characterized by swirling projections at the periphery. - They are generally **non-hemolytic** on blood agar, distinguishing them from other *Bacillus* species. *Pertussis* - *Bordetella pertussis* colonies are characteristic on **Bordet-Gengou agar**, appearing as small, glistening, pearl-like, or "mercury droplet" colonies. - This distinct morphology is crucial for its identification in laboratory cultures. *Yersinia* - *Yersinia pestis* (which causes plague) colonies on blood agar at 28°C often show a **"fried egg" appearance** over several days, with a dark center and lighter periphery. - Other *Yersinia* species like *Y. enterocolitica* can show a **bull's-eye pattern** on CIN (Cefsulodin-Irgasan-Novobiocin) agar.

Q: Which of the following statements about Chromobacterium violaceum is false?

Normal flora in human. **This question asks for the FALSE statement about *Chromobacterium violaceum*.** ***Normal flora in human*** ✓ (FALSE STATEMENT - This is the correct answer) - *Chromobacterium violaceum* is **not considered normal flora** in humans. It is an environmental bacterium typically found in **soil and water** in tropical and subtropical regions. - Its presence in humans usually signifies a serious **opportunistic infection**, often resulting from exposure to contaminated environments. - Since this statement is FALSE, this is the correct answer. *Gram negative* (TRUE statement) - *Chromobacterium violaceum* is indeed a **Gram-negative bacterium**. This characteristic is crucial for its identification and determining appropriate antibiotic treatment. - Like other Gram-negative bacteria, it possesses an **outer membrane** containing lipopolysaccharide (LPS). *Causes cellulitis* (TRUE statement) - *Chromobacterium violaceum* can cause severe infections in humans, including **cellulitis**, often following skin breaches like cuts or abrasions. - The infections are frequently aggressive and can lead to systemic disease such as **sepsis and abscess formation**. *Produces violet-colored pigment* (TRUE statement) - *Chromobacterium violaceum* is notable for producing **violacein**, a distinctive **violet-colored pigment**. - This pigment production is a key identifying feature on culture media and is associated with some of its pathogenic properties.

Q: Which of the following statements about Corynebacterium diphtheriae is true?

Toxin production is dependent on iron concentration. ***Toxin production is dependent on iron concentration*** - The production of **diphtheria toxin** by *Corynebacterium diphtheriae* is directly regulated by the iron concentration in the environment. - When **iron levels are low**, the diphtheria toxin repressor (DTxR) is inactivated, leading to increased toxin production. *All strains produce toxin* - Not all strains of *Corynebacterium diphtheriae* produce the diphtheria toxin; only those strains that are **lysogenized by a bacteriophage carrying the tox gene** are toxigenic. - Non-toxigenic strains can cause other infections but do not produce the classic diphtheria disease. *The toxin is heat stable* - The **diphtheria toxin** is a **heat-labile** protein, meaning its activity can be destroyed by heat. - Heating diphtheria toxin to 60°C for 30 minutes can inactivate its pathogenic effects. *It inhibits cAMP* - The diphtheria toxin does not inhibit **cAMP**; instead, it acts by **ADP-ribosylating and inactivating elongation factor-2 (EF-2)**, thereby inhibiting protein synthesis in eukaryotic cells. - Inhibition of EF-2 ultimately leads to cell death.

Q: Granuloma inguinale is caused by:

Calymmatobacterium granulomatis. ***Calymmatobacterium granulomatis*** - **Granuloma inguinale**, also known as **donovanosis**, is a sexually transmitted infection caused by **_Calymmatobacterium granulomatis_**. - This bacterium is notoriously difficult to culture, so diagnosis is typically made by identifying **Donovan bodies** (macrophages filled with bacteria) in tissue samples. *Haemophilus ducreyi* - **_Haemophilus ducreyi_** is the causative agent of **chancroid**, - Chancroid is characterized by **painful genital ulcers** with a ragged, undermined border, and often accompanied by **tender inguinal lymphadenopathy**. *Chlamydia trachomatis* - **_Chlamydia trachomatis_** is responsible for several conditions, including **chlamydia** (the most common bacterial STI), **lymphogranuloma venereum (LGV)**, and **trachoma**. - LGV presents with a transient, often unnoticed genital lesion followed by painful, suppurative lymphadenopathy, which is distinct from granuloma inguinale. *Treponema pallidum* - **_Treponema pallidum_** is the spirochete that causes **syphilis**, which progresses through several stages. - Primary syphilis manifests as a **painless chancre**, while secondary syphilis can involve a widespread rash, lymphadenopathy, and mucosal lesions.

Q: Listeria escapes from phagosomes (phagolysosomes) due to:

beta-hemolysin. ***beta-hemolysin*** - *Listeria monocytogenes* produces **listeriolysin O (LLO)**, a **beta-hemolysin**, which is a pore-forming toxin that lyses the phagosomal membrane. - This allows the bacteria to escape into the host cell cytoplasm, thus **avoiding destruction** by lysosomal enzymes and neutralizing the microbicidal environment. *Caspases* - **Caspases** are a family of proteases that play essential roles in programmed cell death (apoptosis) and inflammation. - While bacteria can manipulate host cell apoptosis, caspases themselves are **host enzymes** and do not directly confer resistance to phagosome destruction. *Cell membrane adhesion molecules* - **Adhesion molecules** facilitate bacterial attachment to host cells and internalisation, but they do not directly provide a mechanism for **escaping the phagosome** once internalised. - Examples include internalins, which are involved in bacterial entry into cells. *Opacity associated protein (OAP)* - **Opacity associated proteins (OAPs)** are primarily associated with *Neisseria gonorrhoeae* and are involved in adherence to host cells and evasion of the immune response. - They are not a mechanism for **phagosomal escape** or directly related to *Listeria's* intracellular survival.

Q: What is the significance of the absence of Vi-antibody in a patient with typhoid fever?

Indicates a favorable prognosis. ***Indicates a favorable prognosis*** - The **Vi (Virulence) antigen** is a **polysaccharide capsule** that helps *Salmonella typhi* evade the immune system and is associated with **virulence** and **carrier state development**. - **Absence of Vi-antibody** indicates infection with a **less virulent strain**, successful **immune clearance**, and **lower likelihood** of developing a chronic carrier state. *Indicates a poor prognosis* - The **absence of Vi-antibody** is actually associated with **better outcomes**, not worse prognosis. - **Poor prognosis** in typhoid fever is typically related to complications like **intestinal perforation** or **septic shock**, not Vi-antibody status [1]. *No impact on prognosis* - **Vi-antibody status** is a **recognized prognostic marker** in typhoid fever and does have clinical significance. - The **presence of Vi-antibodies** may indicate **persistent infection** or **carrier state development**, making it a relevant prognostic indicator. *Suggests a negative response to treatment* - **Absence of Vi-antibody** typically indicates **successful treatment response** and **effective clearance** of the organism. - **Negative treatment response** would be evidenced by **persistent fever**, **positive cultures**, or **clinical deterioration** despite appropriate antibiotic therapy.

Q: What is the most common cause of lung abscess in comatose patients?

Oral anaerobes. Oral anaerobes - **Comatose patients** are at high risk for **aspiration** of oropharyngeal flora, which predominantly consists of anaerobic bacteria. [1] - Aspiration of these organisms, especially in compromised lung tissue, frequently leads to **necrotizing pneumonia** and subsequent abscess formation. [1] *Staph aureus* - While *Staphylococcus aureus* can cause lung abscesses, particularly in the context of **hematogenous spread** (e.g., endocarditis) or nosocomial infections, it is not the most common cause in *comatose patients* who typically aspirate oral flora. [2] - *S. aureus* lung abscesses are often associated with multiple, smaller lesions rather than a single, large abscess from aspiration. *Klebsiella* - *Klebsiella pneumoniae* can cause severe, **rapidly progressive pneumonia** that may lead to abscess formation, especially in individuals with **alcoholism** or **diabetes**. - However, it is less common than oral anaerobes as the primary cause of abscess in the general population of comatose patients, whose main risk factor is aspiration of normal oral flora. [1] *Tuberculosis* - **Mycobacterium tuberculosis** can cause cavitary lung lesions, but these are typically chronic and result from primary or reactivated tuberculosis disease, not acute aspiration. [3] - Lung abscesses caused by tuberculosis are histologically distinct from pyogenic abscesses and are characterized by **granulomatous inflammation** and caseous necrosis.

Q: A child presents with vomiting and abdominal pain 5 hours after eating. The most likely causative organism is:

Bacillus cereus. ***Bacillus cereus*** - This organism produces **emetogenic toxins** such as cereulide, which cause **short-incubation food poisoning** characterized by vomiting and abdominal pain, typically within 1-6 hours after consumption. - Common sources include **fried rice** and other starchy foods that have been improperly re-heated, allowing spore germination and toxin production. *Cl. perfringens* - This bacterium produces an **enterotoxin** that causes diarrheal illness with a longer incubation period, usually 8-16 hours, and is characterized more by **abdominal cramps and diarrhea** rather than prominent vomiting. - It is typically associated with consumption of contaminated meat and poultry. *V. cholerae* - This bacterium causes **cholera**, an acute diarrheal illness characterized by **profuse watery diarrhea** and severe dehydration, with an incubation period of 2 hours to 5 days. - Vomiting can occur but is secondary to the severe fluid loss and is not the primary symptom in short-incubation cases with abdominal pain. *Cl. botulinum* - This bacterium produces **botulinum neurotoxin**, which causes botulism, a rare but severe illness characterized by **flaccid paralysis**. - While gastrointestinal symptoms like vomiting can occur, the hallmark feature is **neurological dysfunction**, and the incubation period is typically 12-36 hours, not 5 hours with isolated vomiting and abdominal pain.

Q: Heating a bacterial sample at 60°C for 30 minutes would isolate which of the following?

Enterococcus species. ***Enterococcus species*** - **Enterococcus species** are known for their ability to survive harsh conditions, including temperatures of **60°C for at least 30 minutes**. - This characteristic is often used in laboratories for selective isolation and differentiation from other bacteria like streptococci and staphylococci. *Staphylococci* - While some staphylococci are quite hardy, most species, including *Staphylococcus aureus*, typically do not tolerate **60°C for 30 minutes** as well as enterococci. - Exposure to this temperature would likely significantly reduce the viability of most staphylococcal species, making their isolation difficult. *Micrococci* - **Micrococci** are generally less heat-tolerant than enterococci and would likely be killed or severely inhibited by exposure to **60°C for 30 minutes**. - They are generally susceptible to temperatures that would be survivable for thermoduric bacteria. *Streptococci* - Most **streptococcal species** are not highly resistant to heat and would be inactivated by prolonged exposure to **60°C**. - This heat treatment is often used in laboratory procedures to differentiate enterococci from other streptococci, as enterococci were historically classified as Group D streptococci.

Question 1

Which of the following statements about anthrax toxin is false?

Accepted Answer

Inhibits protein synthesis

Answer

Increase cAMP

Answer

Has three components

Answer

Coded by plasmid

Question 2

Draughtsman colonies are seen with:

Accepted Answer

Pneumococci

Answer

Anthrax

Answer

Pertussis

Answer

Yersinia

Question 3

Which of the following statements about Chromobacterium violaceum is false?

Accepted Answer

Normal flora in human

Answer

Gram negative

Answer

Causes cellulitis

Answer

Produces violet-colored pigment

Question 4

Which of the following statements about Corynebacterium diphtheriae is true?

Accepted Answer

Toxin production is dependent on iron concentration

Answer

All strains produce toxin

Answer

The toxin is heat stable

Answer

It inhibits cAMP

Question 5

Granuloma inguinale is caused by:

Accepted Answer

Calymmatobacterium granulomatis

Answer

Haemophilus ducreyi

Answer

Chlamydia trachomatis

Answer

Treponema pallidum

Question 6

Listeria escapes from phagosomes (phagolysosomes) due to:

Accepted Answer

beta-hemolysin

Answer

Opacity associated protein (OAP)

Answer

Caspases

Answer

Cell membrane adhesion molecules

Question 7

What is the significance of the absence of Vi-antibody in a patient with typhoid fever?

Accepted Answer

Indicates a favorable prognosis

Answer

Indicates a poor prognosis

Answer

No impact on prognosis

Answer

Suggests a negative response to treatment

Question 8

What is the most common cause of lung abscess in comatose patients?

Accepted Answer

Oral anaerobes

Answer

Staph aureus

Answer

Klebsiella

Answer

Tuberculosis

Question 9

A child presents with vomiting and abdominal pain 5 hours after eating. The most likely causative organism is:

Accepted Answer

Bacillus cereus

Answer

Cl. perfringens

Answer

V. cholerae

Answer

Cl. botulinum

Question 10

Heating a bacterial sample at 60°C for 30 minutes would isolate which of the following?

Accepted Answer

Enterococcus species

Answer

Staphylococci

Answer

Micrococci

Answer

Streptococci

Bacteriology — MCQs

Bacteriology — MCQs

On this page

Practice by Chapter

Want unlimited practice?