Bacteriology Practice Questions

Q: Pinta is caused by:

Treponema carateum. ***Treponema carateum*** - Pinta is a **non-venereal treponematosis** caused by *Treponema carateum*, primarily affecting the skin. - It leads to **dyspigmented skin lesions**, including polymorphic erythematous, scaly papules and plaques. *Treponema pertenue* - This bacterium causes **yaws**, another non-venereal treponematosis. - Yaws primarily affects the skin, bones, and joints, causing frambesial lesions. *Treponema pallidum* - *Treponema pallidum* subspecies *pallidum* is the causative agent of **syphilis**, a sexually transmitted infection. - Syphilis presents with various stages, including chancres, rashes, and neurological or cardiovascular complications. *Treponema endemicum* - *Treponema pallidum* subspecies *endemicum* causes **bejel** (endemic syphilis). - Bejel is transmitted non-sexually through close contact and primarily affects mucous membranes and bones.

Q: Virulence or pathogenicity of pneumococcus depends on

Capsular polysaccharide. ***Capsular polysaccharide*** - The **polysaccharide capsule** is the primary virulence factor of *Streptococcus pneumoniae*, protecting it from phagocytosis by host immune cells. - Its presence allows the bacterium to evade host defenses and establish infection, leading to diseases like **pneumonia**, **meningitis**, and **otitis media**. *Cell wall antigen* - While present in *S. pneumoniae*, the **cell wall antigens** (like teichoic acid and peptidoglycan) are involved in inducing inflammation and host response, they are not the primary determinant of **virulence** in terms of evading phagocytosis. - They also serve as adherence factors but lack the direct anti-phagocytic role of the capsule. *Flagellar antigen* - *Streptococcus pneumoniae* is a **non-motile bacterium** and therefore does not possess flagella. - Thus, **flagellar antigens** cannot contribute to its virulence or pathogenicity. *Fimbrial antigen* - **Fimbriae (pili)** are involved in adherence to host cells for many bacteria, but they are not the primary determinant of **virulence** for *S. pneumoniae*. - Although some strains may possess pilus-like structures, the **capsule** remains the most critical factor for evading the immune system.

Q: Which organism is primarily responsible for causing primary atypical pneumonia?

Mycoplasma pneumoniae. ***Mycoplasma pneumoniae*** - This organism is the most common cause of **primary atypical pneumonia**, often referred to as "walking pneumonia," due to its mild and insidious presentation. - It lacks a cell wall, making it resistant to many common antibiotics like penicillin and cephalosporins. *Legionella* - **Legionella pneumophila** causes **Legionnaires' disease**, a severe form of pneumonia often associated with contaminated water sources and prominent systemic symptoms. - While it causes an atypical pneumonia, it is typically more severe than that caused by *Mycoplasma pneumoniae*. *Streptococcus pneumoniae* - This bacterium is the most common cause of **typical bacterial pneumonia**, characterized by a more acute onset, high fever, productive cough, and lobar consolidation on chest X-ray. - It is distinguishable from atypical pneumonia by its more severe clinical presentation and response to beta-lactam antibiotics. *Chlamydophila pneumoniae* - This organism can also cause **atypical pneumonia**, but it is less common than *Mycoplasma pneumoniae* as the primary cause. - Infections often have a prodrome of pharyngitis and hoarseness, which is not universally characteristic of primary atypical pneumonia.

Q: Hemorrhagic colitis is caused by which strain of E. coli?

Enterohemorrhagic. ***Enterohemorrhagic*** - **Enterohemorrhagic E. coli** (EHEC), particularly **O157:H7**, produces **Shiga toxins** that damage gut lining, leading to bloody diarrhea (hemorrhagic colitis). - This strain is also associated with **hemolytic uremic syndrome (HUS)**, especially in children, characterized by hemolytic anemia, thrombocytopenia, and acute kidney injury. *Enteropathogenic* - **Enteropathogenic E. coli** (EPEC) causes **watery diarrhea** primarily in infants in developing countries. - It damages the gut epithelium by forming unique "attaching and effacing" lesions, but typically does not cause bloody stools. *Enterotoxigenic* - **Enterotoxigenic E. coli** (ETEC) is a common cause of **traveler's diarrhea**, producing **heat-labile (LT)** and **heat-stable (ST)** toxins. - These toxins stimulate fluid and electrolyte secretion, resulting in profuse watery diarrhea without blood. *Enteroinvasive* - **Enteroinvasive E. coli** (EIEC) invades and destroys the colonic epithelial cells, leading to symptoms similar to **shigellosis**, including **dysentery** (bloody, mucoid stools) and fever. - While it causes bloody diarrhea, the primary term for the E. coli strain causing "hemorrhagic colitis" is EHEC due to its distinct shiga toxin production and association with HUS.

Q: Which one of the following statements is true regarding the pathogenicity of Mycobacteria species?

M. marinum is primarily associated with skin infections.. ****M. marinum is primarily associated with skin infections.**** - *Mycobacterium marinum* is famously associated with "fish tank granuloma" or "swimming pool granuloma," causing **cutaneous lesions** following exposure to contaminated water. - Infection typically occurs through breaks in the skin from contact with infected fish, aquariums, or other aquatic environments. *M. Kansasii is primarily an environmental organism that rarely causes human disease.* - While *M. kansasii* is an environmental organism, it is a significant cause of **nontuberculous mycobacterial lung disease** in humans, resembling tuberculosis. - It does not rarely cause human disease; it's one of the more common causes of atypical mycobacterial infections. *M. Africanum is typically contracted from humans or monkeys.* - *M. africanum* is a species of *Mycobacterium tuberculosis* complex (MTBC) and is primarily a pathogen of **humans**, particularly in parts of West and East Africa. - It is **not typically contracted from monkeys**; the primary reservoir for *M. africanum* is humans. *M. tuberculosis and M. bovis have distinct pathogenic profiles in humans.* - Both *M. tuberculosis* and *M. bovis* are members of the MTBC and cause **tuberculosis in humans**, with *M. bovis* traditionally transmitted through contaminated dairy products. - While *M. tuberculosis* is the primary cause of human TB and *M. bovis* can cause extrapulmonary and pulmonary disease, their pathogenic profiles in humans are often **similar** in presentation with respect to the disease they cause, though modes of transmission differ.

Q: Most common cause of traveler's diarrhea is:

Enterotoxigenic E. coli. ***Enterotoxigenic E. coli (ETEC)*** - **ETEC** is the most common cause of **traveler's diarrhea** worldwide, producing toxins that stimulate intestinal fluid secretion. - It causes a **watery diarrhea** without fever or significant inflammation, primarily through its **heat-labile** and **heat-stable toxins**. *Enterohemorrhagic E. coli (EHEC)* - **EHEC**, particularly O157:H7, is known for causing **hemorrhagic colitis** and **hemolytic uremic syndrome (HUS)**, not typically traveler's diarrhea. - Its pathogenicity is due to **Shiga toxins**, which damage intestinal epithelial cells and red blood cells. *Enteropathogenic E. coli (EPEC)* - **EPEC** is a significant cause of **infant diarrhea** in developing countries, leading to malabsorption. - It attaches to intestinal cells, causing effacement of microvilli, but does not produce toxins typically associated with traveler's diarrhea or invasiveness. *Enteroinvasive E. coli (EIEC)* - **EIEC** is responsible for a syndrome resembling **shigellosis**, involving invasion and destruction of intestinal epithelial cells. - It typically causes **dysentery** with fever, abdominal cramps, and bloody diarrhea, which is less common in traveler's diarrhea than watery symptoms.

Q: The single most important laboratory test for determining the virulence of staphylococci is

Detection of coagulase. ***Detection of coagulase*** - The **coagulase enzyme** is a major virulence factor in *Staphylococcus aureus*, distinguishing it from less pathogenic staphylococci (coagulase-negative staphylococci). - Coagulase allows the organism to clot plasma, forming a fibrin layer that protects it from phagocytosis and immune detection. *Mannitol fermentation* - While *Staphylococcus aureus* can **ferment mannitol** (distinguishing it from some other staphylococci on mannitol salt agar), this characteristic is not directly linked to its virulence in the same critical way as coagulase. - Mannitol fermentation is a metabolic property, not a direct virulence factor that mediates host damage or evasion. *The catalase test* - The **catalase test** is used to differentiate staphylococci (catalase-positive) from streptococci (catalase-negative), but it does not differentiate between virulent and avirulent strains of staphylococci. - All staphylococci, both pathogenic and non-pathogenic, produce catalase to neutralize reactive oxygen species. *Hemolysis of sheep erythrocytes* - Many staphylococci (including *S. aureus*) produce **hemolysins**, which can lyse red blood cells. While a virulence factor, it is less specific and less critical than coagulase for determining overall virulence and pathogen identification. - Other bacteria also exhibit hemolysis, and some coagulase-negative staphylococci can also be hemolytic, making it a less definitive virulence marker for *Staphylococcus aureus* compared to coagulase.

Q: Among the following E. coli variants, which is most commonly associated with persistent diarrhea in adults?

Enteroaggregative Escherichia coli (EAEC). ***Enteroaggregative Escherichia coli (EAEC)*** - EAEC is characterized by its distinctive **aggregative adherence** to intestinal cells, leading to chronic inflammation and persistent diarrhea, particularly in adults and immunocompromised individuals. - It produces **enteroaggregative heat-stable toxin (EAST1)** and **pet-like cytotoxins** that contribute to fluid secretion and mucosal damage. *Enteropathogenic Escherichia coli (EPEC)* - EPEC is a major cause of **infant diarrhea**, especially in developing countries, but is generally not associated with persistent diarrhea in adults. - It forms characteristic **attaching and effacing (A/E) lesions** on intestinal epithelial cells, destroying microvilli and impairing absorption. *Enterotoxigenic Escherichia coli (ETEC)* - ETEC is the most common cause of **traveler's diarrhea** and primarily causes acute, watery diarrhea due to the production of **heat-labile (LT)** and/or **heat-stable (ST) toxins**. - While it can cause significant dehydrating diarrhea, it is typically self-limiting and rarely leads to persistent symptoms in adults. *Enteroinvasive Escherichia coli (EIEC)* - EIEC causes a disease similar to **shigellosis**, characterized by **fever, cramps, and dysentery** (bloody, mucoid stools), by invading and destroying intestinal epithelial cells. - It is not commonly associated with persistent diarrhea but rather with an acute, inflammatory colonic infection.

Q: Which of the following is the most diagnostically significant characteristic of Campylobacter jejuni?

Grows at 42°C. ***Grows at 42°C*** - The ability to grow optimally at **42°C (thermophilic growth)** is a key discriminating characteristic for *Campylobacter jejuni*, differentiating it from other common enteric pathogens. - This property is exploited in selective media (e.g., Skirrow agar) incubated at this higher temperature to aid in its isolation from fecal samples. *Obligate aerobe* - *Campylobacter jejuni* is actually **microaerophilic**, meaning it requires reduced oxygen levels (typically 5% O2) for optimal growth, not completely aerobic conditions. - Obligate aerobes require atmospheric oxygen concentrations for survival, which is contrary to the growth requirements of *C. jejuni*. *Oxidase negative* - *Campylobacter jejuni* is **oxidase positive**, which means it produces the enzyme cytochrome c oxidase. - An oxidase negative result would rule out *Campylobacter jejuni* and is characteristic of other organisms like *Escherichia coli*. *Non-motile* - *Campylobacter jejuni* is **highly motile** due to its characteristic single polar flagellum, which contributes to its invasiveness in the intestinal mucosa. - Non-motility would be inconsistent with the typical microscopic appearance and pathogenic mechanisms of *C. jejuni*.

Q: Actinomycosis is most commonly found in which of the following locations?

Mandible. ***Mandible*** - **Cervicofacial actinomycosis** is the most common form, typically manifesting as a chronic, slowly progressing infection in the face and neck, often involving the jaw. - The organism *Actinomyces israelii* is a normal inhabitant of the oral cavity, and infection often occurs after trauma, dental procedures, or poor oral hygiene. *Tibia* - While actinomycosis can affect bone, **direct involvement of long bones** like the tibia is rare and usually occurs via hematogenous spread or direct extension from adjacent soft tissue infections. - It would be an atypical primary or most common presentation for actinomycosis. *Scapula* - Involvement of the scapula is **extremely uncommon** and would typically signify disseminated disease or direct extension from a rare thoracic or cervicofacial presentation. - The scapula is not a common site for localized actinomycosis. *Femur* - Similar to the tibia, **femur involvement** by actinomycosis is rare and usually secondary to other primary sites or widespread disease. - It does not represent a common or typical anatomical location for actinomycosis.

Question 1

Pinta is caused by:

Accepted Answer

Treponema carateum

Answer

Treponema pallidum

Answer

Treponema endemicum

Answer

Treponema pertenue

Question 2

Virulence or pathogenicity of pneumococcus depends on

Accepted Answer

Capsular polysaccharide

Answer

Cell wall antigen

Answer

Flagellar antigen

Answer

Fimbrial antigen

Question 3

Which organism is primarily responsible for causing primary atypical pneumonia?

Accepted Answer

Mycoplasma pneumoniae

Answer

Legionella

Answer

Streptococcus pneumoniae

Answer

Chlamydophila pneumoniae

Question 4

Hemorrhagic colitis is caused by which strain of E. coli?

Accepted Answer

Enterohemorrhagic

Answer

Enteropathogenic

Answer

Enterotoxigenic

Answer

Enteroinvasive

Question 5

Which one of the following statements is true regarding the pathogenicity of Mycobacteria species?

Accepted Answer

M. marinum is primarily associated with skin infections.

Answer

M. Africanum is typically contracted from humans or monkeys.

Answer

M. Kansasii is primarily an environmental organism that rarely causes human disease.

Answer

M. tuberculosis and M. bovis have distinct pathogenic profiles in humans.

Question 6

Most common cause of traveler's diarrhea is:

Accepted Answer

Enterotoxigenic E. coli

Answer

Enteropathogenic E. coli

Answer

Enteroinvasive E. coli

Answer

Enterohemorrhagic E. coli

Question 7

The single most important laboratory test for determining the virulence of staphylococci is

Accepted Answer

Detection of coagulase

Answer

Mannitol fermentation

Answer

The catalase test

Answer

Hemolysis of sheep erythrocytes

Question 8

Among the following E. coli variants, which is most commonly associated with persistent diarrhea in adults?

Accepted Answer

Enteroaggregative Escherichia coli (EAEC)

Answer

Enteropathogenic Escherichia coli (EPEC)

Answer

Enterotoxigenic Escherichia coli (ETEC)

Answer

Enteroinvasive Escherichia coli (EIEC)

Question 9

Which of the following is the most diagnostically significant characteristic of Campylobacter jejuni?

Accepted Answer

Grows at 42°C

Answer

Obligate aerobe

Answer

Oxidase negative

Answer

Non-motile

Question 10

Actinomycosis is most commonly found in which of the following locations?

Accepted Answer

Mandible

Answer

Tibia

Answer

Scapula

Answer

Femur

Bacteriology — MCQs

Bacteriology — MCQs

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