Bacteriology Practice Questions

Q: Which of the following is a motile member of the Enterobacteriaceae family?

Morganella. ***Morganella*** - *Morganella morganii* possesses **peritrichous flagella** and is motile at **25°C** (room temperature), which is the standard temperature for motility testing. - At 37°C (body temperature), motility may be reduced or absent, but in standard microbiology classification, Morganella is considered a **motile organism**. - This distinguishes it from consistently non-motile genera like Shigella and Klebsiella. *Shigella* - All species within the genus *Shigella* are inherently **non-motile** at all temperatures. - Complete absence of flagella is a fundamental differentiating feature from other Enterobacteriaceae. - This lack of motility is one of the key characteristics used in laboratory identification. *Klebsiella* - Members of the *Klebsiella* genus, notably *Klebsiella pneumoniae*, are **non-motile** and possess a prominent polysaccharide capsule. - Their immobility and large capsule are important identifying characteristics in laboratory settings. - The absence of flagella is consistent across all species. *Yersinia* - *Yersinia enterocolitica* exhibits **temperature-dependent motility** (motile at 25°C, non-motile at 37°C). - However, *Yersinia pestis*, the most clinically significant species causing plague, is **non-motile at all temperatures**. - In standard teaching, Yersinia is often represented by Y. pestis and characterized as non-motile, making Morganella the better answer for a consistently recognized motile member.

Q: Cholera is caused by:

V.cholerae O1 and O139. ***V.cholerae O1 and O139*** - Both serogroups, **O1** and **O139**, are known to cause epidemic and pandemic cholera. - They produce the **cholera toxin**, leading to the characteristic severe watery diarrhea. *V.cholerae O1* - While **V. cholerae O1** is historically the most common cause of cholera, it is not the *only* serogroup responsible for the disease globally. - Limiting the definition to O1 would exclude outbreaks caused by the O139 serogroup. *V. cholerae O139* - **V. cholerae O139** emerged as a significant cause of cholera in Asia in the early 1990s and is capable of causing large outbreaks. - However, stating only O139 would omit the more widespread and historically significant O1 serogroup responsible for most cholera cases. *NAG vibrios* - **NAG vibrios** (Non-agglutinable vibrios), also known as non-O1/non-O139 *Vibrio cholerae*, can cause sporadic cases of diarrheal disease. - They typically cause a milder illness and are not commonly associated with the severe epidemic or pandemic cholera caused by O1 and O139 serogroups.

Q: Which of the following conditions is most commonly classified as a sexually transmitted disease?

Chlamydia. ***Chlamydia*** - **Chlamydia trachomatis** is a bacterial infection that is exclusively transmitted through **sexual contact**, making it a classic sexually transmitted disease. - It often presents with **asymptomatic infections** but can lead to serious complications if untreated, such as pelvic inflammatory disease (PID) and infertility. *Trichomoniasis* - Caused by the **protozoan Trichomonas vaginalis**, it is also a sexually transmitted infection. - While sexually transmitted, **Chlamydia** is generally more prevalent and often considered the *most commonly* classified or reported bacterial STD. *Giardiasis* - Caused by the parasite **Giardia lamblia**, it is typically acquired through the ingestion of contaminated water or food. - It is primarily an **enteric infection** and not classified as a sexually transmitted disease, although anal-oral contact can be a route of transmission in some cases. *Amoebiasis* - Caused by the parasite **Entamoeba histolytica**, it is spread through the fecal-oral route, usually via contaminated food or water. - **Amoebiasis** is an infection of the intestines and liver, and it is not considered a sexually transmitted disease.

Q: Which component of Streptococcus pyogenes is known to mimic human synovial tissue and has cross-reactivity with it?

Capsular hyaluronic acid. ***Capsular hyaluronic acid*** - The **hyaluronic acid capsule** of *Streptococcus pyogenes* is chemically identical to hyaluronic acid found in human connective tissues, including **synovial tissue**. - This molecular mimicry helps the bacteria evade the immune system and is implicated in the pathogenesis of **rheumatic fever** and post-streptococcal arthritis by eliciting an autoimmune response. *Cell proteins* - **M protein** is a significant cell surface protein of *Streptococcus pyogenes* known for its antiphagocytic properties and virulence. - While M protein antibodies can cross-react with human tissues (e.g., cardiac myosin in **rheumatic heart disease**), its mimicry is primarily with heart tissue, not directly synovial tissue. *Group A carbohydrate antigens* - The **Group A carbohydrate** is a major component of the cell wall of *Streptococcus pyogenes* and is used for Lancefield classification. - Antibodies against this carbohydrate are common but are not principally associated with molecular mimicry of synovial tissue; the mimicry relates more to certain heart valve components. *Peptidoglycan* - **Peptidoglycan** is a fundamental component of the bacterial cell wall in most bacteria, including *Streptococcus pyogenes*. - While peptidoglycan can induce inflammation, it does not share the specific molecular mimicry with human synovial tissue that hyaluronic acid does.

Q: Which of the following bacteria is microaerophilic?

Campylobacter. ***Campylobacter*** - **Campylobacter jejuni** is a classic example of a microaerophilic bacterium, thriving in environments with **reduced oxygen (5-10% O2)** and **increased CO2 (5-10%)**. - This specific atmospheric requirement is crucial for its **growth** and **virulence**, often leading to gastroenteritis. *Vibrio cholerae* - **Vibrio cholerae** is a **facultative anaerobe**, meaning it can grow in both the presence and absence of oxygen. - It does not require low oxygen environments; optimal growth occurs **aerobically**. *Pseudomonas* - **Pseudomonas aeruginosa** is an **obligate aerobe**; it requires oxygen for respiration and growth. - It uses oxygen as the **final electron acceptor** in its electron transport chain. *Salmonella* - **Salmonella enterica** is a **facultative anaerobe**, capable of switching between aerobic and anaerobic respiration. - It can grow in the presence of oxygen, as well as in **anaerobic conditions** by fermenting sugars.

Q: Exfoliative toxin A, which causes generalized desquamation, is secreted by which of the following?

Staphylococci. ***Staphylococci*** - **Exfoliative toxins**, specifically ETA and ETB, are produced by *Staphylococcus aureus* and are responsible for **Staphylococcal scalded skin syndrome (SSSS)**, which involves generalized desquamation. - These toxins are **serine proteases** that cleave **desmoglein 1**, a protein essential for cell adhesion in the superficial epidermis. *Streptococcus* - While various *Streptococcus* species produce toxins (e.g., streptolysins, erythrogenic toxins), they are not associated with producing **exfoliative toxins** causing generalized desquamation. - *Streptococcus pyogenes* can cause diseases like **scarlet fever**, which involves a rash and subsequent peeling, but this is distinct from the mechanism of staphylococcal exfoliative toxins. *Pseudomonas aeruginosa* - *Pseudomonas aeruginosa* produces a range of virulence factors like **exotoxin A**, **elastase**, and **pyocyanin**, which contribute to its pathogenicity in various infections. - However, it does not produce **exfoliative toxins** that cause widespread desquamation of the skin in the manner of *S. aureus*. *Streptococcus pneumoniae* - *Streptococcus pneumoniae* is primarily known for causing **pneumonia**, **otitis media**, and **meningitis**. - Its major virulence factors include its **polysaccharide capsule** and **pneumolysin**, but it does not produce exfoliative toxins.

Q: Which of the following organisms is considered the classic example of polysaccharide capsular resistance to phagocytosis?

Streptococcus pneumoniae. ***Streptococcus pneumoniae*** - It possesses a thick **polysaccharide capsule** that is a primary virulence factor, interfering with **phagocytosis** by preventing the binding of phagocytes. - This organism is the **classic textbook example** of capsular resistance to phagocytosis, with over 90 capsular serotypes that determine virulence. - It is a major cause of pneumonia, meningitis, and otitis media, with its capsular resistance being key to its pathogenesis. *Neisseria meningitidis* - While *N. meningitidis* also has an important **polysaccharide capsule** that contributes to its virulence and resistance to phagocytosis, **Streptococcus pneumoniae** is more widely recognized as the classic example for this mechanism in bacterial pathogenesis. - It causes **meningitis** and **meningococcemia**, and its capsule helps it evade immune surveillance in the bloodstream. *Cryptococcus neoformans* - This is an **encapsulated yeast** with a prominent **polysaccharide capsule** (primarily glucuronoxylomannan) that aids in resistance to phagocytosis. - However, when discussing the **classic example** of capsular resistance to phagocytosis in microbiology, **bacterial capsules**, particularly that of *Streptococcus pneumoniae*, are the primary focus. - *C. neoformans* causes meningitis, especially in immunocompromised patients, and its capsule is visualized with India ink staining. *Klebsiella pneumoniae* - *K. pneumoniae* is known for its prominent **polysaccharide capsule**, which is a significant virulence factor, contributing to its resistance to phagocytosis and making it a common cause of healthcare-associated infections. - However, *Streptococcus pneumoniae* is historically and clinically considered the classic prototype when discussing polysaccharide capsules and their role in evading phagocytosis.

Q: Food poisoning has occurred due to the ingestion of contaminated fried rice. Which organism is most likely responsible?

Bacillus cereus (emetic type). ***Bacillus cereus (emetic type)*** - The **emetic toxin** produced by *Bacillus cereus* is commonly associated with food poisoning from **reheated fried rice**. - This toxin causes rapid onset of **nausea** and **vomiting** within 0.5 to 6 hours after ingestion. *Staphylococcus aureus* - While *Staphylococcus aureus* also causes **rapid-onset emetic food poisoning**, it is more typically associated with dairy products, meats, and salads, not specifically fried rice. - The symptoms are primarily due to preformed **enterotoxins**. *Vibrio parahemolyticus* - This bacterium is primarily associated with the consumption of **raw or undercooked seafood**, leading to **diarrhea**, abdominal cramps, nausea, vomiting, and fever. - It is not typically linked to fried rice. *Clostridium perfringens* - *Clostridium perfringens* causes **diarrheal-type food poisoning** characterized by abdominal cramps and diarrhea, usually from contaminated meat or poultry dishes. - It typically has a longer incubation period (6-24 hours) and is not primarily emetic or associated with fried rice.

Q: Nocardia infection is associated most commonly with:

Lung abscess. ***Lung abscess*** - **Nocardia** infections most commonly affect the lungs, leading to **pulmonary nocardiosis** which can manifest as pneumonia, nodules, or abscesses. - Initial infection typically occurs via **inhalation of Nocardia spores** from the dust or soil. *Liver abscess* - **Liver abscesses** are more commonly associated with **bacterial infections** like *Klebsiella pneumoniae* or *Entamoeba histolytica*. - While nocardial disseminated disease can affect the liver, it is not the most common primary site of abscess formation. *Brain abscess* - **Brain abscesses** are a serious complication if Nocardia disseminates, particularly in **immunocompromised individuals**. - However, the most common clinical presentation of Nocardia infection itself is pulmonary, with brain involvement being a secondary event. *Subcutaneous abscess* - **Subcutaneous abscesses** due to *Nocardia* can occur, often following **skin trauma** or direct inoculation, but are less common than pulmonary involvement. - This presentation is typically seen in patients with **cutaneous nocardiosis**, which is distinct from the more common systemic infection.

Question 1

Which of the following is a motile member of the Enterobacteriaceae family?

Accepted Answer

Morganella

Answer

Shigella

Answer

Yersinia

Answer

Klebsiella

Question 2

Cholera is caused by:

Accepted Answer

V.cholerae O1 and O139

Answer

V.cholerae O1

Answer

NAG vibrios

Answer

V.cholerae O139

Question 3

Which of the following conditions is most commonly classified as a sexually transmitted disease?

Accepted Answer

Chlamydia

Answer

Trichomoniasis

Answer

Giardiasis

Answer

Amoebiasis

Question 4

Which component of Streptococcus pyogenes is known to mimic human synovial tissue and has cross-reactivity with it?

Accepted Answer

Capsular hyaluronic acid

Answer

Cell proteins

Answer

Group A carbohydrate antigens

Answer

Peptidoglycan

Question 5

Which of the following bacteria is microaerophilic?

Accepted Answer

Campylobacter

Answer

Pseudomonas

Answer

Salmonella

Answer

Vibrio cholerae

Question 6

Exfoliative toxin A, which causes generalized desquamation, is secreted by which of the following?

Accepted Answer

Staphylococci

Answer

Streptococcus

Answer

Pseudomonas aeruginosa

Answer

Streptococcus pneumoniae

Question 7

Which of the following organisms is considered the classic example of polysaccharide capsular resistance to phagocytosis?

Accepted Answer

Streptococcus pneumoniae

Answer

Neisseria meningitidis

Answer

Klebsiella pneumoniae

Answer

Cryptococcus neoformans

Question 8

Food poisoning has occurred due to the ingestion of contaminated fried rice. Which organism is most likely responsible?

Accepted Answer

Bacillus cereus (emetic type)

Answer

Staphylococcus aureus

Answer

Vibrio parahemolyticus

Answer

Clostridium perfringens

Question 9

A 23-year-old woman with a history of sickle cell disease presents with fever and severe bone pain localized to her left tibia. X-ray reveals a lytic lesion, and blood cultures reveal infection. A bone culture grows gram-negative rods. Which of the following best describes the infecting organism?

Accepted Answer

It is motile and does not ferment lactose, such as Salmonella.

Answer

It is a facultative intracellular parasite, such as Legionella.

Answer

It is a non-motile facultative anaerobe, such as Shigella.

Answer

It is comma-shaped and sensitive to acidic pH, such as Vibrio cholerae.

Question 10

Nocardia infection is associated most commonly with:

Accepted Answer

Lung abscess

Answer

Brain abscess

Answer

Subcutaneous abscess

Answer

Liver abscess

Bacteriology — MCQs

Bacteriology — MCQs

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