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 anticoagulant is commonly used for bacteriological culture?

Citrate. ***Citrate*** - **Sodium citrate** is used as an anticoagulant in some **bacteriological culture systems** as it binds to **calcium ions**, preventing blood coagulation without directly killing bacteria. - However, citrate has limitations: it can **inhibit growth of fastidious organisms** and may affect certain bacterial metabolic processes. - **Note:** Sodium polyanethol sulfonate (SPS) is the **gold standard anticoagulant** for blood cultures in modern practice, but among the listed options, citrate is preferred over the alternatives. *Heparin* - **Heparin** acts by activating **antithrombin III**, which inactivates thrombin and factor Xa. - While effective as an anticoagulant, **heparin can inhibit growth of certain bacteria** (especially Gram-positive cocci) and some fungi, and may interfere with certain laboratory tests. - However, it is occasionally used when other anticoagulants are contraindicated. *EDTA* - **EDTA (ethylenediaminetetraacetic acid)** strongly chelates **calcium and magnesium ions**, effectively preventing coagulation. - **EDTA is toxic to many bacteria** and interferes with bacterial growth, making it **unsuitable for bacteriological cultures**. - It is primarily used for hematology specimens, not cultures. *Mechanical defibrination* - **Mechanical defibrination** physically removes fibrin from blood through agitation, preventing clot formation. - This method is **labor-intensive**, can cause **hemolysis**, and may damage bacterial cells, making it impractical for routine bacteriological cultures.

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: Which bacterial species is commonly found on the skin?

Cutibacterium acnes. ***Cutibacterium acnes*** - **_Cutibacterium acnes_** (formerly **_Propionibacterium acnes_**) is a common commensal bacterium found in the sebaceous glands of the skin. - It plays a role in the development of **acne vulgaris** due to its presence in follicles and its ability to produce inflammatory mediators. *Lactobacillus* - **_Lactobacillus_** species are typically found in the **gastrointestinal tract** and **female genital tract**, where they contribute to maintaining a healthy microbial balance. - They are not a primary component of the normal skin flora. *Streptococcus pyogenes* - **_Streptococcus pyogenes_** is a pathogenic bacterium known for causing various infections, including **strep throat**, **scarlet fever**, and **skin infections** (e.g., impetigo, erysipelas). - While it can cause skin infections, it is not considered a normal, common inhabitant of healthy skin. *Bacteroides fragilis* - **_Bacteroides fragilis_** is a prominent **anaerobic bacterium** found in the **human gut** and is a major component of the fecal microbiota. - It is rarely found on the skin unless there is a breach in the integument or contamination from intestinal sources.

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: 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: Lyme disease is caused by:

B. burgdorferi. ***Correct: B. burgdorferi*** - **Lyme disease** is a **tick-borne illness** caused by the spirochete *Borrelia burgdorferi*. - This bacterium is transmitted to humans through the bite of infected ticks, primarily the **black-legged tick** (*Ixodes scapularis*). *Incorrect: B. vincenti* - *Borrelia vincenti* is associated with **Vincent's angina** (fusospirochetal disease), a severe gingivitis, and periodontitis. - It is not implicated in Lyme disease but rather in an oro-dental infection. *Incorrect: B. recurrentis* - *Borrelia recurrentis* is the causative agent of **epidemic relapsing fever**. - This disease is transmitted by the **human body louse** and is characterized by recurring episodes of fever. *Incorrect: T. pertenue* - *Treponema pertenue* is the bacterium responsible for **yaws**, a chronic, disfiguring skin infection. - It is a related spirochete to *Treponema pallidum* (syphilis) but causes a non-venereal disease primarily in tropical regions.

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 anticoagulant is commonly used for bacteriological culture?

Accepted Answer

Citrate

Answer

Heparin

Answer

EDTA

Answer

Mechanical defibrination

Question 4

Which of the following bacteria is microaerophilic?

Accepted Answer

Campylobacter

Answer

Pseudomonas

Answer

Salmonella

Answer

Vibrio cholerae

Question 5

Which bacterial species is commonly found on the skin?

Accepted Answer

Cutibacterium acnes

Answer

Lactobacillus

Answer

Streptococcus pyogenes

Answer

Bacteroides fragilis

Question 6

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 7

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 8

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 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

Lyme disease is caused by:

Accepted Answer

B. burgdorferi

Answer

T. pertenue

Answer

B. vincenti

Answer

B. recurrentis

Bacteriology — MCQs

Bacteriology — MCQs

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