Bacteriology Practice Questions

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.

Q: Streptococcus pyogenes is classified as which type of bacteria?

Gram positive cocci. ***Gram positive cocci*** - *Streptococcus pyogenes* are **spherical-shaped (cocci) bacteria** that stain **purple** with the Gram stain, indicating a thick peptidoglycan layer characteristic of Gram-positive organisms. - They typically arrange in **chains** and are known for causing **strep throat**, scarlet fever, and rheumatic fever. *Gram negative cocci* - Gram-negative cocci like *Neisseria meningitidis* or *Neisseria gonorrhoeae* stain **pink or red** due to their thin peptidoglycan layer and outer membrane. - While they are also cocci, their Gram stain reaction is distinctly different from *Streptococcus pyogenes*. *Gram positive bacilli* - Gram-positive bacilli are **rod-shaped bacteria** that stain purple, examples include *Bacillus anthracis* or *Clostridium difficile*. - *Streptococcus pyogenes* is clearly a coccus (spherical), not a bacillus (rod). *Gram negative bacilli* - Gram-negative bacilli are **rod-shaped bacteria** that stain pink or red, such as *Escherichia coli* or *Pseudomonas aeruginosa*. - This classification differs from *Streptococcus pyogenes* in both cell shape and Gram stain reaction.

Q: Which of the following conditions is not typically associated with Ureaplasma urealyticum?

Bacterial vaginosis. ***Bacterial vaginosis*** - **Bacterial vaginosis (BV)** is primarily associated with an imbalance in the vaginal microbiota, characterized by an overgrowth of anaerobic bacteria like *Gardnerella vaginalis* and *Prevotella* species, and a decrease in protective *Lactobacillus* species. - While *Ureaplasma urealyticum* can be present in the vaginal flora, it is not considered a primary causative agent of **bacterial vaginosis**, which has a distinct microbiological profile. *Non gonococcal urethritis* - **Non-gonococcal urethritis (NGU)** is a well-established clinical condition where *Ureaplasma urealyticum* is a common cause, often presenting with dysuria, urethral discharge, and itching. - Along with *Chlamydia trachomatis*, *Mycoplasma genitalium*, and *Trichomonas vaginalis*, *Ureaplasma urealyticum* is recognized as a significant pathogen in NGU. *Pelvic inflammatory disease (including salpingitis)* - *Ureaplasma urealyticum* has been implicated in the etiology of **pelvic inflammatory disease (PID)**, including conditions like **salpingitis**, which involves inflammation of the fallopian tubes. - The organism can ascend from the lower genital tract, causing inflammation and damage to the reproductive organs, particularly in cases where typical pathogens like *Neisseria gonorrhoeae* or *Chlamydia trachomatis* are not identified. *Epididymitis* - **Epididymitis**, especially in men under 35, is often caused by sexually transmitted infections (STIs), and *Ureaplasma urealyticum* is recognized as a potential pathogen. - It can lead to inflammation of the **epididymis**, causing pain, swelling, and tenderness in the scrotum, particularly in cases of non-gonococcal, non-chlamydial epididymitis.

Q: Which of the following statements about Streptococcus is false?

Streptolysin O is active in oxidized state.. ***Streptolysin O is active in oxidized state.*** - This statement is **FALSE** because **Streptolysin O** is a **thiol-activated toxin** that is **inactivated by oxygen**. - It is active in the **reduced state**, not the oxidized state. - Its lytic activity on red blood cells is maximal under **anaerobic conditions**, which distinguishes it from streptolysin S (which is oxygen-stable). - This is the correct answer to the question asking for a false statement. *Streptokinase is produced from serotype A, C, K.* - This statement is somewhat misleading in its terminology, but refers to **streptokinase** production by *Streptococcus pyogenes* (Group A Streptococcus). - While the serotype classification mentioned is not standard, streptokinase is indeed produced by Group A streptococci. *Streptodornase cleaves DNA.* - **TRUE statement**: Streptodornase (also known as deoxyribonuclease or DNase) is an enzyme produced by *Streptococcus pyogenes*. - It **cleaves extracellular DNA**, helping the bacteria degrade neutrophil extracellular traps (NETs) and reduce pus viscosity, facilitating bacterial spread. *Pyrogenic toxin A is encoded by a bacteriophage.* - **TRUE statement**: **Streptococcal pyrogenic exotoxin A** (SPEA) is encoded by a **lysogenic bacteriophage**. - This phage integrates into the *Streptococcus pyogenes* chromosome, enabling toxin production. - SPEA is responsible for conditions such as **scarlet fever** and streptococcal toxic shock syndrome.

Q: HACEK group of organisms includes all, except:

Haemophilus ducreyi. ***Haemophilus ducreyi*** - *Haemophilus ducreyi* is the causative agent of **chancroid**, a sexually transmitted infection, and is not considered part of the HACEK group. - The **HACEK group** consists of fastidious, gram-negative bacteria known for causing **endocarditis**. *Haemophilus parainfluenzae* - *Haemophilus parainfluenzae* is one of the five genera included in the **HACEK group** acronym, specifically the 'H'. - This organism is a known cause of **infective endocarditis**, particularly in patients with pre-existing valvular disease. *Cardiobacterium hominis* - *Cardiobacterium hominis* is represented by the 'C' in the **HACEK group** acronym. - It is a significant cause of **culture-negative endocarditis** due to its fastidious nature and slow growth. *Eikenella corrodens* - *Eikenella corrodens* is the 'E' in the **HACEK group** acronym. - It is often associated with **oral cavity infections**, human bite wounds, and can cause **endocarditis** in susceptible individuals.

Question 1

Which of the following bacteria is microaerophilic?

Accepted Answer

Campylobacter

Answer

Pseudomonas

Answer

Salmonella

Answer

Vibrio cholerae

Question 2

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 3

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 4

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 5

Nocardia infection is associated most commonly with:

Accepted Answer

Lung abscess

Answer

Brain abscess

Answer

Subcutaneous abscess

Answer

Liver abscess

Question 6

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 7

Streptococcus pyogenes is classified as which type of bacteria?

Accepted Answer

Gram positive cocci

Answer

Gram negative cocci

Answer

Gram positive bacilli

Answer

Gram negative bacilli

Question 8

Which of the following conditions is not typically associated with Ureaplasma urealyticum?

Accepted Answer

Bacterial vaginosis

Answer

Non gonococcal urethritis

Answer

Epididymitis

Answer

Pelvic inflammatory disease (including salpingitis)

Question 9

Which of the following statements about Streptococcus is false?

Accepted Answer

Streptolysin O is active in oxidized state.

Answer

Pyrogenic toxin A is encoded by a bacteriophage.

Answer

Streptodornase cleaves DNA.

Answer

Streptokinase is produced from serotype A, C, K.

Question 10

HACEK group of organisms includes all, except:

Accepted Answer

Haemophilus ducreyi

Answer

Cardiobacterium hominis

Answer

Eikenella corrodens

Answer

Haemophilus parainfluenzae

Bacteriology — MCQs

Bacteriology — MCQs

On this page

Practice by Chapter

Want unlimited practice?