Bacteriology Practice Questions

Q: Proteus isolated from a patient of UTI will show which biochemical reaction.

Production of phenylpyruvic acid from phenylalanine. ***Production of phenylpyruvic acid from phenylalanine*** - *Proteus* species possess the enzyme **phenylalanine deaminase**, which deaminates phenylalanine to **phenylpyruvic acid**. - This reaction is a **key biochemical test** used to identify *Proteus*, *Providencia*, and *Morganella* species. *Hydrolysis of esculin in bile* - This reaction is characteristic of **Group D streptococci** and **enterococci**, not *Proteus* species. - The organism hydrolyzes **esculin** in the presence of bile, turning the agar black. *Sensitivity to colchicine* - **Colchicine** is an anti-inflammatory drug, not part of standard **biochemical identification tests** for bacteria. - This is not a recognized biochemical reaction used to identify *Proteus* or any bacterial species. *Sensitivity to bacitracin* - **Bacitracin sensitivity** is primarily used to differentiate **Group A streptococci** (e.g., *Streptococcus pyogenes*) from other beta-hemolytic streptococci. - It is an **antibiotic susceptibility test**, not a biochemical reaction characteristic of *Proteus* species.

Q: A chronic alcoholic is presenting with clinical features of meningitis. Most likely organism to grow on CSF culture:

Streptococcus pneumoniae. ***Streptococcus pneumoniae*** - **Chronic alcoholism** is a significant risk factor for **pneumococcal infections**, including meningitis, due to impaired immune function. - **S. pneumoniae** is the most common cause of **bacterial meningitis** in adults, especially in those with underlying conditions like alcoholism. *Neisseria meningitidis* - While a common cause of meningitis, especially in **young adults** and crowded settings, it is not specifically associated with chronic alcoholism as a primary risk factor like *S. pneumoniae*. - **Meningococcal meningitis** often presents with a **petechial rash**, which is not mentioned in the clinical scenario. *Escherichia coli* - **E. coli meningitis** primarily affects **neonates** and **elderly** or immunocompromised individuals, usually associated with healthcare-acquired infections. - It is not a typical cause of community-acquired meningitis in an otherwise healthy adult alcoholic. *Listeria monocytogenes* - **Listeria monocytogenes** is a known cause of meningitis in **immunocompromised individuals**, **neonates**, and **elderly** people, often linked to contaminated food. - While chronic alcoholism does impair immunity, *S. pneumoniae* is a more frequently encountered pathogen in this specific population for meningitis.

Q: Which of the following is a non-motile bacterium?

Clostridium perfringens. ***Clostridium perfringens*** - *Clostridium perfringens* is unique among the *Clostridium* species for being **non-motile**, lacking flagella. - This immotility distinguishes it from other closely related bacteria and is an important characteristic in its identification. *Vibrio* - *Vibrio* species are **highly motile**, possessing a single **polar flagellum** that enables rapid movement in liquid environments. - Their motility is crucial for their survival and pathogenesis, particularly in aquatic habitats and the human intestine. *Legionella* - *Legionella* species, including *Legionella pneumophila*, are **motile** by means of one or more **polar flagella**. - Their motility is important for disseminating within water systems and for infecting macrophages. *Clostridium septicum* - *Clostridium septicum* is a **motile** bacterium, possessing **peritrichous flagella** that allow it to move through tissues. - Its motility contributes to its ability to spread rapidly in infected hosts, often causing severe gas gangrene.

Q: Primary complex of M bovis involves:

Tonsil and intestine. ***Tonsil and intestine*** - *Mycobacterium bovis* is primarily transmitted through **consumption of contaminated milk and dairy products**, making the **alimentary tract** the main route of infection - The primary complex (Ghon complex) involves the **initial site of infection plus regional lymph nodes** - In alimentary tuberculosis, the organisms enter through the **intestinal mucosa** (Peyer's patches) or **tonsillar tissue**, creating foci with associated mesenteric or cervical lymphadenopathy - Both tonsils and intestines are part of the **alimentary system**, representing the typical primary complex for M. bovis in humans *Tonsil and lung* - This incorrectly combines **two different routes of entry** (alimentary and respiratory) - A primary complex involves a **single portal of entry**, not multiple unrelated organ systems - While M. bovis can rarely cause pulmonary TB through inhalation, this would create a separate lung + hilar node complex, not a combined tonsil-lung complex *Tonsil and skin* - **Skin involvement** requires direct inoculation through cuts or abrasions and does not form a primary complex with tonsillar infection - These represent different portals of entry and would not occur together as a primary complex *Skin and Intestine* - **Skin infection** by M. bovis is rare and requires occupational exposure with direct inoculation (e.g., veterinarians, butchers) - This incorrectly pairs two different routes of infection that would not form a single primary complex

Q: Most common site for Staphylococcus carriage?

Nose. ***Nose*** - The **anterior nares** are the most common site for **Staphylococcus aureus** colonization in healthy individuals. - Nasal carriage is a significant risk factor for subsequent **Staphylococcus aureus infections**, both self-acquired and transmitted to others. *Skin* - While Staphylococcus aureus can colonize the skin, especially in areas like the axillae and groin, it is **less common** as a primary carrier site compared to the nose. - Skin colonization often occurs due to spread from **nasal carriage**. *Oropharynx* - The oropharynx can be colonized by various bacteria, but it is **not the primary or most common site** for Staphylococcus aureus carriage. - Other bacteria like **Streptococcus species** are more prevalent colonizers of the oropharynx. *Perineum* - The perineum can harbor Staphylococcus aureus, particularly in specific populations or in individuals with certain skin conditions, but it is **not the most common or primary site** of colonization. - Colonization here is often **secondary** to nasal carriage or contact with contaminated surfaces.

Q: Which of the following is non-motile:

Burkholderia mallei. ***Burkholderia mallei*** - This bacterium is notably **non-motile**, lacking flagella, which is a key characteristic differentiating it from other members of its genus. - It is a **facultative intracellular pathogen** capable of surviving within host cells, primarily causing **glanders** in equids and occasional human infections. - Its immobility is a significant feature in its identification and pathogenesis. *Pseudomonas aeruginosa* - This bacterium is highly **motile** due to the presence of **polar flagella**. - Its motility contributes to its ability to colonize and invade host tissues, common in opportunistic infections. *Burkholderia pseudomallei* - This species is known to be **motile** by means of flagella, which aids its survival and dissemination in diverse environments and within a host. - It is the causative agent of **melioidosis**, a severe infectious disease. *None of the options* - This option is incorrect because **Burkholderia mallei** is indeed non-motile, making it a correct choice among the provided options. - The other specified bacteria, *Pseudomonas aeruginosa* and *Burkholderia pseudomallei*, are motile.

Q: Which of the following is NOT true about Corynebacterium hofmannii?

Toxigenic. ***Toxigenic*** - *Corynebacterium hofmannii* is a **non-toxigenic** species and does not produce **diphtheria toxin**, unlike *C. diphtheriae*. - Its clinical significance primarily relates to its potential role in opportunistic infections, not toxin-mediated diseases. - This is the **correct answer** as C. hofmannii being toxigenic is NOT true. *A diphtheroid* - **Diphtheroid** refers to gram-positive, rod-shaped bacteria morphologically similar to *Corynebacterium diphtheriae*. - *C. hofmannii* fits this description due to its characteristic morphology and belongs to the Corynebacterium genus. - This statement is TRUE. *Non-pathogenic saprophyte* - *C. hofmannii* is commonly found as a **commensal organism** on human skin and mucous membranes as part of normal flora. - While generally non-pathogenic, it can cause opportunistic infections in immunocompromised individuals. - This statement is TRUE. *Commonly found in the normal flora of the throat* - *C. hofmannii* is indeed found as part of the **normal respiratory tract flora**, including the throat and upper respiratory passages. - It is a common colonizer and generally harmless commensal. - This statement is TRUE.

Q: What is the most common age group affected by Streptococcus pyogenes?

5-15 years. ***5-15 years*** - **Streptococcus pyogenes** (Group A Strep) commonly causes **pharyngitis** (strep throat), which primarily affects school-aged children. - This age group is more susceptible due to increased exposure in school and daycare settings. *<5 years* - While younger children can get strep infections, it is less common in those under **3 years of age**, as viral etiologies are more prevalent for pharyngitis in this group. - They are more prone to **non-streptococcal bacterial infections** and certain viral infections. *20-25 years* - Although adults can get **Streptococcus pyogenes** infections, the incidence significantly decreases after childhood. - Pharyngitis in this age group is more often **viral** in origin. *30-40 years* - The prevalence of **Streptococcus pyogenes** infections, particularly pharyngitis, is typically low in this age group compared to children. - Infections, if they occur, may stem from exposure to infected children or close contact environments.

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: 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.

Question 1

Proteus isolated from a patient of UTI will show which biochemical reaction.

Accepted Answer

Production of phenylpyruvic acid from phenylalanine

Answer

Hydrolysis of esculin in bile

Answer

Sensitivity to colchicine

Answer

Sensitivity to bacitracin

Question 2

A chronic alcoholic is presenting with clinical features of meningitis. Most likely organism to grow on CSF culture:

Accepted Answer

Streptococcus pneumoniae

Answer

Neisseria meningitidis

Answer

Escherichia coli

Answer

Listeria monocytogenes

Question 3

Which of the following is a non-motile bacterium?

Accepted Answer

Clostridium perfringens

Answer

Vibrio

Answer

Legionella

Answer

Clostridium septicum

Question 4

Primary complex of M bovis involves:

Accepted Answer

Tonsil and intestine

Answer

Tonsil and skin

Answer

Tonsil and lung

Answer

Skin and Intestine

Question 5

Most common site for Staphylococcus carriage?

Accepted Answer

Nose

Answer

Skin

Answer

Oropharynx

Answer

Perineum

Question 6

Which of the following is non-motile:

Accepted Answer

Burkholderia mallei

Answer

Pseudomonas aeruginosa

Answer

Burkholderia pseudomallei

Answer

None of the options

Question 7

Which of the following is NOT true about Corynebacterium hofmannii?

Accepted Answer

Toxigenic

Answer

Commonly found in the normal flora of the throat

Answer

A diphtheroid

Answer

Non-pathogenic saprophyte

Question 8

What is the most common age group affected by Streptococcus pyogenes?

Accepted Answer

5-15 years

Answer

30-40 years

Answer

<5 years

Answer

20-25 years

Question 9

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 10

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

Bacteriology — MCQs

Bacteriology — MCQs

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