Bacteriology Practice Questions

Q: Granulomatosis infantiseptica is caused by:

Listeria. ***Listeria*** - **Granulomatosis infantiseptica** is a severe manifestation of congenital **listeriosis**, caused by *Listeria monocytogenes*. - This condition is characterized by widespread **granulomas** and **microabscesses** in various organs of the infected newborn. *Pseudomonas* - *Pseudomonas aeruginosa* is a common cause of healthcare-associated infections but is not typically associated with **granulomatosis infantiseptica**. - It can cause severe infections in immunocompromised individuals, including **pneumonia**, **sepsis**, and wound infections. *Chlamydia trachomatis* - *Chlamydia trachomatis* is a common cause of **conjunctivitis** and **pneumonia** in neonates, acquired during passage through the birth canal. - It does not cause **granulomatosis infantiseptica**. *Group D streptococci* - While Group D streptococci (e.g., *Enterococcus faecalis*) can cause neonatal infections like **sepsis** and **meningitis**, they are not the causative agents of **granulomatosis infantiseptica**. - This condition is specifically linked to **Listeria**.

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: 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: Oil paint appearance on nutrient agar is seen in -

Staphylococcus aureus. ***Staphylococcus aureus*** - *Staphylococcus aureus* forms characteristic **golden-yellow, smooth, opaque colonies** on nutrient agar with a **buttery or creamy consistency** - Some texts describe this appearance as **"oil paint-like"** due to the pigmented, smooth, and glistening surface that can resemble brushed paint - Colonies are typically **2-4 mm in diameter**, round, and show **golden pigmentation** (due to carotenoid pigments) - On **blood agar**, *S. aureus* shows **beta-hemolysis** with golden colonies *Streptococcus pyogenes* - *Streptococcus pyogenes* grows poorly on plain nutrient agar and requires **enriched media** like blood agar - On blood agar, it forms **small, translucent, grey-white colonies** surrounded by a wide zone of **beta-hemolysis** - Colonies are typically **pinpoint** in size and do not show pigmentation *Bordetella pertussis* - *Bordetella pertussis* is a **fastidious organism** that does **not grow on plain nutrient agar** - Requires specialized enriched media like **Bordet-Gengou agar** (with potato-glycerol-blood) or **Regan-Lowe agar** - On Bordet-Gengou agar, colonies appear as **small, smooth, pearl-like** or **"mercury droplet"** colonies after 3-7 days *H. influenzae* - *Haemophilus influenzae* is also fastidious and requires **X factor (hemin)** and **V factor (NAD)** for growth - Does **not grow on plain nutrient agar** - On **chocolate agar**, forms **small, smooth, translucent, greyish colonies** with a characteristic musty odor - Colonies are typically **1-2 mm** in diameter

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: Which of the following statements about Corynebacterium diphtheriae is true?

Toxin production is dependent on iron concentration. ***Toxin production is dependent on iron concentration*** - The production of **diphtheria toxin** by *Corynebacterium diphtheriae* is directly regulated by the iron concentration in the environment. - When **iron levels are low**, the diphtheria toxin repressor (DTxR) is inactivated, leading to increased toxin production. *All strains produce toxin* - Not all strains of *Corynebacterium diphtheriae* produce the diphtheria toxin; only those strains that are **lysogenized by a bacteriophage carrying the tox gene** are toxigenic. - Non-toxigenic strains can cause other infections but do not produce the classic diphtheria disease. *The toxin is heat stable* - The **diphtheria toxin** is a **heat-labile** protein, meaning its activity can be destroyed by heat. - Heating diphtheria toxin to 60°C for 30 minutes can inactivate its pathogenic effects. *It inhibits cAMP* - The diphtheria toxin does not inhibit **cAMP**; instead, it acts by **ADP-ribosylating and inactivating elongation factor-2 (EF-2)**, thereby inhibiting protein synthesis in eukaryotic cells. - Inhibition of EF-2 ultimately leads to cell death.

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: Bartonella quintana causes:

Trench fever. ***Trench fever*** - **Bartonella quintana** is the causative agent of **trench fever**, a louse-borne disease historically common during wartime. - Symptoms include **recurrent fevers**, headache, bone pain (especially in the shins), and rash. *Scrub typhus* - Scrub typhus is caused by **Orientia tsutsugamushi**, a rickettsial bacterium, not Bartonella. - It is transmitted by **chiggers** and characterized by a rash, fever, and eschar at the bite site. *Epidemic typhus* - Epidemic typhus is caused by **Rickettsia prowazekii** and is also louse-borne. - It presents with sudden high fever, severe headache, and a maculopapular rash that spares the face, palms, and soles. *Endemic typhus* - Endemic typhus (murine typhus) is caused by **Rickettsia typhi** and is transmitted by **rat fleas**. - Its symptoms are generally milder than epidemic typhus, including fever, headache, and a truncal rash.

Q: Listeria escapes from phagosomes (phagolysosomes) due to:

beta-hemolysin. ***beta-hemolysin*** - *Listeria monocytogenes* produces **listeriolysin O (LLO)**, a **beta-hemolysin**, which is a pore-forming toxin that lyses the phagosomal membrane. - This allows the bacteria to escape into the host cell cytoplasm, thus **avoiding destruction** by lysosomal enzymes and neutralizing the microbicidal environment. *Caspases* - **Caspases** are a family of proteases that play essential roles in programmed cell death (apoptosis) and inflammation. - While bacteria can manipulate host cell apoptosis, caspases themselves are **host enzymes** and do not directly confer resistance to phagosome destruction. *Cell membrane adhesion molecules* - **Adhesion molecules** facilitate bacterial attachment to host cells and internalisation, but they do not directly provide a mechanism for **escaping the phagosome** once internalised. - Examples include internalins, which are involved in bacterial entry into cells. *Opacity associated protein (OAP)* - **Opacity associated proteins (OAPs)** are primarily associated with *Neisseria gonorrhoeae* and are involved in adherence to host cells and evasion of the immune response. - They are not a mechanism for **phagosomal escape** or directly related to *Listeria's* intracellular survival.

Q: Draughtsman colonies are seen with:

Pneumococci. ***Pneumococci*** - **Draughtsman colonies** (or **draughtsman-like colonies**) are a characteristic morphological feature observed when *Streptococcus pneumoniae* (pneumococci) grows on certain agar media, such as blood agar. - This appearance is due to the **central umbilication or depression** of the colony caused by autolytic enzymes that break down the bacterial cells in the center as the colony matures. *Anthrax* - Colonies of *Bacillus anthracis* are typically described as **"Medusa head" colonies**, characterized by swirling projections at the periphery. - They are generally **non-hemolytic** on blood agar, distinguishing them from other *Bacillus* species. *Pertussis* - *Bordetella pertussis* colonies are characteristic on **Bordet-Gengou agar**, appearing as small, glistening, pearl-like, or "mercury droplet" colonies. - This distinct morphology is crucial for its identification in laboratory cultures. *Yersinia* - *Yersinia pestis* (which causes plague) colonies on blood agar at 28°C often show a **"fried egg" appearance** over several days, with a dark center and lighter periphery. - Other *Yersinia* species like *Y. enterocolitica* can show a **bull's-eye pattern** on CIN (Cefsulodin-Irgasan-Novobiocin) agar.

Question 1

Granulomatosis infantiseptica is caused by:

Accepted Answer

Listeria

Answer

Pseudomonas

Answer

Chlamydia trachomatis

Answer

Group D streptococci

Question 2

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 3

Most common site for Staphylococcus carriage?

Accepted Answer

Nose

Answer

Skin

Answer

Oropharynx

Answer

Perineum

Question 4

Oil paint appearance on nutrient agar is seen in -

Accepted Answer

Staphylococcus aureus

Answer

Streptococcus pyogenes

Answer

Bordetella pertussis

Answer

H. influenzae

Question 5

Which of the following is a non-motile bacterium?

Accepted Answer

Clostridium perfringens

Answer

Vibrio

Answer

Legionella

Answer

Clostridium septicum

Question 6

Which of the following statements about Corynebacterium diphtheriae is true?

Accepted Answer

Toxin production is dependent on iron concentration

Answer

All strains produce toxin

Answer

The toxin is heat stable

Answer

It inhibits cAMP

Question 7

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 8

Bartonella quintana causes:

Accepted Answer

Trench fever

Answer

Scrub typhus

Answer

Epidemic typhus

Answer

Endemic typhus

Question 9

Listeria escapes from phagosomes (phagolysosomes) due to:

Accepted Answer

beta-hemolysin

Answer

Opacity associated protein (OAP)

Answer

Caspases

Answer

Cell membrane adhesion molecules

Question 10

Draughtsman colonies are seen with:

Accepted Answer

Pneumococci

Answer

Anthrax

Answer

Pertussis

Answer

Yersinia

Bacteriology — MCQs

Bacteriology — MCQs

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