Bacteriology Practice Questions

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.

Q: Which immunoglobulin does Protein A of Staphylococcus aureus bind to?

IgG. ***IgG*** - **Protein A** of *Staphylococcus aureus* binds to the **Fc region** of IgG antibodies. - This binding mechanism helps *S. aureus* in **evading opsonization** and phagocytosis by interfering with the host immune response. *IgA* - IgA is primarily found in **mucosal secretions** and its primary role is in mucosal immunity. - Protein A does not preferentially bind to IgA; instead, some bacteria produce specific **IgA proteases** to cleave and inactivate IgA. *IgD* - IgD is found mostly on the surface of **B lymphocytes** and its main role is in B cell activation. - Protein A does not have a significant binding affinity for IgD. *IgE* - IgE is involved in **allergic reactions** and defense against parasites. - Protein A does not bind to IgE; binding to IgE is typically mediated by specific IgE receptors on mast cells and basophils.

Q: Which type of DNase produced by Streptococcus is known to be the most antigenic in humans?

DNase B. ***DNase B*** - **DNase B** is the most **antigenic** of the four DNases (A, B, C, D) produced by *Streptococcus pyogenes*. - Antibodies against DNase B are commonly measured as anti-DNase B titers in the diagnosis of **streptococcal infections** and their sequelae, like **acute rheumatic fever** and **post-streptococcal glomerulonephritis**, especially when ASO titers are negative. *DNase A* - While *Streptococcus pyogenes* produces **DNase A**, it is not considered the most antigenically potent or clinically relevant for antibody testing in humans. - Its antigenicity is generally **lower** than that of DNase B in response to streptococcal infection. *DNase C* - **DNase C** is another deoxyribonuclease produced by *Streptococcus pyogenes*. - Similar to DNase A, it does not elicit as strong or as consistent an **antibody response** in human infections compared to DNase B. *DNase D* - **DNase D** is the fourth type of deoxyribonuclease produced by *Streptococcus pyogenes*. - Its **antigenicity** in humans is less pronounced and less diagnostically significant than that of **DNase B**.

Q: Granuloma inguinale is caused by:

Calymmatobacterium granulomatis. ***Calymmatobacterium granulomatis*** - **Granuloma inguinale**, also known as **donovanosis**, is a sexually transmitted infection caused by **_Calymmatobacterium granulomatis_**. - This bacterium is notoriously difficult to culture, so diagnosis is typically made by identifying **Donovan bodies** (macrophages filled with bacteria) in tissue samples. *Haemophilus ducreyi* - **_Haemophilus ducreyi_** is the causative agent of **chancroid**, - Chancroid is characterized by **painful genital ulcers** with a ragged, undermined border, and often accompanied by **tender inguinal lymphadenopathy**. *Chlamydia trachomatis* - **_Chlamydia trachomatis_** is responsible for several conditions, including **chlamydia** (the most common bacterial STI), **lymphogranuloma venereum (LGV)**, and **trachoma**. - LGV presents with a transient, often unnoticed genital lesion followed by painful, suppurative lymphadenopathy, which is distinct from granuloma inguinale. *Treponema pallidum* - **_Treponema pallidum_** is the spirochete that causes **syphilis**, which progresses through several stages. - Primary syphilis manifests as a **painless chancre**, while secondary syphilis can involve a widespread rash, lymphadenopathy, and mucosal lesions.

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: "Citron bodies" are boat- or leaf-shaped pleomorphic organisms found in exudates. This is a characteristic feature of which organism?

Cl. septicum. ***Cl. septicum*** - *Clostridium septicum* characteristically forms **"Citron bodies"** - boat-shaped or leaf-shaped pleomorphic organisms in exudates - These spindle-shaped, cigar-like forms are a **distinctive morphological feature** of this organism - Associated with **gas gangrene** and spontaneous myonecrosis, particularly in patients with underlying malignancy or neutropenia - The pleomorphic morphology distinguishes it from other clostridial species *Cl. welchii* - *Clostridium perfringens* (formerly *Cl. welchii*) appears as **large, rectangular, "boxcar-shaped" Gram-positive rods** - Does **not** form citron bodies or show the characteristic boat/leaf-shaped pleomorphism - Most common cause of gas gangrene but has different morphological appearance *Cl. edematiens* - *Clostridium oedematiens* (now *Clostridium novyi*) appears as **large, Gram-positive rods** with subterminal spores - Does not form citron bodies - Associated with gas gangrene but lacks the pleomorphic morphology described *Cl. tetani* - *Clostridium tetani* has characteristic **terminal spores** giving a "drumstick" or "tennis racket" appearance - Does not form citron bodies or pleomorphic shapes - Morphologically distinct with its terminal spore appearance

Q: A patient presents with purulent urethral discharge and laboratory findings of gram-negative diplococci on modified Thayer-Martin media. What is the most likely diagnosis?

Neisseria gonorrhoeae. ***Neisseria gonorrhoeae*** - **Purulent urethral discharge** and identification of **gram-negative diplococci** on microscopy from a urethral swab are highly characteristic of *Neisseria gonorrhoeae* infection. - *N. gonorrhoeae* grows well on **modified Thayer-Martin media**, a selective medium specifically designed for *Neisseria* species. - This organism is the causative agent of **gonorrhea**, a common sexually transmitted infection. - The combination of clinical presentation (purulent discharge) and laboratory findings (gram-negative diplococci on Thayer-Martin media) makes this the definitive diagnosis. *Haemophilus ducreyi* - Causes **chancroid**, which presents with **painful genital ulcers** and **lymphadenopathy**, NOT purulent urethral discharge. - *H. ducreyi* is a gram-negative **bacillus** (rod-shaped), NOT diplococci. - It requires special media supplemented with X and V factors for growth, not primarily Thayer-Martin medium. *Treponema pallidum* - Causes **syphilis**, which typically presents with a **chancre** (painless ulcer) in primary stage and systemic symptoms in later stages. - Cannot be cultured on routine media and is identified by **darkfield microscopy** or serological tests. - Does not appear as gram-negative diplococci. *Chlamydia trachomatis* - Can cause urethritis with **mucopurulent or watery discharge**, but not typically purulent. - *Chlamydia* are **obligate intracellular bacteria** that cannot be visualized as gram-negative diplococci on gram stain. - Cannot be cultured on standard bacteriologic media like Thayer-Martin medium.

Q: Which organism causes puerperal sepsis?

Group A beta hemolytic streptococci. ***Group A beta hemolytic streptococci*** - **Group A Streptococcus (GAS)**, specifically *Streptococcus pyogenes*, is the **classic and most important cause of puerperal sepsis** (puerperal fever). - Historically, GAS was responsible for devastating epidemics of puerperal fever in maternity wards before the introduction of antiseptic practices by Ignaz Semmelweis. - GAS causes severe, rapidly progressive postpartum infections with **high morbidity and mortality** if untreated. - Clinically presents with fever, severe uterine tenderness, and can progress to **toxic shock syndrome** and septicemia. *Group B beta hemolytic streptococci* - **Group B Streptococcus (GBS)**, *Streptococcus agalactiae*, can cause postpartum endometritis and maternal infections. - However, GBS is **more commonly associated with neonatal sepsis** rather than being the primary cause of classic puerperal sepsis. - While it can colonize the genital tract and cause infection, it is not the historical or most severe cause of puerperal fever. *CMV* - **Cytomegalovirus (CMV)** is a viral infection that causes congenital infections when transmitted in utero. - It is not a bacterial cause of **puerperal sepsis**, which is primarily a bacterial postpartum infection. *Toxoplasma gondii* - **Toxoplasma gondii** is a parasite causing toxoplasmosis, which can lead to congenital abnormalities. - It is not associated with **puerperal sepsis**, which is a bacterial infection of the postpartum period.

Q: What is the most common cause of acute tonsillitis?

Group A beta-hemolytic streptococci. ***Group A beta-hemolytic streptococci*** - **Group A Streptococcus (GAS)**, specifically *Streptococcus pyogenes*, is the most frequent bacterial cause of **acute tonsillitis** and pharyngitis, especially in school-aged children. - Infection can lead to complications such as **rheumatic fever** and **post-streptococcal glomerulonephritis** if not appropriately treated. *Streptococcus pneumoniae* - While *S. pneumoniae* is a common cause of **otitis media**, **sinusitis**, and **pneumonia**, it is less commonly the primary cause of acute tonsillitis. - It typically causes respiratory infections involving the lower airways or adjacent structures rather than primarily tonsillar inflammation. *H. Influenza* - *Haemophilus influenzae* is a significant pathogen for **otitis media**, **epiglottitis**, and **meningitis**, particularly in unvaccinated children. - It is not a common primary cause of acute tonsillitis, which is predominantly bacterial or viral. *Staphylococcus aureus* - *Staphylococcus aureus* is often associated with **skin and soft tissue infections**, as well as more serious conditions like **sepsis** and **endocarditis**. - Although it can cause pharyngeal infections, it is an infrequent cause of acute tonsillitis compared to Group A Streptococcus.

Question 1

Draughtsman colonies are seen with:

Accepted Answer

Pneumococci

Answer

Anthrax

Answer

Pertussis

Answer

Yersinia

Question 2

Which immunoglobulin does Protein A of Staphylococcus aureus bind to?

Accepted Answer

IgG

Answer

IgA

Answer

IgD

Answer

IgE

Question 3

Which type of DNase produced by Streptococcus is known to be the most antigenic in humans?

Accepted Answer

DNase B

Answer

DNase C

Answer

DNase D

Answer

DNase A

Question 4

Granuloma inguinale is caused by:

Accepted Answer

Calymmatobacterium granulomatis

Answer

Haemophilus ducreyi

Answer

Chlamydia trachomatis

Answer

Treponema pallidum

Question 5

Bartonella quintana causes:

Accepted Answer

Trench fever

Answer

Scrub typhus

Answer

Epidemic typhus

Answer

Endemic typhus

Question 6

Listeria escapes from phagosomes (phagolysosomes) due to:

Accepted Answer

beta-hemolysin

Answer

Opacity associated protein (OAP)

Answer

Caspases

Answer

Cell membrane adhesion molecules

Question 7

"Citron bodies" are boat- or leaf-shaped pleomorphic organisms found in exudates. This is a characteristic feature of which organism?

Accepted Answer

Cl. septicum

Answer

Cl. edematiens

Answer

Cl. tetani

Answer

Cl. welchii

Question 8

A patient presents with purulent urethral discharge and laboratory findings of gram-negative diplococci on modified Thayer-Martin media. What is the most likely diagnosis?

Accepted Answer

Neisseria gonorrhoeae

Answer

Treponema pallidum

Answer

Haemophilus ducreyi

Answer

Chlamydia trachomatis

Question 9

Which organism causes puerperal sepsis?

Accepted Answer

Group A beta hemolytic streptococci

Answer

CMV

Answer

Toxoplasma gondii

Answer

Group B beta hemolytic streptococci

Question 10

What is the most common cause of acute tonsillitis?

Accepted Answer

Group A beta-hemolytic streptococci

Answer

Streptococcus pneumoniae

Answer

H. influenzae

Answer

Staphylococcus aureus

Bacteriology — MCQs

Bacteriology — MCQs

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