Bacteriology Practice Questions

Q: Which one of the following is the causative organism of Erythrasma, a mild, localized and superficial skin infection?

Corynebacterium minutissimum. ***Corynebacterium minutissimum*** - This bacterium is the **primary causative agent** of erythrasma, a superficial skin infection. - It produces **porphyrins**, which fluoresce with a characteristic **coral-red color** under a Wood's lamp, aiding in diagnosis. *Corynebacterium matruchotii* - This species is typically found in the **oral cavity** and is associated with dental plaque and periodontal diseases. - It is **not known** to cause erythrasma or superficial skin infections. *Corynebacterium pseudotuberculosis* - This bacterium is a significant pathogen in **animals**, particularly livestock, causing conditions like caseous lymphadenitis. - While it can *rarely* cause infections in humans (e.g., lymphadenitis), it is **not associated** with erythrasma. *Corynebacterium diphtheriae* - This is the causative agent of **diphtheria**, a severe respiratory illness characterized by a pseudomembrane in the throat. - It causes systemic toxemia and is **not responsible** for localized, superficial skin infections like erythrasma.

Q: Gas Gangrene resulting in crepitus in tissues and a sweet smelling brown exudate is caused due to infection by :

Clostridium perfringens. ***Clostridium perfringens*** - **Gas gangrene** is caused by obligate anaerobic, gram-positive rods, notably **Clostridium perfringens**. - This bacterium produces **alpha-toxin (lecithinase)**, which destroys tissues and leads to gas formation (crepitus) and a characteristic **sweet-smelling brown exudate**. *Synergistic bacteria* - While synergistic infections can occur and lead to severe tissue damage, they are not the primary or specific cause of **gas gangrene** with its distinct clinical presentation. - The classic features of gas production and a specific exudate are directly tied to the metabolic activity and toxins of **Clostridial species**. *Anaerobic bacteroides spp.* - **Bacteroides** are common anaerobic bacteria, but they are typically associated with **intra-abdominal abscesses** and **wound infections**, not the specific clinical syndrome of gas gangrene. - They do not produce the potent toxins that lead to extensive gas formation and rapid tissue necrosis characteristic of **Clostridium perfringens**. *Gas-forming Klebsiella spp.* - **Klebsiella spp.** are gram-negative, facultative anaerobic bacteria that can produce gas, especially in deep-seated infections like **emphysematous pyelonephritis** or **liver abscesses**. - However, they do not cause **gas gangrene** with its rapid tissue destruction, crepitus, and sweet-smelling brown exudate, which is pathognomonic for **Clostridial infection**.

Q: Clinical signs and symptoms in tetanus are a result of

Exotoxins fixed to nerve endings. ***Exotoxins fixed to nerve endings*** - Tetanus symptoms are caused by **tetanospasmin**, an exotoxin produced by *Clostridium tetani*, which undergoes **retrograde axonal transport** from peripheral nerve terminals to the CNS. - The toxin **irreversibly binds** to presynaptic terminals of **inhibitory interneurons** (Renshaw cells) in the spinal cord, blocking the release of **glycine and GABA**. - This results in **unopposed excitatory impulses** to motor neurons, causing **spastic paralysis** and characteristic muscle rigidity. *Circulating exotoxins* - While tetanospasmin circulates after production at the wound site, it must **bind to nerve tissue** and reach the CNS to exert its pathogenic effects. - Systemic circulation acts as a transport mechanism; the clinical manifestations result from toxin **fixation at neural synapses**, not from circulating toxin. *Endotoxins* - **Endotoxins** are lipopolysaccharides (LPS) found in the outer membrane of gram-negative bacteria. - *Clostridium tetani* is a **gram-positive, spore-forming anaerobic bacillus** that does not produce endotoxins. - Endotoxins play no role in tetanus pathogenesis. *Both endotoxins and exotoxins* - This option is incorrect because *Clostridium tetani* does **not produce endotoxins**. - The clinical manifestations of tetanus are **exclusively due to tetanospasmin**, an exotoxin that acts by blocking inhibitory neurotransmission in the CNS.

Q: Which one of the following organisms is not associated with synergistic gangrene?

Escherichia. ***Escherichia*** - ***Escherichia coli* is NOT associated with classic synergistic gangrene** (Meleney's gangrene). - While *E. coli* causes many infections (UTIs, peritonitis, wound infections), it is **not a typical organism** in the polymicrobial synergistic gangrene described by Meleney. - Synergistic gangrene specifically involves **aerobic and microaerophilic organisms** working in combination, which is not the typical pattern for *E. coli* infections. *Staphylococcus* - ***Staphylococcus aureus* is a classic component of synergistic gangrene** (Meleney's gangrene). - Typically works in synergy with **microaerophilic streptococci** to cause progressive necrotizing infection. - *S. aureus* creates conditions that allow **anaerobic and microaerophilic organisms** to proliferate. *Clostridium* - ***Clostridium* species are associated with necrotizing soft tissue infections**, particularly gas gangrene (*C. perfringens*). - While gas gangrene differs from classic Meleney's synergistic gangrene, clostridial infections can occur in **polymicrobial settings** with synergistic tissue destruction. - They produce powerful **exotoxins** (alpha toxin, collagenase) causing rapid necrosis and gas formation. *Peptostreptococcus* - ***Peptostreptococcus* species are frequently isolated from synergistic gangrene**. - These **anaerobic gram-positive cocci** are key components of polymicrobial necrotizing infections. - They create an **anaerobic environment** that promotes tissue necrosis and allows other organisms to thrive.

Q: Donovan bodies are associated with :

Granuloma inguinale. ***Granuloma inguinale*** - **Donovan bodies** are characteristic intracellular inclusions found within macrophages in tissue samples from patients with **granuloma inguinale**, also known as **donovanosis**. - These bodies are the causative organism, *Klebsiella granulomatis*, encapsulated within phagosomes, and appear as safety pin-shaped structures. *Gonorrhoea* - This sexually transmitted infection is caused by **Neisseria gonorrhoeae**, a Gram-negative diplococcus. - Diagnosis is typically based on identifying the organism in smears or cultures, not by Donovan bodies. *Chlamydia trachomatis infection* - **Chlamydia trachomatis** is an obligate intracellular bacterium that causes various infections, including cervicitis, urethritis, and lymphogranuloma venereum. - While it causes inclusion bodies within host cells, these are distinct from Donovan bodies and are known as **chlamydial inclusion bodies**. *Herpes genitalis* - This is a viral infection caused by the **herpes simplex virus (HSV)** type 1 or 2. - Diagnosis involves viral culture, PCR, or the identification of **Tzanck cells** (multinucleated giant cells) in vesicular fluid, not Donovan bodies.

Q: The pathogenic organism responsible for the causation of Donovaniasis is

Klebsiella granulomatis. ***Klebsiella granulomatis*** - This bacterium is the causative agent of **granuloma inguinale**, also known as **donovaniasis**. - It infects macrophages and causes chronic, progressive **genital ulcers** with a characteristic beefy-red appearance. *Herpes simplex virus* - This virus causes **genital herpes**, characterized by painful **vesicular or ulcerative lesions** that tend to recur. *Haemophilus ducreyi* - This bacterium causes **chancroid**, characterized by painful, soft chancres with **ragged, undermined borders**. *Chlamydia trachomatis* - This bacterium is responsible for several sexually transmitted infections, including **lymphogranuloma venereum (LGV)**, which presents with transient genital lesions followed by painful, suppurative lymphadenopathy, and **genital chlamydial infections** which often cause urethritis or cervicitis.

Q: All of the following organisms are involved in post-splenectomy sepsis except

Staphylococcus aureus. ***Staphylococcus aureus*** - While *Staphylococcus aureus* can cause various infections, it is **not typically considered a primary encapsulated organism** for which the spleen's filtering function is critical, and therefore, it is **less commonly implicated in overwhelming post-splenectomy infection (OPSI)** compared to encapsulated bacteria. - The risk of OPSI is significantly higher with **encapsulated bacteria** due to the spleen's role in clearing these pathogens. *Neisseria meningitidis* - *Neisseria meningitidis* is an **encapsulated bacterium** and a well-known cause of **meningitis and sepsis**, particularly in individuals with **asplenia**. - The **spleen plays a crucial role in filtering encapsulated organisms** from the bloodstream, making asplenic individuals highly susceptible. *Haemophilus influenzae* - **Encapsulated strains** of *Haemophilus influenzae* (especially type b) are a significant cause of invasive infections in asplenic patients, including **meningitis and epiglottitis**. - The **lack of splenic immune function** impairs the body's ability to clear these bacteria. *Streptococcus pneumoniae* - *Streptococcus pneumoniae* is the **most common cause of OPSI** (overwhelming post-splenectomy infection) due to its **polysaccharide capsule**. - The spleen is essential for **opsonization and phagocytosis** of encapsulated bacteria, a function lost post-splenectomy.

Q: The causative organism of Chancroid is

Haemophilus ducreyi. ***Haemophilus ducreyi*** - **Chancroid** is a sexually transmitted infection characterized by painful genital ulcers and regional lymphadenopathy, caused by the bacterium **Haemophilus ducreyi**. - This bacterium is a **Gram-negative coccobacillus** that requires specific culture media for isolation. *Chlamydia trachomatis* - **Chlamydia trachomatis** is responsible for **chlamydia**, a common STI, and can also cause **lymphogranuloma venereum (LGV)**, which presents with lymphadenopathy and sometimes genital ulcers but not typically the soft, painful ulcers seen in chancroid. - Infections with *Chlamydia trachomatis* are often **asymptomatic** or cause symptoms like urethritis, cervicitis, or proctitis. *Klebsiella granulomatis* - **Klebsiella granulomatis** (formerly *Calymmatobacterium granulomatis*) is the causative agent of **granuloma inguinale** (also known as donovanosis). - **Granuloma inguinale** presents with painless, beefy red, friable ulcerative lesions, which clinically differ from the painful ulcers of chancroid. *Psittacosis lymphogranuloma group* - This option incorrectly groups **psittacosis** (caused by *Chlamydia psittaci*) with **lymphogranuloma venereum (LGV)**, which is caused by specific serovars of *Chlamydia trachomatis*. - **Psittacosis** is primarily a pulmonary infection transmitted by birds, while **LGV** is a sexually transmitted infection distinct from chancroid.

Q: Which of the following cause/causes bacterial vaginosis? 1. Gardnerella 2. Mycoplasma hominis 3. Ureaplasma urealyticum Select the correct answer using the code given below:

1, 2 and 3. ***1, 2 and 3*** - Bacterial vaginosis is a polymicrobial syndrome resulting from an imbalance in the vaginal flora, often characterized by a decrease in **Lactobacilli** and an overgrowth of various anaerobic bacteria. - **Gardnerella vaginalis** is the most commonly associated bacterium, but **Mycoplasma hominis** and **Ureaplasma urealyticum** are also frequently isolated and contribute to the pathogenesis of the condition. *1 and 3 only* - This option incorrectly excludes **Mycoplasma hominis**, which is a recognized contributor to the polymicrobial nature of bacterial vaginosis. - While *Gardnerella* and *Ureaplasma* are significant, the disease involves multiple species. *2 and 3 only* - This option incorrectly excludes **Gardnerella vaginalis**, which is considered the hallmark organism and a primary diagnostic indicator for bacterial vaginosis. - Omitting *Gardnerella* would misrepresent the key infectious agents involved. *1 only* - This option incorrectly suggests that **Gardnerella vaginalis** is the sole causative agent, overlooking the polymicrobial nature of bacterial vaginosis. - The condition is characterized by a shift in the entire vaginal microenvironment, involving multiple types of bacteria.

Question 1

Which one of the following is the causative organism of Erythrasma, a mild, localized and superficial skin infection?

Accepted Answer

Corynebacterium minutissimum

Answer

Corynebacterium matruchotii

Answer

Corynebacterium pseudotuberculosis

Answer

Corynebacterium diphtheriae

Question 2

Gas Gangrene resulting in crepitus in tissues and a sweet smelling brown exudate is caused due to infection by :

Accepted Answer

Clostridium perfringens

Answer

Synergistic bacteria

Answer

Anaerobic bacteroides spp.

Answer

Gas-forming Klebsiella spp.

Question 3

Which one of the following statements regarding Gas Gangrene Infection is correct?

Accepted Answer

It is caused by C. perfringens, a gram positive anaerobic spore-forming bacilli.

Answer

It is caused by C. perfringens, a gram negative aerobic non-spore-forming bacilli.

Answer

It is caused by C. tetani, a gram negative anaerobic non-spore-forming bacilli.

Answer

It is caused by C. tetani, a gram positive anaerobic spore-forming bacilli.

Question 4

Clinical signs and symptoms in tetanus are a result of

Accepted Answer

Exotoxins fixed to nerve endings

Answer

Circulating exotoxins

Answer

Endotoxins

Answer

Both endotoxins and exotoxins

Question 5

Which one of the following organisms is not associated with synergistic gangrene?

Accepted Answer

Escherichia

Answer

Staphylococcus

Answer

Clostridium

Answer

Peptostreptococcus

Question 6

Donovan bodies are associated with :

Accepted Answer

Granuloma inguinale

Answer

Gonorrhoea

Answer

Chlamydia trachomatis infection

Answer

Herpes genitalis

Question 7

The pathogenic organism responsible for the causation of Donovaniasis is

Accepted Answer

Klebsiella granulomatis

Answer

Herpes simplex virus

Answer

Haemophilus ducreyi

Answer

Chlamydia trachomatis

Question 8

All of the following organisms are involved in post-splenectomy sepsis except

Accepted Answer

Staphylococcus aureus

Answer

Neisseria meningitidis

Answer

Haemophilus influenzae

Answer

Streptococcus pneumoniae

Question 9

The causative organism of Chancroid is

Accepted Answer

Haemophilus ducreyi

Answer

Chlamydia trachomatis

Answer

Klebsiella granulomatis

Answer

Psittacosis lymphogranuloma group

Question 10

Which of the following cause/causes bacterial vaginosis?

1. Gardnerella
2. Mycoplasma hominis
3. Ureaplasma urealyticum

Select the correct answer using the code given below:

Accepted Answer

1, 2 and 3

Answer

1 and 3 only

Answer

2 and 3 only

Answer

1 only

Bacteriology — MCQs

Bacteriology — MCQs

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