Bacteriology — MCQs

Bacteriology Indian Medical PG Practice Questions and MCQs

Question 2161: Scarlet fever is caused by?

A. Proteus
B. Klebsiella
C. Streptococci (Correct Answer)
D. Staphylococcus

Explanation: ***Streptococci*** - **Scarlet fever** is caused by **Group A Streptococcus (GAS)**, specifically *Streptococcus pyogenes*. - This bacterium produces **pyrogenic exotoxins** (also known as streptococcal superantigens) that are responsible for the characteristic rash and other systemic symptoms of scarlet fever. *Proteus* - *Proteus* species are commonly associated with **urinary tract infections** and wound infections, not scarlet fever. - They are known for their characteristic "swarming" motility on agar. *Klebsiella* - *Klebsiella* species, particularly *Klebsiella pneumoniae*, are important causes of **pneumonia**, **urinary tract infections**, and **sepsis**. - They are encapsulated, gram-negative rods, distinct from the gram-positive cocci that cause scarlet fever. *Staphylococcus* - **Staphylococci**, such as *Staphylococcus aureus*, cause a variety of infections, including **skin infections** (e.g., impetigo, folliculitis), **food poisoning**, and **toxic shock syndrome**. - While they can produce toxins, the clinical presentation and specific toxins responsible for scarlet fever are distinct and caused by streptococci.

Question 2162: Which of the following is a superantigen?

A. Clostridium difficile toxin
B. Cholera toxin
C. Exfoliative toxin of Staph. aureus
D. Staphylococcal toxic shock syndrome toxin (Correct Answer)

Explanation: ***Staphylococcal toxic shock syndrome toxin*** - The **Staphylococcal toxic shock syndrome toxin (TSST-1)** is a classic example of a **superantigen**. - **TSST-1** binds directly to the MHC class II molecules on antigen-presenting cells and the Vβ region of T-cell receptors, leading to massive, non-specific T-cell activation and a cytokine storm. - Other staphylococcal superantigens include enterotoxins and exfoliative toxins. *Clostridium difficile toxin* - *Clostridium difficile* produces **toxins A and B**, which are **enterotoxins** and **cytotoxins**, respectively, leading to pseudomembranous colitis. - These toxins primarily target intestinal epithelial cells, causing inflammation and fluid secretion, and do not act as superantigens. *Cholera toxin* - **Cholera toxin** is an **AB5 exotoxin** produced by *Vibrio cholerae*, which activates adenylate cyclase in intestinal cells. - This leads to increased cAMP levels, excessive fluid and electrolyte secretion, and severe watery diarrhea, but it does not function as a superantigen. *Exfoliative toxin of Staph. aureus* - **Exfoliative toxins (ETA and ETB)** produced by *Staphylococcus aureus* cause staphylococcal scalded skin syndrome (SSSS). - While these toxins can act as superantigens, they are primarily proteases that cleave desmoglein-1 in the epidermis. - In this question, TSST-1 is the more characteristic and well-established superantigen among the options listed.

Question 2163: Chlamydia trachomatis serovars D-K cause-

A. Lymphogranuloma venereum
B. Trachoma
C. Urethritis (Correct Answer)
D. Arteriosclerosis

Explanation: ***Urethritis*** - **Chlamydia trachomatis serovars D-K** are the most common cause of **nongonococcal urethritis** in males and cervicitis in females. - These serovars infect the **epithelial cells** of the genital tract, leading to inflammation and symptoms such as dysuria and discharge. *Lymphogranuloma venereum* - This condition is caused by **Chlamydia trachomatis serovars L1, L2, and L3**, not serovars D-K. - LGV is characterized by invasive infection involving the **regional lymph nodes**, leading to painful lymphadenopathy, proctitis, or genital ulcers. *Trachoma* - **Trachoma** is caused by **Chlamydia trachomatis serovars A, B, Ba, and C**, not the D-K serovars. - It is a chronic follicular conjunctivitis that can lead to scarring and blindness, primarily affecting the eyes. *Arteriosclerosis* - **Arteriosclerosis** is a condition involving the hardening and narrowing of arteries, primarily linked to factors like **dyslipidemia, hypertension, and diabetes**. - There is currently no direct evidence to suggest that Chlamydia trachomatis, particularly serovars D-K, is a primary or significant cause of arteriosclerosis.

Question 2164: Undulant fever is caused by -

A. Bartonella
B. Bordetella
C. Brucella melitensis (Correct Answer)
D. Borrelia recurrentis

Explanation: ***Brucella melitensis*** - **Brucellosis** is characterized by an **undulant fever**, meaning the fever waxes and wanes over days or weeks, giving it a wave-like pattern. - *Brucella melitensis* is one of the most common species causing human brucellosis, typically acquired through contact with infected animals or contaminated animal products like unpasteurized milk. *Bordetella* - *Bordetella pertussis* causes **whooping cough**, a severe respiratory infection characterized by paroxysmal cough followed by an inspiratory "whoop." - While it causes fever, it does not typically present with the classic undulant fever pattern seen in brucellosis. *Bartonella* - *Bartonella* species can cause various diseases, such as **cat scratch disease** (*Bartonella henselae*), trench fever (*Bartonella quintana*), and Carrion's disease (*Bartonella bacilliformis*). - These infections can present with fever but do not specifically cause an "undulant fever" pattern. *Borrelia recurrentis* - *Borrelia recurrentis* is a spirochete that causes **louse-borne relapsing fever**, characterized by recurrent episodes of high fever separated by afebrile periods. - While it causes episodic fever, the pattern is one of distinct relapses rather than the continuous, undulating pattern of brucellosis.

Question 2165: Trench fever is caused by which of the following organisms?

A. Borrelia recurrentis
B. Tunga penetrans
C. Rickettsia prowazekii
D. Bartonella quintana (Correct Answer)

Explanation: ***Bartonella quintana*** - **Trench fever**, also known as **Wolhynian fever** or quintan fever, is caused by *Bartonella quintana* (formerly *Rickettsia quintana*). - It is a **louse-borne illness** characterized by recurrent fevers, headache, and bone pain, especially in the shins. - The organism was reclassified from Rickettsia to Bartonella based on molecular and phylogenetic studies. *Borrelia recurrentis* - This bacterium is the causative agent of **epidemic relapsing fever**, also transmitted by body lice. - While it causes relapsing fevers, its clinical presentation and causative organism are distinct from trench fever. *Tunga penetrans* - This is a species of **flea** commonly known as the **jigger flea** or sand flea. - It causes a parasitic skin infection called **tungiasis**, characterized by intense itching and inflammation, and is not associated with trench fever. *Rickettsia prowazekii* - This bacterium is the etiologic agent of **epidemic typhus**, also a louse-borne disease. - While *Rickettsia prowazekii* causes a severe febrile illness, it presents differently from trench fever with symptoms like a characteristic rash and neurological complications.

Question 2166: Noguchi's medium is used for

A. Bacillus
B. Klebsiella
C. Spirochetes (Correct Answer)
D. Salmonella

Explanation: ***Spirochetes*** - **Noguchi's media** was historically used for the cultivation of certain **fastidious spirochetes**, particularly *Treponema pallidum* (the causative agent of syphilis) and *Leptospira* species. - This specialized medium contains **serum** and **tissue extracts**, fulfilling the complex nutritional requirements of these delicate microorganisms. *Bacillus* - **Bacillus** species are typically **aerobic or facultative anaerobic** bacteria that can be easily cultured on standard laboratory media like **nutrient agar** or **blood agar**. - They do not require the specialized components found in Noguchi's media for growth. *Klebsiella* - **Klebsiella** species are **Gram-negative bacilli** that are relatively easy to grow and are commonly cultured on general-purpose media such as **MacConkey agar** or **blood agar**. - They do not need the enriched and anaerobic conditions provided by Noguchi's media. *Salmonella* - **Salmonella** species are **Gram-negative rods** that are typically grown on selective and differential media like **Xylose Lysine Deoxycholate (XLD) agar**, **Hektoen enteric agar**, or **MacConkey agar**. - These organisms do not require the specific media components or conditions found in Noguchi's formulation.

Question 2167: Osteomyelitis of spine is caused by the most common organism?

A. Streptococcus
B. Pseudomonas
C. Mycobacterium tuberculosis
D. Staphylococcus aureus (Correct Answer)

Explanation: ***Staphylococcus aureus*** - **_Staphylococcus aureus_** is the most common causative organism for **hematogenous osteomyelitis** in adults, including osteomyelitis of the spine. - It frequently gains access to bone through the bloodstream, leading to infection of the vertebral bodies. *Streptococcus* - While various species of **_Streptococcus_** can cause bone infections, they are **less common** than **_Staphylococcus aureus_** in vertebral osteomyelitis. - **Group A Streptococcus** primarily causes soft tissue infections, and **_S. pneumoniae_** is more associated with pneumonia and meningitis. *Pseudomonas* - **_Pseudomonas aeruginosa_** is a common cause of osteomyelitis, particularly in specific risk groups such as intravenous drug users, patients with puncture wounds (especially through footwear), or those with implanted medical devices. - It is **not the most common** overall cause of general osteomyelitis of the spine. *Mycobacterium tuberculosis* - **_Mycobacterium tuberculosis_** causes tuberculous spondylitis **(Pott's disease)**, which commonly affects the spine, leading to characteristic vertebral destruction and kyphosis. - While significant globally, it is **not the most common bacterial cause** of acute pyogenic vertebral osteomyelitis.

Question 2168: All of the following species of Borrelia are associated with tick-borne relapsing fever, except:

A. Borrelia hermsii
B. Borrelia turicatae
C. Borrelia duttoni
D. Borrelia recurrentis (Correct Answer)

Explanation: ***Borrelia recurrentis*** - This species is primarily associated with **louse-borne relapsing fever**, not tick-borne. - *Borrelia recurrentis* is transmitted by the human body louse (*Pediculus humanus humanus*). - It causes **epidemic relapsing fever**, particularly in conditions of overcrowding and poor hygiene. *Borrelia hermsii* - This is a well-known species that causes **tick-borne relapsing fever** in North America, transmitted by *Ornithodoros* ticks. - It is associated with **endemic outbreaks** of relapsing fever in specific geographic regions. *Borrelia turicatae* - This species is also a cause of **tick-borne relapsing fever** in North America, endemic to the southern United States. - It is transmitted by the soft tick *Ornithodoros turicata*. *Borrelia duttoni* - This species is a primary cause of **tick-borne relapsing fever** in Africa, primarily transmitted by *Ornithodoros moubata*. - It leads to cycles of fever and remission characteristic of relapsing fever.

Question 2169: Endemic typhus cause and vector are

A. R. prowazki and louse
B. R. akari and mite
C. R. conori and tick
D. R. typhi and Rat flea (Correct Answer)

Explanation: ***R. typhi and Rat flea*** - **Endemic typhus**, also known as **murine typhus**, is caused by the bacterium **_Rickettsia typhi_**. - The **vector** for _R. typhi_ is the **rat flea** (_Xenopsylla cheopis_), which transmits the disease to humans through infected flea feces. - **Rats** serve as the natural **reservoir**, but the actual transmission vector is the flea that infests these rodents. - Humans become infected when flea feces contaminated with _R. typhi_ are rubbed into the bite wound or other skin breaks. *R. prowazekii and louse* - **_Rickettsia prowazekii_** is the causative agent of **epidemic typhus**, which is transmitted by the **human body louse** (_Pediculus humanus corporis_). - This form of typhus is typically associated with crowded, unsanitary conditions and can cause severe outbreaks. *R. akari and mite* - **_Rickettsia akari_** is the cause of **rickettsialpox**, which is transmitted by **mites** (_Liponyssoides sanguineus_) from **house mice**. - This disease presents with a characteristic eschar at the bite site followed by a papulovesicular rash. *R. conorii and tick* - **_Rickettsia conorii_** is the causative agent of **Mediterranean spotted fever** (boutonneuse fever), which is transmitted by **dog ticks** (_Rhipicephalus sanguineus_). - This disease typically presents with a fever, rash, and an eschar (tache noire) at the site of the tick bite.

Question 2170: The following pathogen does not satisfy 'Koch's postulates'-

A. Clostridium tetani
B. Lepra bacilli (Correct Answer)
C. Mycobacterium tuberculosis
D. Bacillus anthracis

Explanation: ***Lepra bacilli*** - *Mycobacterium leprae* cannot be **cultured in vitro** on artificial media, failing the third postulate of growing the pathogen in pure culture. - Ethical considerations and the long **incubation period** of leprosy also make experimental infection of healthy hosts problematic. *Clostridium tetani* - This bacterium can be successfully **isolated** and **cultured in vitro**, and inoculation into susceptible animals reproduces tetanus. - *C. tetani* generally satisfies Koch's postulates, as its **toxin production** directly causes the disease. *Mycobacterium tuberculosis* - *Mycobacterium tuberculosis* can be **isolated in pure culture** and causes tuberculosis when inoculated into susceptible animals. - It largely fulfills Koch's postulates, confirming its role as the causative agent of **tuberculosis**. *Bacillus anthracis* - **Robert Koch** himself used *Bacillus anthracis* to demonstrate his postulates, confirming it as the causative agent of anthrax. - It can be **isolated**, **cultured**, and used to **reproduce the disease** experimentally in animals.

Practice by Chapter

Staphylococci

Practice Questions

Streptococci and Enterococci

Practice Questions

Neisseria and Moraxella

Practice Questions

Corynebacterium and Listeria

Practice Questions

Bacillus and Clostridium

Practice Questions

Enterobacteriaceae

Practice Questions

Vibrio, Aeromonas, and Plesiomonas

Practice Questions

Pseudomonas and Related Bacteria

Practice Questions

Haemophilus and HACEK Group

Practice Questions

Bordetella and Brucella

Practice Questions

Mycobacteria

Practice Questions

Spirochetes

Practice Questions

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free