Bacteriology Practice Questions

Q: Scarlet fever is caused by?

Streptococci. ***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.

Q: Which of the following is a superantigen?

Staphylococcal toxic shock syndrome toxin. ***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.

Q: Chlamydia trachomatis serovars D-K cause-

Urethritis. ***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.

Q: Undulant fever is caused by -

Brucella melitensis. ***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.

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

Bartonella quintana. ***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.

Q: Noguchi's medium is used for

Spirochetes. ***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.

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

Staphylococcus aureus. ***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.

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

Borrelia recurrentis. ***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.

Q: Endemic typhus cause and vector are

R. typhi and Rat flea. ***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.

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

Lepra bacilli. ***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.

Question 1

Scarlet fever is caused by?

Accepted Answer

Streptococci

Answer

Proteus

Answer

Klebsiella

Answer

Staphylococcus

Question 2

Which of the following is a superantigen?

Accepted Answer

Staphylococcal toxic shock syndrome toxin

Answer

Clostridium difficile toxin

Answer

Cholera toxin

Answer

Exfoliative toxin of Staph. aureus

Question 3

Chlamydia trachomatis serovars D-K cause-

Accepted Answer

Urethritis

Answer

Lymphogranuloma venereum

Answer

Trachoma

Answer

Arteriosclerosis

Question 4

Undulant fever is caused by -

Accepted Answer

Brucella melitensis

Answer

Bartonella

Answer

Bordetella

Answer

Borrelia recurrentis

Question 5

Trench fever is caused by which of the following organisms?

Accepted Answer

Bartonella quintana

Answer

Borrelia recurrentis

Answer

Tunga penetrans

Answer

Rickettsia prowazekii

Question 6

Noguchi's medium is used for

Accepted Answer

Spirochetes

Answer

Bacillus

Answer

Klebsiella

Answer

Salmonella

Question 7

Osteomyelitis of spine is caused by the most common organism?

Accepted Answer

Staphylococcus aureus

Answer

Streptococcus

Answer

Pseudomonas

Answer

Mycobacterium tuberculosis

Question 8

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

Accepted Answer

Borrelia recurrentis

Answer

Borrelia hermsii

Answer

Borrelia turicatae

Answer

Borrelia duttoni

Question 9

Endemic typhus cause and vector are

Accepted Answer

R. typhi and Rat flea

Answer

R. prowazki and louse

Answer

R. akari and mite

Answer

R. conori and tick

Question 10

The following pathogen does not satisfy 'Koch's postulates'-

Accepted Answer

Lepra bacilli

Answer

Clostridium tetani

Answer

Mycobacterium tuberculosis

Answer

Bacillus anthracis

Bacteriology — MCQs

Bacteriology — MCQs

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