Bacteriology Practice Questions

Q: A 17 year old adolescent, presented with fever since one week which is step-ladder in pattern. He also has loose stools which are "pea-soup" in consistency. Rose spots are seen on his body. He is most probably infected with:

Salmonella typhi. ***Salmonella typhi*** - The combination of **step-ladder fever**, **"pea-soup" diarrhea**, and **rose spots** is a classic presentation of **typhoid fever**, caused by *Salmonella typhi* [1]. - This bacterial infection predominantly affects the gastrointestinal tract and can lead to systemic symptoms [1]. *Adenovirus* - **Adenovirus** typically causes **respiratory tract infections**, **conjunctivitis**, or **gastroenteritis**, but not with the specific symptom profile of step-ladder fever or rose spots. - While it can cause diarrhea, it's usually not described as "pea-soup" and lacks the other systemic features. *Rotavirus* - **Rotavirus** is a common cause of **severe gastroenteritis** in infants and young children, characterized by **watery diarrhea** and vomiting. - It does not present with step-ladder fever or rose spots, which are pathognomonic for typhoid. *Vibrio cholerae* - **Vibrio cholerae** causes **cholera**, an acute diarrheal illness characterized by **profuse watery diarrhea** (often described as "rice-water stools") and rapid dehydration. - It does not typically cause step-ladder fever or skin manifestations like rose spots.

Q: Tetanus affects primarily -

Presynaptic terminal of spinal cord. **Presynaptic terminal of spinal cord** - The **tetanus toxin (tetanospasmin)**, produced by *Clostridium tetani*, acts on the **presynaptic terminals** of inhibitory interneurons in the spinal cord. - It **blocks the release of inhibitory neurotransmitters** like glycine and GABA, leading to uncontrolled muscle spasms and rigidity. *Neuromuscular junction* - While muscles are the target of tetanus symptoms, the primary action of the toxin is not directly at the neuromuscular junction to affect acetylcholine release or receptor function. - Diseases like **myasthenia gravis** or **Lambert-Eaton myasthenic syndrome** primarily affect the neuromuscular junction. *Muscle fibres* - The tetanus toxin does not directly damage or alter the contractile properties of **muscle fibers** themselves. - Muscle pathology in tetanus is secondary to continuous, uncontrolled contraction due to nerve dysfunction. *Postsynaptic terminal of spinal cord* - The toxin's primary effect is on the **presynaptic release** of neurotransmitters, not on the postsynaptic receptors of spinal cord neurons. - Conditions affecting postsynaptic terminals in the spinal cord would involve issues with neurotransmitter reception or integration.

Q: Most common cause of bacterial diarrhea in children of developing countries is:

ETEC. ***ETEC*** - **Enterotoxigenic E. coli (ETEC)** is the most common cause of **bacterial diarrhea** in children in developing countries and a frequent cause of **traveler's diarrhea**. - It produces **heat-labile (LT)** and/or **heat-stable (ST)** toxins that stimulate fluid secretion in the small intestine, leading to watery diarrhea. *EHEC* - **Enterohemorrhagic E. coli (EHEC)**, particularly O157:H7, is primarily known for causing **hemorrhagic colitis** and **hemolytic-uremic syndrome (HUS)**, not the most common diarrhea in developing countries. - While it can cause bloody diarrhea, it is not the predominant pathogen responsible for the overall burden of diarrhea in these regions. *EIEC* - **Enteroinvasive E. coli (EIEC)** causes **dysentery-like illness** by invading and destroying the intestinal epithelial cells, similar to *Shigella*. - While it causes significant disease, it is relatively rare compared to ETEC as a cause of widespread diarrhea in developing countries. *EAEC* - **Enteroaggregative E. coli (EAEC)** is recognized as an important cause of **persistent diarrhea**, especially in children and immunocompromised individuals. - Although implicated in a significant portion of diarrheal episodes, particularly chronic ones, ETEC is still considered the leading single cause of acute sporadic diarrhea in developing countries.

Q: Pinta disease is caused by

Treponema carateum. ***Treponema carateum*** - Pinta is a **non-venereal treponematosis** caused by *Treponema carateum*, primarily affecting the skin. - The disease is characterized by changes in skin pigmentation, including **dyschromic patches**, which can be reddish, bluish, or brownish initially. - Transmitted through **direct skin contact** and endemic in Central and South America. *Leptospira interrogans* - This bacterium is responsible for **leptospirosis**, a zoonotic disease that can cause a wide range of symptoms, from mild flu-like illness to severe conditions like Weil's disease. - It primarily affects the **kidneys** and **liver**, and is not associated with skin lesions characteristic of pinta. *Treponema pallidum* - *Treponema pallidum* subspecies *pallidum* is the causative agent of **syphilis**, a sexually transmitted infection with distinct stages and diverse clinical manifestations. - While related to pinta, it has **different transmission routes** (sexual contact) and presents with chancres and systemic manifestations. *Treponema pertenue* - *Treponema pertenue* causes **yaws**, another non-venereal treponematosis. - Yaws presents with **papillomatous lesions** and bone involvement, distinct from the dyschromic skin changes seen in pinta.

Q: Which of the following about cholera is true ?

Vibriocidal antibody titre measures seroprevalence. **Vibriocidal antibody titre measures seroprevalence** - The vibriocidal antibody test measures the level of antibodies that can kill *Vibrio cholerae* bacteria in a patient's serum, indicating **prior exposure or vaccination** and thus **seroprevalence**. - These antibodies target outer membrane antigens of the bacteria and are a key component of the immune response against cholera. *Invasive* - *Vibrio cholerae* is a **non-invasive bacterium** that colonizes the small intestine but does not penetrate the intestinal mucosa or enter the bloodstream. - Its pathogenesis primarily involves the production of **cholera toxin**, which acts locally on enterocytes. *Endotoxin is released* - *Vibrio cholerae* is a **Gram-negative bacterium**, which possesses **lipopolysaccharide (LPS)** in its outer membrane, commonly referred to as endotoxin. - However, the primary virulence factor responsible for the severe diarrhea in cholera is **cholera toxin**, an exotoxin, not the direct release of endotoxin in quantities sufficient to cause systemic endotoxic shock as seen in other Gram-negative infections. *Recent infections in India are of classical type* - The classical biotype of *Vibrio cholerae* is **rarely associated with recent outbreaks** globally, including in India. - Most recent cholera epidemics and infections worldwide, including in India, are caused by the **El Tor biotype** of *Vibrio cholerae* O1.

Q: Man is the only reservoir for

Salmonella typhi. ***Salmonella typhi*** - *Salmonella typhi* (and *S. paratyphi*) are **unique among Salmonella** species in that **humans are the only natural reservoir**. - Transmission occurs through the **fecal-oral route** via contaminated food or water from infected individuals or chronic carriers. - This is in contrast to non-typhoidal Salmonella, which have extensive **animal reservoirs**. *E. histolytica* - While *Entamoeba histolytica* primarily infects **humans**, it can occasionally infect **non-human primates and dogs**. - Humans serve as the **principal reservoir**, but not the exclusive one, making this option technically incorrect. *Campylobacter jejuni* - **Poultry** (especially chickens), **cattle**, and other animals are common reservoirs for *Campylobacter jejuni*. - Humans become infected primarily through consumption of **contaminated food or water**, particularly undercooked poultry. *Y. enterocolitica* - **Pigs** are a significant reservoir for *Yersinia enterocolitica*, along with other animals like rodents and livestock. - Transmission to humans often occurs via **contaminated pork products** or unpasteurized milk.

Q: Trismus is due to infection by

Clostridium Tetani. ***Clostridium Tetani*** - **Trismus**, or **lockjaw**, is a hallmark symptom of **tetanus**, caused by the neurotoxin **tetanospasmin** produced by **Clostridium tetani**. - The toxin blocks inhibitory neurotransmitters, leading to uncontrolled muscle spasms, particularly in the jaw muscles. *Staphylococci* - **Staphylococci** are common causes of skin infections, abscesses, and some systemic infections, but they **do not produce neurotoxins** that cause trismus. - Infections by *Staphylococci* typically manifest as localized infections or **sepsis**, not muscle spasms like lockjaw. *Streptococci* - **Streptococci** cause a wide range of infections including **strep throat**, **scarlet fever**, and **necrotizing fasciitis**, but they are **not associated with trismus or tetanus-like symptoms**. - Their toxins and virulence factors lead to different pathogenic mechanisms. *Diphtheria* - **Diphtheria** is caused by **Corynebacterium diphtheriae**, which produces a toxin that can lead to **pseudomembrane formation** in the throat and myocarditis or neuritis. - While diphtheria toxin can cause neurological complications (e.g., paralysis of the soft palate), it **does not specifically cause trismus**.

Q: Which of the following is an example of a nonvenereal disease –

Endemic syphilis. ***Endemic syphilis*** - **Endemic syphilis** (also known as bejel or non-venereal syphilis) is a **nonvenereal treponemal infection** that affects the skin, mucous membranes, and bones. - It is typically spread through **direct skin-to-skin contact** or shared eating utensils, particularly among children in specific endemic regions, rather than sexual contact. *Gonorrhea* - **Gonorrhea** is a **classic sexually transmitted infection (STI)** caused by the bacterium *Neisseria gonorrhoeae*. - It primarily affects the **mucous membranes** of the reproductive tract, urethra, rectum, and pharynx, and is transmitted through sexual contact. *Chancroid* - **Chancroid** is a **sexually transmitted infection (STI)** caused by the bacterium *Haemophilus ducreyi*. - It is characterized by **painful genital ulcers** and often **swollen lymph nodes** in the groin, and is spread exclusively through sexual contact. *LGV* - **LGV (lymphogranuloma venereum)** is a **sexually transmitted infection (STI)** caused by specific serovars of *Chlamydia trachomatis*. - It is characterized by **small, painless genital ulcers** followed by painful swelling of the lymph nodes in the groin, and is transmitted through sexual contact.

Q: A 45-year-old construction worker suffers a penetrating wound of the left leg, which is cleaned and sutured. Three days later, the patient presents with sudden onset of severe pain at the site of injury. Physical examination shows darkening of the surrounding skin, hemorrhage, and cutaneous necrosis. The wound shows a thick serosanguinous discharge with gas bubbles and a foul-smelling odor. Which of the following is the most likely etiology of this patient's wound infection?

Clostridium perfringens. ***Clostridium perfringens*** - The sudden onset of severe pain, **darkening of skin**, **hemorrhage**, **cutaneous necrosis**, and especially the presence of **gas bubbles** and a **fragrant odor** (often described as sweet/putrid) point directly to **gas gangrene**, caused primarily by *Clostridium perfringens*. - This bacterium is a **gram-positive, anaerobic rod** that produces powerful **exotoxins**, leading to rapid tissue destruction and gas production. *Staphylococcus epidermidis* - This bacterium is a common **commensal skin organism** and typically causes **indolent infections** associated with foreign bodies (e.g., catheters, prosthetic joints), not rapidly progressing necrosis and gas. - While it can form **biofilms**, it does not produce the extensive tissue destruction, gas, or characteristic odor seen here. *Staphylococcus aureus* - *S. aureus* causes a variety of infections, including cellulitis, abscesses, and necrotizing fasciitis, but typically does **not produce gas** in tissues or the characteristic fragrant odor. - While it can cause rapid progression and necrosis, the specific feature of **gas bubbles** strongly differentiates it from *Clostridium perfringens*. *Clostridium botulinum* - *Clostridium botulinum* causes **botulism**, a neuroparalytic disease, through its potent neurotoxin. - It does **not typically cause wound infections** with severe local tissue destruction, gas production, or a fragrant discharge.

Q: Guests at a party consumed beef broth that was boiled earlier in the day but left at room temperature for several hours. The individuals presented with symptoms of food poisoning, including watery diarrhea and abdominal cramps, 8 to 10 hours later. The symptoms lasted 24 hours. The agent that caused the symptoms is most likely which of the following?

Spore-forming gram-positive bacilli. ***Spore-forming gram-positive bacilli*** - The delayed onset (8-10 hours) of **watery diarrhea** and abdominal cramps, followed by resolution within 24 hours, is characteristic of food poisoning caused by ***Clostridium perfringens*** (a spore-forming gram-positive bacillus). - This organism thrives when food, particularly meat products like beef broth, is cooked and then left to cool slowly at **room temperature**, allowing spores to germinate and vegetative cells to produce toxins. *Gram-negative bacilli* - While some **gram-negative bacilli** (e.g., *E. coli*, *Salmonella*, *Shigella*) can cause food poisoning, the incubation period and typical symptoms often differ. - *Salmonella* and *E. coli* infections usually have a longer incubation period (12-72 hours) and might present with fever and bloody diarrhea, which are not described here. *An opportunistic fungus* - **Fungal infections** are not typically associated with acute food poisoning outbreaks characterized by rapid onset of gastrointestinal symptoms from contaminated food. - **Fungi** are more likely to cause chronic infections or toxin production (mycotoxins) that lead to different clinical pictures. *Gram-positive cocci* - **Gram-positive cocci** like *Staphylococcus aureus* can cause food poisoning, but the symptoms are typically rapid in onset (1-6 hours) due to preformed toxins, and often include vomiting in addition to diarrhea. - The 8-10 hour incubation period described is too long for the typical **staphylococcal enterotoxin**-mediated food poisoning.

Question 1

A 17 year old adolescent, presented with fever since one week which is step-ladder in pattern. He also has loose stools which are "pea-soup" in consistency. Rose spots are seen on his body. He is most probably infected with:

Accepted Answer

Salmonella typhi

Answer

Adenovirus

Answer

Rotavirus

Answer

Vibrio cholerae

Question 2

Tetanus affects primarily -

Accepted Answer

Presynaptic terminal of spinal cord

Answer

Neuromuscular junction

Answer

Muscle fibres

Answer

Postsynaptic terminal of spinal cord

Question 3

Most common cause of bacterial diarrhea in children of developing countries is:

Accepted Answer

ETEC

Answer

EHEC

Answer

EIEC

Answer

EAEC

Question 4

Pinta disease is caused by

Accepted Answer

Treponema carateum

Answer

Leptospira interrogans

Answer

Treponema pallidum

Answer

Treponema pertenue

Question 5

Which of the following about cholera is true ?

Accepted Answer

Vibriocidal antibody titre measures seroprevalence

Answer

Invasive

Answer

Endotoxin is released

Answer

Recent infections in India are of classical type

Question 6

Man is the only reservoir for

Accepted Answer

Salmonella typhi

Answer

Campylobacter jejuni

Answer

E. histolytica

Answer

Y. enterocolitica

Question 7

Trismus is due to infection by

Accepted Answer

Clostridium Tetani

Answer

Staphylococci

Answer

Streptococci

Answer

Corynebacterium diphtheriae

Question 8

Which of the following is an example of a nonvenereal disease –

Accepted Answer

Endemic syphilis

Answer

Gonorrhea

Answer

Chancroid

Answer

LGV

Question 9

A 45-year-old construction worker suffers a penetrating wound of the left leg, which is cleaned and sutured. Three days later, the patient presents with sudden onset of severe pain at the site of injury. Physical examination shows darkening of the surrounding skin, hemorrhage, and cutaneous necrosis. The wound shows a thick serosanguinous discharge with gas bubbles and a foul-smelling odor. Which of the following is the most likely etiology of this patient's wound infection?

Accepted Answer

Clostridium perfringens

Answer

Staphylococcus epidermidis

Answer

Staphylococcus aureus

Answer

Clostridium botulinum

Question 10

Guests at a party consumed beef broth that was boiled earlier in the day but left at room temperature for several hours. The individuals presented with symptoms of food poisoning, including watery diarrhea and abdominal cramps, 8 to 10 hours later. The symptoms lasted 24 hours. The agent that caused the symptoms is most likely which of the following?

Accepted Answer

Spore-forming gram-positive bacilli

Answer

Gram-negative bacilli

Answer

An opportunistic fungus

Answer

Gram-positive cocci

Bacteriology — MCQs

Bacteriology — MCQs

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