Bacteriology Practice Questions

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.

Q: HP bodies (Halberstaedter-Prowazek bodies) are seen in infections caused by which organism?

Chlamydia trachomatis. ***Chlamydia trachomatis*** - **Halberstaedter-Prowazek (HP) bodies** are distinctive **intracytoplasmic inclusions** found in the host cells infected with **Chlamydia trachomatis**. - These inclusions contain replicating **reticulate bodies** and are characteristic of this species. - A key feature is that HP bodies are **glycogen-rich** and **stain with iodine** (iodine-positive), which is a pathognomonic diagnostic feature distinguishing *C. trachomatis* from other Chlamydia species. *Chlamydia psittaci* - While *Chlamydia psittaci* also forms inclusions, they are generally **larger**, **less compact**, and **iodine-negative** (do not contain glycogen) compared to the HP bodies seen in *C. trachomatis*. - *C. psittaci* is primarily associated with **psittacosis**, a respiratory disease transmitted from birds. *Mycoplasma hominis* - *Mycoplasma* species are **wall-less bacteria** and do not form **intracytoplasmic inclusions** like Chlamydia. - They are distinct from Chlamydia in their cellular structure and life cycle. *Chlamydia pneumoniae* - *Chlamydia pneumoniae* forms **inclusions** that are **iodine-negative** (lack glycogen), **pear-shaped**, and morphologically different from the classical compact HP bodies. - This species is a common cause of **atypical pneumonia** and lacks the distinctive cytological features of *C. trachomatis* inclusions.

Q: A 20-year-old man presents with dysuria, urgency, and urethral discharge. Physical examination shows suppurative urethritis, with redness and swelling at the urethral meatus. Which of the following is the most likely etiology of urethritis in this patient?

Neisseria gonorrhoeae. ***Neisseria gonorrhoeae*** - The presentation of **dysuria, urgency, urethral discharge**, and **suppurative urethritis** (purulent discharge with redness and swelling) is highly characteristic of **gonococcal urethritis** [1]. - **Gonorrhea** is a common cause of sexually transmitted urethritis, especially with prominent inflammatory signs [1]. *Haemophilus ducreyi* - This bacterium is the causative agent of **chancroid**, which typically presents as painful genital ulcers with regional lymphadenopathy. - It does not cause urethritis with significant urethral discharge as described. *Chlamydia trachomatis* - While *Chlamydia trachomatis* is a common cause of urethritis, it typically causes **non-gonococcal urethritis (NGU)**, which is often less symptomatic and may present with a thinner, mucoid discharge [1]. - The **suppurative (purulent) nature** of the discharge described points more strongly towards gonorrhea [1]. *Ureaplasma urealyticum* - *Ureaplasma urealyticum* is a known cause of **non-chlamydial, non-gonococcal urethritis**, similarly to *Chlamydia* [1]. - However, its presentation is generally milder and less suppurative than that caused by *Neisseria gonorrhoeae* [1].

Q: Which organism causes prosthetic valve endocarditis within 60 days of surgery?

Staphylococcus epidermidis. ***Staphylococcus epidermidis*** - This organism is the **most common cause of early prosthetic valve endocarditis (within 60 days of surgery)**, accounting for 30-40% of cases. - As a coagulase-negative Staphylococcus, *S. epidermidis* commonly colonizes the skin and can be introduced during the surgical procedure. - It produces **biofilms**, which allow it to adhere to prosthetic surfaces and resist antibiotic treatment. *Staphylococcus aureus* - *Staphylococcus aureus* is the **second most common cause of early prosthetic valve endocarditis** (20-25% of cases) and can cause both early and late infections. - It typically presents with a more **fulminant, aggressive course** compared to *S. epidermidis*. - While both staphylococcal species cause early PVE, *S. epidermidis* remains more frequent. *Fungus* - **Fungal endocarditis** on prosthetic valves (typically *Candida* species) accounts for 5-10% of early PVE cases. - More commonly seen in immunocompromised patients, those with prolonged antibiotic use, or after complicated cardiac surgery. - Its incidence is significantly lower than staphylococcal causes in the early post-operative period. *Streptococcus viridans* - *Streptococcus viridans* is the **most common cause of native valve endocarditis**, particularly in patients with pre-existing valvular heart disease. - It typically causes a **subacute presentation** and is more associated with **late prosthetic valve endocarditis** (>60 days post-surgery), not early PVE. - Rarely implicated in early prosthetic valve infections.

Q: In which year was Helicobacter pylori identified?

1983. ***1983*** - **Barry Marshall** and **Robin Warren** successfully cultured *Helicobacter pylori* from stomach biopsies, challenging the long-held belief that bacteria could not survive in the acidic environment of the stomach. - Their work definitively linked the bacterium to **gastritis** and **peptic ulcers**, revolutionizing understanding and treatment of these conditions. *1976* - This year is not recognized for the identification or significant discovery of *Helicobacter pylori*. - While research into stomach health was ongoing, the specific identification of this bacterium occurred later. *1994* - By 1994, *Helicobacter pylori* was well-established as a major pathogen, and this year saw significant progress in understanding its role in **gastric cancer**, leading to its classification as a Group 1 carcinogen by the WHO. - However, its *identification* happened much earlier. *1969* - Although there were earlier observations of spiral-shaped bacteria in the stomach, particularly by **Waldo L. Stewart** in 1969, these initial findings did not lead to the successful culture and definitive identification of *Helicobacter pylori* as a pathogenic agent. - The crucial link to gastric disease was not established at this time.

Question 1

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 2

Man is the only reservoir for

Accepted Answer

Salmonella typhi

Answer

Campylobacter jejuni

Answer

E. histolytica

Answer

Y. enterocolitica

Question 3

Trismus is due to infection by

Accepted Answer

Clostridium Tetani

Answer

Staphylococci

Answer

Streptococci

Answer

Corynebacterium diphtheriae

Question 4

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

Accepted Answer

Endemic syphilis

Answer

Gonorrhea

Answer

Chancroid

Answer

LGV

Question 5

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 6

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

Question 7

HP bodies (Halberstaedter-Prowazek bodies) are seen in infections caused by which organism?

Accepted Answer

Chlamydia trachomatis

Answer

Chlamydia psittaci

Answer

Mycoplasma hominis

Answer

Chlamydia pneumoniae

Question 8

A 20-year-old man presents with dysuria, urgency, and urethral discharge. Physical examination shows suppurative urethritis, with redness and swelling at the urethral meatus. Which of the following is the most likely etiology of urethritis in this patient?

Accepted Answer

Neisseria gonorrhoeae

Answer

Haemophilus ducreyi

Answer

Chlamydia trachomatis

Answer

Ureaplasma urealyticum

Question 9

Which organism causes prosthetic valve endocarditis within 60 days of surgery?

Accepted Answer

Staphylococcus epidermidis

Answer

Staphylococcus aureus

Answer

Fungus

Answer

Streptococcus viridans

Question 10

In which year was Helicobacter pylori identified?

Accepted Answer

1983

Answer

1976

Answer

1994

Answer

1969

Bacteriology — MCQs

Bacteriology — MCQs

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