Bacteriology Practice Questions

Q: In a 6 months old baby, floppy infant syndrome is seen commonly due to infection with ?

Clostridium Botulinum. ***Clostridium Botulinum*** - **Infant botulism** is caused by the ingestion of **_Clostridium botulinum_ spores**, which colonize the infant's immature gut and produce neurotoxins. - The classic presentation is **floppy infant syndrome**, characterized by **hypotonia**, **weakness**, feeding difficulties, and constipation. *Clostridium welchii* - This is an outdated name for **_Clostridium perfringens_**, which is primarily associated with **food poisoning** and **gas gangrene**. - It does not cause floppy infant syndrome. *Clostridium septicum* - **_Clostridium septicum_** is known to cause **spontaneous gas gangrene** and is often associated with neutropenic enterocolitis (typhlitis). - It is not a cause of floppy infant syndrome. *Clostridium tetani* - **_Clostridium tetani_** produces **tetanospasmin**, a neurotoxin that causes **tetanus**, characterized by muscle spasms and rigidity (lockjaw). - It does not cause the flaccid paralysis seen in floppy infant syndrome.

Q: "Chancroid" is caused by:

H. ducreyi. ***H. ducreyi*** - **Chancroid** is a sexually transmitted infection characterized by painful genital ulcers and is specifically caused by the bacterium **_Haemophilus ducreyi_**. - This organism creates soft chancres (ulcers) that often bleed easily and are frequently accompanied by painful swelling of the lymph nodes in the groin. *H. influenzae* - **_Haemophilus influenzae_** is a common cause of respiratory tract infections, such as otitis media, sinusitis, and pneumonia, and can also lead to meningitis. - It is not associated with sexually transmitted infections or genital ulcers, and therefore does not cause chancroid. *H. aprophilus* - **_Haemophilus aphrophilus_** (now reclassified as _Aggregatibacter aphrophilus_) is a rare cause of human infections, primarily associated with endocarditis and brain abscesses. - This bacterium is part of the **HACEK group** of gram-negative bacteria known to cause infective endocarditis and is not involved in chancroid. *All of the options* - While all listed organisms are types of _Haemophilus_ or former _Haemophilus_ species, only **_H. ducreyi_** specifically causes chancroid. - The other options are responsible for different types of infections and do not cause genital ulcers characteristic of chancroid.

Q: Salmonella typhi is the causative agent of typhoid fever. The infective dose of S. typhi is -

10^2-10^5 bacilli. ***10^2-10^5 bacilli*** - The infective dose of **Salmonella typhi** is relatively low compared to other enteric pathogens, typically ranging from **100 to 100,000 bacteria**. - This low infective dose contributes to its high transmissibility and ability to cause widespread outbreaks. *10^8-10^10 bacilli* - This range represents a significantly **higher infective dose**, which is characteristic of some less virulent or more easily cleared enteric bacteria. - If **Salmonella typhi** required such a high dose, typhoid fever would be a much rarer disease. *1-10 bacilli* - An infective dose this low is characteristic of highly pathogenic organisms with extreme virulence or unique immune evasion mechanisms, such as **Shigella**. - While **Salmonella typhi** is virulent, its infective dose is not typically in this single-digit range. *One bacillus* - It is highly improbable for a single bacterium to consistently establish infection and cause a systemic disease like typhoid fever, even for highly virulent pathogens. - Effective infection usually requires a minimum threshold of bacteria to overcome host defenses and replicate.

Q: Refrigerated blood stored up to 48 hours before transfusion can destroy which of the following ?

Treponema pallidum. ***Treponema pallidum*** - *Treponema pallidum*, the causative agent of **syphilis**, is highly sensitive to cold temperatures and **does not survive well in refrigerated blood** stored for more than a few days (typically 24-48 hours). - This characteristic makes the risk of **transfusion-transmitted syphilis** extremely low for stored blood components. *Hepatitis B* - **Hepatitis B virus (HBV)** is very hardy and can survive for extended periods, even in refrigerated blood. - Blood donations are routinely screened for HBV to prevent **transfusion-associated hepatitis**. *P. Vivax* - *Plasmodium vivax*, one of the species causing **malaria**, can survive in refrigerated blood, as the parasites can remain viable within red blood cells [1]. - Transmission of malaria through blood transfusion is a known risk, especially in endemic areas, and is not mitigated by refrigeration alone. *HIV* - **Human Immunodeficiency Virus (HIV)** can survive in refrigerated whole blood and blood components for the duration of their typical storage periods. - Therefore, strict screening of blood donors for HIV antibodies and antigens is crucial to prevent **transfusion-related HIV transmission**. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, pp. 398-400.

Q: Xanthogranulomatous pyelonephritis is most characteristically associated with:

Proteus. ***Proteus*** - **Proteus mirabilis** is most characteristically associated with xanthogranulomatous pyelonephritis due to its ability to produce **urease**, which hydrolyzes urea to ammonia and carbon dioxide. - This leads to the formation of **struvite stones (magnesium ammonium phosphate)**, causing chronic obstruction and infection, which are key predisposing factors for XGPN. - The classic presentation involves **staghorn calculi** with Proteus infection. *E. coli* - While **E. coli** is the most frequently isolated organism in XGPN cases (found in up to 50% of cases), it is not as specifically associated with the characteristic pathophysiology. - E. coli is the most common cause of uncomplicated UTIs and acute pyelonephritis but lacks the urease production that drives struvite stone formation. *Pseudomonas* - **Pseudomonas aeruginosa** can cause severe and complicated UTIs, especially in catheterized or immunocompromised patients. - However, it is **not typically associated** with the urease activity and struvite stone formation that are hallmark features predisposing to XGPN. *Klebsiella* - **Klebsiella pneumoniae** can cause UTIs and may produce urease, leading to stone formation. - While it can be a cause of pyelonephritis, **Proteus species** are more consistently and strongly associated with the specific pathogenesis that characterizes XGPN.

Q: "School of fish" appearance with bipolar staining is characteristically shown by?

Hemophilus ducreyi. ***Hemophilus ducreyi*** - This bacterium, the causative agent of **chancroid**, classically exhibits a **"school of fish" appearance** with prominent **bipolar staining** when viewed on Gram stain. - The organisms appear as pleomorphic Gram-negative coccobacilli arranged in chains or groups, with bipolar staining giving each bacterium a characteristic appearance. - Identification is typically done through **Gram stain** of a sample from the ulcer base, revealing this distinctive morphology. *Chlamydia* - **Chlamydia trachomatis** is an obligate intracellular bacterium and does not display this morphology; it appears as elementary or reticulate bodies within host cells. - It is known for causing sexually transmitted infections such as **chlamydia** and **lymphogranuloma venereum**. - Cannot be visualized by standard Gram staining. *Donovani granulomatis* - This bacterium, now reclassified as **Klebsiella granulomatis**, causes **granuloma inguinale (donovanosis)** and is characterized by the presence of **Donovan bodies** within macrophages. - Donovan bodies are encapsulated rod-shaped bacteria with a characteristic "closed safety pin" appearance found in the cytoplasm of host cells. - Does not show the "school of fish" arrangement. *Mycoplasma* - **Mycoplasma** species are the smallest free-living bacteria lacking a cell wall, which gives them a pleomorphic (variable) shape. - They do not exhibit bipolar staining or the "school of fish" appearance and cannot be visualized by Gram stain. - Associated with conditions like **atypical pneumonia** and **urethritis**.

Q: Following acute pharyngitis, a patient was on broad spectrum antibiotics. One week later he developed watery diarrhoea with a foul odour and abdominal cramps. Antibiotic induced colitis is confirmed. What is the most common cause of antibiotic induced colitis?

Clostridium difficile. ***Clostridium difficile*** - **Clostridium difficile** infection is the most common cause of **antibiotic-induced colitis** [1], leading to symptoms like **watery diarrhea, foul odor**, and **abdominal cramps** [1]. - Antibiotics disrupt the normal gut flora, allowing **C. difficile** to overgrow and produce toxins that damage the colon [1]. *Esch. coli* - While some strains of *E. coli* can cause **diarrhea** (e.g., ETEC, EHEC), it is not the primary cause of antibiotic-induced colitis [2]. - **Esch. coli** diarrhea is typically acquired through contaminated food or water, not antibiotic use [2]. *Campylobacter jejuni* - *Campylobacter jejuni* typically causes **gastroenteritis** with **bloody diarrhea** and **fever**, often from consuming contaminated poultry. - It is not directly associated with **antibiotic-induced colitis** as the primary causative agent. *Salmonella* - **Salmonella** infections usually result from contaminated food and present with **fever, abdominal cramps**, and **diarrhea** (which can be bloody). - It is not the most common pathogen responsible for **antibiotic-induced colitis**.

Q: Ludwig angina is usually caused by

Streptococci and various mixed anaerobes. ***Streptococci and various mixed anaerobes*** - **Ludwig angina** is a rapidly progressive **cellulitis** of the submandibular and sublingual spaces, predominantly caused by bacteria from the oral flora. - The most common pathogens include **alpha-hemolytic streptococci**, along with various **anaerobes** such as *Bacteroides*, *Peptostreptococcus*, and *Fusobacterium* species, reflecting the polymicrobial nature of dental infections that often precede it. *Anaerobic infection by Prevotella and Fusobacterium* - While *Prevotella* and *Fusobacterium* are important **anaerobic components** of the oral flora and can contribute to Ludwig angina, this option is too restrictive. - It omits the crucial role of **aerobic streptococci** which are frequently isolated alongside anaerobes in this infection. *Paramyxovirus* - **Paramyxoviruses** are a family of RNA viruses that cause diseases such as **mumps**, measles, and respiratory syncytial virus infection. - They are responsible for **viral infections** and do not cause bacterial cellulitis like Ludwig angina. *Candida species* - **Candida species** are yeasts that typically cause **fungal infections**, such as oral thrush or systemic candidiasis. - They are generally not primary causative agents of **bacterial cellulitis** such or severe deep neck infections like Ludwig angina.

Q: A 44-year-old female presented to OPD with complaints of pallor, fatigue, weakness, palpitations and dyspnea on exeion. Blood tests were conducted, which revealed, Anemia Thrombocytopenia Leukocytosis with neutropenia and increased blasts in the peripheral blood smear. Peripheral blood smear The patient was diagnosed with leukemia and she underwent allogenic stem cell transplantation for the same. After 24 days, she again presented with hypotension, tachycardia, and spO2 of 88% along with a new rash from which biopsy was taken and silver staining was done. Lab findings revealed severe Neutropenia. Which is the most likely organism causing the above skin condition: -

Pseudomonas. ***Pseudomonas*** - The clinical presentation of **neutropenia**, fever, and a rapidly progressive skin rash after stem cell transplantation is highly suggestive of **ecthyma gangrenosum**, a severe cutaneous infection typically caused by *Pseudomonas aeruginosa*. - **Silver staining** in a biopsy would highlight bacteria, and *Pseudomonas* is a common cause of severe infections in immunocompromised patients, especially those with **neutropenia**. *Neisseria meningitidis* - While *Neisseria meningitidis* can cause rash (e.g., **petechial or purpuric rash** in meningitis), it is less likely to present as a focal, rapidly necrotic skin lesion like ecthyma gangrenosum, especially in the context of profound neutropenia post-transplant without overt signs of meningococcal disease. - The rash associated with meningococcemia is typically due to **vasculitis and thrombosis**, not direct bacterial colonization leading to necrotic lesions in the same way *Pseudomonas* does. *Staphylococcus aureus* - *Staphylococcus aureus* can cause various skin infections, including **cellulitis, abscesses, or impetigo**, but ecthyma gangrenosum is not its typical presentation. - While *S. aureus* is a significant pathogen in immunocompromised patients, the constellation of severe neutropenia and a rapidly progressive, necrotic skin lesion characteristic of ecthyma gangrenosum points more strongly to *Pseudomonas*. *Vibrio vulnificus* - *Vibrio vulnificus* causes severe skin infections, particularly in individuals with **liver disease** or those exposed to **contaminated seawater** or raw seafood. - This patient's history of leukemia and stem cell transplantation, without mention of relevant exposures, makes *Vibrio vulnificus* a less likely pathogen in this scenario.

Q: Which one of the following gram-positive organisms is the most common cause of UTI among sexually active women?

Staphylococcus saprophyticus. ***Staphylococcus saprophyticus*** - This organism is a common cause of **urinary tract infections (UTIs)**, particularly in sexually active young women. - It is known for its ability to adhere to uroepithelial cells and is **novobiocin-resistant**, distinguishing it from other coagulase-negative staphylococci. *Staphylococcus aureus* - While *Staphylococcus aureus* can cause UTIs, it's typically associated with **catheter-associated infections** or hematogenous spread, not primarily UTIs in sexually active women. - It is a **coagulase-positive** staphylococcus and often linked to more severe infections. *Enterococcus* - **Enterococci**, such as *Enterococcus faecalis*, are a common cause of UTIs, especially in hospitalized patients or those with urinary tract abnormalities. - However, they are less frequently the primary cause in otherwise healthy, sexually active women compared to *S. saprophyticus*. *Staphylococcus epidermidis* - *Staphylococcus epidermidis* is part of the normal skin flora and is a common **contaminant** in urine cultures. - It infrequently causes true UTIs and is generally only pathogenic in immunocompromised individuals or those with **indwelling medical devices**.

Question 1

In a 6 months old baby, floppy infant syndrome is seen commonly due to infection with ?

Accepted Answer

Clostridium Botulinum

Answer

Clostridium welchii

Answer

Clostridium septicum

Answer

Clostridium tetani

Question 2

"Chancroid" is caused by:

Accepted Answer

H. ducreyi

Answer

H. influenzae

Answer

All of the options

Answer

H. aphrophilus

Question 3

Salmonella typhi is the causative agent of typhoid fever. The infective dose of S. typhi is -

Accepted Answer

10^2-10^5 bacilli

Answer

10^8-10^10 bacilli

Answer

1-10 bacilli

Answer

One bacillus

Question 4

Refrigerated blood stored up to 48 hours before transfusion can destroy which of the following ?

Accepted Answer

Treponema pallidum

Answer

Hepatitis B

Answer

P. Vivax

Answer

HIV

Question 5

Xanthogranulomatous pyelonephritis is most characteristically associated with:

Accepted Answer

Proteus

Answer

E. coli

Answer

Pseudomonas

Answer

Klebsiella

Question 6

"School of fish" appearance with bipolar staining is characteristically shown by?

Accepted Answer

Hemophilus ducreyi

Answer

Chlamydia

Answer

Donovani granulomatis

Answer

Mycoplasma

Question 7

Following acute pharyngitis, a patient was on broad spectrum antibiotics. One week later he developed watery diarrhoea with a foul odour and abdominal cramps. Antibiotic induced colitis is confirmed. What is the most common cause of antibiotic induced colitis?

Accepted Answer

Clostridium difficile

Answer

Esch. coli

Answer

Campylobacter jejuni

Answer

Salmonella

Question 8

Ludwig angina is usually caused by

Accepted Answer

Streptococci and various mixed anaerobes

Answer

Anaerobic infection by Prevotella and Fusobacterium

Answer

Paramyxovirus

Answer

Candida species

Question 9

A 44-year-old female presented to OPD with complaints of pallor, fatigue, weakness, palpitations and dyspnea on exeion. Blood tests were conducted, which revealed, Anemia Thrombocytopenia Leukocytosis with neutropenia and increased blasts in the peripheral blood smear. Peripheral blood smear The patient was diagnosed with leukemia and she underwent allogenic stem cell transplantation for the same. After 24 days, she again presented with hypotension, tachycardia, and spO2 of 88% along with a new rash from which biopsy was taken and silver staining was done. Lab findings revealed severe Neutropenia. Which is the most likely organism causing the above skin condition: -

Accepted Answer

Pseudomonas

Answer

Neisseria meningitidis

Answer

Staphylococcus aureus

Answer

Vibrio vulnificus

Question 10

Which one of the following gram-positive organisms is the most common cause of UTI among sexually active women?

Accepted Answer

Staphylococcus saprophyticus

Answer

Staphylococcus aureus

Answer

Enterococcus

Answer

Staphylococcus epidermidis

Bacteriology — MCQs

Bacteriology — MCQs

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