Bacteriology Practice Questions

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**.

Q: All of the following statements about Botulism are true except:

Botulism is caused by endotoxin. ***Botulism is caused by endotoxin*** - Botulism is caused by **exotoxins** produced by *Clostridium botulinum*, specifically neurotoxins, not endotoxins. - **Endotoxins** are lipopolysaccharides found in the cell walls of gram-negative bacteria, whereas botulinum toxin is a protein secreted by gram-positive *C. botulinum*. *Constipation is seen* - **Constipation** is a common symptom in both adult and infant botulism due to the neurotoxin's effect on the parasympathetic nervous system, leading to reduced gut motility. - The toxin inhibits acetylcholine release, affecting smooth muscle contraction in the GI tract. *Detection of toxin in the serum can aid in diagnosis* - The **diagnosis of botulism** can be confirmed by detecting the botulinum toxin in the patient's serum, stool, or gastric aspirate. - Identifying the toxin directly is crucial for diagnosis, especially in cases of suspected foodborne or wound botulism. *Honey ingestion causes infant botulism* - **Infant botulism** is commonly associated with the ingestion of honey, as it can contain *Clostridium botulinum* spores. - An infant's immature gut flora allows these spores to germinate and produce toxin in the intestine, leading to characteristic symptoms.

Q: In cystic fibrosis, the most common organism which causes early infection is

Staphylococcus. ***Staphylococcus*** - **Methicillin-sensitive Staphylococcus aureus (MSSA)** is the most common pathogen isolated in the lungs of young children with **cystic fibrosis** during early infection. - It can cause significant pulmonary morbidity in these patients, making its early detection and management crucial. *Streptococcus* - While *Streptococcus pneumoniae* can cause **respiratory infections**, it is not typically the most common organism associated with early colonization and infection in cystic fibrosis patients. - Early infections in CF are more often dominated by other bacterial species that thrive in the altered **mucus environment**. *Klebsiella* - **Klebsiella species** are Gram-negative bacteria that can cause **nosocomial infections** and are sometimes seen in CF, but they are not the primary cause of early-onset infections. - **Klebsiella** is more commonly associated with opportunistic infections in individuals with compromised immune systems or prolonged hospital stays rather than initial colonization in CF. *Pseudomonas* - **Pseudomonas aeruginosa** is a major pathogen in cystic fibrosis, but it typically establishes chronic infection **later in life** or after initial colonization by other bacteria. - While highly problematic due to its **biofilm formation** and resistance, it is generally preceded by *Staphylococcus aureus* in initial infections.

Q: Phagosome-lysosome fusion in TB-infected macrophages is inhibited by -

Cord factor. ***Cord factor*** - **Cord factor** (trehalose dimycolate) is a major **virulence factor** of *Mycobacterium tuberculosis* that inhibits the maturation of the phagosome and subsequent fusion with the lysosome within macrophages. - This prevents the phagocytosed bacteria from being exposed to the harsh acidic and enzymatic environment of the lysosome, allowing them to **survive and replicate intracellularly**. *Peritrichous flagella* - **Peritrichous flagella** refers to the arrangement of flagella distributed all around a bacterial cell surface, used for motility. - *Mycobacterium tuberculosis* is a **non-motile** organism that lacks flagella entirely, making this completely unrelated to its pathogenesis or phagosome-lysosome fusion inhibition. *Wax D* - **Wax D** is a component of the **mycobacterial cell wall**, specifically a mycolic acid-arabinogalactan-peptidoglycan complex, but it is not the primary factor responsible for inhibiting phagosome-lysosome fusion. - While it contributes to the overall immune-modulating properties of the mycobacterium, **cord factor** is more directly implicated in this specific mechanism. *Muramyl dipeptide* - **Muramyl dipeptide** is the minimal active structure of peptidoglycan that is capable of inducing an immune response by activating **NOD2 receptors**. - It acts as an **adjuvant** and immunostimulant, but it does not directly inhibit phagosome-lysosome fusion; rather, it triggers host immune pathways.

Q: Which of the following microorganisms causes Buruli ulcer?

Mycobacterium ulcerans. ***Mycobacterium ulcerans*** - **Buruli ulcer** is caused by the bacterium *Mycobacterium ulcerans*, which produces a toxin called **mycolactone** that causes tissue destruction. - This disease is characterized by chronic, necrotizing skin and soft tissue lesions, often leading to large skin ulcers. *Mycobacterium marinum* - This bacterium is primarily associated with **"swimming pool granuloma"** or **"fish tank granuloma"**, an infection contracted from contaminated water. - It typically causes skin lesions or nodules, but these are generally less severe and non-ulcerative compared to Buruli ulcer. *Mycobacterium fortuitum* - *Mycobacterium fortuitum* is a **rapidly growing mycobacterium** that commonly causes skin and soft tissue infections, often following trauma or surgical procedures. - It is not associated with the characteristic large, necrotizing ulcers of Buruli ulcer. *Mycobacterium kansasii* - *Mycobacterium kansasii* is a common cause of **non-tuberculous mycobacterial lung disease**, particularly in immunocompromised individuals. - While it can occasionally cause extrapulmonary infections, it rarely causes skin lesions and is not associated with Buruli ulcer.

Q: CSF in meningococcal meningitis shows -

Gm '-ve' Diplococci in pus cells. ***Gm '-ve' Diplococci in pus cells*** - Meningococcal meningitis is caused by *Neisseria meningitidis*, which are characteristic **Gram-negative diplococci**. - In active infection, these bacteria are typically found **intracellularly within polymorphonuclear leukocytes** (pus cells) in the cerebrospinal fluid. *Gm '+ve' bacilli* - This description would suggest a Gram-positive rod-shaped bacterium, such as *Listeria monocytogenes*, which is not the causative agent of meningococcal meningitis. - The morphology and Gram stain reaction are incorrect for *Neisseria meningitidis*. *Gm '+ve' Diplococci, in pus cells* - This describes organisms like *Streptococcus pneumoniae*, which are **Gram-positive diplococci** and a common cause of bacterial meningitis. - However, meningococcal meningitis is specifically caused by **Gram-negative** organisms. *Gm '-ve' bacilli* - This describes Gram-negative rod-shaped bacteria, such as *Haemophilus influenzae* or *Escherichia coli*. - While these can cause meningitis, *Neisseria meningitidis* is specifically a **diplococcus** (spherical in pairs), not a bacillus (rod-shaped).

Q: Most common organism causing UTI:

E. coli. ***E. coli*** - **Uropathogenic *E. coli*** (UPEC) is responsible for 75-95% of all urinary tract infections (UTIs) due to its virulence factors like **fimbriae** that allow adherence to uroepithelial cells. - Its presence in the urethra colonizes the region and ascends to the bladder, making it the most common causative agent. *Klebsiella* - **Klebsiella pneumoniae** is a common cause of UTIs, especially in complicated cases or in patients with indwelling catheters, but it is not the most frequent overall. - It ranks significantly lower than *E. coli* in incidence. *Streptococci* - While certain **Streptococcus species** can cause UTIs, they are a less common cause compared to gram-negative rods like *E. coli*. - For example, **Enterococcus faecalis** (a Group D Streptococcus) can cause UTIs, especially in hospital-acquired infections, but *E. coli* is still more prevalent. *Staphylococci saprophyticus* - **Staphylococcus saprophyticus** is a common cause of UTIs in young, sexually active women but is not the most common organism overall across all demographics. - Its incidence is significant in specific populations but doesn't rival that of *E. coli* generally.

Question 1

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 2

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 3

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 4

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

Question 5

All of the following statements about Botulism are true except:

Accepted Answer

Botulism is caused by endotoxin

Answer

Constipation is seen

Answer

Detection of toxin in the serum can aid in diagnosis

Answer

Honey ingestion causes infant botulism

Question 6

In cystic fibrosis, the most common organism which causes early infection is

Accepted Answer

Staphylococcus

Answer

Streptococcus

Answer

Klebsiella

Answer

Pseudomonas

Question 7

Phagosome-lysosome fusion in TB-infected macrophages is inhibited by -

Accepted Answer

Cord factor

Answer

Wax D

Answer

Muramyl dipeptide

Answer

Peritrichous flagella

Question 8

Which of the following microorganisms causes Buruli ulcer?

Accepted Answer

Mycobacterium ulcerans

Answer

Mycobacterium marinum

Answer

Mycobacterium fortuitum

Answer

Mycobacterium kansasii

Question 9

CSF in meningococcal meningitis shows -

Accepted Answer

Gm '-ve' Diplococci in pus cells

Answer

Gm '+ve' bacilli

Answer

Gm '+ve' Diplococci, in pus cells

Answer

Gm '-ve' bacilli

Question 10

Most common organism causing UTI:

Accepted Answer

E. coli

Answer

Klebsiella

Answer

Streptococci

Answer

Staphylococcus saprophyticus

Bacteriology — MCQs

Bacteriology — MCQs

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