Bacteriology Practice Questions

Q: The term 'leathery' appearance in medical terminology is characteristically used to describe:

Diphtheria. ***Diphtheria*** - The term "leather" in medical terminology is commonly used to describe the **pseudomembrane** found in diphtheria, which is tough, leathery, and firmly adherent. - This **pseudomembrane** is composed of fibrin, bacteria, inflammatory cells, and necrotic tissue, and its removal can cause bleeding. *Anthrax* - Anthrax typically causes a **black eschar** with surrounding edema, which is distinct from the leathery pseudomembrane of diphtheria. - The characteristic lesion is often referred to as a **malignant pustule** and is not described as "leather." *Neisseria* - Infections caused by *Neisseria* species, such as **meningitis** or **gonorrhea**, do not involve the formation of a leathery pseudomembrane. - *Neisseria meningitidis* can cause **purpuric rash** and petechiae, while *Neisseria gonorrhoeae* typically causes mucopurulent discharges. *Proteus* - *Proteus* species are common causes of **urinary tract infections** and wound infections. - These infections do not produce a "leathery" appearance or pseudomembrane and are known for their strong **ammonia-like odor** in urine.

Q: In a patient of the nephrotic syndrome with spontaneous bacterial peritonitis, which one of the following micro-organisms is most commonly involved?

Pneumococcus. ***Pneumococcus*** - **Streptococcus pneumoniae (Pneumococcus)** is the **most common** causative organism of **spontaneous bacterial peritonitis (SBP)** in patients with **nephrotic syndrome**, especially in children. - Nephrotic syndrome causes loss of **immunoglobulins (IgG)** in the urine, leading to **opsonization defects** that increase susceptibility to **encapsulated organisms** like Pneumococcus. - The organism typically reaches the peritoneal cavity via **hematogenous spread** from respiratory or other primary sites. - This contrasts with SBP in **cirrhotic ascites**, where gram-negative enteric organisms predominate. *Escherichia* - **Escherichia coli (E. coli)** is the most common cause of SBP in **cirrhotic patients** with ascites (due to bacterial translocation from the gut). - In **nephrotic syndrome**, E. coli is a less common cause compared to Pneumococcus, as the immune defect specifically affects defense against encapsulated organisms. - The pathophysiology differs between cirrhosis (portal hypertension, bacterial translocation) and nephrotic syndrome (immunoglobulin loss). *Proteus* - **Proteus mirabilis** is an uncommon cause of spontaneous bacterial peritonitis in nephrotic syndrome. - Proteus is more frequently associated with **urinary tract infections**, especially in patients with structural abnormalities or catheterization. *Staphylococcus* - **Staphylococcus** species are rare causes of primary spontaneous bacterial peritonitis in nephrotic syndrome. - When present, Staphylococcus usually suggests **secondary peritonitis** from perforation, surgical complications, or catheter-related peritonitis (e.g., peritoneal dialysis).

Q: All of the following statements about cholera are true except -

O & H antigens measure carrier state. ***O & H antigens measure carrier state*** - **O and H antigens** are primarily involved in serotyping *Vibrio cholerae* and are crucial for the initial classification of different strains, particularly differentiating between toxigenic and non-toxigenic strains. - The detection of **carrier states** in cholera is typically achieved through culturing stool samples for the presence of *Vibrio cholerae*, rather than by measuring O and H antigens, as these antigens reflect the bacterial surface components. *Culture medium is TCBS Agar* - **Thiosulfate-citrate-bile salts-sucrose (TCBS) agar** is a selective and differential medium widely used for isolating *Vibrio* species, including *Vibrio cholerae*, from clinical samples and environmental sources. - It works by inhibiting the growth of most enteric bacteria while allowing *Vibrio* species to grow and produce distinct colonies (e.g., yellow colonies for sucrose-fermenting *V. cholerae*). *Produces indole and reduces nitrate* - *Vibrio cholerae* is biochemically characterized by its ability to **produce indole** from tryptophan and to **reduce nitrates** to nitrites, which are important diagnostic markers. - These metabolic activities are part of the standard battery of biochemical tests used to identify and confirm the presence of *Vibrio cholerae* in laboratory settings. *Synthesize neuraminidase* - *Vibrio cholerae* produces **neuraminidase**, an enzyme that cleaves **sialic acid** residues from mucin, potentially enhancing the binding of cholera toxin to intestinal epithelial cells by exposing GM1 ganglioside receptors. - This enzyme contributes to the pathogen's virulence by modifying the host's intestinal environment, although its direct role in disease pathogenesis is still under investigation.

Q: A 40-year-old woman complained of unrelenting headache, accompanied by fever, chills, and malaise. After 3 to 4 days, a dry cough developed. Her white cell count was normal. Chest x-ray and CT scan were done. A pathogen I suspected which produces colonies like the ones given below. Which of the following is the most likely diagnosis?

Mycoplasma pneumoniae. ***Mycoplasma pneumoniae*** - This presentation of **unrelenting headache, fever, chills, malaise**, followed by a **dry cough** and a **normal white cell count**, is classic for "walking pneumonia" caused by *Mycoplasma pneumoniae*. - Its colonies often have a **fried egg appearance** (although not explicitly stated, this is a common association with suspected pathogens shown colonially) and it's a common cause of **atypical pneumonia**. *Legionella pneumophilia* - While *Legionella* can cause **atypical pneumonia** with similar systemic symptoms and a dry cough, it often presents with **gastrointestinal symptoms** (diarrhea) or **neurological symptoms** (confusion) which are not described here. - *Legionella* usually infects via **aerosolized contaminated water sources** and is often associated with outbreaks. *Streptococcus pneumoniae* - This bacterium typically causes **lobar pneumonia** with a **productive cough**, **purulent sputum**, and often an **elevated white cell count**. - Its onset is usually more acute and severe than described, and it is a **typical pneumonia** pathogen. *Parainfluenza virus* - Parainfluenza viruses primarily cause upper and lower respiratory tract infections, often presenting as **croup** in children or **bronchiolitis**. - While it can cause pneumonia, it typically does not present with such a prominent and unrelenting headache, nor the specific systemic pattern common in atypical bacterial infections.

Q: “Hundred day cough” is the name of

Cough due to Bordetella pertussis. ***Cough due to Bordetella pertussis*** - **Whooping cough**, caused by **Bordetella pertussis**, is colloquially known as the "hundred-day cough" due to its prolonged duration. - The cough can last for weeks to months, especially in unvaccinated individuals, characterized by severe paroxysms followed by a characteristic "whoop" inspiration. *Cough due to Haemophilus influenzae* - **Haemophilus influenzae** can cause respiratory infections like bronchitis or pneumonia, with cough as a symptom, but it is not specifically known as the "hundred-day cough." - This bacterium is more commonly associated with **otitis media**, sinusitis, epiglottitis, and meningitis, rather than a prolonged, distinctive coughing illness. *Cough due to respiratory syncytial virus* - **Respiratory syncytial virus (RSV)** is a common cause of respiratory infections, particularly in infants and young children, leading to bronchiolitis and pneumonia. - While RSV can cause a persistent cough, it is not referred to as the "hundred-day cough"; its symptoms are typically more acute and can involve wheezing and difficulty breathing. *Cough due to adenovirus* - **Adenoviruses** can cause various respiratory illnesses ranging from the common cold to pneumonia, with cough being a frequent symptom. - However, the cough associated with adenovirus infections is generally not as prolonged or severe as "whooping cough" and does not typically fit the "hundred-day cough" description.

Q: A 4-year-old male child presents with fever, anemia and azotemia after an episode of dysentery 9 days earlier. The commonest organism responsible for this condition is?

E. coli. ***E. coli*** - **Enterohemorrhagic E. coli** (EHEC), particularly O157:H7, is the most common cause of **hemolytic uremic syndrome (HUS)**, which presents with the triad of **fever, anemia (hemolytic)**, and **azotemia (acute kidney injury)** following bloody diarrhea (dysentery). - The incubation period of about 7-10 days between the diarrheal episode and the onset of HUS symptoms is consistent with the timeline described. *Meningococcus* - **Neisseria meningitidis** typically causes **meningitis** and **meningococcemia**, characterized by fever, headache, neck stiffness, and a petechial rash. - It is not associated with dysentery or the subsequent development of hemolytic uremic syndrome. *E. histolytica* - **Entamoeba histolytica** causes **amebic dysentery** and can lead to complications such as **liver abscesses**. - While it causes dysentery, it does not typically lead to the systemic complications of hemolytic anemia and azotemia characteristic of HUS. *Staphylococcus* - **Staphylococcus aureus** can cause a wide range of infections, including **skin infections**, **food poisoning**, and **sepsis**, but it is primarily a gram-positive coccus. - It is not a common cause of dysentery leading to HUS; EHEC, a gram-negative rod, is the usual culprit in this clinical scenario.

Q: Not true about meningococcal meningitis

Carriers are treated with penicillin. ***Carriers are treated with penicillin*** - **Penicillin** is not the recommended treatment for eradicating *Neisseria meningitidis* from carriers, as it does not reliably eliminate nasopharyngeal carriage. - Recommended prophylactic regimens for carriers include **rifampicin**, **ceftriaxone**, or **ciprofloxacin** [1]. *Transmitted via droplet infection* - **Meningococcal meningitis** is indeed highly contagious and primarily spreads through **respiratory droplets**, making close contact a significant risk factor. - This mode of transmission is why outbreaks can occur rapidly in crowded settings like dormitories or military barracks. *Is gram negative organism* - *Neisseria meningitidis*, the causative agent of meningococcal meningitis, is a **Gram-negative diplococcus**. - Its unique Gram stain morphology helps in initial laboratory identification. *Carriers are treated with Rifampicin.* - **Rifampicin** is a highly effective antibiotic for eliminating *Neisseria meningitidis* carriage in asymptomatic individuals and is commonly used for prophylaxis [1]. - Its mechanism allows it to penetrate host cells and target the bacteria in the nasopharynx. *Carriers are the source of infection* - **Asymptomatic carriers** of *Neisseria meningitidis*, who harbor the bacteria in their nasopharynx without developing disease, are the primary **reservoir and source of infection**. - These carriers facilitate the spread of the pathogen within communities, often unknowingly.

Q: Which is the most common organism causing acute epiglottitis among the following options?

H. influenzae. ***H. influenzae*** - **_Haemophilus influenzae_ type b (Hib)** was historically the **most common cause** of acute epiglottitis, particularly in children before widespread Hib vaccination. - This remains the **classically taught answer** in medical education and is still relevant in **unvaccinated populations** or areas with low vaccination coverage. - **Important note:** In the **post-vaccine era** with widespread Hib vaccination, the incidence has decreased by >95%, and other organisms (particularly _Streptococcus_ species) have become relatively more common, especially in adults. - However, H. influenzae remains the organism most associated with acute epiglottitis in traditional medical teaching. *N. meningitidis* - **_Neisseria meningitidis_** primarily causes **meningococcal meningitis** and **meningococcemia** (fulminant septicemia). - While it can cause various invasive infections, it is **not a common cause** of acute epiglottitis. - Characteristic features include petechial/purpuric rash in septicemia. *S. pyogenes* - **_Streptococcus pyogenes_** (Group A Streptococcus) is the leading cause of **acute bacterial pharyngitis** ("strep throat"). - It causes complications like **acute rheumatic fever** and **acute post-streptococcal glomerulonephritis**. - In the post-Hib vaccine era, it has emerged as an **increasingly common cause** of epiglottitis, especially in adults, but is still less classically associated than H. influenzae in traditional teaching. *S. pneumoniae* - **_Streptococcus pneumoniae_** is a major cause of **community-acquired pneumonia, acute otitis media, bacterial meningitis**, and **bacteremia**. - While it can cause **supraglottitis/epiglottitis** (particularly in adults in the modern era), it is **less classically associated** with acute epiglottitis compared to the traditional pathogen H. influenzae type b.

Q: Hebra nose is caused by:

Frisch bacillus. ***Frisch bacillus*** - **Frisch bacillus**, also known as *Klebsiella rhinoscleromatis*, is the causative agent of **rhinoscleroma**, which often presents as a condition causing tumor-like growths in the nose, leading to the characteristic "Hebra nose." - **Hebra nose** refers to the chronic, deforming nasal lesion associated with late stages of **rhinoscleroma**, characterized by hardening and widening of the nose. *C. diphtheriae* - *Corynebacterium diphtheriae* causes **diphtheria**, primarily affecting the respiratory tract and skin. - It forms a **pseudomembrane** in the throat and can lead to systemic complications due to toxin production, but it does not cause Hebra nose. *Pseudomonas* - *Pseudomonas aeruginosa* is an opportunistic pathogen commonly causing **nosocomial infections**, such as pneumonia, urinary tract infections, and wound infections. - While it can cause various infections, it is not associated with the specific nasal deformity known as Hebra nose. *Staph aureus* - *Staphylococcus aureus* is a common bacterium causing a wide range of infections, including **skin infections** (e.g., boils, cellulitis), **pneumonia**, and **sepsis**. - Although it can cause nasal colonization and local infections, it does not cause the chronic, deforming condition known as Hebra nose.

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 bacterium requires specialized culture media for isolation, contributing to diagnostic challenges. *N. Gonorrhoeae* - This bacterium is responsible for **gonorrhea**, a common STI causing urethritis, cervicitis, and other inflammatory conditions. - Unlike chancroid, gonorrhea typically presents with purulent discharge and can lead to complications like pelvic inflammatory disease, but not painful genital ulcers as the primary manifestation. *T. Pallidum* - This spirochete is the causative agent of **syphilis**, an STI that progresses through distinct stages. - Syphilis initially presents with a painless chancre, which is a key differentiator from the painful ulcers of chancroid. *H. influenzae* - **Haemophilus influenzae** is a common respiratory pathogen known to cause infections such as otitis media, epiglottitis, and pneumonia. - It is not associated with sexually transmitted infections or genital ulcers.

Question 1

The term 'leathery' appearance in medical terminology is characteristically used to describe:

Accepted Answer

Diphtheria

Answer

Anthrax

Answer

Neisseria

Answer

Proteus

Question 2

In a patient of the nephrotic syndrome with spontaneous bacterial peritonitis, which one of the following micro-organisms is most commonly involved?

Accepted Answer

Pneumococcus

Answer

Proteus

Answer

Escherichia

Answer

Staphylococcus

Question 3

All of the following statements about cholera are true except -

Accepted Answer

O & H antigens measure carrier state

Answer

Culture medium is TCBS Agar

Answer

Produces indole and reduces nitrate

Answer

Synthesize neuraminidase

Question 4

A 40-year-old woman complained of unrelenting headache, accompanied by fever, chills, and malaise. After 3 to 4 days, a dry cough developed. Her white cell count was normal. Chest x-ray and CT scan were done. A pathogen I suspected which produces colonies like the ones given below. Which of the following is the most likely diagnosis?

Accepted Answer

Mycoplasma pneumoniae

Answer

Legionella pneumophilia

Answer

Streptococcus pneumoniae

Answer

Parainfluenza virus

Question 5

“Hundred day cough” is the name of

Accepted Answer

Cough due to Bordetella pertussis

Answer

Cough due to Haemophilus influenzae

Answer

Cough due to respiratory syncytial virus

Answer

Cough due to adenovirus

Question 6

A 4-year-old male child presents with fever, anemia and azotemia after an episode of dysentery 9 days earlier. The commonest organism responsible for this condition is?

Accepted Answer

E. coli

Answer

Meningococcus

Answer

E. histolytica

Answer

Staphylococcus

Question 7

Not true about meningococcal meningitis

Accepted Answer

Carriers are treated with penicillin

Answer

Transmitted via droplet infection

Answer

Is gram negative organism

Answer

Carriers are treated with Rifampicin.

Answer

Carriers are the source of infection

Question 8

Which is the most common organism causing acute epiglottitis among the following options?

Accepted Answer

H. influenzae

Answer

N. Meningitidis

Answer

S. pyogenes

Answer

S. Pneumoniae

Question 9

Hebra nose is caused by:

Accepted Answer

Frisch bacillus

Answer

C. diphtheriae

Answer

Pseudomonas

Answer

Staph aureus

Question 10

Chancroid is caused by ?

Accepted Answer

H. ducreyi

Answer

N. Gonorrhoeae

Answer

T. Pallidum

Answer

H. influenzae

Bacteriology — MCQs

Bacteriology — MCQs

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