Bacteriology Practice Questions

Q: A 19 year old college student presents to the student health clinic complaining of weakness, malaise, and a chronic cough. He has a fever of 100 degrees F and a dry cough; no sputum can be obtained for laboratory analysis, so a bronchial lavage is performed and the washings are submitted to the laboratory. The laboratory reports that the organism is "slow-growing." Serodiagnosis reveals Strep MG agglutinins in the patient's serum. Which of the following organisms is the most likely cause of this student's illness?

Mycoplasma pneumoniae. ***Mycoplasma pneumoniae*** - The combination of **weakness**, **malaise**, **dry cough**, and low-grade fever in a young adult is classic for **atypical pneumonia**, often caused by *Mycoplasma pneumoniae*. - The organism being "slow-growing" and the presence of **Strep MG agglutinins** (cold agglutinins, commonly associated with *M. pneumoniae* infections) further point to this diagnosis. *Respiratory syncytial virus* - RSV is a common cause of **bronchiolitis and pneumonia** in infants and young children, less so in healthy young adults. - While it can cause respiratory symptoms, the presence of **Strep MG agglutinins** is not characteristic of RSV infection. *Klebsiella pneumoniae* - *Klebsiella pneumoniae* typically causes **severe, necrotizing pneumonia**, often in older, immunocompromised, or alcoholic individuals [1]. - It presents with a **productive cough** (currant jelly sputum) and rapid onset, not the atypical, slow-growing pattern described [1]. *Parainfluenza virus* - Parainfluenza viruses are common causes of **croup** (laryngotracheobronchitis) in children and can cause respiratory infections in adults. - However, they do not produce **Strep MG agglutinins**, and the "slow-growing" description in a bronchial lavage is not typical for a viral pathogen.

Q: True about chlamydia

McCoy cells for isolation. ***McCoy cells for isolation*** - *Chlamydia trachomatis* are **obligate intracellular bacteria** and require cell culture for laboratory isolation and propagation. - **Cycloheximide-treated McCoy cells** are the gold standard cell line for isolation of *Chlamydia trachomatis*, though other cell lines like HeLa and HEp-2 cells can also be used. - This characteristic makes their cultivation more challenging compared to extracellular bacteria, necessitating the use of viable host cells. *Extracellular bacteria* - This statement is incorrect because *Chlamydia trachomatis* is an **obligate intracellular bacterium**, meaning it can only replicate and survive within the host cell. - Unlike extracellular bacteria, it cannot be cultured on standard bacterial growth media. *Penicillin is drug of choice* - **Penicillin** is ineffective against *Chlamydia* because these bacteria lack a **peptidoglycan cell wall**, which is the primary target of penicillin. - The drugs of choice for *Chlamydia* infections are typically **macrolides** (e.g., azithromycin) or **tetracyclines** (e.g., doxycycline). *Gram positive* - Though *Chlamydia* has a cell wall, its structure is unique and lacks **peptidoglycan**, which prevents it from staining robustly with the Gram stain. - While it has characteristics of both Gram-negative and Gram-positive bacteria, it is generally considered **Gram-negative** due to its outer membrane, but often described as Gram-variable or not typically Gram-stainable.

Q: True about Legionella pneumonia is -

Can be isolated from lung biopsy. ***Can be isolated from lung biopsy*** - **Legionella pneumophila** is a fastidious bacterium that can be difficult to grow on routine culture media and microscopic examination of sputum may not always reveal the organism. - In cases of severe or persistent pneumonia where a definitive diagnosis is needed, **lung biopsy** provides tissue that can be stained (e.g., with direct fluorescent antibody stain) or cultured on specialized media (like buffered charcoal yeast extract agar) for isolation of *Legionella*. *Sputum shows polymorphonuclear leukocytes with organism* - While **polymorphonuclear leukocytes (PMNs)** are typically present in sputum from bacterial pneumonia, *Legionella* is an **intracellular pathogen** and often difficult to visualize on Gram stain due to its poor staining characteristics. - The absence of readily visible organisms in sputum Gram stain despite abundant leukocytes is a classic clue for **Legionella pneumonia**. *Acid fast* - **Legionella pneumophila** is **not acid-fast**; acid-fast staining is characteristic of mycobacteria (e.g., *Mycobacterium tuberculosis*). - Special stains like **Dieterle silver stain** or **direct fluorescent antibody (DFA) stain** are used to visualize *Legionella* in tissue or samples. *Gram positive* - **Legionella pneumophila** is a **Gram-negative bacterium**, although it stains poorly with standard Gram stain. - It is typically a **rod-shaped bacterium** that requires specialized culture conditions.

Q: A 34-year-old woman is seen in the emergency department. About 5 hours previously, she began to have nausea, vomiting, abdominal cramps, and diarrhea. She then developed double vision, which prompted her to ask her husband to bring her to the emergency department. When she is asked to go into the examining room, she stumbles. When she tries to answer questions, her voice sounds odd and she seems to mumble. Physical examination demonstrates a dry mouth, drooping eyelids, markedly diminished pupillary light reflex, a flaccid facial expression, and difficulty in opening her mouth. Within an hour, her condition has markedly deteriorated. She can no longer stand and is intubated because of difficulty breathing. Which of the following microbial species is MOST likely to have caused her condition?

Clostridium botulinum. ***Clostridium botulinum*** - The rapid onset of **nausea, vomiting, abdominal cramps, and diarrhea** followed by neurological symptoms like **double vision, stumbling, slurred speech (dysarthria), dry mouth, drooping eyelids (ptosis), diminished pupillary light reflex, and progressive muscle weakness** (leading to inability to stand and respiratory failure) is characteristic of **botulism**. - **Botulinum toxin**, produced by *Clostridium botulinum*, is a potent neurotoxin that inhibits acetylcholine release at the neuromuscular junction, causing a **flaccid paralysis** that can rapidly progress to respiratory paralysis. *Clostridium ramosum* - This species is an infrequent cause of **bacteremia and localized infections**, particularly in immunocompromised individuals. - It does not typically produce neurotoxins that lead to the rapid onset of severe neurological symptoms and flaccid paralysis seen in the patient. *Clostridium perfringens* - *Clostridium perfringens* is a common cause of **food poisoning** (characterized by nausea, vomiting, and diarrhea) and **gas gangrene**. - While it causes gastrointestinal symptoms, it does not produce neurotoxins that result in oculomotor dysfunction, dysphagia, or widespread flaccid paralysis. *Clostridium septicum* - *Clostridium septicum* is primarily associated with **gas gangrene** and **severe systemic infections**, often in patients with underlying malignancies. - It does not cause the specific neurological symptoms, particularly the descending flaccid paralysis, observed in this clinical presentation.

Q: A bacterial disease with oral manifestations is

Diphtheria. **Diphtheria** - **Diphtheria** is a bacterial infection caused by *Corynebacterium diphtheriae*, which produces a toxin leading to the formation of a **pseudomembrane** in the throat and tonsils, representing an oral manifestation [1]. - This **pseudomembrane** can cause difficulty breathing and swallowing, and if left untreated, the toxin can lead to systemic complications affecting the heart, kidneys, and nervous system [1]. *measles* - **Measles** (rubeola) is a viral infection characterized by a maculopapular rash and fever, and its classic oral manifestation is **Koplik's spots**, which are small white spots with a red halo found on the buccal mucosa. - Although Koplik's spots are an oral manifestation, measles is a **viral** disease, not bacterial. *Leishmaniasis* - **Leishmaniasis** is a parasitic disease caused by *Leishmania* parasites, transmitted by the bite of infected sandflies, and can present as cutaneous, mucocutaneous, or visceral forms. - While **mucocutaneous leishmaniasis** can affect the nose, mouth, and throat with ulcerative lesions, it is a **parasitic** disease, not bacterial. *Herpes* - **Herpes** is primarily caused by the **Herpes Simplex Virus (HSV)**, which is a **viral** infection, leading to cold sores (herpes labialis) or genital lesions. - Oral manifestations like **herpetic gingivostomatitis** are common, but the causative agent is viral, not bacterial [2].

Q: Which is NOT a sexually transmitted disease?

Yaws. ***Yaws*** - Yaws is a **chronic infectious disease** caused by the bacterium *Treponema pallidum pertenue*, a subspecies of *Treponema pallidum*, the same bacterium that causes syphilis. - It's primarily transmitted through **skin-to-skin contact** with infectious lesions, not sexual contact, and is common in warm, humid, tropical regions. *Granuloma Inguinale* - Also known as **Donovanosis**, this is a chronic, progressive **bacterial infection** caused by *Klebsiella granulomatis*. - It is **sexually transmitted** and primarily affects the skin and mucous membranes of the genital, inguinal, and perianal areas. *LGV* - **Lymphogranuloma Venereum (LGV)** is a sexually transmitted infection (STI) caused by specific serovars of *Chlamydia trachomatis*. - It is characterized by **lymphadenopathy** and can cause invasive infections of the lymph nodes and lymphatic tissue, particularly in the genital and anal regions. *Chancroid* - Chancroid is a **bacterial STI** caused by *Haemophilus ducreyi*. - It is characterized by the development of **painful genital ulcers** and often swelling of the lymph nodes in the groin.

Q: A child with fever with abdominal cramps & pus in stools, causative organism is ?

EAEC. ***EAEC (Enteroaggregative E. coli)*** - Among the E. coli strains listed, EAEC is the answer for this question, though **this is an atypical presentation**. - EAEC classically causes **persistent watery diarrhea** (>14 days) in children, often with **low-grade fever** and **abdominal pain**. - While EAEC primarily causes non-bloody diarrhea, it can occasionally produce **mucoid stools** with inflammatory cells due to mucosal inflammation from biofilm formation. - **Note:** The classic organism for fever + cramps + pus in stools would be **Shigella**, **Campylobacter**, or **EIEC (Enteroinvasive E. coli)** - not listed here. *EHEC (Enterohemorrhagic E. coli)* - EHEC (O157:H7) causes **hemorrhagic colitis** with bloody diarrhea due to **Shiga toxins**. - Can lead to **hemolytic uremic syndrome (HUS)** in children. - Characterized by **blood** rather than pus in stools, distinguishing it from typical dysentery. *ETEC (Enterotoxigenic E. coli)* - Most common cause of **traveler's diarrhea** and watery diarrhea in developing countries. - Produces **heat-labile (LT)** and **heat-stable (ST)** enterotoxins causing secretory diarrhea. - Results in profuse **watery stools without inflammation, blood, or pus**. *EPEC (Enteropathogenic E. coli)* - Leading cause of infantile diarrhea in developing countries. - Causes **attaching and effacing** lesions on intestinal mucosa. - Results in **watery diarrhea without significant inflammatory cells or pus** in stools.

Q: Which of the following are pleomorphic organisms?

Mycoplasma. ***Mycoplasma*** - **Mycoplasma** species are known for their **pleomorphic nature** because they lack a rigid **cell wall**, allowing them to assume various shapes. - This characteristic distinguishes them from most other bacteria, which have a defined shape due to their cell walls. *Pseudomonas* - **Pseudomonas** typically appears as **rod-shaped bacilli** and is not considered pleomorphic. - Its bacterial shape is consistent and relatively stable due to its **peptidoglycan cell wall**. *Corynebacterium* - **Corynebacterium** primarily exhibits a **rod-like** or **club-shaped morphology**, often described as diphtheroid. - While they can have slightly irregular shapes, they are not highly pleomorphic in the same sense as Mycoplasma. *Gonococcus* - **Gonococcus** (Neisseria gonorrhoeae) is characterized by its **gram-negative diplococcus** (kidney-bean shaped pairs) morphology. - Its shape is quite distinct and consistent, and it is not considered pleomorphic.

Q: Which is true about salmonella gastroenteritis?

Diarrhea is nonbloody. **Diarrhea is nonbloody** - In typical **Salmonella gastroenteritis** (non-typhoidal Salmonella), the diarrhea is usually **watery and non-bloody**, though in some cases, microscopic blood may be present [1]. - The illness is self-limiting and rarely progresses to invasive disease, unlike typhoidal salmonellosis. *Is due to exotoxin* - **Salmonella gastroenteritis** primarily results from the bacteria invading the intestinal mucosa and causing inflammation, rather than the action of a preformed exotoxin. - While Salmonella can produce some toxins, their primary pathogenesis involves **endotoxin (LPS)** and direct mucosal invasion, leading to an inflammatory response. *Always associated with blood and mucus in stools* - While some gastrointestinal infections, such as those caused by *Shigella* or enteroinvasive *E. coli*, are classically associated with **bloody and mucoid stools** (dysentery), this is not consistently true for **Salmonella gastroenteritis** [1]. - As mentioned, Salmonella typically causes watery, non-bloody diarrhea; gross blood and mucus are less common unless the infection is more severe or invasive [1]. *Mainly diagnosed by serological testing* - **Salmonella gastroenteritis** is primarily diagnosed by **stool culture**, which identifies the presence of the bacteria in the feces. - **Serological tests** (e.g., Widal test) are rarely used for acute gastroenteritis diagnosis as they detect antibody responses that may take time to develop and can be non-specific.

Q: Organism involved in cellulitis is:

S. pyogenes. ***Strept. pyogenes*** - *Streptococcus pyogenes* (Group A Streptococcus) is a common cause of **cellulitis**, an acute bacterial infection of the deep dermis and subcutaneous tissue. - It often spreads rapidly and can lead to systemic symptoms if untreated. *Strept. mutans* - *Streptococcus mutans* is primarily associated with **dental caries** (tooth decay) and is a significant component of oral biofilm. - It is not a common cause of cellulitis in typical settings. *Pneumococci* - **Pneumococci** (*Streptococcus pneumoniae*) are most commonly known for causing **pneumonia**, otitis media, and meningitis. - While they can cause invasive infections, they are not a primary cause of routine cellulitis. *Klebsiella* - *Klebsiella* species are common causes of **nosocomial infections**, particularly urinary tract infections, pneumonia, and bloodstream infections. - They can cause cellulitis, especially in immunocompromised individuals or those with specific risk factors, but *S. pyogenes* is more common in general cellulitis cases.

Question 1

A 19 year old college student presents to the student health clinic complaining of weakness, malaise, and a chronic cough. He has a fever of 100 degrees F and a dry cough; no sputum can be obtained for laboratory analysis, so a bronchial lavage is performed and the washings are submitted to the laboratory. The laboratory reports that the organism is "slow-growing." Serodiagnosis reveals Strep MG agglutinins in the patient's serum. Which of the following organisms is the most likely cause of this student's illness?

Accepted Answer

Mycoplasma pneumoniae

Answer

Respiratory syncytial virus

Answer

Klebsiella pneumoniae

Answer

Parainfluenza virus

Question 2

True about chlamydia

Accepted Answer

McCoy cells for isolation

Answer

Extracellular bacteria

Answer

Penicillin is drug of choice

Answer

Gram positive

Question 3

True about Legionella pneumonia is -

Accepted Answer

Can be isolated from lung biopsy

Answer

Sputum shows polymorphonuclear leukocytes with organism

Answer

Acid fast

Answer

Gram positive

Question 4

A 34-year-old woman is seen in the emergency department. About 5 hours previously, she began to have nausea, vomiting, abdominal cramps, and diarrhea. She then developed double vision, which prompted her to ask her husband to bring her to the emergency department. When she is asked to go into the examining room, she stumbles. When she tries to answer questions, her voice sounds odd and she seems to mumble. Physical examination demonstrates a dry mouth, drooping eyelids, markedly diminished pupillary light reflex, a flaccid facial expression, and difficulty in opening her mouth. Within an hour, her condition has markedly deteriorated. She can no longer stand and is intubated because of difficulty breathing. Which of the following microbial species is MOST likely to have caused her condition?

Accepted Answer

Clostridium botulinum

Answer

Clostridium ramosum

Answer

Clostridium perfringens

Answer

Clostridium septicum

Question 5

A bacterial disease with oral manifestations is

Accepted Answer

Diphtheria

Answer

measles

Answer

Leishmaniasis

Answer

Herpes

Question 6

Which is NOT a sexually transmitted disease?

Accepted Answer

Yaws

Answer

Granuloma Inguinale

Answer

LGV

Answer

Chancroid

Question 7

A child with fever with abdominal cramps & pus in stools, causative organism is ?

Accepted Answer

EAEC

Answer

EHEC

Answer

ETEC

Answer

EPEC

Question 8

Which of the following are pleomorphic organisms?

Accepted Answer

Mycoplasma

Answer

Pseudomonas

Answer

Corynebacterium

Answer

Gonococcus

Question 9

Which is true about salmonella gastroenteritis?

Accepted Answer

Diarrhea is nonbloody

Answer

Is due to exotoxin

Answer

Always associated with blood and mucus in stools

Answer

Mainly diagnosed by serological testing

Question 10

Organism involved in cellulitis is:

Accepted Answer

S. pyogenes

Answer

S. mutans

Answer

Klebsiella

Answer

Pneumococci

Bacteriology — MCQs

Bacteriology — MCQs

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