Bacteriology Practice Questions

Q: A 36 years male presented with complaint of productive cough and fever for last 2 months. He has undergone kidney transplantation 2 years back. His sputum examination revealed a gram positive filamentous bacteria that showed acid fastness with modified Ziehl-Neelsen staining (1% H2SO4). The most likely etiological agent is ?

Nocardia asteroides. ***Nocardia asteroides*** - This patient, being an **immunocompromised kidney transplant recipient**, is highly susceptible to **opportunistic infections**. *Nocardia* species are **gram-positive, filamentous, branched bacteria** that are **weakly acid-fast** (positive with modified Ziehl-Neelsen staining, typically 1% H2SO4), commonly causing **pulmonary infections** with productive cough and fever. - Pulmonary nocardiosis can mimic tuberculosis or other fungal infections, and the acid-fast staining characteristic helps differentiate it from non-acid-fast filamentous bacteria like *Actinomyces*. *Blastomyces dermatitidis* - This is a **dimorphic fungus** that causes **blastomycosis**, an endemic infection in certain geographic regions, which is usually diagnosed by visualization of broad-based budding yeasts or culture. - It would not appear as a **gram-positive filamentous bacterium** with acid-fast properties in sputum. *Actinomyces israelii* - *Actinomyces israelii* is a **gram-positive, filamentous bacterium** that causes **actinomycosis**, often characterized by chronic abscesses, sinus tracts, and "sulfur granules." - Unlike *Nocardia*, *Actinomyces* species are **not acid-fast**, which rules it out given the staining results. *Cryptosporidium parvum* - This is a **protozoan parasite** that causes **cryptosporidiosis**, primarily manifesting as **gastroenteritis** (diarrhea), especially in immunocompromised individuals. - It would not present as a **filamentous bacterial form in sputum**, nor would it be diagnosed by Gram stain and acid-fast modified Ziehl-Neelsen staining in this context.

Q: A young lady complains of sore throat for 3 days along with fever and headache. On examination, she was severely dehydrated, her BP was found to be 90/ 50 mm Hg and on the distal aspect of the cuff, small red spots were noted. What could be the most probable etiological agent responsible for causing these symptoms -

Neisseria meningitidis. Neisseria meningitidis - The combination of sore throat, fever, headache, severe dehydration, hypotension, and petechiae (small red spots from broken capillaries, often seen with bleeding diathesis) is highly suggestive of meningococcemia [1]. - Neisseria meningitidis can cause fulminant sepsis and meningitis, leading to rapid progression of symptoms including DIC and widespread petechial rashes due to vasculitis [2]. Brucella suis - Brucellosis typically presents as an insidious illness with undulating fever, arthralgia, and organomegaly, not sudden onset severe symptoms with dehydration and petechiae. - While it can be severe, it does not commonly manifest with the acute, dramatic hemorrhagic signs seen in this patient. Brucella abortus - Similar to Brucella suis, Brucella abortus causes brucellosis, which is a chronic or subacute infection. - The clinical picture of acute onset, severe dehydration, hypotension, and petechiae points away from brucellosis. Staphylococcus aureus - Staphylococcus aureus can cause various infections, including sepsis, but a sore throat and the specific presentation of petechiae with hypotension following an apparent upper respiratory tract infection are less characteristic [3]. - While S. aureus can produce toxins leading to toxic shock syndrome, meningococcal sepsis is a more direct fit for the rapid onset and hemorrhagic signs.

Q: The animal model frequently used for M. leprae is -

Nine-banded armadillos. ***Nine-banded armadillos*** - **Nine-banded armadillos** are particularly susceptible to *Mycobacterium leprae* due to their unusually low body temperature (around 30-35°C), which is ideal for the growth of the bacterium. - They are the only other species known to naturally develop **leprosy**, making them an invaluable model for studying the disease and testing vaccines and treatments. *Rabbits* - Rabbits are generally not susceptible to *Mycobacterium leprae* infection and are not used as a primary animal model for leprosy research. - While some mycobacterial infections can be studied in rabbits, they do not mimic the human disease progression of leprosy. *Guinea pig* - Guinea pigs are known for their susceptibility to certain mycobacterial infections, particularly tuberculosis, but they are not a suitable model for *Mycobacterium leprae*. - The unique growth requirements and disease presentation of leprosy are not replicated in guinea pigs. *Mice* - While mice can be experimentally infected with *Mycobacterium leprae*, especially immunodeficient strains (e.g., nude mice, SCID mice), the infection in mice is often limited and does not fully mimic the natural human disease. - The **footpad infection model** in mice is used for drug screening but does not allow for widespread systemic infection characteristic of natural leprosy.

Q: Infective dose of S.typhi is

10³-10⁶ bacilli. ***10³-10⁶ bacilli*** - The **infective dose** for *Salmonella typhi* is generally considered to be in the range of **10³ to 10⁶ bacilli**, making it a relatively high dose required for infection. - This relatively high infective dose contributes to the epidemiology of typhoid fever, often requiring significant contamination for transmission. *10⁷-10¹² bacilli* - This range represents an **extremely high infective dose**, far exceeding the typical amount needed for *S. typhi* to cause infection. - Such a quantity would imply a much greater resistance to host defenses or a much lower virulence for the pathogen than observed. *10 bacilli* - An infective dose of **10 bacilli** is considered very low, characteristic of highly virulent pathogens like *Shigella* species. - *Salmonella typhi* is not typically associated with such a small infective dose, as it requires a larger inoculum to overcome host defenses. *10² bacilli* - An infective dose of **10² (100) bacilli** is still considered a relatively low dose for bacterial pathogens. - While some pathogens can cause infection with this number, *S. typhi* generally requires a larger inoculum to establish an infection and cause typhoid fever.

Q: Legionnaires' disease is caused by?

Motile gram negative. ***Motile gram negative*** - **Legionella pneumophila**, the causative agent of Legionnaire's disease, is a **motile gram-negative** rod. - Its **motility** is due to the presence of flagella, allowing it to move in aqueous environments. *Motile gram positive* - This option is incorrect because Legionella pneumophila is a **gram-negative** bacterium, not gram-positive. - Gram-positive bacteria have a thick peptidoglycan layer that stains purple with gram stain, which is not characteristic of Legionella. *Non-motile gram negative* - While Legionella pneumophila is gram-negative, it is in fact **motile**, making this option incorrect. - The organism uses flagella for movement, which is a key characteristic. *Non-motile gram positive* - This option is incorrect as Legionella pneumophila is both **motile** and **gram-negative**. - Combining these two incorrect characteristics makes this choice definitively false.

Q: Beta phage is seen in:

Corynebacterium diphtheriae. ***Corynebacterium diphtheriae*** - The **toxigenic strains** of *Corynebacterium diphtheriae* carry the diphtheria toxin gene (*tox*) on a **beta phage**. - This phage is a **lysogenic bacteriophage** that infects the bacterium and integrates its genetic material into the bacterial chromosome, leading to toxin production. *Peptostreptococci* - These are **anaerobic gram-positive cocci** that are not typically associated with carrying a beta phage or producing a phage-encoded toxin relevant to human disease in the same manner as diphtheria. - Their pathogenicity is usually due to their ability to cause **abscesses and opportunistic infections**, not phage-mediated toxins. *Bacillus anthracis* - *Bacillus anthracis* produces **anthrax toxin**, which is encoded on **plasmids (pXO1 and pXO2)**, not a bacteriophage. - These plasmids encode for edema factor, lethal factor, and protective antigen, which are essential for its virulence. *Clostridium botulinum* - The neurotoxins (botulinum toxins) produced by *Clostridium botulinum* are encoded by genes located on **plasmids or within the bacterial chromosome**, not specifically a beta phage. - Different strains produce different serotypes of the toxin, and the genetic elements encoding these toxins can vary.

Q: Post operative parotitis is caused by -

Staph aureus. ***Staph aureus*** - **Staphylococcus aureus** is the most common cause of **acute suppurative (post-operative) parotitis** - Post-surgical conditions including **dehydration**, **poor oral hygiene**, **reduced salivary flow**, and **immunosuppression** facilitate **bacterial ascension** through Stensen's duct from the oral cavity - The bacterium proliferates in stagnant saliva, causing acute infection of the parotid gland *E.coli* - **Escherichia coli** is primarily associated with **gastrointestinal and urinary tract infections** - Rarely implicated in salivary gland infections and not a typical cause of post-operative parotitis *Streptococcus* - While **Streptococcal species** can cause various infections, they are less commonly associated with **acute bacterial parotitis** compared to **Staphylococcus aureus** - May occasionally cause parotitis but not the predominant organism in post-operative settings *Pneumococcus* - **Streptococcus pneumoniae** commonly causes **pneumonia, meningitis, and otitis media** - Rarely causes **acute suppurative parotitis** and is not typically associated with post-operative parotitis - When sialadenitis occurs, it usually affects different patient populations

Q: Anaerobic infections can cause:

Both. ***Both*** - Anaerobic bacteria can produce various **toxins** that lead to systemic effects, causing **toxemia** and contributing to the severity of infections like gas gangrene (Clostridium perfringens). - Anaerobic infections can spread beyond localized sites, leading to **systemic infections** such as bacteremia, sepsis, and abscess formation in distant organs. *Causes toxemia* - While anaerobic bacteria can indeed produce toxins that lead to **toxemia**, this option alone does not encompass the full scope of potential complications from anaerobic infections. - Toxemia is a significant aspect, especially in infections like botulism or tetanus, but it's not the only serious outcome. *Cause systemic infection* - Anaerobic bacteria are capable of causing **systemic infections** (e.g., bacteremia, sepsis), but this option alone also does not fully describe the complex pathology that can include toxin-mediated effects. - Systemic infection emphasizes the spread of bacteria through the bloodstream or lymphatics to distant sites, but does not explicitly mention the role of bacterial toxins. *None of the options* - This option is incorrect because anaerobic infections are well-known to cause both **toxemia** (due to toxin production) and **systemic infections** (due to bacterial dissemination). - Many severe anaerobic infections, like those caused by Clostridium species, combine both systemic spread and significant toxin-mediated damage.

Q: The commonest organism causing cellulitis is -

Streptococcus pyogenes. ***Streptococcus pyogenes*** - This organism, also known as **Group A Streptococcus (GAS)**, is the most common bacterial cause of uncomplicated **cellulitis**. - **Cellulitis** is an acute, spreading bacterial infection of the **dermis** and **subcutaneous tissues**, often presenting as a red, swollen, and painful area. ***Streptococcus viridans*** - Primarily found in the **oral cavity** and are common causes of **subacute bacterial endocarditis**, not typically cellulitis. - While they can cause infections, they are not the primary pathogen for uncomplicated skin and soft tissue infections like cellulitis. ***Microaerophilic streptococci*** - These bacteria require a **reduced oxygen environment** for growth and are more often associated with **abscesses** or deep-seated infections. - They are not the most common cause of superficial spreading infections such as typical cellulitis. ***Streptococcus faecalis*** - Now known as **Enterococcus faecalis**, this organism is a common cause of **urinary tract infections** and nosocomial infections. - While it can cause skin and soft tissue infections, particularly in hospitalized or immunocompromised patients, it is not the most common cause of community-acquired cellulitis.

Q: A 2 weeks old infant has conjunctivitis, which later developed into respiratory distress and pneumonia. Chest X-ray showed bilateral lung infiltrates. WBC count was 14,300/dL. Which of the following is the most likely organism?

Chlamydia trachomatis. ***Chlamydia trachomatis*** - **Chlamydia trachomatis** is a common cause of **neonatal conjunctivitis** (ophthalmia neonatorum) and can subsequently lead to **pneumonia** in infants, typically presenting at 2-3 weeks of age. - The characteristic presentation includes **conjunctivitis** followed by **respiratory distress** and **cough** (often staccato), with **bilateral interstitial infiltrates** on chest X-ray and normal to slightly elevated white blood cell count. *Haemophilus influenzae* - While *Haemophilus influenzae* can cause **neonatal infections**, it typically presents as **sepsis**, **meningitis**, or **epiglottitis** rather than a combination of conjunctivitis and pneumonia in a 2-week-old. - It is a less common cause of **neonatal conjunctivitis** and **pneumonia** in this specific sequence compared to *Chlamydia trachomatis*. *Streptococcus agalactiae* - *Streptococcus agalactiae* (**Group B Strep**) is a major cause of **early-onset neonatal sepsis** and **pneumonia** but does not commonly cause **conjunctivitis**. - Infections usually present within the first week of life (early-onset) with **sepsis**, **pneumonia**, or **meningitis**, rather than initial conjunctivitis. *Gonococcus* - **Gonococcal conjunctivitis** (*Neisseria gonorrhoeae*) in neonates is typically severe, purulent, and appears within the **first few days of life** (hyperacute onset), much earlier than two weeks. - While it can be associated with **disseminated infection**, **pneumonia** secondary to **gonococcal conjunctivitis** is rare, and it's not the primary cause of the combined presentation described.

Question 1

A 36 years male presented with complaint of productive cough and fever for last 2 months. He has undergone kidney transplantation 2 years back. His sputum examination revealed a gram positive filamentous bacteria that showed acid fastness with modified Ziehl-Neelsen staining (1% H2SO4). The most likely etiological agent is ?

Accepted Answer

Nocardia asteroides

Answer

Blastomyces dermatitidis

Answer

Actinomyces israelii

Answer

Cryptosporidium parvum

Question 2

A young lady complains of sore throat for 3 days along with fever and headache. On examination, she was severely dehydrated, her BP was found to be 90/ 50 mm Hg and on the distal aspect of the cuff, small red spots were noted. What could be the most probable etiological agent responsible for causing these symptoms -

Accepted Answer

Neisseria meningitidis

Answer

Brucella suis

Answer

Brucella abortus

Answer

Staphylococcus aureus

Question 3

The animal model frequently used for M. leprae is -

Accepted Answer

Nine-banded armadillos

Answer

Rabbits

Answer

Guinea pig

Answer

Mice

Question 4

Infective dose of S.typhi is

Accepted Answer

10³-10⁶ bacilli

Answer

10⁷-10¹² bacilli

Answer

10 bacilli

Answer

10² bacilli

Question 5

Legionnaires' disease is caused by?

Accepted Answer

Motile gram negative

Answer

Motile gram positive

Answer

Non-motile gram negative

Answer

Non-motile gram positive

Question 6

Beta phage is seen in:

Accepted Answer

Corynebacterium diphtheriae

Answer

Peptostreptococci

Answer

Bacillus anthracis

Answer

Clostridium botulinum

Question 7

Post operative parotitis is caused by -

Accepted Answer

Staph aureus

Answer

E.coli

Answer

Streptococcus

Answer

Pneumococcus

Question 8

Anaerobic infections can cause:

Accepted Answer

Both

Answer

Cause toxemia

Answer

Cause systemic infection

Answer

None of the options

Question 9

The commonest organism causing cellulitis is -

Accepted Answer

Streptococcus pyogenes

Answer

Streptococcus viridans

Answer

Microaerophilic streptococci

Answer

Streptococcus faecalis

Question 10

A 2 weeks old infant has conjunctivitis, which later developed into respiratory distress and pneumonia. Chest X-ray showed bilateral lung infiltrates. WBC count was 14,300/dL. Which of the following is the most likely organism?

Accepted Answer

Chlamydia trachomatis

Answer

Haemophilus influenzae

Answer

Streptococcus agalactiae

Answer

Gonococcus

Bacteriology — MCQs

Bacteriology — MCQs

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