MCQs on anaerobic bacteria (normal/commensal and pathogenic anaerobes)identification : Medical microbiology

                                       MCQs on anaerobic bacteria

1. A 42-year-old woman visits the emergency department with abdominal pain, fever, and foul-smelling vaginal discharge. She reports experiencing these symptoms for the past three days. The patient describes sharp, cramp-like pain in the lower abdomen that has been progressively worsening, she reports a thick, grayish-white discharge with a distinct foul odor. She has a high-grade fever with chills.

The patient is not known to have any pre-existing medical conditions or recent surgical procedures.

Upon examination, the healthcare provider observes tenderness in the lower abdomin. Pelvic ultrasound is performed to assess the pelvic organs and look for signs of inflammation.

Which of the following specimen is primarily recommended for collection and culture of the causative anaerobic pathogen?

a) Endocervial tissue specimen

b) Sputum sample 

c) Urine sample 

d) Vaginal and endocervical swabs   

2. What is the recommended storage temperature for anaerobic specimens in the laboratory?

a) Freezing (-20°C)

b) Incubator temperature (37°C)

c) Room temperature     

d) Refrigeration (4°C)

3. During laboratory processing, which environment is used to maintain an oxygen-free condition for anaerobic cultures?

a) Aerobic chamber

b) Anaerobic chamber    

c) Incubator

d) Refrigerator

4. A 48-year-old male farmer visits the clinic with an infected wound located on the lower part of his left leg, below the knee. He reports that the wound occurred 5 days ago when he accidentally cut himself with axe while chopping woods. The patient complains of increasing pain, swelling, and the presence of foul-smelling discharge from the wound. The patient describes a deep puncture wound on lower part of the left leg that bled initially but subsequently became infected.

He has experienced progressively worsening pain and swelling around the wound site. He reports purulent discharge from the wound with a foul odor. 

Upon examination, the healthcare provider observes a 5 cm by 3 cm wound on the lower part of the left leg, with erythema (redness), induration (hardening of the surrounding tissue), and localized edema (swelling). Foul-smelling purulent discharge from the wound was reported.

Based on the patient's wound history, clinical symptoms, and the appearance of the wound, the healthcare provider suspects a wound infection with a possible anaerobic bacterial involvement.

What is the recommended initial treatment for a wound infection suspected to be caused by anaerobic bacteria?

a) Antiviral therapy

b) Topical antifungal cream

c) Empirical antibiotic therapy with broad-spectrum coverage    

d) Physical therapy

5. Which of the following gram-positive cocci bacterium exhibits 'Nagler test'/Nagler reaction positivity and has a sweet, putrid odor?

a) Actinomyces israelii

b) Clostridium perfringens

c) Clostridium septicum

d) Peptostreptococcus anaerobius   

6. Which of the gram-positive, spore-forming rod can fluoresce a 'chartreuse color' when subjected to fluorescent antibody testing or specific culture methods with a horse stable odor?

a) Actinomyces israelii

b) Clostridium perfringens

c) Clostridium difficile    

d) Staphylococcus saccharoyticus 

7. Which of the following gram-negative anaerobic bacillus, has slender cells with pointed ends, and shows growth in bile?

a) Bacteroides ureolyticus

b) Clostridium septicum

c) Fusobacterium nucleatum subsp. nucleatum     

d) Leptotrichia spp.

8. Which anaerobic infection is characterized by rapidly progressing tissue destruction and the presence of gas within affected tissues?

a) Anaerobic cellulitis     

b) Actinomycosis

c) Bacterial vaginosis

d) Clostridial gastroenteritis

9. Which of the following anaerobic bacterium produces one of the most potent neurotoxins known and is a major gastroenteritis pathogen, primarily transmitted to humans by ingesting food contaminated with the toxin produced by the pathogen?

a) Bacteroides fragilis

b) Clostridium difficile     

c) Clostridium botulinum      

d) Clostridium perfringens

10. Which of the following bacterium is characterized by swarming with serpentine-edged colonies?

a) Clostridium baratii

b) Clostridium sordellii    

c) Clostridium bifermentans

d) Clostridium difficile

11. Among the non-spore-forming bacteria, which one is known to be an aerotolerant strain ?

a) Bifidobacterium spp.  

b) Eggerthella lenta

c) Eubacterium spp.

d) Propionibacterium acnes

12. Which of the following bacteria is a strict/obligate anaerobe, predominantely found as a normal flora in human colon and play a crucial role in the digestion of complex carbohydrates?

a) Bacteroides spp    

b) Bifidobacterium spp

c) Clostridium spp

d) Lactobacillus spp.

13. What is the primary pathogenic mechanism in gas gangrene caused by Clostridium perfringens?

a) Chronic abscess formation

b) Foul-smelling discharge

c) Gas production and tissue destruction

d) Neurotoxin production

14. Bacterial vaginosis is often linked to an overgrowth of which of the following anaerobic bacterium?

a) Bacteroides fragilis 

b) Clostridium butyricum

c) Clostridium tetani

d) Gardnerella vaginalis

15. Among the gram positive anaerobes which of the following is a commensal bacterium that is a commensal of the gastrointestinal tract and female genital tract?

a) Bifidobacterium lactis

b) Clostridium baratii

c) Clostridium botulinum

d) Peptostreptococcus anaerobius   

16. Which of the following Gram-positive anaerobic bacillus is commonly present in soil, constitutes a normal component of the human gastrointestinal microbiota, and is associated with infections resulting from childbirth, abortion, and gynecological procedures?

a) Clostridium difficile

b) Clostridium sordellii

c) Peptococcus niger

d) Staphylococcus saccharolyticus

17. Which of the following statement is true regarding obligate anaerobes and facultative anaerobes regarding oxygen tolerance?

a) Obligate anaerobes do not survive and grow in the presence of oxygen, facultative anaerobes do not require atmospheric oxygen but are capable of growth in oxygen and anaerobic environments.

c) Obligate anaerobes and facultative anaerobes do not require atmospheric oxygen but are capable of growth in oxygen and anaerobic environments.

18. Which of the following gram positive non-spore forming anaerobic bacterium is commonly found in the oral cavity of humans and is frequently associated with abscesses and pus infections containing  small, yellowish granules known as "sulfur granules"?

a) Actinomyces israelii

b) Bifidobacterium bifidum

c) Lactobacillus acidophilus

d) Peptostreptococcus anaerobius   

Answers with explanation:

1. d) Vaginal and endocervical swabs 

2. c) Room temperature 

3. b) Anaerobic chamber. Anaerobic chambers, or glove boxes, are made of molded 

or flexible clear plastic. Specimens and other materials are placed in the chamber through an air lock. A gas mixture of 5% CO2, 10% hydrogen, and 85% nitrogen maintain the anaerobic environment inside the chamber.

  

4. c) Empirical antibiotic therapy with broad-spectrum coverage    

5. b)Clostridium perfringens. A positive Nagler test shows a zone of precipitation around the bacterial colonies, indicating lecithinase production. C. perfringens produces lecithinase, resulting in a positive Nagler test. It is commonly used to differentiate between C. perfringens and other bacteria.

6. c) Clostridium difficile. Some strains of C. difficile can fluoresce a chartreuse color when subjected to certain laboratory tests, such as fluorescent antibody testing or specific culture methods. This fluorescence can be used as an additional indicator for the presence of Clostridium difficile in clinical samples.

7. c) Fusobacterium nucleatum subsp. nucleatum 

8. a) Anaerobic cellulitis. It is typically caused by polymicrobial infections involving a mix of anaerobic bacteria. It often begins as an infection of skin or soft tissues. The pathogens involved may include Bacteroides and Clostridium species.  

9. c) Clostridium botulinum

10. b) Clostridium sordellii. It is a member of the Clostridium genus, typically found in soil. It produces several toxins, including the lethal toxin and hemorrhagic toxin. It has been linked to serious infections, including soft tissue infections, endometritis, and bacteremia, and also association with infections following childbirth, particularly after medical or surgical abortions.

11. a) Bifidobacterium spp. Bifidobacterium species are part of the normal flora of the human gut. They are primarily anaerobic and are considered aerotolerant, the bacteria can survive in the presence of small amounts of oxygen. These bacteria are used in various probiotics and dietary supplements due to their potential health benefits.

12. a) Bacteroides spp.   

13. c) Gas production and tissue destruction

14. d) Gardnerella vaginalis

15. d) Peptostreptococcus anaerobius 

  

16. b) Clostridium sordellii. A member of the Clostridium genus, typically found in soil. It produces several toxins, including the lethal toxin and hemorrhagic toxin. It has been linked to serious infections, including soft tissue infections, endometritis, and bacteremia, and also associated with gas gangrene infection of the uterus following childbirth, particularly after medical or surgical abortions.

17. a) Obligate anaerobes do not survive and grow in the presence of oxygen, facultative anaerobes do not require atmospheric oxygen but are capable of growth in oxygen and anaerobic environments.

18. a) Actinomyces israelii. It is a gram positive anaerobic bacteria, possess a characteristic feature of formation of sulfur granules in the abscess or pus. The granules are not composed of elemental sulfur but rather consist of bacterial aggregates and inflammatory debris. Sulfur granules are a diagnostic clue for actinomycosis, and they can be observed in clinical specimens obtained from infected tissues.