MCQs on actinomycetes, Nocardia spp and Streptomyces spp: Medical microbiology

                       MCQs on Nocardia spp and Streptomyces spp

1. What is the primary habitat of Nocardia spp and Streptomyces spp?
a) Air
b) Human skin
c) Human gut flora
d) Soil   

2. Nocardia spp. are typically:

a) Facultative anaerobes

b) Microaerophilic

c) Strict anaerobes

d) Strict aerobes    

3. A 48-year-old male comes to the emergency department with a two-week history of worsening respiratory symptoms. He reports a persistent cough with yellow-green sputum production, shortness of breath, and chest pain. He also mentions fatigue and unintentional weight loss during this period. 

Upon examination, the patient appears unwell and is febrile with a temperature of 101.5°F. His respiratory rate is increased, with decreased breath sounds on the right side of the chest.

A chest X-ray reveals a large right lower lobe infiltrate with cavitation. Blood tests show an elevated white blood cell count and an elevated erythrocyte sedimentation rate (ESR). Blood cultures are drawn.

A sputum sample is obtained and sent for culture and sensitivity testing. A computed tomography (CT) scan of the chest is performed, confirming the presence of a large cavitary lesion in the right lower lobe of the lung.

The sputum culture results come back positive for Nocardia species, confirming the diagnosis of pulmonary nocardiosis.

The patient's poorly managed medical condition may have played a role in the development of the Nocardia infection.What could be the underlying medical condition of the patient?

a) Allergies 

b) Hypertension

c) Hyperthyroidism

d) Type 2 diabetes mellitus    

4. Which of the following diseases is NOT associated with Nocardia skin infections?
a) Actinomycetoma
b) Lymphocutaneous infections

c) Meningitis
d) Skin abscesses or cellulitis  

5. Which type of agar is commonly used for the growth of Nocardia spp. due to its inhibition of fungal contaminants?

a) Blood agar

b) Mycosel agar     

c) Martin Lewis agar       

d) Sabouraud dextrose agar

6. Which staining technique is commonly used to identify Nocardia spp. in clinical specimens?
a) Gram staining
b) Acid-fast staining    
c) Giemsa staining
d) Wright staining

7. Which of the following carbon containing solid medium has been effective for isolating Nocardia spp.?

a) Chocolate agar

b) Martin Lewis medium

c) Paraffin agar     

d) Sabouraud dextrose agar

8. Streptomyces is a genus of bacteria that is best known for its production of which important group of compounds?

a) Antibiotics   

b) Enzymes

c) Toxins

d) Vitamins

9. The primary route of transmission for Nocardia infections in humans is through:
a) Mosquito bites
b) Contaminated food
c) Respiratory droplets  

d) Sexual contact

10. Streptomyces spp. are important for soil health because they are involved in:

a) Nitrogen fixation

b) Organic matter decomposition

c) pH reduction

d) Soil erosion

11. Which of the following is NOT a function of the spores produced by Streptomyces spp.?

a) Reproduction

b) Survival during adverse conditions

c) Dispersal in the air

d) Antibiotic production    

12. Which of the following antibiotics is typically used as a first-line treatment for nocardiosis?
a) Penicillin
b) Ciprofloxacin
c) Trimethoprim-sulfamethoxazole (TMP-SMX)    
d) Erythromycin

13. Which of the following Nocardia species is commonly associated with causing pulmonary infections?
a) Nocardia asteroides 

b) Nocardia brasiliensis   

c) Nocardia cyriacigeorgica

d) Nocardia farcinica

14. Which of the following is NOT a characteristic of Streptomyces spp.?

a) Filamentous growth

b) Formation of spores

c) Gram-negative staining       

d) Production of secondary metabolites

15. Which type of hyphae extends along the agar surface in Nocardia spp. growth?

a) Substrate hyphae    >

b) Aerial hyphae

c) Mycelial hyphae

d) Septate hyphae

16. Which of the following is a common characteristic of Streptomyces colonies on agar plates?

a) Circular with a red coloration

b) Irregular and powdery    

c) Smooth and transparent

d) Square and raised

17. Which staining technique is commonly used to visualize the filamentous structures of Streptomyces spp.?

a) Acid-fast staining

b) Giemsa staining

c) Gram staining    

d) Wright staining

18. Nocardia cell walls contain which amino acid as a component of their peptidoglycan?

a) Lysine

b) Glycine

c) Alanine

d) Meso-diaminopimelic acid (DAP)    

19. Streptomyces coelicolor is known for producing which pigmented compound that is used as a pH indicator?

a) Actinorhodin       

b) Anthocyanin

c) Melanin

d) Xanthomonadin

20. Streptomyces spp. are considered:

a) Gram-negative bacteria

b) Non-pathogenic bacteria     

c) Obligate anaerobes

d) Obligate parasites

21. Nocardia infections are more common in individuals with a history of:
a) Exposure to farm animals   

b) Intravenous drug use

c) Swimming in freshwater lakes
d) Travel to tropical regions

22. The antibiotic streptomycin, produced by Streptomyces griseus, is primarily used to treat infections caused by which group of microorganisms?

a) Fungi

b) Gram-positive bacteria

c) Gram-negative bacteria    

d) Viruses

23. What is the characteristic appearance of Nocardia colonies on agar plates?
a) Bright green with a foul odor
b) Irregular, rough, and chalky    
c) Smooth, shiny, and white

d) Transparent and colorless

Answers:

1. c) Soil

2. d) Strict aerobes. Nocardia spp are variably acid-fast strictly aerobic actinomycetes.   

 

3. d) Type 2 diabetes mellitus. In individuals with poorly controlled diabetes and other immunocompromised conditions, nocardiosis can manifest as a severe lung infection with symptoms similar to tuberculosis or other respiratory conditions. 

4. c) Meningitis 

5. b) Mycosel agar. It is a fungal media containing cycloheximide

6. b) Acid-fast staining

7. c) Paraffin agar. It is composed of a mixture of paraffin wax and agar. Paraffin wax is used as the sole source of carbon in the medium, this agar is selective because it provides a carbon source that is utilized by Nocardia species and some mycobacteria while inhibiting the growth of many other bacteria and fungi.

8. a) Antibiotics

9. c) Respiratory droplets   

10. b) Organic matter decomposition. They are also considered saprophytic bacteria, meaning they play a role in decomposing organic matter.

11. d) Antibiotic production  

12. c) Trimethoprim-sulfamethoxazole (TMP-SMX). It is used as the first-line treatment. 

   

13. a) Nocardia asteroides.  It is commonly found in soil, and organic matter in the environment. 

Nocardia asteroides can cause nocardiosis in humans which is an opportunistic infection that typically affects individuals with compromised immune systems, such as those with HIV/AIDS, organ transplant recipients, or individuals on immunosuppressive medications. It can manifest as pulmonary nocardiosis (lung infection), cutaneous nocardiosis (skin and soft tissue infection), or disseminated nocardiosis (infection that spreads to multiple organs).

14. c) Gram-negative staining

15. a) Substrate hyphae    

16. b) Irregular and powdery 

17. c) Gram staining  

18. d) Meso-diaminopimelic acid (DAP). DAP is an amino acid derivative that is a key component of the peptidoglycan layer in the cell walls of many bacteria. It plays a crucial role in maintaining the structural integrity of the cell wall and is often used in bacterial classification and as a target for some antibiotics. 

 

19. a) Actinorhodin.  It is a secondary metabolite produced by Streptomyces coelicolor. It is a blue-pigmented antibiotic that belongs to a class of compounds known as polyketides. Actinorhodin has been extensively studied for its antibacterial properties and its role in the biology of Streptomyces bacteria.

   

20. b) Non-pathogenic bacteria. Streptomyces bacteria (actinomycetes) are typically gram-positive, do not contain mycolic acids in their cell walls and are therefore non–acid-fast. 

21. a) Exposure to farm animals

22. c) Gram-negative bacteria  

23. b) Irregular, rough, and chalky. Nocardia colonies do not have a smooth, circular shape like many other bacterial colonies. Instead, they appear irregular and may have uneven edges.Colonies is rough to the touch, it may have a grainy or granular texture. Nocardia colonies often have a chalky or powdery appearance, this chalkiness can range from white to creamy or even slightly yellowish.