MCQs on Obligate intracellular bacteria: Unculturable bacteria (do not grow in vitro)

                                 MCQ on Obligate intracellular bacteria

1.  Which term refers to bacteria that can only survive and reproduce within host cells?
a) Aerobic bacteria
b) Anaerobic bacteria
c) Facultative bacteria
d) Obligate intracellular bacteria

2. Chlamydia trachomatis is a primary example of an obligate intracellular bacterium that causes which of the following disease?
a) Trachoma
b) Gonorrhea
c) Syphilis
d) Tuberculosis

3. Which of the following intracellular bacteria is associated with 'Rocky Mountain spotted fever'?
a) Chlamydia psittaci
b) Ehrlichia chaffeensis
c) Orientia tsutsugamushi
d) Rickettsia rickettsii

4. The following gram negative intracellular bacteria is the causative agent of infection called 'Donovanosis', a sexually transmitted disease that is characterized as a painless, beefy-red, raised nodules or papules in the genitalia.
a) Anaplasma phagocytophilum
b) Chlamydia psittaci
c) Klebsiella granulomatis
d) Rickettsia typhi

5. Which bacterial structure is used by Chlamydiae to enter and infect host cells?
a) Capsule
b) Elementary body
c) Flagellum
d) Pili

6. Coxiella burnetii, which causes Q fever, primarily infects which type of host cell?
a) Alveolar macrophages
b) Hepatocytes
c) Neurons
d) Red blood cells

7. Which of the following intracellular bacteria belonging to the family Rickettsiaceae causes Scrub typhus?
a) Ehrlichia chaffeensis
b) Orientia tsutsugamushi
c) Rickettsia typhi
d) Rickettsia prowazekii

8. Chlamydiae has a intracytoplasmic (stage of infection), reproductive forms called .........................................?
a) Donovan bodies
b) Elementary bodies
c) Reticulate bodies
d) All of the above

9. Anaplasma phagocytophilum is an example of an obligate intracellular bacterium that primarily infects:
a) Liver cells
b) Kidney cells
c) Nerve cells
d) White blood cells

10. The "viable but non-culturable" (VBNC) state is often associated with obligate intracellular bacteria due to:
a) Their slow replication rate
b) Their dormancy in harsh conditions
c) Their reliance on oxygen
d) Their ability to replicate in agar media

11. Rickettsia is transmitted to humans primarily through:
a) Arthropod vectors
b) Airborne droplets
c) Contaminated water
d) Direct contact with infected individuals

12. Which of the following is NOT a strategy employed by obligate intracellular bacteria to avoid host immune responses?
a) Escaping from the host cell
b) Inhibiting phagosome-lysosome fusion
c) Modulating host cell gene expression
d) Producing toxins

13.The bacterium responsible for causing Legionnaires' disease, Legionella pneumophila, is an example of an obligate intracellular pathogen that often infects:
a) Intestinal cells
b) Liver cells
c) Lung epithelial cells
d) Red blood cells

14. Which of the following diseases is NOT caused by an obligate intracellular bacterium?
a) Q fever
b) Tuberculosis
c) Typhus
d) Tetanus

15. Which of the following intracellular pathogen causes 'Whipple disease'?
a) Coxiella burnetii 
b) Chlamydia trachomatis
c) Mycoplasma genitalium
d) Tropheryma whipplei
Answers with Explanation:
1. d) Obligate intracellular bacteria, they lack the necessary machinery to survive and replicate outside of host cells.

2. a) Trachoma, chronic inflammation of the conjunctiva (eye) transmitted to humans as a result of contact with infected secretions that contain Chlamydia trachomatis.
Gonorrhea is caused by Neisseria gonorrhoea, Syphilis is caused by a spirochete Treponema pallidum
and Tuberculosis is caused by Mycobacterium tuberculosis, these bacteria are not obligate intracellular bacteria.

3. d) Rickettsia rickettsii, it is transmitted to humans through the bite of infected ticks. The disease is named after the Rocky Mountains, where it was first identified, but it can occur in various regions of North and South America. It is a gram-negative, obligate intracellular bacilli.

4. c) Klebsiella granulomatis, Donovanosis, also known as granuloma inguinale, is a rare bacterial infection caused by the bacterium Klebsiella granulomatis. It primarily affects the genital and perineal regions, leading to the formation of painless, progressive ulcers.

5. b) Elementary body (EB), it is the infective form of Chlamydia. It is the extracellular, environmentally resistant form that is released when an infected host cell bursts.

6. a) Alveolar macrophages, Humans are infected by the inhalation of contaminated aerosols from urine, feces or milk of farm animals. After infection, C. burnetii is phagocytized by host cells and multiplies within vacuoles and the organisms are picked up by macrophages and carried to the lymph nodes, from which they then reach the bloodstream.

7. b) Orientia tsutsugamushi, belongs to family rickettsiaceae, causes scrub typhus transmitted to humans through vector chiggers. 

8. c) Reticulate bodies, Chlamydiae have two developmental cycle: elementary body and reticulate body. After entering a host cell, the elementary body transforms into the reticulate body.

9. d) White blood cells (WBC), the bacteria infection is acquired through a tick bite and disseminates to the bone marrow and spleen and primarily infects neutrophils of WBC, it is responsible for causing the disease anaplasmosis.

10. b) Their dormancy in harsh conditions.  Obligate intracellular bacteria can enter a state known as "viable but non-culturable" (VBNC) when faced with unfavorable conditions due to reduced metabolic activity and inability to replicate, this allows them to survive under stress but remain undetectable using traditional culture methods.

11. a) Arthropod vectors, Rickettsia bacteria are often transmitted to humans through arthropod vectors, such as ticks, lice, and fleas.

12. d) Producing toxins. Producing toxins is a strategy more commonly associated with extracellular bacteria.

13. c) Lung epithelial cells. Legionella pneumophila is an obligate intracellular bacterium that primarily infects and replicates within alveolar macrophages in the lungs, causing a severe form of pneumonia known as Legionnaires' disease.

14. d) Tetanus, it is caused by the bacterium Clostridium tetani, which is not an obligate intracellular bacterium