MCQ Microbiology Answer 45

The answer is: C

Rickettsiae are small bacteria that are obligate, intracellular parasites. Most but not all rickettsiae are transmitted to humans by arthropods. Coxiella is transmitted through the respiratory tract rather than through the skin, and B. henselae, from animal scratches. Coxiella may cause chronic endocarditis that is not very responsive to either antimicrobial therapy or valve replacement. B. henselae is a fastidious Gram-negative rod that causes bacillary angiomatosis, a disease that forms dermal or subcutaneous nodules. The role of B. henselae in cat-scratch disease has recently been recognized. Molecular taxonomic studies have indicated that the causative organism is more closely related to Bartonella than Rochalimaea, hence the name change.

Ehrlichia is an obligate, intracellular parasite that resembles rickettsia. E. chaffeensis has been linked to human ehrlichiosis, although this infection is primarily seen in animals. The majority of patients with this disease report exposure to ticks. It is thought that I. scapularis carries Ehrlichia, although the Lone Star tick, A. americanum, may also transmit the disease.

Chlamydiae are Gram-negative bacteria that are obligate, intracellular parasites. They are divided into three species: C. trachomatis, C. pneumoniae, and C. psittaci. Chlamydiae have a unique developmental cycle. The infectious particle is the elementary body. Once inside the cell, the elementary body undergoes reorganization to form a reticulate body. After several replications, the reticulate bodies differentiate into elementary bodies, are released from the host cell, and become available to infect other cells. Three of the 15 serovars of C. trachomatis (L1, L2, L3) are known to cause lymphogranuloma venereum (LGV), a sexually transmitted disease. C. trachomatis is a leading cause of sexually transmitted disease in the United States. It is insidious because so many early infections are asymptomatic, particularly in women.

Rocky Mountain spotted fever is a spotted fever caused by R. rickettsii and is characterized by acute onset of fever, severe headache, and myalgias. The rash occurs 2 to 6 days later first in the hands and feet and then moves to the trunk. Diagnosis must be made on clinical presentations, and therapy instituted immediately. Laboratory diagnosis is made on a rising antibody titer (delayed). Untreated disease can be fatal.

Category: Microbiology MCQs