Long, slender, helically curved, gram-negative bacilli with hooked ends are identified as belonging to which species?
a. Treponema
b. Leptospira
c. Borrelia
d. Coxiella
B
These spirochetes are all long, slender, helically curved, gram-negative bacilli, with the unusual morphologic features of axial fibrils and an outer sheath. These fibrils, or axial filaments, are flagella-like organelles that wrap around the bacteria's cell wall, are enclosed within the outer sheath, and facilitate the motility of the organisms. The fibrils are attached in the cell wall by platelike structures, called insertion disks, located near the ends of the cells. The protoplasmic cylinder gyrates around the fibrils, causing bacterial movement to appear similar to a corkscrew winding. Leptospirae resemble Borrelias except for their hooked ends; Treponema are slender with tight coils; and Borrelia are somewhat thicker with fewer and looser coils.
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