DISTINCTIVE PROPERTI22 - person This form is characterized...

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DISTINCTIVE PROPERTIES: The genus Yersinia is composed of Gram negative, bipolar staining coccobacilli. Like other Enterobacteriaceae , their metabolism is fermentative. Y. pestis produces a thick anti- phagocytic slime layer, while Y. enterocolitica is motile at 28°. PATHOGENESIS: Plague is a disease that is primarily maintained among rodent populations and transmitted by infected fleas. Urban plague involves rats and has been the major source for human epidemics. Sylvatic plague exists in wild rodent populations. Two distinct forms of plague occur in human populations: 1. Bubonic plague occurs within a week of being bitten by an infected flea. Multiplication of the bacteria produces the characteristic "bubo" (swollen, painful lymph node). Bacteremia follows, causing death in about 75% of those affected. 2. Pneumonic plague occurs under crowded conditions when contaminated respiratory droplets expelled by infected persons are directly inhaled by another
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Unformatted text preview: person. This form is characterized by a shorter incubation period and greater mortality (90%). • Pathogenic Y. pestis produce two antiphagocytic components; F1 antigen and the VW antigens. Both are required for virulence and, interestingly, are only produced when the organism grows at 37°, not at lower temperatures. This might explain why the bacteria are not virulent in their alternate host, the flea, which has a body temperature near 25°. Moreover, the bacteria are capable of surviving and multiplying within monocytes, but not PMNs, and upon emerging from the monocytic host, the bacteria possess their F1 and VW antigens. • Most disease produced by Y. enterocolitica is a typical gastroenteritis characterized by fever, abdominal pain , and diarrhea. Illness generally lasts from 1 to 2 weeks but chronic cases may persist for up to a year....
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DISTINCTIVE PROPERTI22 - person This form is characterized...

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