Rickettsia, Chlamydia, Mycoplasma, Legionella, and …：立克次体，衣原体，支原体，军团菌，和….ppt

Rickettsia, Chlamydia, Mycoplasma, Legionella, and Gardnerella Everything else to the end………. Rickettsia Classification – Family Rickettsiaceae with 3 medically important genera Rickettsia Coxiella Rochlimaea Morphology and cultural characteristics All are obligate intracellular parasites (except Rochlimaea) that can grow in both phagocytic and nonphagocytic cells. Rochlimaea can be cultivated on artificial media containing blood Rickettsia Others are grown in embryonated eggs or tissue culture Cultivation is costly and hazardous because aerosol transmission can easily occur Small, pleomorphic coccobacilli Gram stain poorly, but appear to be G- Stain readily with Giemsa All, except Coxiella, are transmitted by arthropod vectors. Rickettsia Diagnosis/serological tests Direct detection of Rickettsia in tissues (Giemsa stain or direct fluorescent antibody test) Weil-Felix reaction – in certain rickettsial infections (typhus group) antibodies are formed that will agglutinate OX strains of Proteus vulgaris. This is used as a presumptive evidence of typhus group infection, however, the test is not very sensitive or specific and many false positives occur. Rickettsia Agglutination or complement fixation tests using specific Rickettsial antigens are better serological diagnostic tests. Virulence factors Rickettsial sp. Induced phagocytosis Recruitment of actin for intracellular spread Coxiella burnetti Is resistant to lysosomal enzymes Rickettsia cell-to-cell spread Rickettsia rickettsii Rickettsia Clinical significance – the diseases caused by Rickettsia are all characterized by fever, headache, myalgias, and usually a rash. Typhus fevers – incubation is 5-18 days. Symptoms include a severe headache, chills, fever, and after a fourth day, a maculopapular rash caused by subcutaneous hemorrhaging as Rickettsia invade the blood vessels. The rash begins on the upper trunk and spread to involve the whole body except the face, palms of the hands, and the soles of the f