PRIMARY CULTURE OF BORRELIA-BURGDORFERI FROM IXODES-RICINUS TICKS

A total of 971 Ixodes (I.) ricinus ticks field-collected in May and Ju ne 1993 and 1994 in two different geographic regions (Middle Hesse and Lower Saxony) were examined for the presence of Lyme borreliosis spir ochetes (Borrelia burgdorferi sensu lato) by primary culture using non selective and selective BSK II medium. Modifications of BSK II medium with varying concentrations of bovine serum albumin and with rabbit se rum being replaced by horse serum were examined for their ability to s upport growth of borreliae from ticks. Spirochetes were isolated from 17.8% each of female and male I. ricinus from Lower Saxony. Isolation rates from female and male I. ricinus originating from Middle Hesse we re 13.5% and 19.6%, respectively. In comparison to nonselective BSK II medium the isolation rate of borreliae from the tick midgut was incre ased significantly (35%) by additional culture in selective BSK II med ium. Most spirochetal isolates (85%) were detected within three weeks of incubation. Compared to isolation in standard BSK II medium, reduct ion of bovine serum albumin by 50% did not diminish the isolation rate of borreliae from ticks. Spirochetal isolates were identified as Borr elia burgdorferi sensu late by PCR using a primer set based on ribosom al DNA sequences to amplify the variable spacer region between two con served structures, the 3'end of the 5S rRNA and the 5'end of the 23S r RNA.