Comparison of dark-field microscopy, culture, and polymerase chain reaction (PCR) for detection of Borrelia burgdorferi in field-collected Ixodes ricinus ticks.

In a study based on 100 field-collected female Ixodes (I.) ricinus ticks from the surroundings of Giessen, dark-field microscopy (DFM), culture, and PCR were compared as procedures for detecting Lyme borreliosis spirochetes in ticks. By DFM, 16 ticks were found to be infected with spirochetes. From the midgut of 18 ticks (including 14 microscopically positive specimens), spirochetes were cultured in BSK II medium and in BSK II medium supplemented with either co-trimoxazole (500 micrograms/ml) or 5-fluorouracil and kanamycin (200 micrograms/ml and 8 micrograms/ml). Using these selective media, the isolation rate was increased by 50% compared to BSK II medium without additives. Midgut homogenates of 22 ticks (including 13 ticks positive by culture and 12 microscopically positive ticks) were found to contain Borrelia (B.) burgdorferi-specific DNA by PCR using a primer set based on sequences of the flagellin gene of B. burgdorferi.