This study was to develop a modified selective medium to improve the recovery rate of Brachyspira hyodysenteriae and other clinically significant intestinal spirochetes from porcine faces.The susceptibility of five Brachyspira spp. type strains and five Thai field isolates of B. hyodysenteriae to the antimicrobials halquinol and flavomycin was determined by in vitro susceptibility tests in the agar dilution method, and optimal incorporation rates were confirmed by broth dilution. All the spirochetes were susceptible to halquinol at <1 μg/ml, while 16 μg/ml of flavomycin (F) allowed their growth, and therefore, only the later was selected for further use. F and different combinations of colistin (C), spectinomycin (S) and rifampacin (R) were incorporated into pre-enrichment broths and/or agar plates, and growth of the spirochetes from seeded feces was determined. Two solid media were selected for further testing using feces from 90 finishing pigs on 10 farms. A previously recommended method of pre-enrichment did not increase the recovery rate. The use of blood agar modified medium (BAM) containing F (16 μg/ml), S (400 μg/ml), R (30 μg/ml) and colistin (C, 25 μg/ml)1(assigning as BAM-CSRF) reduced the growth of contaminating intestinal microbiota and resulted in a significantly higher rate of spirochete recovery than the previous recommended medium.In the summary, BAM-CSRF is a useful new selective medium for the isolation of B. hyodysenteriae and other intestinal spirochetes from pig feces.
