Development of a modified selective medium to enhance the recovery rate of Brachyspira hyodysenteriae and other porcine intestinal spirochaetes from faeces

Aims:  The aim of this study was to develop a modified selective medium to improve the recovery rate of Brachyspira hyodysenteriae and other clinically significant intestinal spirochaetes from porcine faeces.

Methods and Results:  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 spirochaetes were susceptible to halquinol at ≤1 μg ml⁻¹, while 16 μg ml⁻¹ of flavomycin (F) allowed their growth, and therefore, only the latter 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 spirochaetes from seeded faeces was determined. Two solid media were selected for further testing using faeces 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⁻¹), S (400 μg ml⁻¹), R (30 μg ml⁻¹) and colistin (C, 100 U ml⁻¹) (assigning as BAM-CSRF) reduced the growth of contaminating intestinal microbiota and resulted in a significantly higher rate of spirochaete recovery than the previous recommended medium.

Conclusion:  BAM-CSRF is a useful new selective medium for the isolation of B. hyodysenteriae and other intestinal spirochaetes from pig faeces.

Significance and Impact of the Study:  The new selective medium for isolating B. hyodysenteriae and other Brachyspira spp. from pig faeces will improve their recovery and subsequent disease diagnosis.