Evaluation of culture media for the isolation of Salmonellae from feces

Abstract

A study conducted on 300 fecal samples from a cow and a pig, each artificially contaminated with approximately four Salmonella organisms revealed that, of the three enrichment broths used in conjunction with the three selective media, the maximum number of isolations were obtained with Brilliant Green MacConkey broth (BGMB), followed by those obtained with tetrathionate (TTB), and the least with selenite broth. The combination of BGMB with Brilliant Green-neutral red-lactose agar (BGNRLA), and TTB with desoxycholate citrate agar (DCA) gave an equal number of isolations. Of the three selective media used in conjunction with the three enrichment broths, the maximum number of recoveries were obtained on BGNRLA, followed by those on DCA, and least number of isolations on bismuth sulfite agar (BSA). The combination of selenite F broth-BSA appeared to be somewhat inhibitory for the growth of Salmonella organisms. Of the two selective media combinations, the DCA-BGNRLA combination yielded the highest number of isolations. The use of all three selective media gave still better results. Selenite and tetrathionate broths were found unsuitable for isolating Salmonella choleraesuis from feces. BGMB, containing 100 mug of Brilliant Green per ml, proved to be a useful enrichment medium for the isolation of this organism from cow and pig fecal samples, each inoculated with 16 organisms. Observations recorded seemed to suggest that contaminant bacteria perhaps outgrow and mask S. choleraesuis. An incubation period of 24 to 30 hr was found optimum for the three enrichment broths. A longer period was detrimental in the case of TTB but not with selenite broth and BGMB.