Low nutrient R2A culture medium for bacterial enumeration from poultry feeds

Poultry feed matrices can be particularly stressful to bacterial populations and limit recovery and accurate enumeration of viable organisms. The objectives in this study were to enumerate bacterial populations with either tryptic soy plate medium or an R2A minimal nutrient medium from commercial poultry and turkey dry feeds and compare enumerations from the two media with feed composition. Total population estimates from tryptic soy plates varied between 3.7 and log(10) 5.4 CFU per g feed and depended upon poultry feed source (P<0.05). R2A plate counts varied between 2.7 and log(10) 5.4 CFU per g feed, but were not significantly different among poultry feed sources. Feed R2A plate count populations were significantly correlated (P<0.01) with tryptic soy plate count populations enumerated from the feed sources, but not protein and fat content of the feed source. It is apparent that bacterial counts recovered by minimal R2A medium are similar to enumerations using tryptic soy plate medium and that R2A medium could be substituted for tryptic soy plate medium for bacterial enumeration in poultry feeds.