CYCLOHEXIMIDE AS A MEDIA AMENDMENT FOR ENUMERATING BACTERIAL POPULATIONS IN ANIMAL FEEDS

The present study was designed to evaluate cycloheximide as a potential media amendment for differential bacterial and fungal enumeration of animal feeds. The objectives of this study were to determine the effect of cycloheximide on bacterial growth rates and to evaluate its efficacy for the reduction of indigenous spreading fungi when enumerating bacterial populations in three types of feeds and after short or long-term storage. Escherichia coli, Bacillus cereus, Staphylococcus aureus, Listeria monocytogenes and Pseudomonas fluorescens were grown in tryptic soy broth containing cycloheximide to determine its effect on bacterial specific growth rates. Growth rates of B. cereus and S. aureus were significantly decreased by the addition of 600 and 1000 mg/L cycloheximide respectively, but other pure cultures were not significantly influenced by cycloheximide addition. Intrinsic bacterial populations from feed were not significantly affected by cycloheximide additions at concentrations from 10 to 300 mg/L, but the indigenous spreading molds from feeds were significantly decreased by these cycloheximide concentrations and were decreased below detection levels by 300 mg/L of cycloheximide. The addition of 300 mg/L of cycloheximide effectively eliminates fungal growth for accurate enumeration of bacterial populations in feeds.