Using Modified PCA Medium to Detect Difficult Cultivable Bacteria from Chicken Carcasses
改良PCA培养基检测鸡肉胴体中的污染细菌

Investigation of microbial spoilage in meats is usually hindered by the lack of suitable growth media and protocols to characterize the causative agents. A near-native medium of chicken extract agar (CEA), developed by the addition of sterile chicken extract into conventional plate count agar (PCA), was utilized to detect difficult cultivable bacteria on chicken carcasses. Suitable additive concentration was selected. Bacteria absent on conventional PCA medium but recovered by CEA were identified based on morphology, biochemical features and 16S rRNA gene sequencing. The colony form unit (CFU) was significantly greater (P < 0.05) and microflora more diversified on CEA than on PCA. CEA containing 3.0% (W/V) chicken extract gave the highest microbial enumeration at 64 CFU/g, almost twice that in PCA. Three species of bacteria absent on conventional PCA medium were recovered by CEA. According to their morphology and biochemical features, three bacteria recovered were identified as Enterococcus sp., Rothia sp., and Staphylococcus sp., respectively. The bacterial identification was confirmed by 16S rRNA sequence analysis with the similarity being 99% for both Enterococcus faecalis and Staphylococcus saprophyticus subsp. saprophyticus, and 96% for Rothia mucllaginosa. Three bacteria recovered by CEA are considered as either spoilage (Enterococcus sp.), opportunistic pathogen (Rothia sp.), or pathogen (Staphylococcus sp.) in foods, thus to cause problems associated with food safety.