Purpose: The aim of this study was to evaluate the effect of high concentration of polymyxin B on the detection ability and selectivity of mCCDA to isolate C. jejuni and C. colifrom chicken carcass rinse.
Methods: Modified mCCDA (P-mCCDA) was made by adding 100,000 IU of polymyxin B to 1 liter of mCCDA. Chicken carcasses were rinsed with 400 ml of buffered peptone water. To ensure even distribution, the carcass rinse was mixed thoroughly by gently shaking the sample for 1 min. A 25 ml test portion from the 400 ml rinse was enriched with 25 ml of 2× blood-free Bolton enrichment broth in a 50-ml screw-cap conical tube. Less than 0.5 cm of headspace was left in the tubes and the lids were tightly capped. Each sample (50 ml) was enriched at 42°C for 48 h. A loopful of the enrichment broth was streaked onto mCCDA, Campy-Cefex agar, and P-mCCDA followed by incubation under microaerobic condition at 42°C for 48 h. Suspected colonies (maximum-10) were removed and sub-cultured onto 5% horse blood agar. Presumptive C. jejuni and C. coli colonies were confirmed with colony PCR. We compared the number of plates of C. jejuni/ C. coli and competing organisms in terms of isolation rate and selectivity, respectively.
Results: The number of P-mCCDA (70 out of 80) plates positive for both C. jejuni and C. coli was significantly higher (P < 0.05) than those of positive mCCDA (51 out of 80) and Campy-Cefex (36 out of 80) plates. Furthermore, fewer (P < 0.05) P-mCCDA plates (31 out of 80) were contaminated than other media plates (mCCDA, 34 out of 80; Campy-Cefex, 79 out of 80), indicating the superior selectivity of P-mCCDA.
Significance: Addition of high concentration of polymyxin B to conventional media could be a useful option to improve selectivity and isolation rate in chicken carcass rinse.