Purpose: The goal of the study was to evaluate the effect of a high concentration of polymyxin B on the ability and selectivity of the modified Karmali agar to isolate Campylobacter jejuni and C. coli from whole chicken carcass rinse.
Methods: A total of 80 whole chickens were rinsed with 400 ml of buffer peptone water. The rinsed samples were incubated with 2 × blood-free modified Bolton enrichment broth for 48 h and then streaked onto unmodified Karmali agar and modified Karmali agar [polymyxin B (100,000 IU/l) supplemented Karmali agar; P-Karmali agar]. The suspected colonies were finally confirmed by colony PCR.
Results: The P-Karmali agar exhibited a significantly better (P < 0.05) isolation rate than the unmodified Karmali agar (P-Karmali agar, 73.8%; unmodified Karmali agar, 33.8%). Moreover, the selectivity of the P-Karmali agar was also better (P < 0.05) than that of the other selective agar when comparing the number of contaminated plates (P-Karmali agar, 68.8%; unmodified Karmali agar, 87.5%) and growth index (P-Karmali agar, 1.4; unmodified Karmali agar, 2.7) of competing flora.
Significance: The improved selective agar excluded competing flora resistant to antibiotic agents in unmodified Karmali agar, increasing isolation rate and selectivity for C. jejuni and C. coli.