Survey on contamination to Yersinia entrocolotica in raw cow milk distributed in Ahvaz area and evaluation of antibiotic resistance of isolates

Totally 150 samples of cow milk were collected in Ahvaz within 6 months. The collected samples were sent to the lab in cool conditions. The amount of 25 ml of each sample was added to 225 ml of Tris-Buffered Peptone Water with pH=8 as enrichment medium and stored at 4°C for three weeks. Then in 7th, 14th and 21th days of storage, one loopful equal to 10 µL of enriched broth were streaked out in plates of Cefsulodin-Irgasan-Novobiocin agar contained supplement and incubated at 30°C for 24 hours. Then 3 to 5 colonies of typical bulls-eye appearance with 0.5-2 mm diameter with a deep red center and sharp border surrounded by a translucent zone were selected as suspect to Yersinia enterocolitica and cultured in TSA medium. After gram staining and observe gram negative rod and also implement some biochemical tests in next step due to absolute identification, specific primers for 16srRNA were used. Boiling method was used to extract DNA. The isolation of Yersinia entroclitica was confirmed from 36 samples (24%) of milks. The confirmed isolates due to antibiogram were spread out in agar culture and the antibiotic susceptibility was surveyed with utilization of antibiotic discs and CLSI tables. The results showed that the sensitivity to Ciprofloaxin, Gentamicin, Tetracycline, Ceftazidime, Nalidixic Acid, Kanamycin, Trimethoprim Sulfametaxazole, Amoxicillin and Cephalotin were 100%, 97.05%, 91.17%, 85.29%, 82.35%, 79.41%, 67,64%, 17.64% and 14.7% respectively. None of the isolates were susceptible to Erythromycin which shows that the isolates have the most resistance against this antibiotic.