The effect of third generation cephalosporin use on antimicrobial resistance in domestic dairy farms in Korea = The effect of third generation cephalosporin use on antimicrobial resistance in domestic dairy farms in Korea

다국어 초록 (Multilingual Abstract)

Introduction: The antimicrobial resistance to the third-generation cephalosporins (3G-Ceph) in gram negative bacteria is an emerging concern worldwide. The prevalence of 3G-Ceph resistant bacteria in livestock has also increased in Korea over the past few years. It is important to elucidate the relatedness between the use of 3G-Ceph and the increased antimicrobial resistance to these antimicrobials in local farms. This study was conducted to evaluate the effect of 3G-Ceph (ceftiofur) use on the increase of antimicrobial resistance by comparing the antimicrobial resistant rates between 3G-Ceph using and non-using farms.
Methods: A total of 490 raw milk samples were collected from ceftiofur using (n =240) and non-using farms (n=250). E. coli were isolated using EC broth enrichment followed by streaking on ECC agars and confirmed by a specific PCR. Antimicrobial susceptibility tests were conducted according to the guidelines of Clinical Laboratory Standards Institute. Antimicrobial resistance genes related to 3G-Ceph resistance were detected by specific PCRs.
Results: A total of 160 E. coli (123 from using and 37 from non-using farms) were isolated. The antimicrobial resistant rate to 3G-Ceph was significantly higher in 3G-Ceph using farms (9.8%) than in non-using farms (2.7%). The MICs of 3G-Ceph were measured as less than 4 ug/ml in isolates from non-using farms and 64-1024 ug/ml from using farms. All the resistant isolates from using farms harbored a CTX-M gene, whereas none from non-using farms.
Conclusion: Contaminated raw milk can be a vehicle for transmission of antimicrobial resistant bacteria from dairy to humans. The current study indicates the overuse of 3G-Ceph in dairy farms could increase the risk of transmission of 3G-Ceph resistant bacteria to a human community. Therefore, prudent use of this category of antimicrobials in dairy farms is warranted to prevent the dissemination of 3G-Ceph bacteria from animals to humans.