Antimicrobial resistant bacteria in dairy cattle: A review
Dr Sara Burgess and Professor Nigel French
The development and transmission of bacterial antimicrobial resistance (AMR) is a complex and multifaceted process. One of the main drivers identified for the development and spread of AMR is the use of antimicrobials in human and veterinary medicine as well as for agricultural use. Although agricultural use from high antimicrobial use sectors such as pigs and poultry contribute to the emergence of resistant strains (and transmission via food does occur), current evidence indicates that human use is believed to be the main driver for emergence and persistence of AMR in humans. Despite New Zealand having a low use of antimicrobials in food producing animals compared with other developed countries there is room for improvement. In the dairy sector blanket dry cow therapy (DCT) is being used on some farms; where targeted treatment would suffice. In addition, judicious use of antimicrobials, (particularly those identified as being red tier by the NZVA) is required.
In New Zealand there is no evidence to date that the use of antimicrobials in dairy cattle has resulted in the emergence of pathogens that are multidrug resistant. At present the risk of AMR developing in bacteria carried by dairy cattle and potential transmission to humans is not able to be assessed because of the lack of New Zealand data. However, research carried out overseas suggests that there is the potential for antimicrobial resistance to increase due to the use of antimicrobials in the dairy industry, particularly through the use of third and fourth generation cephalosporins. Although there is limited evidence for the transmission of antimicrobial resistant bacteria and their genes between dairy cattle and humans, it is clear that antimicrobial use can lead to bacteria in the gut of dairy cattle developing AMR.
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