Antimicrobial resistance in aquaculture.

Appropriate antimicrobial therapy represents one of the most effective management responses to emergencies associated with infectious disease epizootics. The use of these agents, however, has the potential to increase the frequencies of bacterial resistance and this would have a negative impact on the subsequent use of these agents to control infectious disease in aquaculture. There is also a possibility that the enrichment of resistant bacteria or genes encoding resistance could have an adverse impact on the use of antimicrobial agents to control diseases in humans and other land-based animals. Attempts to apply formal risk analysis to this problem have been frustrated by the extreme diversity of aquaculture and by the general shortage of relevant data. A central argument made in this paper is, however, that not only do we lack the data this exercise would require; we also lack validated methods for collecting those data in the first place. At the most fundamental level we do not even possess validated methods for determining whether a bacterium isolated from an aquaculture site should or should not be classified as resistant. In the absence of any significant risk assessment, current attempts at risk management are centred on the development of lists of critically important antimicrobials for the various users of these agents. It is argued here that studies of gene ecology and models of gene flow in the environment are urgently required if we are to be able to evaluate this risk management approach, to predict its consequences or to generate more appropriate strategies.