Does the use of antifungal agents in agriculture and food foster polyene resistance development? A reason for concern

Environmental fungicides are used in agriculture to reduce fungal spoilage of crops to a minimum, and the polyene macrolide natamycin is used as a food preservative. The use of natamycin in yoghurt has recently been authorised in the USA and some other countries. However, resistance development is a serious risk associated with the use of antimicrobials as food additives and environmental fungicides. Cross-resistance between agricultural and medical azoles and between azoles and amphotericin B (AMB) not being used in agriculture has been demonstrated in clinical and environmental isolates. Polyene resistance can be elicited in vitro by the use of subinhibitory polyene concentrations and a large number of transfers. This condition may mirror the exposure of faecal Candida spp. to natamycin following consumption of natamycin-containing food. A large number of environmental and clinical isolates are resistant to AMB, and strong evidence linking farm antibiotic use and multidrug resistance, including AMB resistance, in human infections has been provided. In contrast to the acquisition of resistant environmental strains, consumption of natamycin-containing food may expose the gastrointestinal fungal flora directly to resistance selective pressure. So far, whether natamycin itself may cause the emergence of polyene resistance in gastrointestinal fungal flora and/or may act as an AMB resistance selector is probable but speculative. Use of any anti-infective agent as a food preservative should be limited to an absolute minimum as the clinical efficacy of anti-infectives used to treat serious life-threatening infections has to be preserved.