Antibiotic Resistance: How Much Do We Know and Where to Go From Here?

The rapid dissemination of antibiotic resistant (ART) pathogens threatens human health and may have significant social and financial impacts. It is well recognized that applications of antibiotics in human clinical therapy, aquaculture, and food animal production all contribute to the emergence and amplification of ART pathogens due to selective pressure (8, 14). Restricting the therapeutic and prophylactic use of antibiotics in clinics and food animal production has been the primary strategy for antibiotic resistance (AR) mitigation to date. However, despite these efforts, which include changes in medical practice guidelines and government policies in both the European Union and the United States, the rising trend of AR has not changed much in recent years. In the past several years, evidence showing a much more complicated picture of AR has emerged. Data from both organism-specific and population-based studies have suggested that various mechanisms contribute to the retention of AR determinants, and in certain cases ART bacteria become the dominant microbial population, even in the absence of a corresponding antibiotic selective pressure (7, 9, 17, 18). ART bacteria have been found not only in various food products and environmental samples but also in hosts without a history of direct exposure to antibiotics (6, 20, 25). The existence of large AR gene pools in food-borne commensal bacteria present in many ready-to-consume food items suggested that human beings are constantly inoculated with large numbers of ART bacteria through daily food intake, independent of clinical antibiotic exposure (3, 19, 28). A broad spectrum of commensal bacteria, including lactic acid bacteria, have been identified as being carriers of AR genes and are able to transmit those genes to other bacteria in laboratory settings, leading to increased resistance in the recipient organisms (4, 28). While the impacts of commensal bacteria in food, host, and environmental ecosystems on AR origination, dissemination, and persistence have yet to be fully appreciated, it is evident that underestimating the roles of commensals and other AR dissemination channels in the AR picture may have hindered the development of effective mitigation (1, 26). To fill in the critical knowledge gaps and facilitate the development of targeted control strategies, USDA-CSREESNIFSI and The Ohio State University cosponsored the international conference “Food Safety and Public Health Frontier: Minimizing Antibiotic Resistance Transmission through the Food Chain,” which took place 2 and 3 April 2009 in Arlington, VA. The conference brought together experts from academia, industry, and federal agencies for a balanced and scientific review of AR. Invited senior experts shared their most recent discoveries, visions of AR management, and successful experiences in AR mitigation. The resultant expert report recommended that systematic studies for a comprehensive understanding, at both the macroscopic and microscopic levels, of AR connected to the food chain are central to the design of targeted and integrated intervention strategies for effective mitigation of AR (27). The conference organizers sincerely appreciate ASM and Applied and Environmental Microbiology for recognizing the scientific significance of the event and providing the platform by which to systematically present related work contributed by the conference speakers. This special issue addresses several questions imperative to the fundamental understanding of AR and with direct impact on mitigation efforts. As mentioned above, antibiotics selectively enrich ART bacteria and the corresponding AR gene pools in the microbiota. A critical issue of relevance to control strategies is whether antibiotic selective pressure is the only factor responsible for the amplification, maintenance, and transmission of ART bacteria in microbial ecosystems. To reveal the baseline of ART bacteria in host gastrointestinal tracts, Stanton et al. (24) examined chlortetracycline (CTC)-resistant Escherichia coli, Megasphaera elsdenii, and anaerobic bacteria in swine feces. Up to 10 CTC-resistant (at 64 g/ml) anaerobic bacteria were detected in fecal samples from organically raised swine, while the number was significantly lower in fecal samples from feral swine. The data illustrated the prevalence of ART bacteria in the gastrointestinal tracts of animals lacking direct exposure to antibiotics. Meanwhile, the results also suggested an impact of human activities, environmental factors, and also possibly host specificity on AR development. More directly, Zhang et al. (29) illustrated that levels of ART bacteria rose to between 10 and 10 CFU/g in the infant gut microbiota within days after birth, independent of exposure to antibiotics and intake of ART bacterium-rich conventional foods. The results illustrated a potentially significant route of AR dissemination from * Corresponding author. Mailing address: Department of Food Science and Technology, The Ohio State University, Parker FST Building, 2015 Fyffe Ct., Columbus, OH 43210-1007. Phone: (614) 292-0579. Fax: (614) 292-0218. E-mail: wang.707@osu.edu. Published ahead of print on 9 September 2011.