Antibiotic Resistance and Water Quality: Land Application of Swine Lagoon Effluent as a Potential Source of Antibiotic Resistant Genes in Surface Water
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Date
2009-12-01
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Abstract
The use of antibiotics in animals is suspected to be a major route for transfer of antibiotic resistance genes (ARGs) to human pathogens, although different antibiotics are used in animals than in humans. North Carolina has the second largest swine production industry in the USA which is concentrated in a small geographical area in the southeastern area of the state. This may increase the risk of antibiotic resistant bacteria reaching nearby surface waters. The goals of this study were 1) to identify and quantify ARGs in Escherichia coli isolates from swine feces, lagoon effluent, cattle, wildlife and ground and surface waters 2) to develop a data base for antibiotic resistance patterns for E. coli isolated from these sources 3) to evaluate the possible use of this database in tracking movement of fecal bacteria from confined swine operations to a nearby stream 4) to determine the relationship between antibiotic resistance genes found in E. coli strains from manure and water with the actual phenotypic expression of the resistance to their corresponding antibiotics. Escherichia coli isolates were recovered from manure and water samples by basic microbiological culture and IDEXX Colilert methods, respectively. Antibiotic resistance genes were identified from the isolates using the polymerase chain reaction (PCR) method. On average, E.coli counts in the surface water were 272.1 CFU/100 mL, 10 fold higher than that in ground water (21.1 CFU/100 mL). A total of 1,208 E. coli isolates from swine feces, lagoon effluent, cattle, deer, dog, bird and nearby ground and surface waters (n=238, 234, 192, 48, 48, 48, 200, and 200, respectively) were evaluated for ARGs. A total of 5909 E. coli isolates were evaluated for phenotypic expression of resistance to various concentrations of the following antibiotics: erythromycin, neomycin, oxytetracycline, streptomycin, tetracycline, cephalothin, apramycin, trimethoprim, and rifampicin. About 96% of the isolates displayed multiple antibiotic resistances. Genotypic evaluation indicated the presence of aadA, strA, strB, tetA, tetB, tetC, sul1, sul2, sul3, and Aac(3)IV ARGs in all the sources of isolates. Resistance genes that code for resistance to spectinomycin (aadA), low level streptomycin (str), tetracycline (tetA) and sulfonamide (sul1) were present in highest frequency. The database developed from antibiotic resistance patterns
(ARP) and antibiotic resistant genes (ARGs) of E. coli isolates from the known sources were able to associate fecal bacteria in ground and surface water to lagoon effluent and to livestock respectively. The results clearly show that the presence of ARGs does not always result in phenotypic expression of the resistance and vice versa. The results will increase awareness on the widespread of antibiotic resistance in both agricultural systems and environmental pools within confined swine farms. Even though good management practices for swine waste management (anaerobic lagoon systems) are effectively mitigating fecal pollution, there is a need for prudent and responsible use of antibiotics especially with those prone to induce resistance.
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Soil, Animal Waste, Fecal Indicator Bacteria, Microbial Source Tracking
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Degree
MS
Discipline
Soil Science
