Prevalence of Sulfonamide Resistance Genes in Bacterial Isolates from Manured Agricultural Soils and Pig Slurry in the United Kingdom

Abstract

ABSTRACT The prevalences of three sulfonamide resistance genes, sul1 , sul2 , and sul3 and sulfachloropyridazine (SCP) resistance were determined in bacteria isolated from manured agricultural clay soils and slurry samples in the United Kingdom over a 2-year period. Slurry from tylosin-fed pigs amended with SCP and oxytetracycline was used for manuring. Isolates positive for sul genes were further screened for the presence of class 1 and 2 integrons. Phenotypic resistance to SCP was significantly higher in isolates from pig slurry and postapplication soil than in those from preapplication soil. Of 531 isolates, 23% carried sul1 , 18% sul2 , and 9% sul3 only. Two percent of isolates contained all three sul genes. Class 1 and class 2 integrons were identified in 5% and 11.7%, respectively, of sul -positive isolates. In previous reports, sul1 was linked to class 1 integrons, but in this study only 8% of sul1 -positive isolates carried the intI1 gene. Sulfonamide-resistant pathogens, including Shigella flexneri , Aerococcus spp., and Acinetobacter baumannii , were identified in slurry-amended soil and soil leachate, suggesting a potential environmental reservoir. Sulfonamide resistance in Psychrobacter , Enterococcus , and Bacillus spp. is reported for the first time, and this study also provides the first description of the genotypes sul1 , sul2 , and sul3 outside the Enterobacteriaceae and in the soil environment.