Molecular Epidemiology of Ampicillin Resistance in Salmonellaspp. and Escherichia colifrom Wastewater and Clinical Specimens

AbstractMolecular epidemiology at local scale in Sicily (Italy) of ampicillin resistance in Salmonellaspp. isolates from municipal wastewater (n= 64) and clinical specimens (n= 274) is described in comparison with previously examined Escherichia coliisolates (n= 273) from wastewater. High prevalence of antibiotic resistance (28.9%) with highest resistance rates against ampicillin (22.7%) was observed in E. coliisolates. Different resistance rates were observed in Salmonellaaccording to the serovars, with prevalences of the same order in both wastewater and clinical isolates belonging to the same serovar (e.g., 91.7% ampicillin resistance in wastewater isolates vs. 70.8% in clinical isolates of the Salmonellaserovar Typhimurium and 0% ampicillin resistance in both wastewater and clinical isolates of the Salmonellaserovar Enteritidis). The β-lactam resistance gene blaTEMwas present in both wastewater and clinical Salmonellaspp. isolates, with the exception of Salmonella entericaserovar Typhimurium isolates with a typical six-drug resistance pattern AmpChlSulTeStrSp that had the blaPSE-1gene. The blaTEMgene was present in all the E. coliisolates but one had the blaSHVgene. Several E. coliand some Salmonellaisolates were positive for class 1 integrons with variable regions of 1.0 or 1.5 kb containing aadA1, dfrA17-aadA5, or dfrA1-aadA1gene cassettes, whereas Salmonellaserovar Typhimurium isolates with the six-drug resistance pattern were positive for both 1.0 and 1.2 kb integrons. Polymerase chain reaction replicon typing demonstrated the presence of multireplicon resistance plasmids in several isolates of E. coli, containing two to four of the replicons IncF, IncI1, IncFIA, and IncFIB, whereas other isolates showed resistance plasmids with only IncF, IncP, or IncK replicons. Replicon IncI1 was detected in one Salmonellaisolate, whereas other isolates belonging to different serovars had IncN replicons. Analysis of isolates from wastewater can be a useful epidemiologic tool to monitor the prevalence of antibiotic resistance and genetic elements related to antibiotic resistance in Salmonellaclones circulating in the human population.