University of Arkansas, Fayetteville Division of Agriculture


Antibiotic resistance genes (ARGs) among bacterial populations are causing increasing concern with medical and agricultural implications. While the effluent of wastewater treatment plants (WWTPs) is treated with a variety of antimicrobial methods, bacteria and the genetic material that is able to pass on antibiotic resistance to environmental populations are not completely destroyed. Ampicillin (amp), tetracycline (tet), and sulfonamide (sul) antibiotics have been detected in Northwest Arkansas (NWA) streams, and IncP plasmids—which are especially notorious for containing antibiotic resistance genes and have been detected after disinfection in NWA WWTPs—are known to carry ARGs for those antibiotics. The objective of this inquiry was to determine whether ARGs of commonly used antibiotics (ampC and oxa2 for ampicillin, tetA for tetracycline, and sul1 for sulfonamide resistance) were present in effluent following disinfection that demonstrated variable reduction in IncP plasmid numbers. DNA was extracted from water collected from a WWTP that uses ultraviolet light and a WWTP that uses chlorination and was participating in a pilot-scale ozonation test. Three of the four ARGs were detected using polymerase chain reaction (PCR) both before and after all three disinfection methods. The ampicillin resistance gene ampC was the only gene that was detected in less than two-thirds replications either before or after disinfection. Given the PCR results and previous quantitative PCR analysis of IncP plasmid concentrations, it appears there is little reduction of ARGs after disinfection. These data are important in understanding the role of WWTPs in contributing to the spread of antibiotic resistance in the environment.