The effectiveness of traditional water disinfection methods against both environmental antibiotic resistant bacteria (ARB) and antibiotic resistant genes (ARGs) is still not well understood. The study objective was to evaluate two common methods for reducing concentrations of not only culturable tetracycline-resistant bacteria but also a resistance tet(W) gene fragment that has been frequently detected in the environment. Disinfection experiments were performed by exposing tetracycline-resistant isolates to various dosages of sodium hypochlorite or ultraviolet irradiation _____________________

Aims: The objective of this study was to determine whether varying levels of urbanization influence the dominant bacterial species of mildly resistant (0Á03 mmol l À1 tetracycline) and highly resistant (0Á06 mmol l À1 tetracycline) bacteria in sediment and water. Also, the level of urbanization was further evaluated to determine whether the diversity of tetracycline resistance genes present in the isolates and the capability of transferring their resistance were influenced. Methods and Results: Sediment and water samples collected from five sampling sites were plated in triplicate on nutrient agar plates with a mild dose (0Á03 mmol l À1 ) and a high dose (0Á06 mmol l À1 ) of tetracycline. Five colonies from each plate plus an additional five from each triplicate group were randomly selected and isolated on nutrient agar containing 0Á03 mmol l À1 tetracycline (400 isolates). The isolates were identified by 16S rRNA gene sequencing and comparison to GenBank using BLAST. The isolates were also screened for 15 tetracycline resistance genes using a multiplex PCR assay and their ability to transfer resistance through conjugation experiments using a kanamycin-resistant Escherichia. coli K-12 strain labelled with a green fluorescent protein gene. Results from this study indicate that the dominant resistant organisms in this watershed are Acinetobacter spp., Chryseobacterium spp., Serratia spp., Pseudomonas spp., Aeromonas spp. and E. coli. All of these organisms are Gram negative and are closely related to pathogenic species. A majority of the isolates (66%) were capable of transferring their resistance, and there was a greater incidence of tet resistance transfer with increasing urbanization. Also, it was determined that the dominant resistance genes in the watershed are tet(W) and tet(A). Conclusion: Urbanization significantly affected dominant tetracycline-resistant bacteria species, but did not affect dominant resistance genes. There was correlation between increased urbanization with an increase in the ability to transfer tetracycline resistance. This indicates that urban areas may select for bacterial species that are capable of transferring resistance. Significance and Impact of Study: These results indicate that urbanization influences the occurrence of tetracycline-resistant bacteria and the potential for transfer of resistance genes.

The ubiquitous use of antibiotics has led to an increasing number of antibiotic-resistant bacterial strains, including strains that are multidrug-resistant, pathogenic, or both. There is also evidence to suggest that antibiotic resistance genes (ARGs) spread to the environment, humans, and animals through wastewater effluents. The overall objective of this study was to investigate the effect of ultraviolet (UV) light disinfection on antibiotic-resistant bacteria. Wastewater effluent samples from a wastewater treatment plant (WWTP) in Texas were evaluated for differences in tetracycline-resistant bacteria before and after UV treatment. The effects of photoreactivation or dark repair on the reactivation of bacteria present in WWTP effluent after UV disinfection were also examined. Culture-based methods were used to characterize viable heterotrophic, tetracycline-resistant heterotrophic, Escherichia coli, and tetracycline-resistant E. coli bacteria present before and after UV treatment. UV disinfection was found to be as effective at reducing concentrations of resistant heterotrophs and E. coli, as it was at reducing total bacterial concentrations. The lowest survival ratio following UV disinfection was observed in tetracycline-resistant E. coli showing particular susceptibility to UV treatment. Photoreactivation and dark repair rates were found to be comparable to each other for all bacterial populations.

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