characterization of beta-lactamase producing enterobacterales isolated from an urban community wastewater treatment plant in iran

Background and objectives: he occurrence and characteristics of extended spectrum- and ampc-β-lactamase producing enterobacterales (esbl-pe and ampc-pe) in an urban wastewater treatment plant (wwtp) were investigated. materials and methods: a total of 30 wastewater samples were collected from all sections of wwtp. enterobacterales were isolated and identified using standard microbiological tests. the antibiotic resistance profile was determined by the kir- by–bauer disk diffusion method. phenotypic screening for esbl-pe and ampc-pe isolates was performed by double-disk synergy and boronic acid disk potentiation tests, respectively. the isolates were examined for ampc- and esbl-encoding genes by pcr and sequencing methods. results: among 146 enterobacterales isolates, 8.9% (n=13) [esbl-only; 5.48% (n=8) and esbl + ampc; 3.42% (n=5)] were esbl-producers and 15.75% (n=23) [ampc-only; 12.33% (n=18) and esbl + ampc; 3.42% (n=5)] ampc-produc- ers. hafnia spp. with 33.33% (n=1/3) and e. coli with 20.58% (n=7/34) [esbl-only; 17.64% (n=6/34) and esbl + ampc; 2.94% (n=1/34)] were the most common esbl-producing bacteria. enterobacter spp. with 37.50% (n=6/16) of isolates were the most common ampc-producing organisms. esbl- and/or ampc-producing isolates were identified in all parts of the wwtp including 80% (n=8/10) of samples taken from effluent. among esbl-producing isolates, bla ctx-m tem , and bla shv esbl-encoding genes were found in 61.5% (n=8), 15.3% (n=2), and 7.7% (n=1) of isolates, respectively. all ctx-m- type enzymes belonged to the ctx-m-1 group and ctx-m-15 subgroup. bla tem and bla shv type genes belonged to bla tem-20 and bla hsv-12 subtypes, respectively. bla with 73.9% (n=17/23), and bla cit and bla with 30.4% (n=7/23) each, were the most common ampc-encoding genes among ampc-producing isolates. overall, 75% of esbl-producing and 55.5% of ampc-producing isolates exhibited multi-drug resistance phenotypes. the organisms were most resistant against ampicillin (82.2%) nalidixic acid (43.8%) and cephalexin (41.1%). conclusion: esbl- and ampc-producing enterobacterales spp. with diverse genetic resistance backgrounds in wwtp effluent poses a significant risk to public health.