Antibiotic Resistance and intI1 Carriage in Waterborne Enterobacteriaceae

The spread of antimicrobial resistance (AMR) is a global concern, high research priority being given to the environmental contamination, as the prevalence of organisms exhibiting AMR continues to increase. Multiresistant bacteria carrying different mobile genetic elements have been detected in sites with different degrees of urbanization, surface waters receiving insufficiently treated effluents being at high risk. The aim of the present study was to investigate the loads, antibiotic susceptibility, and class 1 integron carriage of Enterobacteriaceae isolated from surface waters and wastewaters around a large Romanian city. Searching for a valuable genetic marker of the displayed antibiotic resistance, the link between the AMR and the presence of int1I gene was explored in a total of 166 waterborne strains. Overall, amoxicillin-clavulanate resistance displayed the highest frequency (71.1 %), followed by ampicillin (63.9 %), cefuroxime (21.1 %), ciprofloxacin (17.5 %), cefotaxime (15.7 %), ceftriaxone (10.8 %), and gentamicin (6.6 %). The frequencies of isolates resistant to ampicillin, amoxicillin-clavulanate, ciprofloxacin, and gentamicin and also the prevalence of multiresistant strains were greater in surface waters, compared to wastewaters. The Int1I gene was detected in 21.7 % waterborne Enterobacteriaceae. A decrease in coliform counts and intI1-bearing cells, but a general increase in AMR and multiresistant bacteria, occurred during the wastewater treatment. A weak positive correlation was found between multidrug resistance int1I carriage in wastewater effluent but no sufficient evidence of a linkage between phenotypic AMR and int1I, overall. The presence of class 1 integron can be associated with anthropogenic influence, but the simple detection of intI1 gene cannot explain the complex antibiotic resistance phenotype.