The most menacing sources of environmental contamination with antibiotic resistant bacteria are effluents derived from anthropic activities. Even when wastewater treatment processes are implemented, conventional methods are not able to completely retain the antibiotic resistance determinants. We propose an antibiotic resistance risk assessment, incorporating the characterisation of ARB, ARGs and MGEs in different environmental compartments.

Antibiotic susceptibility testing of 678 Enterobacterales isolates revealed an increased degree of intrinsic resistance to erythromycin (77.9 %), high level of resistance to ampicillin (39.7 %), low frequency of carbapenem resistance (2.36 %), and a percentage of 34.4 % MDR strains. The most frequent resistance determinants were blaTEM-1 (26.5 %) and tetA (8.26 %), while the intI1 gene was found in 7.37 % of isolates. Resistant Enterobacterales from aquatic matrices with different degrees of contamination were identified as Citrobacter spp. (n = 46), Enterobacter spp. (n = 35), Klebsiella spp. (n = 54) and Escherichia coli (n = 107). A strong statistical correlation was observed between the presence of intI1 and the ARG index (0.768) in resistant Enterobacter spp.

Distinct clustering of strains was not observed across different environmental matrices, especially in those directly impacted by human-derived bacteria. Also, distribution of ARB patterns and diversity of ARGs was stable from the taxonomic perspective. Dendrogram analysis based on ERIC-PCR profiles confirmed the presence of strains with identical DNA fingerprints in non-related aquatic ecosystems. The epidemiology of resistant Citrobacter, Enterobacter, Klebsiella and Escherichia isolates confirmed an extensive migration and environmental dispersion of strains with human health significance, particularly important for water resources.