Abstract

Since human-associated bacteria have been recognized as vectors in two - way gene transmission between the pathogenic and environmental populations, health hazard connected with wastewater discharge requires reevaluation. In this paper the particular attention was given to antimicrobial-resistance of Escherichia coli and enterococci isolated from wastewater and wastewater impacted environments. The obtained results showed that during the wastewater treatment processes the fecal indicators with antimicrobial resistance patterns were positively selected. Among enterococci isolates resistant to high-level aminoglycoside (HLAR) were detected, while among E. coli - extended spectrum β-lactamases producing isolates were found. Detailed analysis of E. coli producing extended-spectrum β-lactamases (ESBL) indicated CTX-M β-lactamase type, which is produced by nosocomial and community strains of Enterobacteriaceae in different countries. The recently discovered, plasmid-borne sulfonamide resistance gene - sul3 was also detected in the WWTP effluent. Additionally among E. coli the positive correlations was found between antimicrobial resistance of clinical relevance and presence of class 1 integrons with occasional occurrence of class 2 integrons. Among E. faecium subjected to typing hospital-adapted polyclonal high-risk enterococcal complex (HiRECC) constituted altogether 25% of all isolates and were present at all sampling points. This suggests the ability of such clones to survive the wastewater treatment processes. The HiRECC often carried resistance determinants (located on mobile genetic elements) and pathogenicity factors The conventional wastewater processes do not prevent the receiver from dissemination of fecal bacteria with clinically relevant resistance patterns. It is suspected that antimicrobial-resistance patterns found in hospital settings could be also beneficial for survival in other compartments. With reference to the above, in the environmental risk assessment, the resistant bacteria should be monitored in both, treated wastewater and its receiver.

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