Abstract
Hospital wastewaters often carry multidrug-resistant bacteria and priority pathogens, such as methicillin-resistant Staphylococcus aureus (MRSA). Pathogens and antibiotic resistance genes present in wastewaters may reach the natural environment facilitating their spread. Thus, we aimed to isolate MRSA from wastewater of 3 hospitals located in the north of Portugal and to characterize the isolates regarding the antimicrobial resistance and genetic lineages. A total of 96 wastewater samples were collected over six months. The water was filtered, and the filtration membrane was immersed in BHI broth supplemented with 6.5% of NaCl and incubated. The inoculum was streaked in ORSAB agar plates for MRSA isolation. The isolates susceptibility testing was performed against 14 antimicrobial agents. The presence of resistance and virulence genes was accessed by PCR. Molecular typing was performed in all isolates. From the 96 samples, 28 (29.2%) were MRSA-positive. Most isolates had a multidrug-resistant profile and carried the mecA, blaZ, aac(6′)-Ie-aph(2″)-Ia, aph(3′)-IIIa, ermA, ermB, ermC, tetL, tetM, dfrA dfrG and catpC221 genes. Most of the isolates were ascribed to the immune evasion cluster (IEC) type B. The isolates belonged to ST22-IV, ST8-IV and ST105-II and spa-types t747, t1302, t19963, t6966, t020, t008 and tOur study shows that MRSA can be found over time in hospital wastewater. The wastewater treatment processes can reduce the MRSA load. The great majority of the isolates belonged to ST22 and spa-type t747 which suggests the fitness of these genetic lineages in hospital effluents.
Highlights
Introduction conditions of the Creative CommonsHospitals are ecological niches for antimicrobial resistant bacteria since up to one third of the hospitalized patients receive antibiotic therapy [1]
Hospital wastewaters contribute to high rates of antibiotic resistant bacteria discharged in the natural environment [30]
S. aureus is present in Wastewater Treatment Plants (WWTPs) due to ineffective technological processes, yet, it has been shown that treatment significantly reduces the number of S. aureus in wastewaters [31]
Summary
Hospitals are ecological niches for antimicrobial resistant bacteria since up to one third of the hospitalized patients receive antibiotic therapy [1]. These bacteria may be spread by colonized patients, including through sewage and hospital wastewaters [2]. The sub-inhibitory concentrations present in wastewater are sufficient to induce a selective pressure on bacteria and are probably one of the drivers for resistance. It favours the intraspecies and interspecies horizontal transfer of resistance genes [6,7]. Many studies have shown that hospital wastewaters contribute to the mobilization and dissemination of important nosocomial pathogens as well as antimicrobial resistance genes and genetic determinants which may reach surface waters, influencing the aquatic ecosystems and interfering with the food chain [8–12]
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