Austria-wide survey on resistant, potentially pathogenic bacteria at Austrian bathing sites, 2017

Nowadays, antimicrobial resistance (AMR) is a major health threat, and according to the World Health Organization (WHO), we are in severe danger of entering a post-antibiotic era, where simple bacterial infections will become untreatable (WHO, 2017). AMR is a phenomenon that has probably existed since microorganisms exist. Microorganisms produce antimicrobials to outcom-pete other microorganisms in their struggle for limited resources. The discovery of antimicrobials by man, their use, and overuse in our fight against infectious disease and the resulting environmental pollution caused by diverse anthropogenic activities (human medicine, veterinary medicine, agriculture) are factors that have been facilitating the development and spread of AMR. The development of AMR and the emergence of resistant microorganisms are linked to the use of antimicrobials (Goossens et al., 2005). The dramatic health threat caused by AMR is illustrated by the development of a common “One Health” global action plan on AMR by the WHO (WHO, 2015), by the World Organization for Animal Health (OIE, 2016), and the Food and Agriculture Organization (FAO, 2016) with the aim to minimize the impact of AMR. The focus areas of this global action plan include implementing AMR surveillance and antimicrobial residue monitoring in the environment (FAO, 2016). There is an increasing number of reports on the occurrence of clinically relevant multidrug-resistant (MDR) pathogens in the aquatic environment (Zurfluh et al., 2013; Mahon et al., 2017; Zarfel et al., 2017; Khan et al., 2018; Lepuschitz et al., 2017, 2018, 2019). Water is one of the most important habitats for bacteria. It is also a major medium for bacteria to disseminate and potentially to exchange among different environmental compartments, such as waste, surface, and drinking water (Vaz-Moreira et al., 2014). Studies increasingly emphasize the importance of aquatic systems as antibiotic resistance reservoirs, including antibiotic residues, antibiotic-resistant bacteria, and antibiotic-resistant genes, which can be exchanged between pathogenic and nonpathogenic bacteria (Baquero et al., 2008; Zhang et al., 2009; Rizzo et al., 2013; Manaia et al., 2016). However, at present, it is not clear to what extent environmental bacteria are a source for novel resistance mechanisms or which circumstances force them to spread antibiotic resistance. Therefore, the question how antibiotic resistance in the water environment affects human health still needs to be investigated and discussed (Vaz-Moreira et al., 2014). The aim of our study was to assess the burden of AMR caused by Enterobacteriales, enterococci, methicillin-resistant Staphylococcus aureus (MRSA), and Pseudomonas spp. (organisms commonly considered microbial indicators for water contamination (WHO, 2003)) in Austrian bathing sites, an aqueous environment supposedly less prone to anthropogenic influence than regular surface waters.

In our study, the screening for antimicrobial-resistant bacteria was negative in 23 of the 27 samples. Resistant bacteria were detected from 4 of the 27 bathing sites. Two of the four isolates carried plasmids: E. cloacae yielded three plasmids and the E. coli isolate one plasmid. These findings indicate that antibiotic resistance genes were acquired by multiple separate acquisition events mediated by plasmids (Villa et al., 2012; Voulgari et al., 2014). The occurrence of plasmids raises concerns about the possibility of the detected strains contributing to the dissemination of resistance genes among bacterial species in the water environment (Cloutier and McLellan, 2017; Rothenheber and Jones, 2018; Schang et al., 2016). Vancomycin-resistant enterococci were not detected in any of the water samples. In Austrian hospitals, these grampositive bacteria never reached the high clinical importance observed in the United States (BMG, 2017). In 2017, the ratio of vancomycin resistance among blood culture isolates from Austria was 0% for Enterococcus faecalis and only 3.2% for Enterococcus faecium (BMG, 2017).

The detection of MRSA was negative in all investigated isolates, and there are only a few studies describing the cultivation of MRSA from water samples (Tolba et al., 2008; Boopathy 2017; Lepuschitz et al., 2017, 2018). Up to date there are no official guidelines for the detection of MRSA from water samples, which might lead to the underestimation of MRSA in the environment. According to the definition by Magiorakos et al. (2012), three of the four bacteria isolated in our study on Austrian bathing sites were non-susceptible to at least one agent in three or more antimicrobial categories and therefore categorized as MDR bacteria (Magiorakos et al., 2012). Only the P. aeruginosa isolate must not be considered multidrug resistant. Non-fermenting bacteria, such as P. aeruginosa, are not only found in the clinical setting but also occur naturally in the aquatic environment (Kittinger et al., 2017). Our findings are in accordance with those of Suzuki et al., who in 2013 postulated that in advanced nations where the majority of the population is urban and where medical services are widespread, antibiotic-resistant bacteria such as P. aeruginosa are likely to be widely distributed, even in apparently pristine rivers (Suzuki et al., 2013). In 2017, the ratio of antibiotic resistance among P. aeruginosa blood culture isolates from Austria was 5% for aminoglycosides, 8.7% for ceftazidime, 13.5% for piperacillin/tazobactam, 12.3% for fluoroquinolones, and 13.9% for carbapenems (BMG, 2017). Pseudomonads can carry multiple intrinsic and acquired resistance genes and mobile genetic elements, exchange them with other Enterobacteriaceae, and are known to be the origin of several carbapenemase families (Pfeifer et al., 2010; Farinas and Martinez, 2013). The risk of intrinsic resistances found in environmental microorganisms being transferred to pathogens is an international concern (Forsberg et al., 2012; Cox and Wright, 2013; Singer et al., 2016). Two of the four antibiotic-resistant bacteria isolated in our study belonged to the genus Enterobacter. Although not surveyed under the European Antimicrobial Resistance Surveillance Network (EARS-Net), Enterobacter spp. have great relevance as invasive clinical pathogens. In 2017, the WHO published it’s first-ever list of antibiotic-resistant “priority pathogens”—a catalog of 12 families of bacteria that pose the greatest threat to human health. The most critical group of all includes Acinetobacter, Pseudomonas, and Enterobacteriaceae. Enterobacter spp. have become resistant to a large number of antibiotics, including carbapenems and third-generation cephalosporins—the main antibiotics for treating infections caused by MDR bacteria. The detection of a carbapenem-resistant E. mori isolate at a Carinthian bathing site clearly underlines this resistance threat. Recently, the first clinical carbapenemase-carrying E. mori isolate was described in Austria (Hartl et al., 2019). This isolate was obtained from a 59-year-old patient suffering from acute otitis externa after visiting a thermal bath, which indicates water as the source of infection with antibioticresistant bacteria (Hartl et al., 2019). Also the finding of an ESBL-producing E. coli mirrors the situation in clinical microbiology. According to the “Der Österreichische Resistenzbericht” (AURES) report 2017, 49.5% of invasive E. coli isolates were resistant to aminopenicillins, 20.5% resistant to fluoroquinolones, 9.6% to third-generation cephalosporins, and 7.7% to aminoglycosides (BMG, 2017). Rivers and lakes are considered relevant reservoirs for MDR bacteria, because they pool materials from different origins, such as wastewater plants, water of urban or industrial effluents, agricultural activities, or rain (Lupo et al., 2012; Zurfluh et al., 2013; Kittinger et al., 2017). Our findings reveal that even ecologically pristine waters used for recreational activities can harbor resistant isolates. Exner et al. (2018) who evaluated potential health risks of water bodies contaminated with antibiotic-resistant pathogens reported that bathers without increased vulnerability and bathers with increased vulnerability should be differentiated. Ingestion of bathing water can theoretically lead to colonization of the gastrointestinal tract, but this is considered unlikely, given the low levels of swallowed bathing water or concentrations of antibiotic-resistant pathogens in open water. With regard to bathing in water authorized under the EU Bathing Water Directive, possible exposure to antibiotic-resistant bacteria according to the current knowledge poses no increased health risk for bathers without increased vulnerability; this assumes that the criteria of the EU Bathing Water Directive are met. They include intact skin of the bather and no antibiotics taken, observing the general rules of hygiene. For bathers with increased vulnerability or predisposition, risk of infection cannot be ruled out under the following conditions: open, extensive wounds; extensive skin disease; or prolonged intake of antibiotics. For these reasons, these persons should generally not bathe in open and untreated water irrespective of the presence of antibiotic-resistant pathogens (Exner et al., 2018).

We consider the public health risk at Austrian bathing sites authorized under the EU Bathing Water Directive to be low despite the occurrence of MDR bacteria. However, our results confirm the existing risk for dissemination of MDR bacteria via the aquatic environment.