Introduction
Both humans and animals are colonized by microorganisms from the first moments of their lives. Escherichia coli bacteria colonize mainly the large intestine and can enter the organism with food or water and through contact with the surrounding natural world (Katouli, 2010). MostE. coli strains are a natural component of the host microbiota and exist as commensal bacteria; however, there are pathogenic strains that can cause intestinal and extraintestinal infections (Van Elsas, Semenov, Costa, & Trevors, 2011).
A serious threat to human health posed by E. coli is the capability of easy transfer of resistance and virulence genes between strains. This bacterium has been recognized as an indicator microorganism by the European Centre for Disease Prevention and Control (ECDC) and is used to monitor the occurrence of specific resistance determinants in various sources. For example, according to the ECDC report, the number of E. coli strains resistant to the extended spectrum of β-lactam antibiotics (ESBL) and fluoroquinolones exhibits a growing trend in Poland as well (ECDC, 2019). Moreover, there are many reports of carriage and transmission of multidrug-resistant E. coli strains between different host species both in our country and in the world (Nowakiewicz et al., 2020; Hassell et al., 2019; Osińska et al., 2020).
Clinical symptoms caused by E. coli are closely correlated with their rich and diverse panel of virulence factors (Chapman et al., 2006). Pathogenic E. coli strains are highly specialized and adapted microorganisms that have developed many features that facilitate pathogenesis, e.g. adhesins, iron acquisition systems, serum resistance, invasins, and miscellaneous factors (Nowak et al., 2017). These strains are generally divided into diarrhoeagenic (IPEC) and extraintestinal (ExPEC) strains. Strains with the ETEC (enterotoxigenic) and EHEC (enterohaemorrhagic) pathotype are mainly responsible for diarrhoea (Dubreuil, Isaacson, & Schifferli, 2016; Nagy & Fekete, 2005). However, E. coli strains with the ExPEC pathotype are considered the most common gram-negative pathogens in humans (Wasiński, 2019). ExPEC strains cause many infections in both humans (Khairy, Mohamed, Ghany, & Abdelrahim, 2019; Dadi et al., 2020) and animals (Nowak et al., 2017; Velhner, Suvajdžić, Todorović, Milanov, & Kozoderović, 2018; Borges et al., 2017). Unlike E. coli intestinal pathotypes, ExPEC can cause urinary tract infections, pyelonephritis, pneumonia, meningitis, and septicaemia in specific groups in the population such as immunocompromised patients, newborns, and elderly people (Wasiński, 2019). Blood infections caused by ExPEC strains are one of the main causes of hospitalization of patients from nursing homes. These infections are particularly difficult to treat when the strains are resistant to antimicrobials (Bélanger et al., 2011). Moreover, avian pathogenic E. coli (APEC) found in poultry can cause serious losses in the poultry industry. APEC strains attack the respiratory tract of poultry, which further leads to the development of sepsis and generalized infection (Bélanger et al., 2011; Wasiński, 2019).
Studies conducted over many years have shown the importance of monitoring not only livestock and humans but also different ecosystems and different reservoirs in terms of both resistance and the presence of pathogens including specific pathotypes of E. coli (Dolejska & Literak, 2019). There are many ways of transferring bacterial strains carrying resistance and virulence genes between wildlife animals, environment, livestock, and humans. Due to the limitation of their territory by urbanization, many species of free-living animals undergo synanthropization, increasingly becoming part of urban and suburban forests and parks. Lower numbers of natural enemies in the environment (reduced population of predators) are also conducive to the increase in the population of large herbivores. Thus, the risk of exchange and spread in both directions (man-wildlife, including the environment) of adverse microorganisms is constantly increasing. Especially in the case of rodents, the spread of bacteria in this group of animals is associated with their specific behaviour, e.g. rats living near households for easy access to food.
Therefore, the aim of our research was to assess whether non-predatory wildlife animals can be substantial reservoirs of resistant and pathogenic E. coli strains only as a result of close contact with the human environment. We hypothesized that not only predatory animals are included in the circulatory cycle of strains that potentially threaten public health.