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.