**1. Introduction**

Resistance to antibacterial agents is an increasing problem in public health and veterinary medicine worldwide [1–3]. The major public health concern which has been expressed for several decades is still the potential for transmission of antibiotic-resistant bacteria from animals to humans [4]. Most of the amounts of antibiotics used (30–80%) in livestock farming are excreted by the animals directly into the environment via urine and feces because of partial metabolization of antibacterial agents and residue in manure [5–7]. Resistance to antibacterial agents in Gram-negative bacteria is on the rise in pathogens as well as in commensal bacterial flora, particularly in *Escherichia coli*. *E. coli* constitutes the majority of invasive Gram-negative isolates for humans in European countries [8]. The natural habitat of *E. coli* is the gastrointestinal tract of mammals and birds [9]. It is considered as an indicator bacteria for resistance detection. *E. coli* also has the ability to survive in and adapt to various extra intestinal habitats and to spread resistances between humans, animals, and the environment [10].

Antibacterial agents in livestock production have been either used to prevent diseases and promote animal growth or for therapeutic purposes [11,12]. The total sales of veterinary antibacterial agents during 2015 in the European Union (EU) amounted to approximately 8361 tons [13]. The average antibacterial consumption by humans (124 mg/kg) was lower than in animals (152 mg/kg) [3]. The resistance level of avian isolates to *E. coli* in Germany, for example, exceeded the level determined by the Federal Office of Consumer Protection and Food Safety for other veterinary pathogens in other animal species [14]. In the past, in relation to their respective fattening periods, in poultry, antibacterial agents have been used more often and for a longer duration compared with cattle and pigs [15].

Fluoroquinolones (FQ) have been classified as being critically important for human health and animal farms by the World Health Organization [4]. An unfavorable situation has arisen in Europe: Resistance to these antibiotics is widespread and the incidence of resistance increased significantly between 2012 and 2015 [3]. The application of FQ agents in poultry husbandry has led to increasing problems with resistance to antibacterial agents [16,17]. The level of fluoroquinolone consumption showed a significant correlation with antibiotic resistance in *E. coli* in livestock husbandry [3,18,19]. In turkeys, commensal and pathogenic *E. coli* are often resistant to quinolones, including enrofloxacin, and to β-lactams [2,13]. Commensal *E. coli* isolates gained from turkey meat in Germany showed higher rates of resistance to FQ than *E. coli* from broilers [20].

In commercial poultry meat production in Europe, turkeys are reared on littered concrete floor. During the fattening period, the primary litter material becomes mixed with poultry excreta, feathers, feed, and spilt drinking water [21], the resulting mixture being referred to as poultry manure. Therefore, close contact with their litter or rather manure is common for turkeys during their productive life. More than 95% of the dry matter in manure consists of excreta [22]. This material can contain residues of antibacterial agents as well as resistant bacteria [17]. On almost every farm (62.3%), *E. coli* can be isolated from manure [23]. The poultry environment has long been acclaimed as a potential source of antibiotic-resistant bacteria [5,17], acting as a possible reservoir for the dissemination of these organisms to humans via the food chain (poultry meat), person-to-person contact (food handlers), and environment (poultry waste disposal, organic fertilizers). A significant proportion of these antibiotics is excreted unchanged in animal urine and feces. These antibiotics can remain potent for a longer time in manure during storage [5,24].

Information concerning the effects of separating animals from their excreta on the development of resistance to antibacterial agents in commensal *E. coli* in rearing turkeys has only been described in the study by Chuppava et al. [25]. The aim of the present study was to evaluate the effect of double antibiotic treatment (at days 10–14 and at days 26–30) with enrofloxacin or solely environmental exposition (at days 10–14 and days 26–30 directly into the litter) on resistance against antibacterial agents in commensal *Escherichia coli* in comparison with the control (without treatment), depending on different flooring. The different types of flooring design were distinguished by means of the contact intensity of birds to their excreta.
