Characterization of multidrug-resistant strains
Multidrug-resistant strains accounted for 71.4% of all the different isolated E. coli strains. Ampicillin resistance was observed in 95.7% of the isolates; however, eight strains were classified as intermediate. Only three strains isolated from the rats were found to be susceptible to this antibiotic. More than half of the isolates showed resistance to tetracycline (64.3%) or streptomycin (51.4%). We also found that 45.7% of the isolates were resistant to sulfamethoxazole. Kanamycin resistance was observed in 19 strains, and only one strain was resistant to gentamicin (from the squirrel). In total, 38.6% of the isolates had a chloramphenicol resistant profile, but eight of them were classified as intermediately resistant. Nitrofurantoin resistance was noted in 31.4% of the strains, but most (n=16) were intermediately resistant isolates. The nalidixic acid-resistant isolates accounted for 24.3%, and those with resistance to ciprofloxacin represented 12.9% (Table S3; Fig. 1).
Among isolates obtained from the squirrels, 70.8% of the strains (n=17) had a multidrug-resistant profile. In this group of samples, we also detected one E. coli ESBL producer. In addition to resistance to ampicillin and tetracycline, a high proportion (from 37.5 to 45.8%) of strains resistant to sulfamethoxazole, chloramphenicol, nalidixic acid, and streptomycin were observed as well.
The multidrug-resistant profile in samples isolated from the rats was observed in 57.1% of the strains. High aminoglycoside resistance was noted, i.e. 35.7% for streptomycin and 42.9% for kanamycin. Almost half of the strains were resistant to nitrofurantoin. Resistance to tetracycline and sulfamethoxazole remained at a high level, as in the case of isolates obtained from the squirrels.
All E. coli strains isolated from the hedgehogs showed a multidrug-resistant profile. In this group, the highest resistance was observed for ampicillin (100%) and nitrofurantoin (75%). Moreover, half of the strains were resistant to tetracycline and/or sulfamethoxazole.
The isolates obtained from the ungulates were characterized by high resistance to ampicillin, streptomycin, sulfamethoxazole, and tetracycline. All E. coli strains isolated from roe deer had a multidrug-resistance profile and resistance to five groups of antimicrobials predominated. However, in the case of the red-deer isolates, 53.3% (n=8) showed multidrug resistance. Similarly, the analysis of the diversity of resistance depending on the source of the strain (host species) showed statistically significantly higher resistance to tetracycline, streptomycin, sulphametoxazole, and ciprofloxacin among strains isolated from the roe deer. Statistically, resistance to chloramphenicol, kanamycin, nalidixic acid, and nitrofurantoin was most frequently reported in the isolates from the red deer, rats, squirrels, and hedgehog, respectively (Fig 1).
We also examined the single strain obtained from the beaver. It showed a multidrug-resistance profile as well (Table 1).