Antimicrobial resistance of Escherichia coli and Enterococcus spp. isolated from Estonian cattle and swine from 2010 to 2015

Background: The prevalence of resistant Escherichia coli and Enterococcus spp. in food-producing animals has increased worldwide. The objective of the study was to investigate the occurrence of antimicrobial resistance of Escherichia coli, Enterococcus faecium and Enterococcus faecalis isolated from healthy and diseased swine and cattle in Estonia. Clinical specimen and faecal samples were collected during 2010 to 2015. The in vitro antimicrobial susceptibility was determined using the microdilution method. The most prevalent resistance of E. coli isolates from clinically healthy swine was observed against streptomycin (39.2%), tetracycline (32.5%) and sulfamethoxazole (30.0%), whereas in clinically healthy cattle, the resistance was the highest against aminoglycosides (7.0-8.8%) and tetracycline (7.0%). The E. coli isolates from clinically healthy swine showed significantly higher multidrug-resistance compared to isolates originated from clinically healthy cattle. E. coli isolates from diseased swine showed highest resistance to sulfamethoxazole (68.6%), tetracycline (60.2%) and streptomycin (54.6%). The proportion of resistant E. coli isolates from diseased cattle (clinical submissions) was highest to streptomycin (63.5%), sulfamethoxazole (60.3%) and tetracycline (58.8%). The proportion of multidrug-resistant isolates did not differ significantly between animal species. Among E. coli isolates, four strains representing AmpC phenotypes were found. One plasmid-encoded AmpC type beta-lactamases producing E. coli from clinically healthy cattle was found to harbour the bla (CMY-1) gene, and another from clinically healthy swine carried the bla (CMY-2) gene. Among nine E. coli strains exhibiting an ESBL phenotype three strains was found to be the same genotype bla (TEM-52C). Enterococci from healthy swine and cattle showed high resistance to tetracycline and erythromycin. Regarding enterococci, the number of multidrug-resistant strains was significantly higher in swine isolates compared to isolates originated from cattle. The antimicrobial resistance of E. coli isolates was high in both Estonian swine and cattle. However, swine isolates, especially E. coli from healthy swine, had developed a higher level of resistance. The amount of multidrug-resistant E. coli isolates was also significantly higher in clinically healthy swine compared to that in cattle.