Abstract
ObjectivesThis study investigated the antimicrobial resistance of Escherichia coli and enterococci isolated from free-ranging Tibetan pigs in Tibet, China, and analyzed the influence of free-ranging husbandry on antimicrobial resistance.MethodsA total of 232 fecal samples were collected from Tibetan pigs, and the disk diffusion method was used to examine their antimicrobial resistance. Broth microdilution and agar dilution methods were used to determine minimum inhibitory concentrations for antimicrobial agents for which disks were not commercially available.ResultsA total of 129 E. coli isolates and 84 Enterococcus isolates were recovered from the fecal samples. All E. coli isolates were susceptible to amoxicillin/clavulanic acid, and 40.4% were resistant to tetracycline. A small number of isolates were resistant to florfenicol (27.9%), ampicillin (27.9%), sulfamethoxazole/trimethoprim (19.4%), nalidixic acid (19.4%), streptomycin (16.2%) and ceftiofur (10.9%), and very low resistance rates to ciprofloxacin (7.8%), gentamicin (6.9%), and spectinomycin (2.3%) were observed in E. coli. All Enterococcus isolates, including E. faecium, E. faecalis, E. hirae, and E. mundtii, were susceptible to amoxicillin/clavulanic acid and vancomycin, but showed high frequencies of resistance to oxacillin (92.8%), clindamycin (82.1%), tetracycline (64.3%), and erythromycin (48.8%). Resistance rates to florfenicol (17.9%), penicillin (6.0%), ciprofloxacin (3.6%), levofloxacin (1.2%), and ampicillin (1.2%) were low. Only one high-level streptomycin resistant E. faecium isolate and one high-level gentamicin resistant E. faecium isolate were observed. Approximately 20% and 70% of E. coli and Enterococcus isolates, respectively, were defined as multidrug-resistant.ConclusionsIn this study, E. coli and Enterococcus isolated from free-ranging Tibetan pigs showed relatively lower resistance rates than those in other areas of China, where more intensive farming practices are used. These results also revealed that free-range husbandry and absence of antibiotic use could decrease the occurrence of antimicrobial resistance to some extent.
Highlights
Escherichia coli is a commensal bacterium and opportunistic pathogen that is commonly found in the intestinal tracts of animals and humans [1]
To examine the antimicrobial resistance of E. coli and enterococcal isolates collected from free-ranging livestock in their natural environment, the Tibetan pig was chosen for investigation in this study
Antimicrobial resistance of the isolates All 129 E. coli isolates were susceptible to amoxicillin/clavulanic acid (Table 1)
Summary
Escherichia coli is a commensal bacterium and opportunistic pathogen that is commonly found in the intestinal tracts of animals and humans [1]. Because it is regarded as an indicator organism of antimicrobial resistance for a wide range of bacteria [2], data on antimicrobial resistance of E. coli is available from many countries [3,4,5,6], including the northern, central, and southern areas of China [7]. To examine the antimicrobial resistance of E. coli and enterococcal isolates collected from free-ranging livestock in their natural environment, the Tibetan pig was chosen for investigation in this study
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