title: Investigation of antimicrobial resistance in Escherichia coli and enterococci isolated from Tibetan pigs.
abstract: OBJECTIVE
  This 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.
  
  
  METHODS
  A 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.
  
  
  RESULTS
  A 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.
  
  
  CONCLUSIONS
  In 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.
authors.affiliation: Department of Small Animal Clinical Sciences, College of Veterinary Medicine, China Agricultural University, Beijing, P. R. China; College of Agricultural and Animal Husbandry, Tibet University, Linzhi, P. R. China.
authors.forename: Peng
authors.initials: P
authors.lastname: Li
authors.affiliation: National Center for Veterinary Drug Safety Evaluation, College of Veterinary Medicine, China Agricultural University, Beijing, P. R. China.
authors.forename: Dongfang
authors.initials: D
authors.lastname: Wu
authors.affiliation: Department of Pharmaceuticals, China Institute of Veterinary Drugs Control, Beijing, P. R. China.
authors.forename: Kunyao
authors.initials: K
authors.lastname: Liu
authors.affiliation: College of Agricultural and Animal Husbandry, Tibet University, Linzhi, P. R. China.
authors.forename: Sizhu
authors.initials: S
authors.lastname: Suolang
authors.affiliation: National Center for Veterinary Drug Safety Evaluation, College of Veterinary Medicine, China Agricultural University, Beijing, P. R. China.
authors.forename: Tao
authors.initials: T
authors.lastname: He
authors.affiliation: National Center for Veterinary Drug Safety Evaluation, College of Veterinary Medicine, China Agricultural University, Beijing, P. R. China.
authors.forename: Xuan
authors.initials: X
authors.lastname: Liu
authors.affiliation: National Center for Veterinary Drug Safety Evaluation, College of Veterinary Medicine, China Agricultural University, Beijing, P. R. China.
authors.forename: Congming
authors.initials: C
authors.lastname: Wu
authors.affiliation: National Center for Veterinary Drug Safety Evaluation, College of Veterinary Medicine, China Agricultural University, Beijing, P. R. China.
authors.forename: Yang
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Department of Small Animal Clinical Sciences, College of Veterinary Medicine, China Agricultural University, Beijing, P. R. China.
authors.forename: Degui
authors.initials: D
authors.lastname: Lin
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D024881:Drug Resistance, Bacterial; D024901:Drug Resistance, Multiple, Bacterial; D016983:Enterococcus / Q000187:drug effects* / Q000302:isolation & purification; D004926:Escherichia coli / Q000187:drug effects* / Q000302:isolation & purification; D008826:Microbial Sensitivity Tests; D013552:Swine / Q000382:microbiology*
chemical_list: D000900:Anti-Bacterial Agents
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