, 2005), whereas other studies have reported that AMR and VGs are only weakly linked, if at all (Johnson et al., 2003). Recently, some studies investigating antibiotic resistance in relation to phylogenetic origin have found that resistance to ampicillin, tetracycline, chloramphenicol, streptomycin, extended-spectrum cephalosporins, cephamycins, and sulfonamides was

associated with decreased virulence traits among human clinical E. coli isolates (Johnson et al., 2003; Moreno et al., 2006), whereas resistance was not associated with decreased Selleck PD0325901 virulence traits among animal E. coli isolates (Johnson et al., 2003). However, there is no conclusive evidence to indicate whether resistance to antimicrobials is associated with differences in the prevalence of certain VGs in swine E. coli isolates. Therefore, we investigated the prevalence of AMR phenotypes, virulence factors, and phylogenetic groups of E. coli isolates.

Specifically, we explored whether AMR and virulence traits among E. coli isolates from diseased pigs were significantly associated. Numerous diseased or dead animals were submitted to the Veterinary Research Institute, Ku-0059436 chemical structure Guangdong Academy of Agricultural Sciences, for diagnostic investigation. For our study, we selected all the E. coli isolates in this collection that came from pigs with diarrhea or edema disease between March 2002 and May 2008. These diseased animals were housed on 58 farms all over Guangdong Province. Each of the farms typically housed approximately 5000 animals. Between one and six herds were sampled from each farm, and each sample was from an individual animal. Isolates were recovered from rectal swabs of 2–10-week-old diseased piglets as well as from the intestinal contents of dead piglets. All E. coli organisms were isolated and purified on MacConkey agar. The bacterial strains were identified using classical biochemical Cyclic nucleotide phosphodiesterase methods and confirmed using the API-20E system (bioMérieux, France). All confirmed E. coli isolates were

stored at −80 °C in Luria–Bertani broth medium containing 10% glycerol. Antimicrobial susceptibility testing was performed on all 167 E. coli isolates using the microdilution broth method according to the guidelines of the Clinical and Laboratory Standards Institute (CLSI) (2004). As there are no CLSI breakpoints for doxycycline that are applicable to E. coli of animal origin, the breakpoints of doxycycline (≥16 mg L−1) were referred to Clinical and Laboratory Standards Institute (CLSI) (2008) document M100-S18 for isolates of human origin. The reference strain, E. coli ATCC 25922, was used as a quality control strain for determining the minimum inhibitory concentrations of 12 antimicrobial agents (Table 1). All isolates were assigned to one of the four main phylogenetic groups of E. coli (A, B1, B2, and D) by multiplex PCR, as described by Clermont et al. (2000).