Abstract: To determine the antimicrobial resistance and the phylogenetic background of E.coli strains in Guangdong province, a total of 264 E.coli isolates were collected from diseased swine in 2011, which contained 131 strains from feces and 133 strains from liver. Antimicrobial susceptibility test was performed with agar dilution method and the phylogenetic background was determined by multiplex PCR. Statistical methods were used to analyze the relationship between antimicrobial resistance and the distribution of phylogenetic group among the E. coli strains isolated from feces and liver. The results showed that the multi-drug resistance (MDR) of the isolates was serious and there were 128 kinds of drug-resistant spectrum. The resistance rates of the isolates to ampicillin, sulfamethoxazole/trimethoprim, nalidixic acid and tetracycline were very high, and the isolates were sensitive to colistin, ceftazidime and amikacin. The majority of isolates belonged to phylogenetic groups A and B1 (91.66%). There were no significant differences in distribution of phylogenetic group between the E.coli strains isolated from feces and liver (P＞0.05), but the resistance rates to certain antimicrobials were significantly different in different phylogenetic groups (P＜0.05). The study was to investigate antimicrobial resistance and the distribution of phylogenetic groups of the E.coli isolates so as to provide a foundation for the use of antimicrobials in veterinary clinical medication.

Key words: E.coli; antimicrobial resistance; phylogenetic analysis