Molecular typing of avian pathogenic Escherichia coli O78 strains in Japan by using multilocus sequence typing and pulsed-field gel electrophoresis.

Avian pathogenic Escherichia coli (APEC) serogroup O78 isolates in Japan were characterized using multilocus sequence typing (MLST) and pulsed-field gel electrophoresis (PFGE). Thirty-four of the serotype O78 isolates were clustered into 11 PFGE types with 80% similarity and were classified into 5 sequence types (STs), ST23, ST117, ST155, ST369 and 1 novel ST (ST1645). The most dominant ST was ST23 (54.3%). Fluoroquinolone-resistant strains belonged to ST23 (9 strains), ST155 (3 strains) and ST117 (1 strain). The combined findings of MLST and PFGE suggested that 1 genotype belonging to ST23 was the genotype specific to fluoroquinolone-resistant strains. These results indicate that the combination of MLST and PFGE is useful for conducting epidemiological studies on APEC O78 strains.