Ninety (90) strains of Escherichia coli were isolated from intestine with fecal contents and liver of seven days old commercial layers presenting diarrhea, and their pathogenicity was determined by in vivo inoculation into the air sacs of day-old chicks. The test revealed 44 strains with high and intermediate pathogenicity level that were analyzed by PCR for the presence of eight virulence genes, and their serogroups were indentified using a set of anti-O antisera. Results demonstrate that these isolated strains contained at least one of the eight genes searched and the majority of them (93.20%) possessed gene iss. Seventeen (17) different genetic patterns have been detected with 15 having combinations of two or more genes representing 70.45% of all analyzed strains. Eleven different serogroups were identified, and the highest frequent was O8 (15.89%). Results demonstrate that strains that harbor genes iss or astA and some that belonged to serogroups O133 and O142 may have been crucial for the pathogenesis in the studied chicks, since several of these strains were pathogenic. The obtained results demonstrated the importance of studies in E. coli of avian origin in regions engaged in intensive poultry industry, aiming at evaluating the predominant strains and also acquiring preventive measures to minimize losses due to colibacillosis.
Key words: avian pathogenic Escherichia coli (APEC), layer chicks, polymerase chain reaction (PCR), virulence genes
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