Genotypes and Pathogenicity of Cellulitis Isolates Reveal Traits That Modulate APEC VirulenceReportar como inadecuado

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We characterized 144 Escherichia coli isolates from severe cellulitis lesions in broiler chickens from South Brazil. Analysis of susceptibility to 15 antimicrobials revealed frequencies of resistance of less than 30% for most antimicrobials except tetracycline 70% and sulphonamides 60%. The genotyping of 34 virulence-associated genes revealed that all the isolates harbored virulence factors related to adhesion, iron acquisition and serum resistance, which are characteristic of the avian pathogenic E. coli APEC pathotype. ColV plasmid-associated genes cvi-cva, iroN, iss, iucD, sitD, traT, tsh were especially frequent among the isolates from 66.6% to 89.6%. According to the Clermont method of ECOR phylogenetic typing, isolates belonged to group D 47.2%, to group A 27.8%, to group B2 17.4% and to group B1 7.6%; the group B2 isolates contained the highest number of virulence-associated genes. Clonal relationship analysis using the ARDRA method revealed a similarity level of 57% or higher among isolates, but no endemic clone. The virulence of the isolates was confirmed in vivo in one-day-old chicks. Most isolates 72.9% killed all infected chicks within 7 days, and 65 isolates 38.1% killed most of them within 24 hours. In order to analyze differences in virulence among the APEC isolates, we created a pathogenicity score by combining the times of death with the clinical symptoms noted. By looking for significant associations between the presence of virulence-associated genes and the pathogenicity score, we found that the presence of genes for invasins ibeA and gimB and for group II capsule KpsMTII increased virulence, while the presence of pic decreased virulence. The fact that ibeA, gimB and KpsMTII are characteristic of neonatal meningitis E. coli NMEC suggests that genes of NMEC in APEC increase virulence of strains.

Autor: Nicolle Lima Barbieri, Aline Luísa de Oliveira, Thiago Moreira Tejkowski, Daniel Brisotto Pavanelo, Débora Assumpção Rocha, L



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