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Effect of autogenous vaccine on the prevalence of virulence-associated genes in avian pathogenic Escherichia coli (APEC) strains isolated from broiler breeder farm

Escherichia coli continuously causes severe production decrease and high mortality rates in poultry, usually with reproductive and respiratory tract disorders, which represents a serious problem to the poultry industry. Struggle with bacterial infections has led to the excessive and uncontrolled use of antibiotics and development of the multidrug- resistant bacteria. Since the use of commercial E. coli vaccine is often unsuccessful, implementation of autogenous vaccine to the immunoprophylaxis programme is frequently initiated.Avian pathogenic E. coli (APEC) belongs to the extra-intestinal E. coli (ExPEC) group. There are five virulence-associated genes considered common for APEC- iroN, ompT, hlyF, iss and iutA. The purpose of this study was to determine the occurrence of mentioned virulence genes and to compare their prevalence in the isolates originating from the flock vaccinated with commercial vaccine (Flock 1), to the ones originating from the flock vaccinated with the autogenous vaccine (Flock 2).Thirteen isolates from each farm were investigated. DNA was isolated using Maxwell RSC Cultured Cells DNA Kit (Promega). Fragment libraries were constructed using Nextera XT kit (Illumina), followed by paired-end sequencing (MiSeq, Illumina) according to manufacturer’s instructions. CGE tool MyDbFinder was used to evaluate the occurrence of the virulence genes. In the Flock 1, the prevalence of ompT, iss and iutA was 92, 3%, while for iroN and hlyF it was 76, 9% and 23, 1%, respectively. In the Flock 2, prevalence of iroN, ompT and iss was 92, 3%, while for hlyF and iutA it was 53, 8% and 100%, respectively. According to PathogenFinder, all the isolates were predicted to be human pathogens with average probabilities of 93, 5% and 93, 7% for the Flock 1 and 2, respectively. The results show that implementation of autogenous vaccine in the immunoprophylaxis programme reduces the incidence of colibacillosis, as well as the need for repetitive therapy, but also enables the emergence of new strains with increased rates of virulence genes associated with pathogenicity. Although further research of the examined strains is needed, the data indicate that use of autogenous vaccine could lead to elimination of the less virulent strains from the farms. In addition, it confirms the common practice that continuous monitoring is needed to cope with the new strains by isolation and implementation into the vaccine.

E. coli, APEC, poultry, broiler breeder, autogenous vaccine, virulence genes, whole genome sequencing

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