Longitudinal analysis of avian pathogenic Escherichia coli (APEC) serogroups and pathotypes from avian colibacillosis in Georgia: A continued investigation - year 2 analysis.

Avian pathogenic Escherichia coli (APEC) is a significant cause of worldwide morbidity, mortality, and production loss in the poultry industry. Here, we characterized 115 E. coli isolates from avian-diagnosed colibacillosis cases from Georgia, USA in 2022 as part of a year two follow on surveillance using both current and a newly developed serogrouping tool (Klao9-SeroPCR). The isolates examined were classified into 18 serogroups with the majority classifying as O78, O25, O86, O2, O8, and O1 with 32 isolates classified as untypable serogroups. In this study, the Klao9-seroPCR was able to identify serogroups of 72/115 isolates (62.6 %) using the multiplex PCR assay. This diagnostic PCR assay proved to be a potential technique for the rapid identification of the most common APEC serogroups dominating in Georgia poultry. Genotyping based on detection of selected virulence genes (VAGs) found that 22.6 % of isolates did not harbor any of the targeted genes. This analysis also confirmed that the CoIV plasmid-associated genes (iroN, ompT, hlyF, iss, and aerJ,) are still frequently found among APEC isolates (54-65 %) with a slightly lower prevalence compared to the previous year's study. Phylogenetic analysis showed that the isolates belong to phylogenetic groups G (43 %), group B2 (13 %), group F (6 %), and group A (5 %). Of interest, 30 % were identified as an unknown or cryptic phylogenetic group. This study highlights that there is a shift in the APEC causing disease in birds in the state of Georgia with virulence commonly associated with the presence of the CoIV plasmid in disease strains. Of interest, the new serogrouping panel that is designed to target more common serogroups seen in Georgia has proven to be a rapid screening/ diagnostic tool for implementation in our workflow. This study highlights a need to continue to monitor the APEC serogroups in the field to apply appropriate preventive plans against colibacillosis.