HTS-based control of Salmonella Enteritidis vaccines for chickens - pilot study

Salmonella vaccines constitute the largest group of antibacterial immunological veterinary medicinal products (IVMPs) introduced to the EU market by the Polish Official Medicines Control Laboratory (OMCL). This is especially relevant, as Poland is the EU's leading producer of poultry meat. The General European OMCL Network is coordinated by the European Directorate for the Quality of Medicines & HealthCare (EDQM). Despite strict control of IVMPs, genomic aspect has not yet been controlled in veterinary pharmacy. The aim of the project was to assess the usefulness of High-throughput sequencing (HTS) for the genetic control of vaccines. The research was conducted on the most commonly marketed serovar in Poland - Salmonella enterica subspecies enterica serovar Enteritidis (SE). Live attenuated Salmonella vaccines for chickens were tested - three batches of different vaccines (coded B-01, B-05, B-07). Several publicly available genomic tools were applied for comprehensive characterization of vaccines. Generated sequences confirmed that the main genetic component of each vaccine was S. enteritidis without significant contaminants and with stability across batches. Comparative analysis showed that B-05 and B-07 IVMPs were genetically almost identical, while B-01 was quite distant. No major antibiotic resistance genes or point mutations were detected. HTS confirmed presence of multiple virulence markers in all tested batches. Further data indicated presence of multireplicon plasmid IncF in B-05 and B-07, harbouring two virulence cassettes - pef (plasmid-encoded fimbriae) and spv (type III secretion system). The presented work is an interdisciplinary project linking quality control of IVMPs with advanced genomics. This study provides the first comprehensive genomic characterization of Salmonella enterica vaccine strains on the European market, confirming their safety, genetic stability, compliance with manufacturer declarations, and highlighting HTS as a valuable tool for vaccine quality assessment. As a supplement to phenotypic methods, HTS implementation requires coordination with manufacturers and EDQM before routine use in OMCLs.