Abstract

The purpose of the study was to examine the genetic mechanisms and regulation of biofilm formation in Salmonella enteritidis and Salmonella typhimurium isolated at industrial poultry farms. The methodology included the collection of 340 samples from industrial poultry production facilities in Kazakhstan, Latvia, and Turkey between 2022 and 2025. The isolated strains were serotyped, genomic deoxyribonucleic acid was extracted, and the presence of the csgD, bcsA, adrA, rpoS, and fimA genes was detected using polymerase chain reaction (PCR). The level of gene expression was determined using quantitative polymerase chain reaction, and the phenotypic ability to form biofilms was evaluated by crystal violet staining. The results showed the isolation of 238 Salmonella strains, including 124 S. enteritidis and 114 S. typhimurium. The highest contamination was recorded in slaughter lines, accounting for 43.3% of the total positive samples. The analysis showed varying Salmonella serotype prevalence across countries, with S. enteritidis dominant in Kazakhstan (45.9%), S. typhimurium in Latvia (64.7%), and a balanced distribution in Turkey. The analysis revealed a high prevalence of biofilm formation genes, particularly fimA (94.1%), while rpoS ranged from 66.7% to 85.5%. According to quantitative polymerase chain reaction data, the expression of csgD (P = 0.003), bcsA (P = 0.005), and adrA (P = 0.007) was significantly higher in S. typhimurium, indicating its greater potential for biofilm formation. The phenotypic assessment confirmed this: 65% of S. typhimurium were strong or very strong biofilm producers, compared with 45% in S. enteritidis (OD570: 1.42±0.15 and 0.97±0.12, respectively). The results can be practically applied in the development of sanitary control programmes, including the implementation of protocols for periodic assessment of biofilm-forming strains using qPCR screening. Based on the expression profile of key genes, criteria can be developed for selecting effective disinfectants (e.g., peroxide compounds or quaternary ammonium compounds) and for creating regulations targeting critical areas, such as poultry slaughterhouses and evisceration equipment.