Molecular Characterization of Salmonella Isolates Circulating in the Layer Farms of Bangladesh

Abstract

Background: Salmonella infections are a major concern for the layer poultry industry in Bangladesh and pose a significant public health risk due to their zoonotic potential. Effective control depends on accurate isolation and molecular identification of circulating strains. Therefore, this study aimed to isolate and molecularly characterize Salmonella strains circulating in layer farms in Bangladesh.

Methods: The study was conducted at Krishibid Farm, Valuka Upazila, Mymensingh district, and in the Department of Pathology, Faculty of Veterinary Science, Bangladesh Agricultural University, Mymensingh. Cloacal swab samples were collected from layer chickens. Isolation was performed using standard bacteriological culture techniques. DNA was extracted from cultured isolates, quantified, and subjected to PCR targeting the invA and ITS genes. Amplified products were purified using a gel extraction method and subsequently sequenced. Sequence data were analyzed using BLAST, and phylogenetic relationships were assessed through phylogenetic tree construction.

Results: PCR amplification identified Salmonella enteritidis and Salmonella gallinarum in 32 out of 100 field samples. Sequence analysis and BLAST comparison demonstrated 100% homology with corresponding sequences available in GenBank. Alignment of nucleotide and deduced amino acid sequences revealed no mutations relative to reference strains. Five representative isolates were selected for phylogenetic analysis. The constructed phylogenetic tree showed that the isolates clustered in a monophyletic group with global reference strains.

Conclusion: The molecular identification and characterization of circulating Salmonella strains provide essential information for controlling zoonotic transmission, particularly of Salmonella enteritidis, to humans. These findings also support efforts to improve biosecurity and facilitate the production and potential export of Salmonella-free poultry meat and eggs.