Molecular characterisation of hydrogen sulfide negative Salmonella enterica serovar Havana

Hydrogen sulfide (H₂S) detection is a screening method for distinguishing and identifying Salmonella strains from other bacteria in the intestine. Incidences of H₂S-negative Salmonella have recently been reported in different countries. Although a high resistance rate against antimicrobial agents has been reported for H₂S-positive Salmonella in many regions of the world, there is increasing evidence that high resistance to antibiotics has also increased in many H₂S-negative Salmonella isolates. In this study, molecular characterisation of three H₂S-negative Salmonella Havana, isolated from cloacal swab samples of broiler chickens, was performed. The phsA, phsB and phsC genes of the phs operon, which is responsible for hydrogen sulfide production, were amplified. Sequence analysis was then performed to identify mutations in the gene cluster. The antimicrobial resistance profiles of the isolates were determined by disc diffusion. Molecular characterisation was performed by multilocus sequence typing (MLST) and pulsed field gel electrophoresis (PFGE). The sequence analysis showed identified five point mutations in the phsA gene and one point mutation in the phsC gene in all isolates. The antibiotic resistance profile showed that the strains were resistant to cefoxitin and ceftazidime. MLST analysis showed that all strains belonged to sequence type (ST) 1621. This study is the first to report the H₂S-negative S. Havana serotype.