Antibiotic resistance and molecular characterization of the hydrogen sulfide-negative phenotype among diverse Salmonella serovars in China.

Background: Among 2179 Salmonella isolates obtained during national surveillance for salmonellosis in China from 2005 to 2013, we identified 46 non-HS-producing strains originating from different sources.

Methods: The isolates were characterized in terms of antibiotic resistance and genetic variability by pulsed-field gel electrophoresis and multilocus sequence typing. Mutation in the phs operon, which may account for the non-HS-producing phenotype of the isolated Salmonella strains, was performed in this study.

Results: Among isolated non-HS-producing Salmonella strains, more than 50% were recovered from diarrhea patients, of which HS-negative S. Gallinarum, S. Typhimurium, S. Choleraesuis and S. Paratyphi A isolates constituted 76%. HS-negative isolates exhibited a high rate of resistance to ticarcillin, ampicillin, and tetracycline, and eight of them had the multidrug resistance phenotype. Most HS-negative Salmonella isolates had similar pulsed-field gel electrophoresis profiles and the same sequence type as HS-positive strains, indicating a close origin, but carried mutations in the phsA gene, which may account for the non-HS-producing phenotype.

Conclusions: Our data indicate that multiple HS-negative strains have emerged and persist in China, emphasizing the necessity to implement efficient surveillance measures for controlling dissemination of these atypical Salmonella strains.