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

Jing Xie, Fuli Wu, Xuebin Xu, Xiaoxia Yang, Rongtao Zhao, Qiuxia Ma, Peng Li, Ligui Wang, Rongzhang Hao, Leiji Jia, Xinying Du, Shaofu Qiu, Hongbin Song

Among 2179 Salmonella isolates obtained during national surveillance for salmonellosis in China from 2005 to 2013, we identified 46 non-H2S-producing strains originating from different sources. 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-H2S-producing phenotype of the isolated Salmonella strains, was performed in this study. Among isolated non-H2S-producing Salmonella strains, more than 50% were recovered from diarrhea patients, of which H2S-negative S. Gallinarum, S. Typhimurium, S. Choleraesuis and S. Paratyphi A isolates constituted 76%. H2S-negative isolates exhibited a high rate of resistance to ticarcillin, ampicillin, and tetracycline, and eight of them had the multidrug resistance phenotype. Most H2S-negative Salmonella isolates had similar pulsed-field gel electrophoresis profiles and the same sequence type as H2S-positive strains, indicating a close origin, but carried mutations in the phsA gene, which may account for the non-H2S-producing phenotype. Our data indicate that multiple H2S-negative strains have emerged and persist in China, emphasizing the necessity to implement efficient surveillance measures for controlling dissemination of these atypical Salmonella strains.