Antimicrobial Resistance and Molecular Investigation of H(2)S-Negative Salmonella enterica subsp. enterica serovar Choleraesuis Isolates in China

Salmonella enterica subsp. enterica serovar Choleraesuis is a highly invasive pathogen of swine that frequently causes serious outbreaks, in particular in Asia, and can also cause severe invasive disease in humans. In this study, 21 S. Choleraesuis isolates, detected from 21 patients with diarrhea in China between 2010 and 2011, were found to include 19 H(2)S-negative S. Choleraesuis isolates and two H(2)S-positive isolates. This is the first report of H(2)S-negative S. Choleraesuis isolated from humans. The majority of H(2)S-negative isolates exhibited high resistance to ampicillin, chloramphenicol, gentamicin, tetracycline, ticarcillin, and trimethoprim-sulfamethoxazole, but only six isolates were resistant to norfloxacin. In contrast, all of the isolates were sensitive to cephalosporins. Fifteen isolates were found to be multidrug resistant. In norfloxacin-resistant isolates, we detected mutations in the gyrA and parC genes and identified two new mutations in the parC gene. Pulsed-field gel electrophoresis (PFGE), multilocus sequence typing (MLST), and clustered regularly interspaced short palindromic repeat (CRISPR) analysis were employed to investigate the genetic relatedness of H(2)S-negative and H(2)S-positive S. Choleraesuis isolates. PFGE revealed two groups, with all 19 H(2)S-negative S. Choleraesuis isolates belonging to Group I and H(2)S-positive isolates belonging to Group II. By MLST analysis, the H(2)S-negative isolates were all found to belong to ST68 and H(2)S-positive isolates belong to ST145. By CRISPR analysis, no significant differences in CRISPR 1 were detected; however, one H(2)S-negative isolate was found to contain three new spacers in CRISPR 2. All 19 H(2)S-negative isolates also possessed a frame-shift mutation at position 760 of phsA gene compared with H(2)S-positive isolates, which may be responsible for the H(2)S-negative phenotype. Moreover, the 19 H(2)S-negative isolates have similar PFGE patterns and same mutation site in the phsA gene, these results indicated that these H(2)S-negative isolates may have been prevalent in China. These findings suggested that surveillance should be increased of H(2)S-negative S. Choleraesuis in China.