Antimicrobial Resistance and Molecular Investigation of H<sub>2</sub>S-Negative <i>Salmonella enterica</i> subsp. <i>enterica</i> serovar Choleraesuis Isolates in China
<div><p><i>Salmonella enterica</i> subsp. <i>enterica</i> 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 <i>S</i>. Choleraesuis isolates, detected from 21 patients with diarrhea in China between 2010 and 2011, were found to include 19 H<sub>2</sub>S-negative <i>S</i>. Choleraesuis isolates and two H<sub>2</sub>S-positive isolates. This is the first report of H<sub>2</sub>S-negative <i>S</i>. Choleraesuis isolated from humans. The majority of H<sub>2</sub>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 <i>gyrA</i> and <i>parC</i> genes and identified two new mutations in the <i>parC</i> 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<sub>2</sub>S-negative and H<sub>2</sub>S-positive <i>S</i>. Choleraesuis isolates. PFGE revealed two groups, with all 19 H<sub>2</sub>S-negative <i>S</i>. Choleraesuis isolates belonging to Group I and H<sub>2</sub>S-positive isolates belonging to Group II. By MLST analysis, the H<sub>2</sub>S-negative isolates were all found to belong to ST68 and H<sub>2</sub>S-positive isolates belong to ST145. By CRISPR analysis, no significant differences in CRISPR 1 were detected; however, one H<sub>2</sub>S-negative isolate was found to contain three new spacers in CRISPR 2. All 19 H<sub>2</sub>S-negative isolates also possessed a frame-shift mutation at position 760 of <i>phsA</i> gene compared with H<sub>2</sub>S-positive isolates, which may be responsible for the H<sub>2</sub>S-negative phenotype. Moreover, the 19 H<sub>2</sub>S-negative isolates have similar PFGE patterns and same mutation site in the <i>phs</i>A gene, these results indicated that these H<sub>2</sub>S-negative isolates may have been prevalent in China. These findings suggested that surveillance should be increased of H<sub>2</sub>S-negative <i>S</i>. Choleraesuis in China.</p></div
