Epidemiology and Characterization of CTX-M-55-Type Extended-Spectrum β-Lactamase-Producing Serovar Enteritidis Isolated from Patients in Shanghai, China

The emergence of extended-spectrum β-lactamase-producing serovar Enteritidis (ESBL-SE) in humans and foods has gained global attention. In particular, CTX-M-type ESBL-SE are increasingly being detected from various sample types. The aim of this study was to comprehensively analyze the epidemiology and characteristics of -carrying ESBL-SE isolates of clinical origin in Shanghai, China. A total of 292 Enteritidis isolates were recovered from the feces and blood of outpatients and inpatients between 2006 and 2014. Overall, there was a high frequency of cefotaxime-resistant isolates (97.3%), which was significantly higher ( < 0.01) than that of isolates resistant to the other tested antibiotics. All Enteritidis isolates exhibited resistance to ≥1 antibiotic, and 98.0% were multidrug resistant. A total of 233 isolates were identified as ESBL-SE, 166 of which were CTX-M type. Six subtypes of CTX-M-encoding genes were detected, among which (91.6%, 152/166) was the most prevalent genotype. There was high genetic similarity among -positive ESBL-SE. The gene in the ESBL-SE donor strains could be easily transferred into recipient strains. This study highlights that CTX-M-55 should be considered an important surveillance target in Shanghai, China. Cephalosporins, especially cefotaxime, must be used with caution in empirical treatment for infections.