Rapid Emergence and Clonal Dissemination of CTX-M-15–Producing Salmonella enterica Serotype Virchow, South Korea

Nontyphoidal salmonella, a foodborne pathogen, causes human gastroenteritis worldwide. Among >2,500 different Salmonella enterica serotypes, Salmonella Enteritidis and Salmonella Typhimurium are the most common serotypes responsible for human salmonellosis (1). In Europe, Salmonella Virchow has recently increased in prevalence, and a high proportion of isolated strains are resistant to multiple antimicrobial drugs (2–4). Third-generation cephalosporins are widely used to treat major bacterial infections in humans and animals (5). However, the emergence and rapid spread of drug-resistant bacteria has become a serious public health concern. Extended-spectrum β-lactamases (ESBLs) are known to confer antimicrobial drug resistance by hydrolyzing most β-lactam antimicrobial drugs, including third-generation cephalosporins (5). Since the first report from Spain in 2000 of strains producing CTX-M-9 (6), which confers resistance to cefotaxime, various CTX-M–type ESBLs have been identified in Salmonella Virchow. In Spain, Belgium, and France, CTX-M-9 and CTX-M-2 producers spread clonally in humans and poultry (7,8). In addition, the blaCTX-M-15 gene was identified in porcine isolates in South Korea (9). These reports demonstrate that CTX-M–producing Salmonella Virchow clones can be easily transmitted to humans through food products of animal origin. In South Korea, the incidence of Salmonella Virchow infections in humans has increased over the years, necessitating a nationwide survey of antimicrobial drug resistance in Salmonella Virchow isolates.