Multidrug‐ResistantShigella sonneiandSalmonella entericaSerotype Typhimurium Isolates Producing CTX‐M β‐Lactamases as Causes of Community‐Acquired Infection in France

SIR—Production of extended-spectrum β-lactamases (ESBLs) is uncommon among strains of Shigella sonnei and Salmonella enterica serotype Typhimurium, compared with the prevalence among other enterobacterial species. Three CTX-M-type ESBLs (CTX-M-2, CTX-M-3, and CTX-M-14) have been reported in Shigella isolates (S. sonnei and Shigella flexneri) in Argentina, Turkey, and Korea, and 8 different CTX-M β-lactamases (CTX-M-2 to -7, CTX-M-9, and CTX-M-15) have been reported in S. enterica isolates in South America, Europe, and Lebanon [1–3]. We report here the first identification of strains of Shigella sonnei and CTX-M-1 S. Typhimurium that produce CTX-M-15 ESBLs and that were associated with community-acquired infections likely originating in France. In October 2004, a 4-year-old child was admitted in the Dourdan Hospital (Paris metropolitan area, France) for acute gastroenteritis. The patient had severe diarrhea. He was cured with an amoxicillin/clavulanate regimen. In September 2004, a 42-year-old woman had been admitted at the Bicêtre Hospital (in the Paris area), also for acute gastroenteritis. The patient had had gastrointestinal disorders 1 week before admission, with severe diarrhea and dehydration, for which she had first received empirical treatment with trimethoprim-sulfamethoxazole. Subsequently, the patient was treated with oral ciprofloxacin. She was cured and discharged from the hospital without sequelae. Cultures of stool specimens from the child and the woman yielded S. sonnei and S. Typhimurium, respectively. Both strains were resistant to amoxicillin, ticarcillin, piperacillin, cephalothin, extended-spectrum cephalosporins, trimethoprim, and streptomycin. They remained susceptible to imipenem, cefoxitin, amikacin, gentamicin, netilmicin, tobramicin, and nalidixic acid. The strains were intermediately susceptible to amoxicillin/clavulanate, ticarcillin/clavulanate, and piperacillin/sulbactam. In addition, the S. Typhimurium isolate was resistant to sulfamides and chloramphenicol. A cefotaxime/amoxicillin/clavulanate synergy test [4] yielded positive results for both isolates. Neither patient had travelled abroad in the past few years. The woman had had no exposure to animals. The local health departments reported no additional cases of infection due to S. Typhimurium or S. sonnei. Plasmid analysis [4] identified a single plasmid (130 kb in size) in the S. Typhimurium NC strain and 6 plasmids (160, 110, 7, 6, 3, and 4 kb in size) in the S. sonnei strain. With use of ampicillin (100 µg/mL) and sodium azide (100 µg/mL; Sigma-Aldrich, Saint-Quentin-Fallavier, France) as selection agents and Escherichia coli J53AzR as the recipient strain [5], plasmid transfer of the ESBL phenotype was obtained for both strains. PCR amplification was performed with whole-cell DNA of both strains using primers specific for blaCTX-M [4], and results were positive. Sequencing of PCR products identified the blaCTX-M-1 gene in the S. Typhimurium strain and the blaCTX-M-15 gene in the S. sonnei strain. PCR experiments with primers hybridizing to the ends of insertion sequence ISEcp1 identified this insertion upstream of both blaCTX-M genes, providing promoter sequences responsible for their high level expression, as reported elsewhere [4]. This is the first report of CTX-M-15 ESBL-producing S. sonnei. However, production of this β-lactamase is widely disseminated, particularly in the United Kingdom among E. coli strains isolated from nosocomial infections, and now from community-acquired cases [6]. The emergence of CTX-M ESBL-producing strains of Shigella and Salmonella in patients with community-acquired infections in France may represent a threat to public health. It also underlines that ESBL genes have a novel reservoir among enterobacterial species responsible for community-acquired infections. Financial support. This work was funded by a grant from the Ministère de l'Education Nationale et de la Recherche (grant UPRES-EA3539), Université Paris XI, France, and by the European Community (grant LSHM-CT-2003-503335). Potential conflicts of interest. All authors: no conflicts.