1 Service de Bactériologie-Virologie, Hôpital de Bicêtre, 78 rue du Général Leclerc, Assistance Publique/Hôpitaux de Paris, Faculté de Médecine Paris-Sud, 94275 Le Kremlin-Bicêtre, France; 2 Service de Microbiologie, Centre Hospitalier Universitaire, Constantine, Algérie; 3 Laboratoire de Bactériologie des Hôpitaux Universitaire de Strasbourg, France
Keywords: ESBLs , nosocomial , CTX-M-3
Sir,
Extended-spectrum ß-lactamases (ESBLs) are uncommon in Salmonella enterica strains as compared with other enterobacterial species, such as Escherichia coli and Klebsiella pneumoniae. However, eight different CTX-M ß-lactamases (CTX-M-2 to -7, CTX-M-9 and CTX-M-15) have been reported in S. enterica in South America, Europe and Lebanon.14 We report here the first identification of CTX-M-producing S. enterica serotype Senftenberg isolates associated with nosocomial diarrhoea in newborns from North Africa.
In November 2004, a 45-day-old newborn was admitted at the Neonatology Unit of the University Hospital of Constantine, Algeria, for acute diarrhoea and dehydration. Concomitantly, a 15-day-old newborn was admitted for fetal distress. Two days after his admission he developed severe diarrhoea and dehydration. Both patients were treated initially with a combination of ampicillin, amikacin and ceftriaxone, but this was subsequently changed to imipenem, which resulted in both patients being cured.
Stool cultures of both patients yielded S. enterica serotype Senftenberg, as identified with the API-20E system (bioMérieux, Marcy-l'Étoile, France) and agglutination assay for serotyping (Bio-Rad, Marnes-La-Coquette, France). The local health department reported additional cases of infection due to S. enterica serotype Senftenberg, suggesting an outbreak at the Neonatology ward of the Hospital of Constantine.
Routine antibiograms, which were determined by a disc diffusion method on MuellerHinton agar (Bio-Rad), revealed that both isolates were resistant to amoxicillin, ticarcillin, piperacillin, cefalothin, extended-spectrum cephalosporins, trimethoprimsulfamethoxazole, amikacin, gentamicin, netilmicin, tobramycin and streptomycin. The isolates remained susceptible to imipenem, cefoxitin and nalidixic acid, and showed intermediate susceptibility to co-amoxiclav, ticarcillinclavulanate, and piperacillintazobactam. A cefotaxime and co-amoxiclav synergy test4 was positive for both isolates, indicating ESBL production. They each carried a single plasmid of 130 kb, and were indistinguishable by pulsed-field gel electrophoresis. Their ESBL phenotypes were transferred to E. coli J53AzR5 in vitro using ampicillin (100 mg/L) and sodium azide (100 mg/L; SigmaAldrich, Saint-Quentin-Fallavier, France) as the selection agents. PCR amplification with blaCTX-M-specific primers4 and subsequent sequencing of PCR products identified the blaCTX-M-3 gene. In addition, both isolates harboured blaTEM-1. Insertion sequence ISEcp1 was identified upstream of the blaCTX-M-3 genes, providing the promoter sequences responsible for their high level expression, as reported previously.4 ISEcp1 was inserted in the same position as that known for other blaCTX-M-3-type ß-lactamase genes.4
Salmonella infections in hospitals are usually food-borne. However, food could be excluded as a source in this instance because the milk, which was commercially prepared, was fed to other infants on the ward who did not become infected with this strain. Therefore, it is likely that horizontal transmission of the strain occurred.
This is the first report of a CTX-M enzyme in Algeria and in S. enterica serotype Senftenberg. CTX-M-3 belongs to the most widespread group of CTX-M enzymes in Europe including the UK, in nosocomial and community-acquired E. coli isolates.6 The emergence of CTX-M-ESBL-producing Salmonella in hospital-acquired infections is worrying. It further underlines that Salmonella may be a reservoir for ESBL genes in the community, and that these bacteria may then be responsible for hospital-acquired infections and thus contribute to the spread of the ESBL genes in hospital facilities.
Acknowledgements
This work was funded by grants from the Ministère de l'Education Nationale et de la Recherche (UPRES-EA3539), Université Paris XI, France, from the European Community (6th PCRD, LSHM-CT-2003-503335).
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