Characterization of a novel extended-spectrum beta-lactamase phenotype from OXA-1 expression in Salmonella Typhimurium strains from Africa and Ireland

Salmonella enterica (S. Typhimurium) strains from Kenya, Malawi, and Ireland showing elevated cefepime MIC values carried bla(OXA-1). These strains were not detected by current guidelines for extended-spectrum beta-lactamase production based on MIC values or clavulanate inhibition, since cefepime is a preferred substrate for OXA-1 and this enzyme is reported to be resistant to clavulanate inhibition. bla(OXA-1) was located within a class I integron and an activated P(2) promoter was identified upstream of bla(OXA-1). P(2) was activated by the insertion of a triplet GGG upstream of the -10 signal. All African strains were ST313, prevalent in this continent, and the Irish isolate belonged to ST19. (C) 2011 Elsevier Inc. All rights reserved.