Genetic characterization of the mechanisms of resistance to amoxicillin/clavulanate and third-generation cephalosporins in Salmonella enterica from three Spanish hospitals

摘要

The mechanisms of antimicrobial resistance were characterized in 90 Salmonella enterica isolates either resist-ant or with intermediate resistance to amoxicillin/clavulanate (AMC~(R/I)) or resistant to third-generation cephalosporins (C3G~R). These isolates were recovered in three Spanish hospitals during 2007-2009. The C3G~R phenotype was expressed by three isolates that carried the following extended-spectrum β-lactamase genes: phage-associated bla_(CTXM-10) in S. Virchow, surrounded by ISEcp1 and 1S903 in S. Enteritidis, and bla_(CTM-M-15) linked to ISEcp1 and orf477 in S. Gnesta (first description in this serotype). The AMC~(R/I) phenotype was found in 87 isolates (79 S. Typhimurim, 7 S. Enteritidis, and one S. Thompson). The bla_(PSE-1) gene, followed by bla_(OXA-1) was mostly found among S. Typhimurim, and the bla_(TEM-1) gene among S. Enteritidis. Three different gene combinations [b1a_(PSE-1)+floR+aadA2+sul+tet(G);bla_(OXA-1)+catA+aadAl/strA-strB+sul+tet(B) and bla_(TEM-1)+ cmlAl+aadA/strA-strB+sul+tet(A)/tet(B) genes] were associated with the ampicillin-chloramphenicol-streptomycin-sulfonamides-tetracycline phenotype in 68 AMC~(R/I) S. enterica isolates. Class 1 integrons were observed in 79% of the isolates and in most of them (45 isolates) two integrons including the aadA2 and bla_(PSE-1) gene cassettes, respectively, were detected. The bla_(OXA-1)aadAl arrangement was detected in 23 isolates, and the aac(6')-Ib-cr+bla_(OXA-1)+catB3+arr3 in another one. Non-classic class 1 integrons were found in three isolates: dfrAl2+orfF+aadA2+cmlAl+aadA1 (1 isolate), dfrA12+orfF+aadA2+ cmlA1+aadA1+qacH+IS440+sul3 (1 isolate) and dfrA12+orfF+aadA2+cmlA1+aadA1+qacH+IS440+ sul3+orfl+meAB)Δ-IS26 (1 isolate). Taken together, these results underline the need for clinical concern regarding β-lactam resistance in Salmonella and thus for continuous monitoring.