Distribution of the Multidrug Resistance Genecfrin Staphylococcus Species Isolates from Swine Farms in China

Abstract

ABSTRACTA total of 149 porcineStaphylococcusisolates with florfenicol MICs of ≥16 μg/ml were screened for the presence of the multiresistance genecfr, its location on plasmids, and its genetic environment. In total, 125 isolates carried eithercfr(16 isolates),fexA(92 isolates), or both genes (17 isolates). The 33cfr-carrying staphylococci, which included isolates of the speciesStaphylococcus cohnii,S. arlettae, andS. saprophyticusin which thecfrgene has not been described before, exhibited a wide variety of SmaI pulsed-field gel electrophoresis patterns. In 18 cases, thecfrgene was located on plasmids. Four different types ofcfr-carrying plasmids—pSS-01 (n= 2; 40 kb), pSS-02 (n= 3; 35.4 kb), pSS-03 (n= 10; 7.1 kb), and pBS-01 (n= 3; 16.4 kb)—were differentiated on the basis of their sizes, restriction patterns, and additional resistance genes. Sequence analysis revealed that in plasmid pSS-01, thecfrgene was flanked in the upstream part by a completeaacA-aphD-carrying Tn4001-like transposon and in the downstream part by a completefexA-carrying transposon Tn558. In plasmid pSS-02, an insertion sequence IS21-558and thecfrgene were integrated into transposon Tn558and thereby truncated thetnpAandtnpBgenes. The smallestcfr-carrying plasmid pSS-03 carried the macrolide-lincosamide-streptogramin B resistance geneerm(C). Plasmid pBS-01, previously described inBacillusspp., harbored a Tn917-like transposon, including the macrolide-lincosamide-streptogramin B resistance geneerm(B) in thecfrdownstream region. Plasmids, which in part carry additional resistance genes, seem to play an important role in the dissemination of the genecframong porcine staphylococci.