Distribution of Florfenicol Resistance Genes <i>fexA</i> and <i>cfr</i> among Chloramphenicol-Resistant <i>Staphylococcus</i> Isolates

<jats:title>ABSTRACT</jats:title> <jats:p> A total of 302 chloramphenicol-resistant <jats:italic>Staphylococcus</jats:italic> isolates were screened for the presence of the florfenicol/chloramphenicol resistance genes <jats:italic>fexA</jats:italic> and <jats:italic>cfr</jats:italic> and their localization on mobile genetic elements. Of the 114 isolates from humans, only a single <jats:italic>Staphylococcus aureus</jats:italic> isolate showed an elevated MIC to florfenicol, but did not carry either of the known resistance genes, <jats:italic>cfr</jats:italic> or <jats:italic>fexA</jats:italic> . In contrast, 11 of the 188 staphylococci from animal sources were considered florfenicol resistant and carried either <jats:italic>cfr</jats:italic> (one isolate), <jats:italic>fexA</jats:italic> (five isolates), or both resistance genes (five isolates). In nine cases we confirmed that these genes were carried on a plasmid. Five different types of plasmids could be differentiated on the basis of their sizes, restriction patterns, and resistance genes. The gene <jats:italic>fexA</jats:italic> , which has previously been shown to be part of the nonconjugative transposon Tn <jats:italic>558</jats:italic> , was identified in 10 of the 11 resistant isolates from animals. PCR assays were developed to detect different parts of this transposon as well as their physical linkage. Complete copies of Tn <jats:italic>558</jats:italic> were found in five different isolates and shown by inverse PCR to be functionally active. Truncated copies of Tn <jats:italic>558</jats:italic> , in which the <jats:italic>tnpA-tnpB</jats:italic> area was in part deleted by the integration of a 4,674-bp segment including the gene <jats:italic>cfr</jats:italic> and a novel 2,446-bp IS <jats:italic>21</jats:italic> -like insertion sequence, were seen in a plasmid present in three staphylococcal isolates. </jats:p>