Incidence of Mupirocin Resistance in Staphylococcus pseudintermedius Isolated from a Healthy Dog
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Mupirocin is a bacteriostatic antibiotic that is used to decolonize people who carry methicillin-resistant staphylococci, primarily methicillin-resistant Staphylococcus aureus (MRSA). Mupirocin reversibly binds to bacterial isoleucyl tRNA synthetase to disrupt protein synthesis. Resistance to mupirocin is due either to a point mutation to the ileS gene that encodes the isoleucyl tRNA synthetase, classified as low-level mupirocin resistance; or, bacteria may obtain a plasmid that carries the ileS2 gene encoding an alternate isoleucyl tRNA synthetase, conferring high-level resistance. Mupirocin resistance plasmids contain insertion sequence (IS) 257 repeats, into which the ileS2 gene is inserted. Such plasmids have been characterized by their IS257-ileS2 junctions in both S. aureus and, recently, in Staphylococcus pseudintermedius in a dog from Croatia. The primary goals of this study were to determine the prevalence of mupirocin resistance in isolates of S. pseudintermedius in Texas, to determine whether resistance was due to point mutations in the native ileS or due to carriage of mupirocin resistance plasmids, and to characterize the structure of the mupirocin resistance genes carried on plasmids. In this study, 572 S. pseudintermedius isolates, collected from veterinary patients from across Texas were screened for their susceptibility to low levels of mupirocin. Of these isolates, only one out of 572 (0.17%) tested positive for mupirocin resistance and was found by polymerase chain reaction (PCR), using previously published primers mupA and mupB, to have a 458 bp fragment and, with primers M1 and M2 to have a 237 bp fragment, indicating the presence of the high-level mupirocin resistance gene, ileS2. The arrangement of the IS257-ileS2 junctions was then analyzed by PCR and the products, bands at 1816 bp for primers ileS2-5’ and IS257R and at 1127 bp for primers ileS2-3’ and IS257F, which are consistent with the amplification pattern for an S2 plasmid, were cloned into a plasmid, pT7Blue, and sequenced for comparison to published sequences in GenBank. BLAST analyses in NCBI, comparing the isolate to recently published sequences for mupirocin-resistant S. pseudintermedius isolated from a dog with pyoderma in Croatia, indicate a 100% similarity to the upstream junction, JX186508, and 97% to the downstream junction, JX186509.
Godbeer, Stacey Marie (2013). Incidence of Mupirocin Resistance in Staphylococcus pseudintermedius Isolated from a Healthy Dog. Master's thesis, Texas A & M University. Available electronically from