Novel Pseudo-Staphylococcal Cassette Chromosome mec Element (ΨSCCmec57395) in Methicillin-Resistant Staphylococcus pseudintermedius CC45

Genetic characterization of methicillin-resistant Staphylococcus pseudintermedius (MRSP) from Thailand and Israel revealed the presence of a predominant atypical clonal lineage which was not typeable by SmaI-PFGE and SCCmec typing. All the atypical isolates (n = 34) belonged to CC45 (30 ST45 and 2 ST179 isolates, 1 ST57 isolate, and 1 ST85 isolate). The isolates originated from healthy and diseased dogs and cats, as well as from the environment of one clinic. Cfr9I-pulsed-field gel electrophoresis (Cfr9I-PFGE) and dru typing permitted the further distinction of CC45 isolates from the two different countries. Microarray analysis identified genes that confer resistance to beta-lactams (mecA; blaZ), aminoglycosides [aac(6')-Ie-aph(2')-Ia; aph(3')-III; ant(6)-Ia], macrolides and lincosamides [erm(B)], tetracyclines [tet(M)], trimethoprim [dfr(G)], streptothricin (sat4), and chloramphenicol (cat(pC221)). Fluoroquinolone resistance was attributed to specific amino acid substitutions, i.e., Ser84Leu in GyrA and Ser80Ile and Asp84Asn in GrlA. A novel pseudo-staphylococcal cassette chromosome (Psi SCCmec(57395)) element was identified in MRSP strain 57395 (sequence type ST45) by whole-genome sequencing. The 12,282-bp Psi SCCmec(57395) element contained a class C1 mec gene complex but no ccr genes. In addition to the methicillin resistance gene mecA, Psi SCCmec(57395) also carried determinants of resistance to heavy metals, such as arsenic, cadmium, and copper. Bsu36I restriction analysis of the Psi SCCmec(57395) element amplified by long-range PCR revealed the presence of Psi SCCmec(57395) in the 33 additional isolates of MRSP CC45. The Psi SCCmec(57395) element represents a new class of SCCmec and has been identified in MRSP of CC45, which is a predominant clonal lineage in Israel and Thailand.