Evidence for the geographic spread of a methicillin-resistant Staphylococcus aureus clone between Portugal and Spain

Methicillin-resistant Staphylococcus aureus (MRSA) isolates collected during a 7-month period in 1992 and 1993 at Hospital Pulido Valente (340 beds), Lisbon, Portugal, were characterized by a combination of genotypic and phenotypic methods. Clonal identities were determined by probing ClaI digests (i) with a mecA probe and (ii) with a Tn554 probe and (iii) by pulsed-field gel electrophoresis (PFGE) patterns of chromosomal SmaI digests. mecA-ClaI type I was predominant among these isolates (38 of 43). Most of these (37 of 38 [97.4%]) were associated with a single Tn554 pattern, pattern E, and the majority (23 of 38 [61%]) also showed a relatively uniform chromosomal background, as indicated by PFGE (PFGE pattern A). The major clone (mecA-ClaI type I::Tn554 type E and PFGE pattern A) at Hospital Pulido Valente was indistinguishable by these molecular typing criteria from the dominant clone that had been identified in two major current outbreaks of MRSA disease in Spain (Barcelona and Madrid). The Portuguese and Spanish clones also had a common heterogeneous class 3 phenotype and identical multidrug resistance patterns. The data presented in this work support the notion that MRSA clones can spread across considerable geographic distances.