Carriage of Methicillin-Resistant Staphylococci and Their SCC mec Types in a Long-Term-Care Facility

Abstract

ABSTRACT Following an outbreak caused by staphylococcal cassette chromosome mec (SCC mec ) type V methicillin (meticillin)-resistant Staphylococcus aureus (MRSA), a point-prevalence survey of the nasal carriage of staphylococci was conducted in a long-term-care facility in northern Finland in 2004. The focus was directed at methicillin-resistant coagulase-negative staphylococci (MR-CNS) and their SCC mec elements. A nasal swab was taken from 76 of the 80 residents 6 months after the onset of the outbreak. Staphylococcal isolates were identified by conventional methods and the GenoType Staphylococcus test, and their SCC mec elements were analyzed. Of the 76 individuals, 24 (32%) carried S. aureus and 67 (88%) CNS in their nostrils. Of the CNS carriers, 41 (61%) had at least one mecA -positive MR-CNS, and two individuals (3%) had both MRSA and methicillin-resistant Staphylococcus epidermidis (MRSE). Among the 61 MR-CNS isolates identified, 49 (80%) were MRSE. The distribution of the SCC mec types was diverse: 20 (33%) were of type IV, 11 (18%) of type V, 4 (6%) of type I or IA, 3 (4%) of type II, and 23 (38%) of new types (with six different combinations of ccr and other mec genes or only mecA ). Both of the individuals with MRSA and MRSE shared SCC mec type V among their isolates. Nasal MR-CNS carriage was common among the residents of this long-term-care facility. A variety of SCC mec types, including many new types, were identified among the MR-CNS strains. The horizontal transfer of SCC mec elements is speculated based on the sharing of SCC mec type V between MRSA and MRSE.