Carriage of methicillin-resistant Staphylococci and their SCCmec types in a long-term-care facility

Abstract

Following an outbreak caused by staphylococcal cassette chromosome mec (SCCmec) 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 SCCmec 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 SCCmec 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 SCCmec 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 SCCmec type V among their isolates. Nasal MR-CNS carriage was common among the residents of this long-term-care facility. A variety of SCCmec types, including many new types, were identified among the MR-CNS strains. The horizontal transfer of SCCmec elements is speculated based on the sharing of SCCmec type V between MRSA and MRSE.

FIG. 1.

SCCmec multiplex patterns of MR-CNS strains (31). M, molecular size markers (in kilodaltons). Lanes 1 to 4 and 21 to 24, control MRSA of type IA (locus A, upstream of the pls gene; locus G, left of the junction between IS431 and pUB110; and locus D, the dcs region), type II (loci G, D, and B, kdp operon; locus C, mecI gene), type IIIA (locus F, between Tn554 and orfX; locus E, between integrated pI258 and Tn554; and locus C) and SCCmec type IV (locus D) and internal control mecA. The sizes of amplicons, by locus, are the following: A, 495 bp; B, 284 bp; C, 209 bp; D, 342 bp; E, 243 bp; F, 414 bp; G, 381 bp; and mecA, 160 bp. Lanes 5 to 20, MRSE isolates; lanes 25 to 31 and 33, methicillin-resistant S. capitis; lane 32, methicillin-resistant S. haemolyticus; and lane 34, methicillin-resistant S. hominis.

FIG. 2.

Three multiplex PCRs for the SCCmec type assignment of the staphylococcal isolates from the two patients colonized with MRSA and MRSE. Lanes M1 and M2, molecular size markers. Lanes 1 to 5, control MRSA for SCCmec type IA (ccrA1, class B), SCCmec type II (ccrA2, class A), SCCmec type IIIA (ccrA3, class A), SCCmec type VI (ccrA4, class B), and SCCmec type V (ccrC and class C). (A) Multiplex PCR patterns (31). Lanes 1 to 4, controls; lanes 1a and 2a, MRSA isolates; lanes 1b, 1c, 1d, and 2b, MRSE isolates. (B) Multiplex PCR for the typing of ccr genes. Lanes 1 to 5, control MRSA isolates for ccr types. (C) Multiplex PCR for typing of mec genes (19). Lanes 1 to 3, control MRSA isolates for mec classes. Lanes 1a and 2a, MRSA (ccrC, class C); lane 1b, MRSE (ccrC, class A); lane 1c, MRSE (ccrA2, class A); lanes 1d and 2b, MRSE (ccrC, class C); lane 2a, MRSA (ccrC) and MRSE (ccrC).

FIG. 3.

PFGE dendrogram of the methicillin-resistant staphylococcal isolates from two patients colonized with MRSA and MRSE. The distribution of the SCCmec types/elements for each strain is included. The scale bar at the top of the dendrogram represents similarity.