Clonal Features of Community-Acquired Methicillin-Resistant Staphylococcus aureus in Children

Recent studies from Chicago noted an increase in isolation of community-acquired (CA) clindamycin-susceptible methicillin-resistant Staphylococcus aureus (MRSA) from children [1, 2]. We studied MRSA isolates from children that were recovered at the University of Illinois Hospital (62 isolates) and Michael Reese Hospital (8 isolates) in Chicago. Related clinical and epidemiological methods and data have been reported elsewhere [2, 3]. All MRSA isolates were stored in skim milk at −80°C since 1987 (1994 at Michael Reese Hospital). Antibiotic susceptibility testing for all isolates was performed by means of MicroScan technology (Dade International, West Sacramento, CA), and oxacillin MICs for 10 selected isolates were determined by broth macrodilution testing according to the guidelines of the National Committee for Clinical Laboratory Standards [4]. All organisms were typed by pulsed-field gel electrophoresis (PFGE) by use of SmaI (a modified version of the method described by Matushek et al. [5]). Isolates with the same restriction pattern were considered identical; those with ≤6 band differences were considered possibly related [6] and were grouped with the identical isolates in the same pulsotype group. Detection of mecA followed the PCR methods described by Carroll et al. [7]. Fisher's exact test was used for statistical analysis.