Scientific Publications by FDA Staff

FEMS Immunol Med Microbiol 2011 Oct;63(1):16-24

Capsular serotype of Staphylococcus aureus in the era of community acquired MRSA.

Sutter DE, Summers AM, Keys CE, Taylor KL, Frasch CE, Braun LE, Fattom AI, Bash MC

Background: Capsular polysaccharide (CP) serves an important role in pathogenicity and immunogenicity of Staphylococcus aureus, yet the common serotypes of S. aureus isolated from U.S. pediatric patients have not been reported. We investigated capsular serotype as well as methicillin-susceptibility, presence of Panton-Valentine Leukocidin (PVL), and clonal relatedness of pediatric S. aureus isolates obtained over 12 months. Methods: All pediatric S. aureus isolates from August 2004 to July 2005 (N=91), and archived methicillin-resistant strains (MRSA) from 2001-2004 (N=24) at the Walter Reed Microbiology Laboratory were tested for methicillin-susceptibility, presence of mecA, lukS-PV and lukF-PV, cap5 and cap8 genes by PCR, and for capsular or surface polysaccharide expression (CP5, CP8, or 336 polysaccharide) by agglutination. Genetic relatedness was determined by pulsed-field gel electrophoresis. Results: All S. aureus isolates encoded cap5 or cap8. Sixty-nine percent of 2004-2005 isolates were methicillin-susceptible (MSSA) and most expressed detectable capsule. The majority of MRSA isolates (82%) were unencapsulated, exposing an expressed cell wall techoic acid antigen 336. Pulsed-field type (PFT) USA300 were MRSA, PVL-positive, unencapsulated strains that were associated with deep skin infections and recurrent disease. Over half (58%) of all isolates from invasive pediatric dermatologic infections were USA300. Conclusions: All pediatric isolates contained either capsule type 5 or capsule type 8 genes, and roughly half of the S. aureus clinical disease isolates from our population were diverse MSSA encapsulated strains. The majority of the remaining pediatric clinical disease isolates were unencapsulated serotype 336 strains of the PVL (+) USA300 CA-MRSA clone.