Strain Specificity of Capsular Polysaccharide Production by Staphylococcus aureus

摘要

Staphylococcus aureus is the leading cause of nosocomial infections in the US and is becoming increasingly difficult to treat due to the limited antibiotics available. Capsular polysaccharides (CP), a virulence factor produced by the bacterium, allows S. aureus to evade the uptake and killing by host neutrophils. It has been shown previously that CP serotype 5 retains more cell-associated CP while type 8 tends to release more CP into the supernatant. This research focused on whether this phenomenon is dependent upon the serotype-specific capHIJK genes that vary between the two serotypes. 6850, a methicillin- sensitive S. aureus (MSSA) serotype 8 strain, is a well characterized clinical isolate that was used in this study. This strain was subjected to two allelic replacement steps: the first step to replace the cap8HIJK genes with an ermB cassette, creating mutant 6850 (CP-); the second step to replace the ermB cassette with the cap5HIJK genes, which resulted in the creation of mutant 6850 (CP5). All 3 strains were characterized genotypically by PCR and phenotypically for growth rate, metabolic profile, and CP production. ELISA inhibition studies revealed that serotype 5 and the serotype 8 variants of S. aureus 6850 produced similar levels of cell-associated CP. These results suggest that cell wall anchoring of S. aureus CP5 and CP8 is not serotype specific, but instead is dependent on the genetic background of the bacterial strain. A better understanding of the anchoring mechanism may allow for development of alternative immunotherapeutics for S. aureus.