Molecular characterization of the capsule locus from non-typeable Staphylococus aureus (published on line 17/11/2005)

COCCHIARO, JORDAN L.; GOMEZ, MARISA I.; RISLEY, ALLISON; SOLINGA, ROBERT M.; SORDELLI, DANIEL O.; LEE, JEAN C.

MOLECULAR MICROBIOLOGY

Blackwell Publishing LTD

Lugar: Oxford, U.K.; Año: 2006 vol. 59 p. 948 - 960

0950-382X

Most Staphylococcus aureus express a serotype 5 or 8 capsular polysaccharide (CP).  However, 20-25% of human isolates and up to 86% of bovine strains of S. aureus are nontypeable (NT), i.e., nonreactive with antibodies to CP types 1, 2, 5, or 8.  A vaccine that targets the S. aureus CP would not protect against NT strains.  The aim of this study was to characterize NT S. aureus isolates at the molecular level to explain their lack of type 5 or 8 capsule production.  The cap5(8) locus was present in all 22 NT clinical isolates from humans, 8 of 21 bovine isolates, and in all eight sequenced strains.  NT strains positive for the cap5(8) transcript had mutations within essential capsule genes and could be complemented in trans.  S. aureus strains with reduced cap5(8) transcript had mutations within the cap5A promoter, decreased RNAIII levels, or a truncated arlR gene product.  More than one mutation was identified in several isolates.  The cap5(8) locus was replaced by IS257 in 13 of 21 NT bovine isolates of S. aureus.  Lack of capsule expression in NT S. aureus can be explained by multiple mechanisms, and the data argue against the existence of capsule serotypes other than 1, 2, 5, and 8.