Reduced expression of the atl autolysin gene and susceptibility to autolysis in clinical heterogeneous glycopeptide-intermediate Staphylococcus aureus (hGISA) and GISA strains

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Abstract
Objectives: To assess a link between resistance to Triton X-100 induced autolysis (TIA) and lowered atl expression in a collection of clinical glycopeptide-intermediate Staphylococcus aureus (GISA) and heterogeneous GISA (hGISA). Methods: Nine clinical GISA, 11 hGISA and 11 glycopeptide-susceptible S. aureus (GSSA), including three pairs of related isolates, were analysed using TIA assays. Lysostaphin MICs were determined by a broth microdilution technique and reverse transcriptase PCR was used to compare atl expression levels in all isolates. Results: Eight of nine clinical GISA and six of 11 hGISA exhibited lower susceptibility to TIA and higher MICs of lysostaphin than GSSA. Eight of nine GISA and all hGISA strains had lowered atl expression levels compared with GSSA. Conclusions: The majority of GISA and hGISA isolates exhibited lowered susceptibility to TIA and lysostaphin and reduced atl expression when compared with GSSA isolates. These factors could contribute to, or predispose to the development of, a thickened cell wall and glycopeptide-intermediate resistance.

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