Suppression of Glycopeptide Resistance in a Highly Teicoplanin-Resistant Mutant of Staphylococcus aureus by Transposon Inactivation of Genes Involved in Cell Wall Synthesis

ABSTRACT

The teicoplanin-resistant laboratory mutant TNM of Staphylococcus aureus strain COL (minimal inhibitory concentration for teicoplanin increased from 3 to 200 μg/ml) produced an abnormal peptidoglycan in which the proportion of cross-linked oligomeric muropeptides (pentameric and higher than pentameric species), representing ∼60% of all muropeptide species in the parental strain, was reduced to ∼17% in the mutant. In parallel, there was an increase in the representation of the monomeric muropeptides from 4% (in the parent) to 20% in the resistant strain. The mutant cell wall showed greatly increased porosity for the detergent extraction of cytoplasmic proteins, and this property was abolished in a Tn551 insertional derivative of TNM, which was selected for reduced (parental level) teicoplanin resistance. Transposon inactivation of the global regulatory genes Sigma-B and sar, and several genes involved in early steps of staphylococcal peptidoglycan synthesis, all caused extensive reduction of teicoplanin resistance in mutant TNM, in some cases to levels close to or below the MIC value of the parental strain.