The nasal carriage rate of was examined in a longitudinal study of 31 healthy Danish volunteers. Each person was classified as persistent (>8 positive cultures from 10 examinations), an intermittent carrier (50–80% positive cultures) or an ocassional carrier (positive cultures on 10–40% of ocassions only). One hundred and twenty strains from these persons were subjected to phage typing and random amplification of polymorphic DNA (RAPD) analysis. Phage and RAPD typing were in close agreement. RAPD confirmed the spread of a particular clone (phage type 95) throughout Denmark. However, no common genotype or phenotype characteristics of that could separate persistent from intermittent or incidental colonisers were identified. The immunoglobulin binding protein A and the prothrombin binding coagulase protein are both putative virulence or defence factors. Analysis of polymorphisms in the variable repeat regions in the genes for these proteins showed no correlation between the number of repeat units and, consequently, the protein structure with the ability of strains to persist in the human nasal mucosa. The amount of protein A, detectable by its IgG binding activity, appeared not to be correlated to persistence of carriage. Thus protein A and coagulase -gene polymorphisms do not seem to play a significant role in the propensity of to colonise human nasal epithelium. Furthermore, based on the genetic heterogeneity encountered among the strains it is suggested that within the current study population, no single clonal lineage of has increased capability to colonise the human nasal epithelium.


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