Virulent Staphylococcus aureus colonizes pediatric nares by resisting killing of human antimicrobial peptides.

BACKGROUND:The nasal carriage of Staphylococcus aureus introduces risks for subsequent infections, the rate of which is particularly high in children. The colonization mechanisms of S. aureus are not fully understood. METHODS:The epidemiological characteristics of nasal colonizing strains from pediatric patients undergoing liver transplantation and healthy pre-school children were analyzed first. Phenotypes, including biofilm formation and hemolytic activity, were tested for all the isolates. Bacterial pathogenicity indicated by a mouse skin abscess model and resistance to antimicrobial peptides (AMPs) was compared between the predominant genotypes from each group. RESULTS:The ST188 clone dominated in healthy children, whereas ST59 was prevalent for the pediatric patients. Although ST22 was the second most abundant genotype in the patient group, it was rarely found in healthy children. Interestingly, the colonizing ST59 and ST22 genotypes were more virulent, as indicated by the increased ability for hemolysis in vitro and severe subcutaneous abscesses in the mouse model, compared with ST188. We observed that the virulent ST59 and ST22 displayed higher resistance to antibiotics compared with ST188. Most of the ST59 and ST22 were methicillin-resistant S. aureus (MRSA), and all of the ST188 strains were methicillin-susceptible (MSSA). Moreover, we observed that the virulent ST59 and ST22 can resist killing by human antimicrobial peptides (AMPs). Mechanically, upon stimulation by AMPs, the virulent S. aureus can induce high expression of a phenol-soluble modulin transporter (Pmt) system. CONCLUSION:Pediatric patients can be colonized by virulent S. aureus clones, which are able to resist AMPs' killing through the Pmt system. The residence of virulent strains necessitates the continuous monitoring of potential infections, as well as annealing, to take protective decolonization measures.