Risk Factors And Molecular Characterization Of Staphylococcus Aureus Causing Colonization And Infections

Objective: Staphylococcus aureus is often carried on the skin surface and mucosa of healthy individuals and S.aureus is also one of the most important pathogen always causing skin and soft tissue infections(SSTIs)and surgical site infections(SSIs).In some patients,S.aureus can cause severe infections and bacteremia leading to high mortality.This study foucused on the nursing home residents,patients with SSTIs and patients with SSIs,and aimed to discuss the risk factors for S.aureus carriage among nursing home residents and the molecular characterization of S.aureus isolates causing colonization and infections as well as the relationship of S.aureus isolates between colonization and infections.Methods: The residents from 7 nursing homes(NHs)in Shanghai were enrolled in the study.Specimens including nasal swabs,axillary swabs and skin swabs were collected among NH residents.Laboratory identification for S.aureus was performed when isolated.Data including individual-resident characteristics and nursing home characteristics were collected and analyzed.The Risk factors for S.aureus colonization and molecular characterization of S.aureus isolates were studied.On the other hand,a total of 117 patients with S.aureus SSTIs(including 52 non-native and 65 native patients)and 82 patients with S.aureus SSIs were enrolled and the S.aureus isolates from SSTIs and SSIs were collected.S.aureus isolates were characterized by antimicrobial susceptibility testing,toxin gene detection,and molecular typing with sequence type,spa type,agr group and SCCmec type.Results:(1)A total of 491 NH residents participated in the study.Forty-eight residents were removed for some reasons and 443 residents were enrolled in the study of risk factors for S.aureus colonization.Consequently,99(22.3%)and 45(10.2%)residents were colonized by S.aureus and methicillin-resistant S.aureus(MRSA)respectively.Previous hospitalization,invasive device,chloramphenicol therapy and macrolides therapy were independent risk factors for MRSA colonization.The significant risk factors independently for S.aureus colonization were previous hospitalization,invasive device and chloramphenicol therapy.The low expenditure per month and less good sanitary condition would also increase the risk for MRSA and S.aureus colonization.As to the screening among the 491 residents,a total of 141 S.aureus isolates(isolated from 109 residents)and 68 MRSA isolates(isolated from 52 residents)were collected.Ten residents presented S.aureus in all three sample types and 12 residents presented S.aureus in two of the three sample types collected.Molecular analysis revealed CC1(29.1%)to be the dominant clone in this study,followed by CC398(19.9%),CC188(13.5%)and CC5(12.8%).(2)Among the 117 S.aureus isolates from SSTIs,22 MRSA isolates(18.8%)were detected.Overall,antibiotic resistance rates of S.aureus isolated from native patients were found higher than those from non-native patients.luk S/F-PV encoding Panton-Valentine leukocidin was more frequent in isolates originating from non-native patients with SSTIs compared to native patients(31 vs.7,P<0.0001).Molecular analysis revealed CC59(14/117,12.0%)to be the most common clone,followed by CC7(12/117,10.3%)and CC398(11/117,9.4%).Among the 82 S.aureus isolates from SSIs,36 MRSA isolates(43.9%)were detected.The gene sea encoding staphylococcal enterotoxins SEA was the most frequently found and luk S/F-PV was discovered in 10 isolates(12.2%).CC8(30/82,36.6%)was the most common clone in molecular types followed by CC59(8/82,9.8%)and CC7(8/82,9.8%).(3)There was no outstanding difference in antibiotic resistance rates of S.aureus isolates causing colonization and infections.The positive rates of a number of toxin genes such as luk S/F-PV and enterotoxins genes showed significant differences between S.aureus isolates causing colonization and infections.Simultaneously,CC398,CC5 and CC7 were the common clones in the S.aureus isolates causing colonization and infections,suggesting the relationship and interaction of S.aureus isolates between colonization and infections.Conclusion: A high prevalence of S.aureus and MRSA colonization was revealed in nursing home residents in Shanghai,and CC1 was the most common clonal complex among NH residents.CC59 and CC8 was the most common clonal complex among patients with S.aureus SSTIs and patients with S.aureus SSIs.The common clone CC398,CC5 and CC7 simultaneously found in S.aureus isolates causing colonization and infections might suggest the relationship and interaction of S.aureus isolates between infections and colonization.