Nasal Carriage,Phenotypic And Molecular Characteristics Of Staphylococcus Aureus Among Men Who Have Sex With Men

ObjectiveTo investigate the prevalence,risk factors,antimicrobial susceptibility and molecular characteristics of Staphylococcus aureus(S.aureus)isolated from men who have sex with men(MSM)in Guangzhou,thus providing scientific proof for prevention and control of Staphylococcus aureus transmission in MSM.MethodsCross-sectional design and random sampling method were used to enroll MSM in an HIV Voluntary Counseling Testing Clinic of Guangzhou.All MSM were requested to complete a questionnaire and collect nasal swabs.A series of traditional microbiologic assays were conducted to isolate and confirm S.aureus,including Methicillin-resistant Staphylococcus aureus(MRSA)and Methicillin-susceptible Staphylococcus aureus(MSSA)strains.Kirby-Bauer disk diffusion method was used to investigate the antimicrobial resistance of S.aureus strains.Polymerase Chain Reaction(PCR)assays was applied to detect 16 SrRNA gene,nuc gene,mecA gene,virulence genes and antimicrobial resistant genes of S.aureus.Multilocus sequence typing(MLST)was performed to identify the molecular type of S.aureus.Whole-Genome Sequencing(WGS)was implementated to identify the molecular characteristics of MRSA.Chi-square test or Fisher exact test and logistic regression models were used to analyze the factors of S.aureus and MRSA isolates.Chi-square test or Fisher exact test was used to compare different groups of antimicrobial resistance and molecular characteristics.The BURST algorithm and dendrogram tree softwares(PHYLOVIZ 2.0,MEGA-X)were used to compare the evolutionary relationship of alleles of strains.ResultsDemographic information: A total of 911 MSM were enrolled,aged from 16 to 58 years old,with average age 27.70±3.38 years old.Most of them were unmarried(91.55%),the education background of 86.72% MSM was college degree or above,and most of them(86.50%)had homosexual behaviors in the last half year.The prevalence and factors of S.aureus and MRSA: The prevalence of S.aureus,MRSA and MSSA was 33.70%(307/911)、3.62%(33/911)and 30.08%(274/911),respectively.Finding male sexual partners using Internet/App was a risk factor of S.aureus colonization(OR=1.574,95%CI: 1.095-2.263).Smoking cessation(OR=7.166,95%CI: 1.662-30.895)was a risk factor of MRSA colonization.Antimicrobial susceptibility: most S.aureus isolates were susceptible to trimethoprim-sulfamethoxazole and gentamicin,but resistant to penicillin(83.06%),erythromycin(52.77%),furadantin(45.93%)and teicoplanin(45.93%).49.51% S.aureus isolates were multi-drug resistant(MDR).The proportions of resistance to penicillin,cefoxitin,erythromycin,clindamycin,trimethoprim-sulfamethoxazole and moxifloxacin in MRSA were higher than that in MSSA,but proportions of resistance to teicoplanin,linezolid and furadantin were lower than that in MDRMSSA.The predominant MDR pattern of MRSA was co-resistant to cefoxitin,erythromycin and clindamycin.The predominant MDR pattern of MSSA was co-resistant to erythromycin,teicoplanin and linezolid.Molecular types: Overall,82 STs were detected from S.aureus isolates.Four of the most predominant STs were ST188(13.03%),ST15(9.45%),ST7(7.49%)and ST398(7.17%).Among 33 MRSA isolates,22 STs,6 SCCmec types and 14 SPA types were detected.Two predominant STs were ST59(24.24%)and ST(9.09%).The most predominant SCCmec type was IV(39.39%),followed by V(27.27%),NT(24.24%),I(3.03%),II(3.03%)and III(3.03%).Five predominant SPA types were t437(21.21%),t164(6.06%),t311(6.06%),t1451(6.06%)and t4549(6.06%).The most predominant molecular type of MRSA was t437-ST59-SCCmecIV.According to the dendrogram analysis,there was potentional cross-transmission between the communities,healthcare settings and animals.Gene screening of S.aureus: The most predominant resistant genes were blaZ(68.08%),erm(C)(34.85%)and tet(K)(26.38%).The most prevalent toxin genes were sak(92.83%)and scn(74.27%).12.05% S.aureus were tst positive.2.93% S.aureus were pvl positive,3.58% were etb positive,0.65% were eta positive,which were all MSSA isolates.The proportions of bla Z and mecA genes in MRSA were higher than MSSA isolates with higher proportion of sak gene.The ST15 S.aureus carry more resistant and toxin genes,ST188 and ST1281 S.aureus carry more toxin genes.Gene screening of MRSA: Among 33 MRSA isolates,19 resistance genes and 26 toxin genes were detected.The most predominant resistance genes were bla Z(96.97%),mecA(78.79%),erm(C)(39.39%),tet(K)(24.24%)and aph(3’’)-III(24.24%).The most predominant toxin genes were aur(72.73%),hlgA(69.70%),hlgB(69.70%),hlgC(69.70%),scn(63.64%)and sak(60.61%).The ST59,ST874 and ST5697 MRSA carry 8 resistance genes,ST5 and ST25 MRSA carry 18 toxin genes.ConclusionsThe prevalence of S.aureus nasal carriage was moderate among MSM in Guangzhou while the status of MRSA carriage was rather serious.Finding male sexual partners using Internet/App was a risk factor of S.aureus colonization.Smoking cessation was a risk factor of MRSA colonization.The multidrug resistance of S.aureus isolated from MSM in Guangzhou was serious,long-term dynamic monitoring is necessary for the resistance level of S.aureus.The most predominant molecular type of S.aureus and MRSA was ST188 and t437-ST59-SCCmecIV,respectively.There was potentional cross-transmission between the communities,healthcare settings and animals.