Distribution Characteristics And Influencing Factors Of Methicillin-resistant Staphylococcus Among Drug Users

ObjectiveTo investigate the prevalence,risk factors,antimicrobial susceptibility,molecular characteristics of methicillin-resistant Staphylococcus aureus(MRSA)and methicillin-resistant coagulase-negative staphylococci(MRCoNS)isolates among drug users of Guangzhou,thus providing scientific basis for prevention and control to the epidemic and the spread of MRSA and MRCoNS in drug users.MethodsCross-sectional study and random sampling method were conducted in our study to enroll drug users in 3 hospital-affiliated oral maintenance programs(Longfeng maintenance programs,Jianghai maintenance programs and Dongren maintenance programs)of Guangzhou.Epidemiologic information was obtained by self-designed questionnaire while anterior nares swabs were collected.With a series traditional biochemical assays for Staphylococcus aureus(S.aureus)and coagulase-negative staphylococci(CoNS)strains positive samples,further combined with PCR amplification of 16SrRNA gene and nuc gene were identified as S.aureus and CoNS positive strains.12 antibiotics were tested by Kirby Bauer disk diffusion for all S.aureus and CoNS strains.PCR assay had been tested for mecA gene,virulence genes,antibiotics resistant genes and SCCmec(Staphylococcal Cassette Chromosome mec)genotyping.The multilocus sequence typing(MLST)was performed to identify the molecular type of all S.aureus isolates.The chi-square test was conducted to investigate the influencing factors of MRSA and MRCoNS colonization and non conditional logistic regression models were constructed to multivariable analysis.The risk resistance and gene analysis using non conditional logistic regression or exact logistic regression.Dendrogram analysis was conducted to identify the clonal relatedness and potential epidemiologic origin by eBURST algorithm and dendrogram software.ResultsDemographics characteristic: A total of 353 drug users were eligible for enrollment with average age 50.75±6.09.All participants were Chinese Han population,87.54% of participants were male,95.47% of participants were local residents.Carrigae rate of MRSA and MRCoNS: Among 353 drug users,15.01%(53/353)of them were S.aureus positive,with 6.80%(24/353)were MRSA positive.Prevalence of CoNS and MRCoNS carriage was 42.78%(151/353)and 29.18%(103/353),respectively.Multiple logistic revealed that obesity(aOR=5.028,95%CI: 1.550-16.305)was risk factor of S.aureus carriage.Hospitalized within 1 year(aOR=2.959,95%CI: 1.056-8.290)was risk factor of MRSA carriage in multiple logistic analysis.Multiple logistic revealed that history of incarceration(aOR=1.851,95%CI: 1.031-3.323)was risk factor of CoNS carriage.Married(aOR=0.547,95%CI: 0.309-0.967)was protective factor while history of incarceration(aOR=2.533,95%CI: 1.161-4.726)was risk factor of MRCoNS carriage in multiple logistic analysis.Virulence genes and antibiotics resistant genes detection: The most prevalent virulence genes in MRSA isolates were seg gene(54.17%,13/24),followed by sed gene(45.83%,11/24),sei gene(37.50%,9/24),selk gene(33.33%,8/24)and selu gene(29.17%,7/24).Half of MRSA isolates carring blaZ gene(50%),and other common antibiotics resistant genes of MRSA were ermC gene(20.83%,5/24)and linA gene(12.50%,3/24).Similarly,the most prevalent antibiotics resistant in MRCoNS isolates were blaZ gene(51.79%,58/112),followed by msrA gene(24.11%,27/112),linA gene(23.21%%,26/112),ermC gene(21.43%,24/112)and tetK gene(19.64%,22/112).The sea gene,seb gene,see gene,tetM gene,VanA gene and VanB gene were not detected in all MRSA isolates.The detection rate of selk gene,ermC gene,tetK gene and mrsA gene were statistical significant between MRSA and MSSA isolates(P<0.05).The pvl gene,VanA gene and VanB gene were not detected in all MRCoNS isolates.Carriage of tetM gene in MSCoNS isolates was statistically higher than MRCoNS(P=0.01).SCCmec typing: Among 24 MRSA isolates,only 4.17%(1/24)belonged to hospital-associated MRSA(HA-MRSA)and 75.00%(18/24)belonged to community-associated MRSA(CA-MRSA),with predominant isolates of type IVa(20.83%,5/24)and type IVd(50.00%,12/24),while 5 isolates were non-typeable.MLST: The most prevalent ST types in MRSA isolates were ST188(25.00%,6/24)ST59(25.00%,6/24),while the most common ST types in MSSA isolates were ST188(17.24%,5/29),ST5(13.79%,4/29)and ST7(13.79%,4/29).17 ST types were assigned to 8 international clonal complexs(CC5,CC7,CC30,CC45,CC59,CC182,CC398 and CC2483)and 1 signleton(ST1222).The most predominant clonal complexes in all S.aureus isolates were CC5(64.15%,34/53),followed by CC59(11.32%,6/53)and CC7(7.55%,4/53).According to tree diagram analysis,cluster occurred among 3 hospital-affiliated oral maintenance programs.Antimicrobial susceptibility test: The antibiotic resistance rates of MRSA isolates were especially high in penicillin(95.83%),erythromycin(62.50%),and clindamycin(62.50%).Resistance rates of teicoplanin and clindamycin in MRSA isolates were statistically higher than MSSA isolates(P<0.05).Multidrug resistant MRSA strains carried of drug users was 70.83% and the risk of multidrug-resistance of MRSA isolates was 3.44 times than MSSA isolates.Multidrug-resistant pattern of S.aureus was co-nonsusceptible to penicillin,erythromycin and clindamycin.The highest antibiotic resistance rate of MRCoNS was penicillin(89.29%),followed by erythromycin(47.32%)and trimethoprim-sulfamethoxazole(44.64%).There was statistical difference toward moxifloxacin,clindamycin,penicillin,tetracycline,gentamicin,and erythromycin resistant rate between MRSA isolates and MSSA isolates.Multidrug resistant rate in all MRCoNS strains was statistically higher than MSCoNS(P<0.001),and the risk of multidrug-resistance of MRCoNS isolates was 4.55 times than MSCoNS isolates.Multidrug-resistant pattern of CoNS was co-nonsusceptible to penicillin,cefoxitin and trimethoprimsulfamethoxazole.ConclusionsThe prevalence of S.aureus and CoNS carriage among drug users of Guangzhou was in a middle level while the status of MRSA and MRCoNS carriage was rather serious.Hospitalized within 1 year were risk factors of MRSA carriage.History of incarceration was risk factor of MRCoNS carriage.The prevalent MRSA isolates were CA-MRSA and the main virulence genes were sed,seg and sei.The predominant ST types were ST188 and ST59,which were similar to the predominant types in Chian and were relative to international prevalent clones.The multidrug resistance of MRS isolated from drug users in Guangzhou of China is serious,and long-term dynamic monitoring is need for the resistance level of MRS.