The Longitudinal Study Of Phenotypic And Molecular Characteristics Of Staphylococcus Aureus On The Environmental Surface Of Computer Room

ObjectiveWe carried out this study mainly to predominate the epidemic characteristics of Staphylococcus aureus and MRSA contamination on the environmental surface of a computer room in a university,to assess the potential threat of environmental MRSA contamination to the population,to understand the antibiotics resistance pattern,the molecular characteristics such as molecular typing,toxin gene of Staphylococcus aureus and MRSA strains,and then analyze the potential associations between molecular typing and molecular characteristics so as to understand the genetic background of these strains.In addition,we also explored the similarities in genetic backgrounds between environmental strains and population strains to reveal the potential cross-transmission risks.MethodsWe used the longitudinal design to collect the samples.For four consecutive days,the keyboard and mouse surfaces of all 155 computers in a computer room in a university were sampled with cotton swabs according to the same sampling method.All isolates were tested for antibiotic susceptibility.Molecular typing was performed by multi-locus sequence typing(MLST).And the toxin genes,antibiotic resistance genes,Spa typing,and SCCmec typing were tested after splicing the sequences by full gene sequencing.The UPGMA cluster analysis and?~2 test were used to explore the potential association between the molecular typing and its phenotypic and molecular characteristics of the strains.ResultsA total of 1240 surface samples were collected for this study.The total contamination rate on the surface sample was 4.1%(51/1240)for Staphylococcus aureus,0.5%(6/1240)for MRSA,and 1.5%(19/1240)for MDRSA.For four consecutive days,the Staphylococcus aureus contamination rate on the surface of the computer room was 2.6%to5.2%,the MRSA contamination rate was 0.3%to 0.7%,and the MDRSA contamination rate was 0.7%to 2.3%.Notably,37.3%of strains were multi-drug resistant Staphylococcus aureus(MDRSA)and the linezolid resistance rate of MDRSA was as high as 63.2%.The main antibiotics resistance pattern of MDRSA was non-susceptible to rifampicin,erythromycin,clindamycin,ciprofloxacin,linezolid and quinucline.It was noteworthy that persistent contamination was observed in 4 machines and most of them were contaminated with MDRSA.The main STs of Staphylococcus aureus were ST5,ST6,ST7,and ST188,and the main Spa types were t701,t189,and t3169.When combined with both of them,the main molecular typing of Staphylococcus aureus were ST6-t701 and ST188-t189.The main SCCmec typing of MRSA strains were type IV and type IVa.Having compared the phenotypic and molecular characteristics of MDRSA and non-MDRSA strains,we found the significant difference that the resistance rates to rifampicin,erythromycin,clindamycin,linezolid and quinupristin/dalfopristin of MDRSA strains were higher than that of non-MDRSA strains,and the mecA and fosB-positive genes of MDRSA strains were also higher than that of non-MDRSA strains.But when carrying the hemolytic toxin genes(hlgA,hlg B,hlgC),leukotoxin genes(lukD,lukE)and extracellular enzyme genes(aur,spl A,splB,splE),the MDRSA strains were lower than non-MDRSA.The results of UPGMA cluster analysis and?~2 test showed that there were significant correlations between molecular typing and antibiotics resistance and carrying enterotoxin genes.ST6-t701 and ST45 S.aureus strains were associated with sensitivity to all antibiotics,and ST5 S.aureus were associated with resistance to erythromycin and clindamycin.ST5 and ST6 S.aureus strains were associated with carrying more enterotoxin genes(seg-sei-sem-sen-seo-seu).When we compared and clusterd the strains on environmental surface of a computer room with the population strains,we found there were significant differences that the resistance rate to gentamicin of S.aureus in computer room was higher than that of the general population,and the resistance rates to cefoxitin and tetracycline were lower than that of the general population.In addition,the S.aureus strains on environment surface of the computer room were carrying more hemolysin genes(hlgC),leukotoxin genes(lukD,lukE),immune escape genes(scn,sak),and extracellular enzyme genes(splA,splB,splE)than the general population.Notably,the cluster analysis showed that the various STs of environmental strains and the general population strains were clustered into the same groups,which suggests the similarities in genetic backgrounds between environmental strains and population strains.ConclusionsFor four consecutive days,the contamination rates on the environmental surface of a computer room were 2.6%?5.2%for S.aureus,0.3%?0.7%for MRSA,0.7%?2.3%for MDRSA.Notably,the persistent contamination of S.aureus was observed in four machines and most of them were contaminated by MDRSA in this longitudinal study.Thus,it is necessary to monitor the contamination of S.aureus on the environmental surface of a computer room.Among all S.aureus strains,the proportion of MDRSA was 37.3%.And it was worth noting that the linezolid resistance rate in MDRSA strains was as high as 63.2%,revealing the serious situation of multi-drug resistant strains on the surface of the environment.More importantly,we found the similarities in genetic backgrounds between the major S.aureus clones(ST5,ST6,ST7,and ST188)collected from the environmental surface of a computer room and the human-related clones associated with hospitals or communities in China,indicating that the environmental surface may be a hazardous reservoir for transmission of S.aureus or MRSA to humans.This study also revealed the correspondence between various molecular characteristics of S.aureus,that is,the S.aureus strains of ST5and ST6 were associated with carrying more enterotoxin genes(seg-sei-sem-sen-seo-seu)than other STs.And this finding might provide important ideas for analyzing and distinguishing the potential pathogenicity of strains.