Application Of MALDI-TOF MS In The Diagnosis Of Prosthetic Joint Infection

Objective: 1.To evaluate the reliability and practicality of matrix-assisted laser desorption ionization-time of flight mass spectrometry(MALDI-TOF MS)system in the identification of microorganisms isolated from Prosthetic joint infection(PJI).2.To evaluate the ability of MALDI-TOF MS to identify the phenotype of Staphylococcus epidermidis resistance related gene(mec A),disinfectant resistant gene(qac A)and biofilm associated gene(ica A)in PJI.Method: From January 2016 to February 2017,there are 41 cases with PJI(Prosthetic joint infection),suspected infection or aseptic failure(AF)which needed revision were treated in our hospital,include 17 Total Hip Arthoplasty and 24 Total Knee Arthoplasty respectively.Synovial fluid were collected by puncture preoperatively or intra-operatively,and tissues from five different parts around the prosthesis were collected intra-operatively.Synovial fluid were injected to Bac T/Alert culture bottle immediately after obtained.The tissue specimens were injected into the Bac T/Alert culture bottle after homogenized to slurry.All specimens were cultured for aerobic,anaerobic and fungal.MALDI-TOF MS and VETEK-2 were used to identify the pathogen at the same time.Antibiotic resistance test results were obtained by VETEK-2 according to the identification results.And the pathogen distribution and antibiotic resistance of PJI were analyzed.The main pathogens of PJI were Staphylococcus epidermidis.PCR amplification of drug resistance related gene(mec A),disinfectant resistant genes(qac A)and biofilm associated gene(ica A)were based on analysis of drug resistance rate,pathogenicity,disinfectant resistant characteristics.According to whether carry the mec A,qac A and ica A genes,the Staphylococcus epidermidis were divided into positive group and negative group,and then,MALDI-TOF-MS were used to analysis the existence of protein differences between mec A,qac A and ica A gene positive group and negative group.Result : According to the Infectious Diseases Society of America(IDSA)or Musculoskeletal Infection Society(MSIS)on the diagnosis standard of prosthetic joint infection,there were 31 PJIs and 10 AFs in 41 cases.A total of 26 strains of pathogen were obtained,after the synovial fluid or tissue around the prosthesis were cultured(the same pathogen was removed from the same patient).MALDI-TOF MS and VETEK-2 were used to identify the 26 pathogens at the same time,and identified pathogens to the species level all.The identification were consistent,the coincidence rate of the two was 100%.Staphylococcus epidermidis was the most isolated among the 26 strains(13/26,50%),followed by Staphylococcus aureus.VETEK-2 antibiotic resistance test results showed that the pathogenic of PJI highly resistant to oxacillin,penicillin,erythromycin and clindamycin,and have different degrees of resistance to other antibiotics.These bacterium were all sensitive to vancomycin,linezolid and fluconazole.The majority of Staphylococcus epidermidis was multiple antibiotic resistance,among which methicillin resistant Staphylococcus epidermidis(MRSE)accounted for 76.92%.The mec A,qac A and ica A gene which carried by13 strains of Staphylococcus epidermidis were amplified by PCR,and the positive rate was 92.31%,23.08%,23.08% respectively.MALDI-TOF-MS was detected in 3 groups with negative and positive gene expression.There is a significant specific peak in the mass spectrum of 2412m/z in a strain of mec A(+),but no significant difference was found between the qac A gene and ica A gene.Conclusion: MALDI-TOF-MS has been suggested as a reliable method for identification pathogen from PJI,and shorten the identification time.The main pathogen of PJI in our hospital were Staphylococcus epidermidis,and most of them were MRSE.MALDI-TOF-MS can be used to identify the MRSE related gene mec A(+)strains by the identification of the characteristic peaks,so as to provide the basis for clinical application.Maybe because of the small sample size of this study,MALDI-TOF-MS was not found the specific peak in the mass spectrum from the analysis of biofilm associated gene(ica A)and disinfectant resistant gene(qacA).