Application Of Matrix-assisted Laser Desorption/ionization Time-of-flight Mass Spectrometry In Detection Of MRSA Delta Toxin

Objective In this study,matrix-assisted laser desorption/ionization time-of-flight mass spectrometry(MALDI-TOF MS)was used to detect methicillin-resistant Staphylococcus aureus(MRSA)delta toxin and evaluate its significance in rapid typing of MRSA.Methods 1.A total of 83 non repetitive MRSA isolates were collected from clinical isolates.They were divided into HA-MRSA and CA-MRSA groups according to the definition of community acquired MRSA(CA-MRSA)of the Centers for Disease Control and Prevention.2.Staphylococcal chromosome cassette mec(SCCmec)typing and staphylococcal protein A(spa)typing were used to classify the experimental strains and PCR was used to detect the Panton-valentine leukocidin(PVL)and delta-toxin(hld)genes.3.The MALDI-TOF MS protein fingerprint of the experimental strains was collected,and the instrument matching software was used to analyze the fingerprint.Results 1.In the 83 strains of MRSA,HA-MRSA and CA-MRSA each accounted for 47% and 53%.The percentage of HA-MRSA from the Department of orthopedics,Department of ENT,Department of respiratory medicine,ICU were 12.8%,10.3%,10.3%,10.3%,and CA-MRSA from the Department of Dermatology,Department of ENT,Department of vascular surgery were 34.1%,31.8%,13.6%,respectively.2.The SCCmec type I,II,III,IV and the untyped strains each accounted for 1.2%,3.6%,65.1%,28.9%,1.2%;Among the 39 strains of HA-MRSA,SCCmec III accounted for 82.1%,while SCCmecIII and IVa 44 strains accounted for 50.0% of CA-MRSA strains,comparison of SCCmec III and IV type between HA-MRSA and CA-MRSA showed significant difference(P = 0.002,P = 0.000);15 types are detected in the spa typing,t437,t062,t015 accounted for 39.8%,21.7%,10.8%,respectively.Type t437 and t062 each took up 28.2%,23.1% in HA-MRSA,and 50%,20.5% in CA-MRSA,the difference of t437 type was significant(P = 0.043).3.The total positive rate of PVL was 24.3%,and HA-MRSA and CA-MRSA were 10.3% and 36.4% respectively,there was a significant difference between the two groups(P=0.006).The PVL positive rate of t437 MRSA in the 33 strains of was 54.5%.4.39 strains of MRSA were detected the delta toxin wild type,with the signal peak of 3005±5m/z,of which 19 were HA-MRSA and 20 were CA-MRSA,and there was no significant difference between them(P=0.766).33 strains of MRSA were detected the delta toxin G10 S variant,whose signal peak was 3035±5m/z,of which 9 were HA-MRSA,and 24 were CA-MRSA,they showed significant difference(P=0.003).In the spa typing,15(18.1%)strains of t062,8 strains t015(9.6%)and 4 strains of t030(4.8%)strains had been found delta toxin wild type(P=0.000).31(37.3%)strains of t437 and 2(2.4%)strain t8660 were detected the delta toxin G10 S variant(P=0.000).11 strains did not found delta toxin,these were all HA-MRSA.5.The delta toxin G10 S variant was used as a specific marker of spa t437 type with a sensitivity of 93.9%,specificity of 96.0%,and an area under the ROC curve of 0.89(P=0.000).Conclusions 1.In this study,the spa t437 is the major genotype of CA-MRSA and HA-MRSA,the genotype PVL positive rate 54.5%,suggesting that the CA-MRSA carrying higher virulence has entered the hospital environment and causes hospital acquired infections.2.MALDI-TOF MS technique can quickly detect the MRSA delta toxin wild type and delta toxin G10 S variant,the signal peaks are 3005 ± 5m/z and 3035 ±5m/z.The delta toxin G10 S variant can be used as a specific marker for spa t437 which is the main genotype of CA-MRSA.MALDI-TOF MS technology can get MRSA protein fingerprints at one time,only through the instrument matching software to check if there is a signal peak of 3035 ±5m/z,we can quickly identify the main current epidemic CA-MRSA clones in the region.