Rapid Identification Of Resistant Bacteria By Matrix-assisted Laser Desorption/ionization Time-of-flight Mass Spectrometry

Objectives:To evaluate the performance of Matrix-assisted Laser Desorption/Ionization Time-of-flight Mass Spectrometry(MALDI-TOF MS) VITEK MS mas spectrometer in detection of methicillin-resistant Staphylococcus aureus(MRSA) and vancomycin-resistant enterococci(VRE).Methods: A total of 279 S. aureus clinical isolates were collected, identification of isolates was conducted by VITEK MS, disk diffusion method was performed for screening of resistant isolates with oxacillin and cefoxitin, and detection of mec A was done by PCR. After establishment of MRSA and methicillin-sensitive S. aureus(MSSA) Super Spectra by VITEK MS, characteristic peaks of MRSA and MSSA were obtained, then clinical isolates were used for validation of the new method.Similarily, 196 Enterococcus faecium clinical isolates were collected, after identification by VITEK MS, disk diffusion method was performed for screening of resistant isolates with vancomycin and teicoplanin, while detection of vancomycin-resistant genes(including van A, van B and van M) were conducted by PCR. After establishment of VRE and vancomycin-sensitive enterococci(VSE) Super Spectra, characteristic peaks were obtained for differentiation between the two groups, and then clinical isolates were used for validation of the new method.Results: Of the 279 collected clinical isolates, 275 were confirmed as S. aureus by VITEK MS, among which, 143 were resistant to oxacillin and cefoxitin, additionally, were positive for mec A detection, while 132 isolates were MSSA without carrying mec A. Antimicrobial susceptibility result by disk diffusion method was 100% in agreement with mec A detection by PCR. Mass spectra profiles of 65 clinical MRSA isolates and ATCC43300 were collected for establishment of MRSA Super Spectra, while mass spectra profiles of 64 clinical MSSA isolates and 2 standard isolates(including ATCC25923 and ATCC 29213) were collected for establishment of MSSA Super Spectra. Afer a comparison between MRSA and MSSA Super Spectra, two characteristic peaks located at 2305.6 Da and 3007 Da were representitive for MRSA, while the peak at 6816.7 Da was considered as representitive peak for MSSA with relatively high signals. Validation results indicated that with this method, the accuracy of identifying MRSA could be 84.21%, the accuracy of identifying MSSA cound reach 90.91%, and the overall accuracy was 87.32%.Of the 196 E. faecium isolates collected, all were verified as E. faecium by VITEK MS, among which, 105 isolates were identified as VRE(66 were positive for van A, 39 were positive for van M), while 91 were VSE without carrying van A, van B or van M, our results indicated disk diffusion method was totally in consistent with PCR detection. Mass spectra profiles of 62 VRE and 58 VSE clinical isolates were randomly collected for the establishment of VRE and VSE Super Spectra, respectively. After a comparison between the two Super Spectra, the peak located at 6601.4 Da was considered representative for VRE, while two peaks at 3723.9 Da and 3883.1 Da were characteristic for VSE. Validation with clinical isolates indicated that with this method the accuracy of VRE identification was 88.37%, accuracy of VSE identification could be 75.76%, and the overall accuracy for E. faecium was 82.89%.Conclusions: Super Spectra could be established by collecting mass spectra profiles of sensitive and resistant pathogens with VITEK MS, and characteristic peaks of ensitive isolates and resistant isolates could be obtained. After activation, Super Spectra could be applied for the rapid detection of resistant isolates, which is rather speedy and of high accuracy, and will pose revolutionary impact on clinical detection of resistant isolates.