Species Identification of Clinical Coagulase-negative Staphylococci Isolated in Al-Shifa Hospital Gaza using Matrix-assisted Laser Desorption/Ionization-time of Flight Mass Spectrometry

摘要

Background: Staphylococcal species, notably, coagulase negative staphylococci (CoNS) are considered important causative agents of hospital-acquired infections (HAI) associated with catheters and implanted medical devices. The increasing incidence of CoNS in HAI confirms the need for an accurate and simple identification method at the species level. Here, the capacity of MALDI-TOF MS was compare in comparison of VITEK-2 and ID32STAPH to accurately identify clinical CoNS species and to determine its ability to correctly distinguish between methicillin resistant CoNS (MR-CoNS) and methicillin sensitive CoNS (MS-CoNS). Materials and Methods: In this study, MALDI-TOF MS, VITEK-2 and ID32STAPH was compared for phenotypic identification of CoNS at species level. Eighty one clinical isolates of CoNS representing six species that collected from different clinical samples were analyzed. All CoNS isolates were tested by catalase, Pastorex?, coagulase, nuc and mecA genes. Statistics were performed with Statistical Package for Social Sciences (SPSS?) program version 20 (Chicago, IL, USA). Results: Our results showed correct species identification by MALDI-TOF MS was obtained in 98.8% in comparison to 96.3 and 75.3% correct identification for the VITEK-2 and ID32STAPH, respectively. Only one strain was identified by MALDI-TOF MS at the genus level. In addition, MALDI-TOF MS identified staphylococcal to subspecies level including Staphylococcus hominis subsp., novobiosepticus and subsp., hominis, S. saprophyticus subsp., saprophyticus. Also the single strain of S. auricularis was only identified by MALDI-TOF MS. There were 60 (74.1%) MR-CoNS that showed mecA positive and 21 (25.9%) were MS-CoNS. The MALDI-TOF MS technique was unable to discriminate between MR-CoNS and MS-CoNS, because the topology of dendrogram generated from the spectra of MR-CoNS and MS-CoNS strains were almost the same. Conclusion: These results confirm the value of MALDI-TOF MS as simple, accurate and rapid method for phenotypic identification of clinical CoNS isolates. However, this technique was unable to discriminate between MR-CoNS and MS-CoNS strains.