Comparison of Matrix-Assisted Laser Desorption/Ionization-Time of Flight Mass Spectrometry, VITEK-2 and ID32STAPH for Species Identification of Clinical Coagulase-Negative Staphylococci Isolated from Al Shifa Hospital in Gaza Strip

Abstract

Staphylococcal species, notably, coagulase negative staphylococci (CoNS), are considered important causative agents of health-care associated 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. Recently, matrix-assisted laser-desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) was introduced as a useful and simple method for the rapid identification of CoNS. In this study we compared MALDI-TOF MS, VITEK-2 and ID32STAPH for phenotypic identification of CoNS at species level. Eighty one clinical isolates of CoNS representing six species that were collected from different clinical samples were analyzed. All CoNS isolates were tested for catalase, Pastorex™, coagulase, nuc and mecA genes. Our results showed correct species identification by MALDI-TOF MS which 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 staphylococci to subspecies level including Staphylococcus hominis subsp. novobiosepticus and subsp. hominis; S. saprophyticus subsp. saprophyticus. S. auricularis was only identified by MALDI-TOF-MS. There were 60 (74.1%) methicillin resistant CoNS (MR-CoNS) that showed mecA positive. Using MALDI-TOF MS technique, we were 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.

These findings confirm the value of MALDI-TOF MS as simple, accurate and rapid method for phenotypic identification of clinical CoNS isolates.