Purpose Coagulase negative staphylococci (CNS) have been one of the major pathogens responsible for prosthetic joint infections, and are showing increasing multiple-antibiotics resistance. Intact cell mass spectrometry (ICMS), based on the analysis of bacterial surface proteins, has been recognised as a new technique for identification of micro-organisms. The aim of this study was to evaluate the ability of ICMS for species level identification of clinical CNS isolates.

Method A total of 50 CNS strains from revision joint replacement operations were studied. ICMS and commercial identification kits were used for identification of those CNS. The commercial kits were used following the manufacturer’s recommendations. For ICMS, single colonies were smeared onto five spots on a sample slide. After drying, a 1 μl of aliquot of matrix solution was added to each spot. Analysis of strains was performed using a Kompact MALDI 2 linear, time of flight mass spectrometer and 3-ns pulse width nitrogen laser light. Combined spectra were constructed from 100 shots at each spot on the sample slide.

Results In this study, the commercial kit did not require any special equipment, but required overnight incubation and could not identify at least seven strains. On the other hand, the ICMS method was rapid, accurate and highly reproducible. The mass: charge spectra produced by ICMS contained potential biomarker peaks that could be used for species level identification.

Conclusions ICMS has the potential as a powerful tool for species level identification of clinical CNS isolates in terms of rapidity, accuracy and cost effectiveness. This study suggested that ICMS is a possible new method of identifying causative organism in infected joint replacements.