MALDI-TOF MS (Matrix-assisted laser desorption ionization-time of flight mass spectrometry) and CHROMagar media are widely used in clinical microbiology laboratories to facilitate the rapid selection and identification of pathogens. Therefore, the question arises whether they are fully compatible.

A multicentre study has been recently published at the Journal of Microbiological Methods to evaluate the “Identification of microorganisms grown on chromogenic media by MALDI-TOF MS” with excellent results.

The aim of this study was to evaluate the performance of MALDI-TOF MS for identification of bacteria and yeasts grown on CHROMagar media. The study was performed at five independent laboratories in five countries, to control for systematic factors related to single laboratories, and to cover microbial isolates from different geographical regions.

For that, a total of 386 clinical bacterial and Candida isolates were investigated. Isolates were grown on relevant CHROMagar media, including CHROMagar Orientation, CHROMagar MRSA, CHROMagar VRE, CHROMagar Salmonella PLUS, CHROMagar StrepB, CHROMagar Listeria and CHROMagar Candida. In parallel, the isolates were cultured on non-selective agar, i.e. blood agar for bacteria and Sabouraud dextrose agar for Candida.

This study shows that CHROMagar media has no influence on microbial identification by MALDI-TOF MS and that both technologies can be used combined for identification of microorganisms. ¹

Other publications about the same subject have been released, like the review “A Decade of Development of Chromogenic Culture Media for Clinical Microbiology in an Era of Molecular Diagnosis” ², stating the value and compatibility of MALDI-TOF MS when used in conjunction with chromogenic media, or the “Routine identification and mixed species detection in 6.192 clinical yeast isolates” ³, which concludes that combining chromogenic media and MALDI-TOF MS was particularly effective in detecting mixed yeasts in clinical samples.

References: 1 - Petra Lüthje 2017. Identification of microorganisms grown on chromogenic media by MALDI-TOF MS - Journal of Microbiological Methods 136 (2017) 17–20

2- Perry JD. 2017. A decade of development of chromogenic culture media for clinical microbiology in an era of molecular diagnostics. Clin Microbiol Rev 30:449–479

3 - Carole Cassagne. Routine identification and mixed species detection in 6,192 clinical yeast isolates. Med Mycol 2016; 54 (3): 256-265. doi: 10.1093/mmy/myv095