Raman spectroscopic typing reveals the presence of carotenoids in Mycoplasma pneumoniae

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Abstract
Raman spectroscopy has previously been demonstrated to be a highly useful methodology for the identification and/or typing of micro-organisms. In this study, we set out to evaluate whether this technology could also be applied as a tool to discriminate between isolates of Mycoplasma pneumoniae, which is generally considered to be a genetically highly uniform species. In this evaluation, a total of 104 strains of M. pneumoniae were analysed, including two reference strains (strains M129 and FH), and 102 clinical isolates, which were isolated between 1973 and 2005 and originated from various countries. By Raman spectral analysis (Raman typing) of this strain collection, we were able to reproducibly distinguish six different clusters of strains. An unequivocal correlation between Raman typing and P1 genotyping, which is based on sequence differences in the P1 (or MPN141) gene of M. pneumoniae, was not observed. In the two major Raman clusters that we identified (clusters 3 and 6, which together harboured 81 % of the strains), the different P1 subtypes were similarly distributed, and ∼76 % isolates were of subtype 1, ∼20 % of subtype 2 and ∼5 % of variant 2a. Nevertheless, a relatively high prevalence of P1 subtype 2 strains was found in clusters 2 and 5 (100 %), as well as in cluster 1 (75 %) and cluster 4 (71 %); these clusters, however, harboured a small number of strains. Only two of the strains (2 %) could not be typed correctly. Interestingly, analysis of the Raman spectra revealed the presence of carotenoids in M. pneumoniae. This finding is in line with the identification of M. pneumoniae genes that have similarity with genes involved in a biochemical pathway leading to carotenoid synthesis, i.e. the 2-C-methyl-d-erythritol 4-phosphate (MEP) pathway. Therefore, we hypothesize that M. pneumoniae hosts an MEP-like pathway for carotenoid synthesis. We conclude that Raman spectroscopy is a convenient tool for discriminating between M. pneumoniae strains, and that it presents a promising supplement to the current methods for typing of this bacterium.