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Because of the alarming expansion in the diversity and occurrence of bacteria displaying virulence and resistance to antimicrobial agents, it is increasingly important to be able to detect these microorganisms and to differentiate and identify closely related species, as well as different strains of a given species. In this study, a mass spectrometry proteomics approach is applied, exploiting lipid-based protein immobilization (LPI), wherein intact bacterial cells are bound, via membrane-gold interactions, within a FlowCell. The bound cells are subjected to enzymatic digestion for the generation of peptides, which are subsequently identified, using LC-MS. Following database matching, strain-specific peptides are used for subspecies-level discrimination. The method is shown to enable a reliable typing and identification of closely related strains of the same bacterial species, herein illustrated for Helicobacter pylori .

Stenotrophomonas species are found commonly in environmental and clinical samples; Stenotrophomonas maltophilia is an important opportunistic pathogen of humans. Traditional phenotyping protocols, as well as genotyping by 16S rRNA gene sequence analysis, do not reliably distinguish the species of Stenotrophomonas. Sequence analyses of two targeted PCR-amplified regions of the gyrB gene, which encodes the β-subunit of DNA gyrase, enabled resolution and identification of these species. Most type strains of the different species of Stenotrophomonas exhibited more than 7% dissimilarity in the gyrB gene sequences. Among these, strains identified as the same species exhibited sequence dissimilarities up to 4.6% and 5.9% for the two regions, respectively. Strains identified as S. maltophilia, with 16S rRNA gene sequence similarities > 99.0%, were grouped within a 'S. maltophilia complex'; these organisms exhibited gyrB similarities as low as 93%. Many of these strains possessed genomic DNA similarities with the type strain of S. maltophilia CCUG 5866(T) below 70%. These data, including gyrB sequence comparisons, indicate that strains identified as S. maltophilia may comprise distinct, new species.

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