Long-chain alpha-hydroxy-(omega-1)-oxo fatty acids and alpha-hydroxy-1,omega-dioic fatty acids are cell wall constituents of Legionella (L. jordanis, L. maceachernii and L. micdadei)

Assessing direct analysis in real-time mass spectrometry for the identification and serotyping of Legionella pneumophila

AIMS

The efficacy of ambient mass spectrometry to identify and serotype Legionella pneumophila was assessed. To this aim, isolated waterborne colonies were submitted to a rapid extraction method and analysed by direct analysis in real-time mass spectrometry (DART-HRMS).

METHODS AND RESULTS

The DART-HRMS profiles, coupled with partial least squares discriminant analysis (PLS-DA), were first evaluated for their ability to differentiate Legionella spp. from other bacteria. The resultant classification model achieved an accuracy of 98.1% on validation. Capitalising on these encouraging results, DART-HRMS profiling was explored as an alternative approach for the identification of L. pneumophila sg. 1, L. pneumophila sg. 2-15 and L. non-pneumophila; therefore, a different PLS-DA classifier was built. When tested on a validation set, this second classifier reached an overall accuracy of 95.93%. It identified the harmful L. pneumophila sg. 1 with an impressive specificity (100%) and slightly lower sensitivity (91.7%), and similar performances were reached in the classification of L. pneumophila sg. 2-15 and L. non-pneumophila.

CONCLUSIONS

The results of this study show the DART-HMRS method has good accuracy, and it is an effective method for Legionella serogroup profiling.

SIGNIFICANCE AND IMPACT OF THE STUDY

These preliminary findings could open a new avenue for the rapid identification and quick epidemiologic tracing of L. pneumophila, with a consequent improvement to risk assessment.

Chemical characterization of two lipopolysaccharide species isolated from Rhizobium loti NZP2213

Phenol-water extraction of Rhizobium loti NZP2213 cells allowed a simultaneous isolation of two structurally different lipopolysaccharides from the aqueous (LPS-W) and phenol (LPS-P) phase that differed in their sodium deoxycholate-PAGE pattern and composition. LPS-W showed a profile indicating an R-type LPS; LPS-P had a cluster of poorly resolved bands in the high-molecular-weight region. LPS-P contained large amounts of 6-deoxy-L-talose (6dTal), and a small amount of 2-O-methyl-6-deoxy-talose (molar ratio approximately 30:1), both of which were completely absent in LPS-W. Methylation analysis gave only one major product, 2,4-di-O-methyl-6dTal, indicating that the O-chain is composed of a homopolymer of 1,3-linked 6dTal, having the methylated 6dTal (2-O-Me-6dTal) probably localized at the non-reducing end of the O-chain. This homopolymeric O-chain was additionally O-acetylated, as evidenced by GC-MS and by 13C NMR analysis. The lipid A moieties of both LPS-W and LPS-P showed almost identical composition, with six different 3-OH fatty acids and with two, so far not described, long-chain 4-oxo-fatty acids, all being amide-linked, and with 27-OH-28:0 as the main ester-linked fatty acid. Lipid A was of the lipid ADAG-type, i.e., having a (phosphorylated) 2,3-diamino-2,3-dideoxy-D-glucose-containing lipid A backbone. Lipid ADAG is widespread among species of the alpha-2 group of Proteobacteria, but has so far not been encountered in any other rhizobial or agrobacterial species.

Analysis of the lipid moiety of lipopolysaccharide from Rhizobium tropici CIAT899: identification of 29-hydroxytriacontanoic acid

The lipid moieties of two lipid A's isolated from the phenolic and aqueous fractions of lipopolysaccharide from Rhizobium tropici CIAT899 have been studied. Several 3-hydroxy fatty acids and two long-chain hydroxy fatty acids, 27-hydroxyoctacosanoic acid, and 29-hydroxytriacontanoic acid were identified; the ratios of these acids are the same in both lipid A's. These results can be used for chemotaxonomic purposes.