Hydroxy-fatty acid profiles of Legionella species: diagnostic usefulness assessed by principal component analysis

Twenty-nine species (76 strains) of members of the genus Legionella were analyzed for their cellular hydroxylated fatty acids (OH-FAs). The individual patterns were unusually complex and included both monohydroxylated and dihydroxylated chains of unbranched or branched (iso and anteiso) types. Comparison of the strain profiles by SIMCA (Soft Independent Modelling of Class Analogy) principal component analysis revealed four main groups. Group 1 included Legionella pneumophila plus L. israelensis strains, and group 2 included L. micdadei and L. maceacherneii strains. These two closely related groups were characterized by the occurrence of di-OH-FAs and differed mainly in the amounts of 3-OH-a21:0, 3-OH-n21:0, 3-OH-n22:0, and 3-OH-a23:0. Group 3 (13 species) was distinguished by i14:0 at less than 3%, 3-OH-3-OH-n14:0 at greater than 5%, 3-OH-n15:0 at greater than 2%, and minute amounts of OH-FAs with chains longer than 21:0. Group 4 (12 species) was heterogeneous. Its main characteristics were the presence of 3-OH-n12:0 and 3-OH-n13:0, 3-OH-i14:0 at greater than 5%, as well as significant amounts of 3-OH-a21:0 and 3-OH-n21:0. The groupings obtained by OH-FA profiles were found to reflect DNA-DNA homology groupings reasonably well, and the profiles appear to be useful for differentiation of Legionella species.