Delineation of Stenotrophomonas spp. by multi-locus sequence analysis and MALDI-TOF mass spectrometry

The genus Stenotrophomonas is genetically and phenotypically heterogeneous. Of the nine species now accepted, only S. maltophilia is of clinical importance. Based on DNA-sequences of seven house keeping genes, it encompasses genogroups of DNA-similarity below 97% that predominantly comprise strains of environmental origin. Therefore, in order to unravel the uneven distribution of environmental isolates within genogroups and reveal genetic relationships within the genus, there is need for an easy and reliable approach for the identification and delineation of Stenotrophomonas spp. In this first study, a multi-locus sequence analysis (MLSA) with seven housekeeping genes (atpD, gapA, guaA, mutM, nuoD, ppsA and recA) was applied for analysis of 21 S. maltophilia of environmental origin, Stenotrophomonas spp. and related genera. The genotypic findings were compared with the results of matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF MS) analyses. Our MLSA provided reliable inter- and intra-species discrimination of all tested isolates that correlated with the MALDI-TOF mass spectrometry data. One distantly related genogroup of environmental S. maltophilia strains needs to be reclassified as S. rhizophila. However, there are still remaining delineated S. maltophilia genogroups of predominantly environmental origin. Our data provide further evidence that ‘Pseudomonas’ beteli is a heterotypic synonym of S. maltophilia. Based on MLSA and MALDI-TOF data, Stenotrophomonas sp. (DSM 2408) belongs to S. koreensis.