A multi-locus sequence typing scheme for Stenotrophomonas maltophilia

Abstract number: P1674

Kaiser S., Biehler K., Jonas D.

Stenotrophomonas maltophilia is ubiquitous in nature, but also a highly resistant pathogen and cause of nosocomial infections. In the past, there have been several changes in the taxonomy of Stenotrophomonas spp. and delineation of S. africana from S. maltophilia has been debated. Using Amplified Fragment Length Polymorphism (AFLP), strains were assigned to genogroups.

Apparently, isolates of environmental and clinical origin predominate in different groups.

The MLST scheme was developed on the basis of a selected highly diverse S. maltophilia strain collection comprising 52 strains of clinical and 16 strains of environmental origin from seven countries in all continents. They included the type strains of S. maltophilia, S. africana, S. acidaminaphila, S. nitrireducens, as well as strains belonging to the 10 different S. maltophilia genogroups, as previously defined on the basis of AFLP-patterns.

Compared with all S. maltophilia isolates, the DNA similarity of S. africana was on average of all seven loci 95.8%, which was above the average of all S. maltophilia strains (95.1%). Following this it was considered that the S. africana type strain belongs to the species S. maltophilia. Sequence data on 70 S. maltophilia strains, including the strains R551–3 and K279a from genome sequencing projects, were assigned to 54 sequence types (ST) based on the allelic profiles in the seven loci (atpD, gapA, guaA, mutM, nuoD, ppsA and recA). Analysis of strains from five outbreaks demonstrated the stability of the allelic profile over at least a 90-day period. A neighbour-net presentation of the concatenated sequences confirmed previously defined nine genogroups and revealed five additional groups. 18 out of 31 isolates from respiratory tract specimens, including 12 out of 14 isolates from cystic fibrosis patients, belonged to genogroup 6. However, 16 invasive strains isolated from blood cultures belonged to nine different genogroups. Three genogroups contained isolates of strictly environmental origin only.

This MLST scheme for S. maltophilia presents a discriminatory typing method with stable markers appropriate for studying the population structure. According to DNA similarities S. africana belongs to the species S. maltophilia. MLST data confirmed the existence of previously defined genogroups and an additional five genogroups on the basis of the isolates examined in this study. The predominance of clinical isolates in genogroup 6 requires further elucidation.