Abstract

Stenotrophomonas maltophilia is a highly versatile bacterial species, belonging to the γ-β subclass of proteobacteria. It is ubiquitously distributed in the environment, but recently its role as nosocomial pathogen became more evident. In our previous work we analyzed genetic diversity of S. maltophilia by rep-PCR fingerprinting and gyrB gene sequencing, for a collection of 171 environmental and clinical strains.

This revealed 11 genetic subgroups for S. maltophilia. A subset of 50 representative isolates for these groups was then used for further investigation of phenotypic properties. With respect to the increasing importance as an opportunistic pathogen, potential virulence traits, as the production of extracellular proteases, haemolysins and siderophores were investigated. Furthermore, factors supporting colonization of a human host were examined by swimming and twitching motility and biofilm assays.

Virulence was tested by co-culturing the bacteria with the amoebae Dictyostelium discoideum and Acanthamoeba castellanii as model organisms. After testing twenty different antibiotics on a small subset of strains, gentamicin, vancomycin, norfloxacin, tetracycline and co-trimoxazole, were chosen to determine MICs for the 50 S. maltophilia isolates. Nearly all investigated isolates produced proteases and haemolysins and all of them produced siderophores.

Motility assays revealed differences in swimming and twitching motility. Biofilm formation generally differed, but did not correspond to their genetic subgroups of the isolates. An exception is that all isolates from environmental group E2 showed only slight potential for biofilm formation. Virulence for amoebae was shown for about one third of the tested isolates and was in no relationship to clinical or environmental origin.

All isolates were resistant to vancomycin and most to gentamicin. Most of them showed intermediate MICs for norfloxacin and tetracycline, and all isolates were susceptible to co-trimoxazole. For motility assays, biofilm formation, virulence and antibiotic resistance generally no correlation to the previously defined genetic groups was found. In this context it was expected that housekeeping genes and rep-PCR fingerprints are not suitable markers to determine phenotypic properties of S. maltophilia.