Phenotypic properties of S. maltophilia
isolates in relation to their genetic subgroups
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.