Comparison of antifungal activities and 16S ribosomal DNA sequences of clinical and environmental isolates of Stenotrophomonas maltophilia

In recent years, the gram-negative bacterium Stenotrophomonas maltophilia h as become increasingly important in biotechnology and as a nosocomial patho gen, giving rise to a need for new information about its taxonomy and epide miology. To determine intraspecies diversity and whether strains can be dis tinguished based on the sources of their isolation, 50 S. maltophilia isola tes from clinical and environmental sources, including strains of biotechno logical interest, were investigated. The isolates were characterized by in vitro antagonism against pathogenic fungi and the production of antifungal metabolites and enzymes. Phenotypically the strains showed variability that did not correlate significantly with their sources of isolation. Clinical strains displayed remarkable activity against the human pathogenic fungus C andida albicans, Antifungal activity against plant pathogens was more commo n and generally more severe from the environmental isolates, although not e xclusive to them. All isolates, clinical and environmental, produced a rang e of antifungal metabolites including antibiotics, siderophores, and the en zymes proteases and chitinases, From 16S ribosomal DNA sequencing analysis, the isolates could be separated into three clusters, two of which consiste d of isolates originating from the environment, especially rhizosphere isol ates, and one of which consisted of clinical and aquatic strains. In contra st to the results of other recent investigations, these strains could be gr ouped based on their sources of isolation, with the exception of three rhiz osphere isolates. Because there was evidence of nucleotide signature positi ons within the sequences that are suitable for distinguishing among the clu sters, the clusters could be defined as different genomovars of S. maltophi lia. Key sequences on the 16S ribosomal DNA could be used to develop a diag nostic method that differentiates these genomovars.