Stenotrophomonas maltophilia in nosocomial infections: PCR-based rapid genotyping and mechanisms of pathogenicity

Stenotrophomonas maltophilia is an environmental multi-drug-resistant bacterium increasingly involved in nosocomial infections. The role of this opportunistic pathogen in cystic fibrosis has not yet been clearly established, but its involvement in the pathogenesis of very severe infections in immunocompromised patients has been demonstrated. The former aim of this work has been for the first time the setting up of a genotyping method known as MultiLocus Variable number of tandem repeat Analysis (MLVA) for Stenotrophomonas maltophilia. The availability of the whole DNA sequence of the S. maltophilia strain K279a allowed us to set up a fast and accurate PCR-based diagnostic protocol relied on the measurement of length variations of loci carrying a variable number of short palindromic repeats marking the S. maltophilia genome. The utilization of the present protocol allows to type several S. maltophilia isolates in hours. The results are immediately interpretable without the need for sophisticated softwares. The data can be easily reproducible, and compared among different laboratories. The latter aim of this work has been the study of mechanisms of pathogenicity of S. maltophilia, assessing in vitro interactions of environmental and clinical S. maltophilia strains with monocyte-derived dendritic cells (DCs). Our data suggest that the internalization, the intracellular survival and the ability to interfere with normal DCs maturation of S. maltophilia are deeply strain-dependent. We believe that the ability of some tested strains to subvert DC function may be relevant in the pathogenesis of S. maltophilia infections in immunocompromised patients and in patients with cystic fibrosis. Therefore further investigations will be needed to test whether DCs exposed to these bacteria are still able to induce naïve T lymphocytes activation.