Objective: To study the beta-lactamases content of Stenotrophomonas maltophilia strains and to evaluate the virulence potential of these strains with the in vivo Caenorhabditis elegans model.
Methodology: From 1st January 2006 to 31st December 2006, a monitoring programme to study multidrug resistant Gram-negative bacteria including extended-spectrum beta-lactamases (ESBL)-producing S. maltophilia was conducted at Nîmes University Hospital and Perpignan Hospital. The ESBL production was confirmed by the double-disk synergy test using ceftazidime, cefotaxime and cefepime disks associated with clavulanic acid disk. The strains were characterized phenotypically (beta-lactamase[s] identification) and genotypically (pulsed-field gel electrophoresis, plasmid analysis) and evaluated for their virulence with the in vivo nematode C. elegans model (establishment of survival curves [LT50]).
Results: Twelve ESBL-producing S. maltophilia strains were isolated in eight patients (median age: 65 years+/-19) mainly during skin infections (41.7%). The ESBL content revealed the presence of four CTX-M-15-producing strains at the same patient. The analysis by ECP confirmed that the four strains were identical. The plasmid analysis demonstrated that the plasmid carrying CTX-M-15 in the worldwide clonal Escherichia coli O25-ST131 strain and S. maltophilia were different. The C. elegans model confirmed that S. maltophilia strains presented a low virulence potential (LT50=4.5days+/-0.5 according to the strains and nematode death in 10days+/-1) whatever their resistance.
Conclusion: For the first time in France, a CTX-M-15-producing S. maltophilia strain has been identified. The in vivo model confirmed that these bacteria have a low potential virulence. However, these strains were isolated from "immunocompromised" and multihospital patients demonstrating the necessary monitoring of these patients. The CTX-M after diffusing in hospitals and community in E. coli strains seem to spread in other Gram-negative bacteria.