Biofilm Formation among Stenotrophomonas maltophilia Isolates Has Clinical Relevance: The ANSELM Prospective Multicenter Study

The ability to form biofilms is a recognized trait of Stenotrophomonas maltophilia, but the extent of its clinical relevance is still unclear. The present multicenter prospective study (ANSELM) aims at investigating the association between biofilm formation and clinical outcomes of S. maltophilia infections. One hundred and nine isolates were collected from various geographical origins and stratified according to their clinical relevance. Biofilm formation was evaluated by the microtiter plate assay and correlated with microbiological and clinical data from the associated strains. Antibiotic susceptibility of the planktonic cells was tested by the disk diffusion technique, while antibiotic activity against mature biofilms was spectrophotometrically assessed. Most strains (91.7%) were able to form biofilm, although bloodborne strains produced biofilm amounts significantly higher than strains causing hospital- rather than community-acquired infections, and those recognized as definite pathogens. Biofilm formation efficiency was positively correlated with mechanical ventilation (p = 0.032), whereas a negative relationship was found with antibiotic resistance (r(2) = 0.107; p < 0.001), specifically in the case of the pathogenic strains. Mature S. maltophilia biofilms were markedly more resistant (up to 128 times) to cotrimoxazole and levofloxacin compared with their planktonic counterparts, especially in the case of bloodborne strains. Our findings indicate that biofilm formation by S. maltophilia is obviously a contributing factor in the pathogenesis of infections, especially in deep ones, thus warranting additional studies with larger cohort of patients and isolates.

Automated summary

The ability of Stenotrophomonas maltophilia to form biofilms is a significant factor in the pathogenesis of infections, especially in deep infections. Biofilm formation is positively correlated with clinical outcomes such as mechanical ventilation, and negatively correlated with antibiotic resistance, particularly in pathogenic strains. Mature biofilms of S. maltophilia are much more resistant to antibiotics compared to planktonic cells, especially in the case of bloodborne strains. Additional studies with larger patient cohorts and isolates are warranted to further investigate this phenomenon.