Activity of levofloxacin and ciprofloxacin on biofilms and planktonic cells of Stenotrophomonas maltophilia isolates from patients with device-associated infections.

The aim of this work was to compare the in vitro effects of levofloxacin and ciprofloxacin on pre-formed biofilms and planktonic populations of Stenotrophomonas maltophilia isolates from device-associated infections recovered over the period 2004-2008 at a university hospital in Argentina. For planktonic susceptibility studies, the minimum inhibitory concentrations (MICs) of fluoroquinolones were determined by the broth microdilution method. From the 32 isolates recovered, 84.4% were sensitive to levofloxacin and 43.8% were sensitive to ciprofloxacin. Biofilm susceptibility was evaluated by the minimum re-growth concentration (MRC) assay. Stenotrophomonas maltophilia isolates sensitive to fluoroquinolones according to their MICs were highly resistant according to the MRC values. Thus, currently used concentrations of fluoroquinolones cannot be used in monotherapy for eradication of a biofilm. Nevertheless, these agents could be used for the lock technique. Interestingly, for some isolates fluoroquinolone concentrations achievable during therapy caused a reduction in viable cells of 99% and promoted disruption of biofilms, evaluated by spectrophotometric and microscopic analysis. These results suggest that fluoroquinolones, particularly levofloxacin due to its better pharmacokinetic parameters, are candidates for synergy studies.

Biofilm formation by Stenotrophomonas maltophilia isolates from device-associated nosocomial infections / Formación de biopelículas por aislamientos de Stenotrophomonas maltophilia recuperados de infecciones nosocomiales asociadas al uso de dispositivos médicos

Medical devices are often colonized by bacteria which may cause severe infections. The aim of this work was to evaluate biofilm formation by S. maltophilia isolates from device-associated nosocomial infections. The 13 local isolates exhibited different capacities of biofilm formation on hydrophilic and hydrophobic surfaces. All isolates formed strong biofilms in polystyrene microplates, while strong, moderate or weak biofilms were detected in borosilicate (BS) or polypropylene (PP) tubes. The proficiency of biofilm formation was better evaluated by the level of crystal violet staining expressed relative to the final culture density. The microscopic analysis of biofilms formed on glass coverslips revealed the presence of a matrix of exopolysaccharides and microcolonies typical of biofilm architecture. Isolates with increased adhesion to BS showed larger microcolonies. According to our results, twitching correlated well with attachment to the three abiotic surfaces tested, while swimming only showed a slight correlation with biofilm formation on PP. Poor correlation was observed between cell surface hydrophobicity and biofilm formation. One of the highest biofilm-producing isolates adhered to urethral catheters of different materials, and exhibited an increased resistance to oxidative stress, one of the common stresses encountered by bacteria during the infection process due to the immune response.

El objetivo de este trabajo fue evaluar la formación de biopelículas por parte de aislamientos de Stenotrophomonas maltophilia. Los 13 aislamientos locales evaluados mostraron diferente capacidad de formar biopelículas en superficies hidrofílicas e hidrofóbicas. Todos ellos formaron biopelículas fuertes en microplacas de poliestireno (PS), mientras que se observaron biopelículas fuertes, moderadas o débiles en tubos de borosilicato (BS) o polipropileno (PP). La medida del cristal violeta unido a la biopelícula expresada en función de la densidad final de los cultivos permitió una mejor evaluación de la eficiencia de formación de biopelículas. El análisis microscópico de biopelículas formadas sobre cubreobjetos mostró la presencia de una matriz de exopolisacáridos y microcolonias típicas de la arquitectura de las biopelículas. Los aislamientos con mayor adhesión a BS mostraron microcolonias de mayor tamaño. La motilidad asociada a superficies ( twitching) presentó buena correlación con la adhesión a BS, PP y PS, mientras que la motilidad asociada a flagelos solo correlacionó ligeramente con la adhesión a PP. La correlación entre la hidrofobicidad de la superficie bacteriana y la formación de biopelículas fue escasa. Uno de los aislamientos productores de biopelículas fuertes evidenció capacidad de adhesión a catéteres uretrales de diferentes materiales y mayor resistencia al estrés oxidativo.

Biofilm formation by Stenotrophomonas maltophilia isolates from device-associated nosocomial infections.

Medical devices are often colonized by bacteria which may cause severe infections. The aim of this work was to evaluate biofilm formation by S. maltophilia isolates from device-associated nosocomial infections. The 13 local isolates exhibited different capacities of biofilm formation on hydrophilic and hydrophobic surfaces. All isolates formed strong biofilms in polystyrene microplates, while strong, moderate or weak biofilms were detected in borosilicate (BS) or polypropylene (PP) tubes. The proficiency of biofilm formation was better evaluated by the level of crystal violet staining expressed relative to the final culture density. The microscopic analysis of biofilms formed on glass coverslips revealed the presence of a matrix of exopolysaccharides and microcolonies typical of biofilm architecture. Isolates with increased adhesion to BS showed larger microcolonies. According to our results, twitching correlated well with attachment to the three abiotic surfaces tested, while swimming only showed a slight correlation with biofilm formation on PP. Poor correlation was observed between cell surface hydrophobicity and biofilm formation. One of the highest biofilm-producing isolates adhered to urethral catheters of different materials, and exhibited an increased resistance to oxidative stress, one of the common stresses encountered by bacteria during the infection process due to the immune response.