Inhibition by EGTA of the formation of a biofilm by clinical strains of Staphylococcus aureus.

The effect of EGTA on the adhesion and on the formation of a biofilm by two reference and eight clinical strains of Staphylococcus aureus was studied. All the clinical strains were isolated from patients from Kinshasa. Spa typing confirmed that these clinical strains were distinct. The Biofilm Ring Test (BFRT®) showed that EGTA (100 µM-10 mM) inhibited the adhesion of the four clinical methicillin-resistant (MRSA) strains and the crystal violet staining method that it inhibited the formation of a biofilm by all the strains. Divalent cations abolished the effect of EGTA on the formation of a biofilm, specially in the clinical MRSA strains. EGTA had no effect on established biofilms. Only concentrations of EGTA higher than 10 mM were toxic to eukaryotic cells. Our results establish the effectiveness and the safety of lock solutions with EGTA to prevent the formation in vitro of biofilms by S. aureus.

Evaluation de la sensibilite aux antibiotiques des mycobacteries a croissance rapide

La sensibilite aux antibiotiques des Mycobacteries a Croissance Rapide (MCR) par la methode de microdilution en milieu liquide; et la mesure de la repetabilite des CMI ont ete evaluees sur 15 souches cliniques de mycobacteries a croissance rapide (4 Mycobacterium chelonae; 6 Mycobacteriun abscessus; 3 Mycobacteriun fortuitum; et 2 Mycobacterium peregrinum). Les souches de reference Staphylococcus aureus ATCC 29213 et Mycobacterium peregrinum ATCC 700686 ont ete utilisees pour le controle de qualite. Les resultats ont montre que le controle de qualite etaitacceptable car les valeurs obtenues etaient comprises dans la gamme de Concentrations Minimales Inhibitrices (CMI) proposee par le Clinical and Laboratory Standard Institute (CLSI). Une repetabilite des valeurs de CMI a ete observee. L'amikacine et la clarithromycine etaient les antibiotiques les plus actifs sur presque toutes les MCR etudiees. La tobramycine etait active exclusivement sur M. chelonae (100sensibles) et les fluoroquinolones (Ciprofloxacine et moxifloxacine) sur M. fortuitum (100de sensibilite). Il n'a pas ete observe de correlation entre la methode de microdilution en milieu liquide et celle de Canetti

Study of the formation of a biofilm by clinical strains of Staphylococcus aureus.

A study on biofilm formation was carried out using five methicillin-sensitive [MSSA] and five methicillin-resistant [MRSA] strains of S. aureus. In each group, there were four strains isolated from patients from Kinshasa (Democratic Republic of Congo, DRC) and one reference strain. All of the strains were hydrophobic. The adherence of the bacteria to an abiotic surface was studied with the Biofilm Ring Test (BFRT®) and the crystal violet staining method (CVSM). Both techniques showed that eight of the strains formed biofilms within 2-3 h. The extent of the biofilm formed by one strain could only be observed with the CVSM. Periodate prevented the formation of biofilms and, in separate experiments, destroyed the biofilm pre-formed by the MSSA reference, but not those pre-formed by the clinical strains. Proteinase K destroyed all pre-formed biofilms. Six of the strains were icaA+; the clinical MSSA strains were not. The results also indicated different mechanisms of biofilm development between MSSA and MRSA clinical strains. The BFRT® and the CVSM are complementary techniques to study the adhesion of bacteria and the development of biofilms.