BIOFILM PRODUCTION UNDER STATIC AND DYNAMIC CONDITIONS BY GENETICALLY CHARACTERIZED S. AUREUS CAUSING DAIRY COW MASTITIS.

Staphylococcus aureus (S. aureus) biofilm formation has been pointed out as an important factor in the establishment of bovine mastitis, particularly in its chronic form. Biofilm characterization of bovine isolates generally applies static systems and matrices other than milk, which is probably not adequate to access the potential of this bacterial trait in the pathogenesis of mastitis. The objectives of the study were: (1) to investigate the occurrence of biofilm associated genes icaA/D and bap in Italian S. aureus strains; (2) to characterize biofilm formation using a static and a dynamic assay and (3) to look for genetic markers to identify strains capable of biofilm formation in the dynamic system. Out of 112 PCR tested S. aureus strains, 73 (65.18%) carried both icaA and icaD, 2 (1.79%) only icaA, 15 (13.39%) only icaD, 22 (19.64%) were negative for both genes and only 7 (6.25%) carried the bap gene. Biofilm characterization of the same 112 strains using a standard static method (TCP) classified 88 (78.57%) as non-biofilm forming and 24 (21.43%) as biofilm forming. Twelve biofilm-forming and 18 non biofilm-forming strains, selected out of the 112 TCP tested strains, were further characterized by a dynamic, milk flow based assay (MFC). Six strains (20%) formed biofilm in the dynamic system and only a limited number of genes (n= 14), according to microarray results, was statistically related to strain ability to form biofilm in milk. This study indicates that the biofilm-forming potential of S. aureus strains should be critically evaluated and tested applying conditions similar to mammary environment.