Fibronectin and laminin induce biofilm formation by Streptococcus uberis and decrease its penicillin susceptibility

Abstract

The aim of this study was to determine the effect of fibronectin and laminin on the in vitro biofilm formation byStreptococcus uberis and the susceptibility to penicillin under planktonic and biofilm growth conditions. Weobserved that a high percentage (76.5%) of the S. uberis isolates was weak biofilm producers in Todd HewittBroth (THB). A high percentage of moderate (38.2%) or strong (53%) biofilm producers was observed in THBsupplemented with laminin or fibronectin, respectively. All S. uberis isolates growing as planktonic cells weresensitive to penicillin. Minimum biofilm inhibitory concentrations (MBICs) were ranging between 0.25 and 2 μg/ml, whereas minimum biofilm eradication concentrations (MBECs) ranging from 8 to 256 μg/ml. These resultsshow that biofilm-growing S. uberis cells required higher concentrations of the antibiotic than those needed toinhibit planktonic cells. Similar MBICs of penicillin were obtained when S. uberis cells growing in THB supplementedor not with laminin or fibronectin, whereas the MBECs markedly increased when one of two proteinswere added to culture medium compared with the medium without proteins. To the best of our knowledge, thisis the first report of decreased susceptibility to penicillin likely related to a higher production of biofilms stimulatedby laminin or fibronectin. Therapeutic failures of penicillin to treat S. uberis infections may be due tobiofilm formation.