Increase in the binding of transferrin on the surface of M. catarrhalis as a result of cold shock. A, strain O35E and its isogenic mutant O35E.tbpB exposed to 26°C or 37°C for 3 h were incubated with fluorescein isothiocyanate (FITC)-conjugated transferrin (0.1 μg/mL) and flow cytometry analysis was performed. Shown are representative flow cytometry profiles of strain O35E and O35E.tbpB after exposure at 26°C (gray) or at 37°C (black), which demonstrate that TbpB is required for maximum binding of transferrin on the surface of cold shock-induced Moraxella catarrhalis. The dotted line represents the negative control (bacteria only). The mean fluorescence intensity ± 1 standard deviation for three experiments performed is shown in panel B. *, P< 0.05 for 26°C versus 37°C (one-way analysis of variance).