Analysis was performed in a Bioscreen C Microbiological Analyser
(Labsystems Helsinki, Finland). Cultures were grown overnight
and serial dilutions of each strain were prepared in fresh
media. A 200 ml aliquot of each serial dilution were dispensed into
the wells of a Bioscreen plate and optical density (OD) of each well
was recorded at 600 nm every 10 min for 48 h at 30 C in shaking
mode. For each dilution, results for two independent biological
replicates were generated. Results were recorded as TTD where
TTD equates to the time taken for the OD600 to increase to 0.2.
Standard calibration curves were obtained for each strain by
plotting TTD against the concentration of the initial inoculums
(log10 CFU/ml). The slope was calculated using standard Microsoft
Excel regression analysis software and growth rate calculated from
1/slope ln(10) 60.