Kinetic effect of human lactoferrin on the growth of Escherichia coli 0111.

Previous studies have suggested that human lactoferrin has a bacteriostatic effect on Escherichia coli 0111 growth. Determination of the time required for cultures to reach one-half maximal cell density (t1/2) indicates that within the concentration range of lactoferrin used in this study, its effect in vitro on the growth of E. coli 0111 is kinetic rather than bacteriostatic. Compared to a control, added apo-lactoferrin (250-1000 micrograms/ml) produced only a delay effect as seen by an increase in the t1/2 indicating these concentrations are probably within the subinhibitory concentration range. The kinetic delay effect of apo-lactoferrin is also consistently increased in the presence of Zn2+ and Cu2+ cations. Cu2+, Zn2+ and NTA (nitrilotriacetate) did not affect the growth rate of this organism in the absence of lactoferrin compared to the control. These studies indicate that the mechanism by which lactoferrin alters the bacterial growth of E. coli 0111 is more complex than simple iron deprivation.