Bactericidal Effect of Lactoferrin and Its Amidated and Pepsin-Digested Derivatives on Pseudomonas fluorescens: Influence of Environmental and Physiological Factors

Abstract

The influence of environmental and physiological factors such as substrate composition and inoculum characteristics on the bactericidal activity of bovine lactoferrin (LF) and its amidated and pepsin-digested derivatives against Pseudomonas fluorescens was investigated. Amidated LF (AMILF) exerted the most potent bactericidal activity, with a 5.8-log decrease in P. fluorescens counts, and LF the lowest, with just a 1-log decrease, whereas pepsin-digested LF (PDLF) reduced bacterial counts by 2.7 log, after 1 h at 30°C. Amidation of PDLF increased effectiveness by 1.2 log, whereas pepsin digestion of AMILF decreased effectiveness by 2.8 log. Bactericidal activity of LF and its derivatives was higher in Tris buffer than in phosphate buffer. The bactericidal effect of AMILF and PDLF was enhanced as medium pH was increased from 5.5 to 8.5, whereas LF showed higher activity under acidic or basic conditions than at neutral pH. The presence of cations affected the activity of LF and its derivatives, from a concentration of 10 mM for K+, 1 mM for Na+, and 0.1 mM for Ca2+, Co2+, Cu2+, Mg2+, Zn2+, and Fe3+. Bactericidal effectiveness diminished as the bacterial inoculum was increased. Log-phase cultures (10-h incubation) were less sensitive to the bactericidal activity of LF and its derivatives than stationary cultures (20- and 30-h incubation). All these factors should be considered when applications of LF and its derivatives in foods and other complex systems are investigated.