Damage of the outer membrane of enteric gram-negative bacteria by lactoferrin and transferrin

Abstract

Many studies have shown that lactoferrin and transferrin have antimicrobial activity against gram-negative bacteria, but a mechanism of action has not been defined. We hypothesized that the iron-binding proteins could affect the gram-negative outer membrane in a manner similar to that of the chelator EDTA. The ability of lactoferrin and transferrin to release radiolabeled lipopolysaccharide (LPS) from a UDP-galactose epimerasedeficient Escherichia coli mutant and from wild-type Salmonella typhimurium strains was tested. Initial studies in barbital-acetate buffer showed that EDTA and lactoferrin cause significant release of LPS from all three strains. Further studies found that LPS release was blocked by iron saturation of lactoferrin, occurred between pH 6 and 7.5, was comparable for bacterial concentrations from 104 to 107 CFU/mI, and increased with increasing lactoferrin concentrations. Studies using Hanks balanced salt solution lacking calcium and magnesium showed that transferrin also could cause LPS release. Additionally, both lactoferrin and transferrin increased the antibacterial effect of a subinhibitory concentration of rifampin, a drug excluded by the bacterial outer membrane. This work demonstrates that these iron-binding proteins damage the gram-negative outer membrane and alter bacterial outer membrane permeability.

Specific binding of lactoferrin to Aeromonas hydrophila

“…Lf elicits an enhanced antimicrobial effect when adsorbed to the bacterial surface [11,18], a process that may contribute to the host defence. On the other hand, certain microorganisms seem to utilize the iron bound to Lf via specific Lf receptors expressed in the outer membrane [19][20][21], a property that may contribute to the bacterial virulence.…”

Lactoferrin a multiple bioactive protein: An overview

“…Lf's bactericidal function has been attributed to its direct interaction with bacterial surfaces. In 1988, it was shown that Lf damages the external membrane of Gram-negative bacteria through an interaction with lipopolysaccharide (LPS) [66]. The positively charged N-terminus of Lf prevents the interaction between LPS and bacterial cations (Ca + 2 and Mg + 2 ) [67,68] and interferes with aggregative proliferation in E. coli [52].…”

“…The positively charged N-terminus of Lf prevents the interaction between LPS and bacterial cations (Ca + 2 and Mg + 2 ) [67,68] and interferes with aggregative proliferation in E. coli [52]. The interaction between Lf and LPS or other surface proteins also potentiates the action of natural antibacterials such as lysozyme, which is secreted from the mucosa at elevated concentrations along with Lf [66]. It has also been demonstrated that the N-terminal lobe of Lf possesses a serine protease-like activity [39].…”

Evaluation of the antimicrobial effect of lactoferrin on Porphyromonas gingivalis, Prevotella intermedia and Prevotella nigrescens

“…Second, Lf might bind to and block bacterial surface receptors for haemin, so preventing cell acquisition of haemin. Third, Lf may have a direct antimicrobial e¡ect on the cells, perhaps by directly damaging the cell membrane, as has been previously suggested [11].…”

“…It is not known whether Lf interacts with haemin. Second, Lf may damage the outer membrane of Gram-negative bacteria by causing the release of lipopolysaccharides and inducing permeability changes [11].…”