Antimicrobial effect of lactoferrin and glycerol monolaurate on selected bacteria associated with newborn infections

Abstract

Human breast milk contains a rich array of bioactive substances, such as immunoglobulins, lactoferrin antimicrobial peptides, and glycerol monolaurate, which play a crucial role in providing immune protection to infants. Infant formula manufacturers strive to match mother's milk's nutritional makeup, including immune-boosting ingredients. Lactoferrin and glycerol monolaurate (GML) are important antibacterial compounds in human milk. The study aimed to investigate the effect of bovine lactoferrin (bLf) and GML in preventing the growth of inoculated bacteria into infant formula. The study examined both individual and combined use of these components. The bacteria that were tested included: 1) Gram-negative bacteria: Cronobacter sakazakii strains 12868 and 29004, Pseudomonas aeruginosa, Salmonella enterica Typhimurium, and 2) Gram-positive bacteria: Methicillin-resistant Staphylococcus aureus (MRSA), and Listeria monocytogenes. The result of the agar diffusion assays showed that bLf, at a concentration of 16 mg/disc, exhibited strong inhibition (≥20 mm) of all the selected bacterial strains. On the other hand, GML at a concentration of 8 mg/disc showed strong inhibition of all strains; however, Gram-positive bacteria were more susceptible, so a concentration of 5 mg/disc was enough to achieve strong inhibition of these strains. The minimal bactericidal concentrations (MBC) analysis aimed to achieve a >3-log reduction in the growth of various bacterial strains. The results showed that S. enterica Typhimurium and L. monocytogenes were more susceptible to bLf than the other strains (MBC: 7 and 4.8 mg/ml, respectively, vs. 14.9–18.4 mg/ml for the other strains). In contrast, MRSA and L. monocytogenes were more susceptible to GML (MBC: 6 and 10 mg/ml, respectively, vs. 16–18 mg/ml for Gram-negative strains). The results of reconstituted powdered infant formulas (RPIF), with the addition of bLf, GML, or both at pathogen-specific MBC, showed significant log reductions in the growth of experimentally inoculated bacteria compared to the control at different time intervals. All bacterial strains exposed to bLf and GML exhibited >3-log reduction within 72 h, with Gram-positive strains showing >7-log reduction. GML and bLf combined had a stronger anti-bacterial activity than individual components, indicating the potential of combining GML and bLf as natural agents against specific pathogenic bacteria. Future studies are needed to understand the potential use of these compounds in different food matrices and clinical settings.