The Human Milk Protein-Lipid Complex HAMLET Sensitizes Bacterial Pathogens to Traditional Antimicrobial Agents

Abstract

The fight against antibiotic resistance is one of the most significant challenges to public health of our time. The inevitable development of resistance following the introduction of novel antibiotics has led to an urgent need for the development of new antibacterial drugs with new mechanisms of action that are not susceptible to existing resistance mechanisms. One such compound is HAMLET, a natural complex from human milk that kills Streptococcus pneumoniae (the pneumococcus) using a mechanism different from common antibiotics and is immune to resistance-development. In this study we show that sublethal concentrations of HAMLET potentiate the effect of common antibiotics (penicillins, macrolides, and aminoglycosides) against pneumococci. Using MIC assays and short-time killing assays we dramatically reduced the concentrations of antibiotics needed to kill pneumococci, especially for antibiotic-resistant strains that in the presence of HAMLET fell into the clinically sensitive range. Using a biofilm model in vitro and nasopharyngeal colonization in vivo, a combination of HAMLET and antibiotics completely eradicated both biofilms and colonization in mice of both antibiotic-sensitive and resistant strains, something each agent alone was unable to do. HAMLET-potentiation of antibiotics was partially due to increased accessibility of antibiotics to the bacteria, but relied more on calcium import and kinase activation, the same activation pathway HAMLET uses when killing pneumococci by itself. Finally, the sensitizing effect was not confined to species sensitive to HAMLET. The HAMLET-resistant respiratory species Acinetobacter baumanii and Moraxella catarrhalis were all sensitized to various classes of antibiotics in the presence of HAMLET, activating the same mechanism as in pneumococci. Combined these results suggest the presence of a conserved HAMLET-activated pathway that circumvents antibiotic resistance in bacteria. The ability to activate this pathway may extend the lifetime of the current treatment arsenal.

Synergistic Interactions of Vancomycin with Different Antibiotics against Escherichia coli: Trimethoprim and Nitrofurantoin Display Strong Synergies with Vancomycin against Wild-Type E. coli

“…Of particular interest are potentiators of existing antibiotics, or codrugs, a number of which have been used in both laboratory (18)(19)(20)(21)(22)(23) and clinical (24)(25)(26) settings. Also, Collins and coworkers have demonstrated that specific metabolites can potentiate aminoglycosides acting on E. coli and Staphylococcus aureus biofilms (27).…”

The Use of Liprotides To Stabilize and Transport Hydrophobic Molecules

“…The incorporation of antibiotics in liprotides has the potential to be exploited in a similar way. The synergetic effect of using antibiotics together with HAMLET is already known (32) , but might be further exploited if the antibiotics could be incorporated in the liprotide structure thereby potentially increasing the solubility, stability and transport of the antibiotic to a target cells. However, the antibiotics investigated in this study were not able to form a complex with aLA and OA, highlighting that not all small molecules are able to bind to liprotides.…”

Study of the Response Regulator Rrp1 Reveals Its Regulatory Role in Chitobiose Utilization and Virulence of Borrelia burgdorferi

“…Cells were then resuspended in fresh PBS. SEM determinations were performed as described before (47,48). Briefly, 10 l of cell suspensions was settled on poly-L-lysine-coated round coverslips (BD BioSciences, San Jose, CA).…”