The Impact of HAMLET, a Human-Milk Protein Complex, on the Ecology of the Oral Microbiome
Objectives: Antibiotic treatment not only affects pathogenic bacteria, but also provides the potential to impact the whole human microbiome. To prevent unwanted changes by antibiotics that may favor overgrowth of pathogens, combination therapies with prebiotic agents have received increased attention. Recent studies shows that the protein-lipid complex from human milk, called HAMLET (human alpha-lactalbumin made lethal to tumor cells) exhibits direct bactericidal activity against multiple pathogens and hinders antibiotic-resistance development.
Methods: The aim of this study was to explore HAMLET’s potential as a prebiotic to modulate microbiome changes induced by amoxicillin. We utilized an ex vivo oral microbiome model with a highly complex microbial diversity that allows growth of uncultivated oral species.
Results: We first exposed preformed biofilms to amoxicillin alone at concentrations ranging from 0.025 µg/ml to 0.1 µg/ml. After 24 hours, none of the amoxicillin concentrations had any significant impact on the total CFUs (colonies forming units) recovered from the microbiomes, while the dry biomass weight increased in the highest concentrations. When exposed to HAMLET at 125 µg/ml and 250 µg/ml, the CFUs decreased significantly at the highest concentration, compared to controls with no treatment. The dry biomass weight increased by 20%. RT-PCR analysis for HAMLET-treated biofilms showed a significant increase in the relative abundance of Neisseria and Streptococcus at 125 µg/ml. While treatment with 250 µg/ml HAMLET significantly decreased the abundance of both genera. Combination therapy of 0.1 µg/ml amoxicillin and 250 µg/ml HAMLET reduced the CFUs compared to HAMLET alone, and showed nearly a 2-log10 reduction compared to biofilms without treatment.
Conclusions: Our results suggest that HAMLET affects the composition of ex vivo oral microbiomes. Additionally, HAMLET has the potential to modify the response of the microbiome to low amoxicillin concentrations. Further, metagenomic studies will be conducted to deepen our understanding of the impact on microbiome composition and resistome development.