Spent coffee grounds extract: antimicrobial activity against Paenibacillus larvae and its effect on the expression of antimicrobial peptides in Apis mellifera

Abstract

In recent years, natural alternatives have been sought for the control of beekeeping pathologies; in the case of American Foulbrood (AFB) disease, the use of synthetic antibiotics was prohibited due to honey contamination and the generation of resistant bacteria. The significant increase in population growth worldwide has led to great concern about the production of large amounts of waste, including those from agribusiness. Among the most important beverages consumed is coffee, generating thousands of tons of waste called spent coffee grounds (SCG). The SCG is a source of many bioactive compounds with known antimicrobial activity. The aims of the present work were: (1) to obtain and chemically analyse by HPLC of SCG extracts (SCGE), (2) to analyse the antimicrobial activity of SCGE against vegetative form of Paenibacillus larvae (the causal agent of AFB), (3) to evaluate the toxicity in bees of SCGE and (4) to analyse the effect of the extracts on the expression of various genes of the immune system of bees. SCGs have a high content of phenolic compounds, and the caffeine concentration was of 0.3%. The MIC value obtained was 166.667 µg/mL; the extract was not toxic to bees, and interestingly, overexpression of abaecin and hymenoptaecin peptides was observed. Thus, SCGE represents a promising alternative for application in the control of American Foulbrood and as a possible dietary supplement to strengthen the immune system of honeybees. Therefore, the concept of circular bio-economy could be applied from the coffee industry to the beekeeping industry.