Abstract
Grapefruit and lemon pectin obtained from the respective waste citrus peels via hydrodynamic cavitation in water only are powerful, broad-scope antimicrobials against Gram-negative and -positive bacteria. Dubbed IntegroPectin, these pectic polymers functionalized with citrus flavonoids and terpenes show superior antimicrobial activity when compared to commercial citrus pectin. Similar to commercial pectin, lemon IntegroPectin determined ca. 3-log reduction in Staphylococcus aureus cells, while an enhanced activity of commercial citrus pectin was detected in the case of Pseudomonas aeruginosa cells with a minimal bactericidal concentration (MBC) of 15 mg mL−1. Although grapefruit and lemon IntegroPectin share equal MBC in the case of P. aeruginosa cells, grapefruit IntegroPectin shows boosted activity upon exposure of S. aureus cells with a 40 mg mL−1 biopolymer concentration affording complete killing of the bacterial cells. Insights into the mechanism of action of these biocompatible antimicrobials and their effect on bacterial cells, at the morphological level, were obtained indirectly through Fourier Transform Infrared spectroscopy and directly through scanning electron microscopy. In the era of antimicrobial resistance, these results are of great societal and sanitary relevance since citrus IntegroPectin biomaterials are also devoid of cytotoxic activity, as already shown for lemon IntegroPectin, opening the route to the development of new medical treatments of polymicrobial infections unlikely to develop drug resistance.
Highlights
Causing annually 700,000 deaths worldwide [1], antimicrobial resistance (AMR) represents one of today’s main societal burdens in both developed and developing countries
2020, 9, and quantifying the high in vitro antibacterial activity of both lemon3 of and grapefruit IntegroPectin against S. aureus and P. aeruginosa bacterial strains in comparison to that shown by commercial citrus pectin, this study offers the first insight into the mechanism(s) of action by these commercial citrus pectin, this study offers the first insight into the mechanism(s) of actionon of semithese of new natural antimicrobials derived from agri-food industry by-products directly new natural antimicrobials derived from agri-food industry by-products directly on semi-industrial industrial scale [11], based on structural investigation via Fourier transform infrared (FTIR)
Likewise to the orange pectin analyzed by these authors, grapefruit IntegroPectin contains longer and more numerous hydrophilic RG-I regions in comparison to pectin from lemon, being comprised of randomly coiled molecular chains promoting a flexible conformation in solution and lower viscosity [46]
Summary
Causing annually 700,000 deaths worldwide [1], antimicrobial resistance (AMR) represents one of today’s main societal burdens in both developed and developing countries. A recent estimate of the implications and costs of AMR assessed more than EUR 9 billion and USD 20 billion to be the Antibiotics 2020, 9, 586; doi:10.3390/antibiotics9090586 www.mdpi.com/journal/antibiotics. Antibiotics 2020, 9, 586 economic costs due to clinical interventions and productivity losses [2]. Current projections indicate that by 2050 the annual death toll could reach 10 million people, with an economic impact comparable to the 2008 financial crisis [3]. Intense research activities aimed to find or synthesize new efficacious antimicrobials to counteract AMR infections are carried out worldwide in public research centers and pharmaceutical and biotechnology companies [4]. The almost concomitant introduction and subsequent widespread use of antibiotics led to ignoring this remarkable property of pectins until the late 1990s [6], leaving unveiled, for the most part, their mechanism(s) of action and their potential for different applications in medicine and pharmacology [7,8,9]
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