Abstract
Green tea-derived galloylated catechins have weak direct antibacterial activity against both Gram-positive and Gram-negative bacterial pathogens and are able to phenotypically transform, at moderate concentrations, methicillin-resistant Staphylococcus aureus (MRSA) clonal pathogens from full β-lactam resistance (minimum inhibitory concentration 256–512 mg/L) to complete susceptibility (~1 mg/L). Reversible conversion to susceptibility follows intercalation of these compounds into the bacterial cytoplasmic membrane, eliciting dispersal of the proteins associated with continued cell wall peptidoglycan synthesis in the presence of β-lactam antibiotics. The molecules penetrate deep within the hydrophobic core of the lipid palisade to force a reconfiguration of cytoplasmic membrane architecture. The catechin gallate-induced staphylococcal phenotype is complex, reflecting perturbation of an essential bacterial organelle, and includes prevention and inhibition of biofilm formation, disruption of secretion of virulence-related proteins, dissipation of halotolerance, cell wall thickening and cell aggregation and poor separation of daughter cells during cell division. These features are associated with the reduction of capacity of potential pathogens to cause lethal, difficult-to-treat infections and could, in combination with β-lactam agents that have lost therapeutic efficacy due to the emergence of antibiotic resistance, form the basis of a new approach to the treatment of staphylococcal infections.
Highlights
Antibiotics are among the most beneficial drugs ever introduced into clinical practice [1]
Nature’s chemical and biological diversity has been fruitfully exploited with regard to therapeutics that target bacterial infections; approximately 75% of antibacterial New Chemical Entities introduced into the clinic over the last forty years have been derived from natural products [9,10], without exception from moulds and actinomycetes, notably Streptomyces spp [11]
These studies have shown that tea can inhibit and kill some but not all Gram-positive and Gram-negative bacterial species at or slightly below the typical concentrations found in brewed tea [19]; activity is attributable to the polyphenolic catechins, in particular (−)-epigallocatechin (EGC), (−)-epigallocatechin gallate (EGCg) and (−)-epicatechin gallate (ECg) [20,21], and is generally modest
Summary
Antibiotics are among the most beneficial drugs ever introduced into clinical practice [1]. Nature’s chemical and biological diversity has been fruitfully exploited with regard to therapeutics that target bacterial infections; approximately 75% of antibacterial New Chemical Entities introduced into the clinic over the last forty years have been derived from natural products [9,10], without exception from moulds and actinomycetes, notably Streptomyces spp [11]. There is a large body of data describing the in vitro activity of plant extracts and constituents, in part due to the low barrier for entry into this field by underfunded laboratories The majority of these studies have utilised unfractionated extracts with weak antibacterial activity as determined by the minimum inhibitory concentration (MIC) against common pathogens such as K. pneumoniae, P. aeruginosa and S. aureus [7]. It is clear that a minority of phytochemical compounds have the capacity to non-lethally modify the properties of major pathogens in a way that could be exploited from a pharmaceutical perspective; green tea-derived catechin gallates fall into this category and will be the focus of this review
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