Polyphenolic Secondary Metabolites Synergize the Activity of Commercial Antibiotics against Clinical Isolates of ß-Lactamase-producing Klebsiella pneumoniae.

Emergence of worldwide antimicrobial resistance prompted us to study the resistance modifying potential of plant-derived dietary polyphenols, mainly caffeic acid, ellagic acid, epigallocatechin-3-gallate (EGCG) and quercetin. These compounds were studied in logical combination with clinically significant antibiotics (ciprofloxacin/gentamicin/tetracycline) against Klebsiella pneumoniae, after conducting phenotypic screening of a large number of clinical isolates and selecting the relevant strains possessing extended-spectrum ß-lactamase (ESBL) and K. pneumoniae carbapenemase (KPC)-type carbapenemase enzymes only. The study demonstrated that EGCG and caffeic acid could synergize the activity of tested antibiotics within a major population of ß-lactamase-producing K. pneumoniae. In spectrofluorimetric assay, ~17-fold greater ciprofloxacin accumulation was observed within K. pneumoniae cells pre-treated with EGCG in comparison with the untreated control, indicating its ability to synergize ciprofloxacin to restrain active drug-efflux. Further, electron micrograph of ESBL-producing K. pneumoniae clearly demonstrated the prospective efficacy of EGCG towards biofilm degradation.

Antimicrobial activity of pomegranate fruit constituents against drug-resistant Mycobacterium tuberculosis and ß-lactamase producing Klebsiella pneumoniae.

CONTEXT: The global surge in multi-drug resistant bacteria and the imminence of tuberculosis pandemic necessitate alternative therapeutic approaches to augment the existing medications. Pomegranate, the fruit of Punica granatum Linn. (Punicaceae), widely recognized for potency against a broad spectrum of bacterial pathogens, deserves further investigation in this respect. OBJECTIVE: This study determines the therapeutic potential of pomegranate juice, extracts of non-edible peel prepared with methanol/water, and its four polyphenolic constituents, namely caffeic acid, ellagic acid, epigallocatechin-3-gallate (EGCG) and quercetin, against drug-resistant clinical isolates. MATERIALS AND METHODS: Phenotypic characterisation of Mycobacterium tuberculosis, extended-spectrum ß-lactamase (ESBL) and KPC-type carbapenemase producing Klebsiella pneumoniae was performed by biochemical and molecular methods. Resistance profiles of M. tuberculosis and K. pneumoniae were determined using LJ proportion and Kirby-Bauer methods, respectively. Pomegranate fruit extracts, and the compounds, were evaluated at a dose range of 1024-0.5 µg/mL, and 512-0.25 µg/mL, respectively, to determine minimum inhibitory (MIC) and bactericidal concentrations (MBC) against the drug-resistant isolates by the broth micro-dilution method. RESULTS: The peel extracts exhibited greater antimycobacterial activity (MIC 64-1024 µg/mL) than the potable juice (MIC 256 - > 1024 µg/mL). EGCG and quercetin exhibited higher antitubercular (MIC 32-256 µg/mL) and antibacterial (MIC 64-56 µg/mL) potencies than caffeic acid and ellagic acid (MIC 64-512 µg/mL). DISCUSSION AND CONCLUSION: The pomegranate fruit peel and pure constituents were active against a broad panel of M. tuberculosis and ß-lactamase producing K. pneumoniae isolates. EGCG and quercetin need further investigation for prospective application against respiratory infections.

Antitubercular and antibacterial activity of quinonoid natural products against multi-drug resistant clinical isolates.

Multi-drug resistant Mycobacterium tuberculosis and other bacterial pathogens represent a major threat to human health. In view of the critical need to augment the current drug regime, we have investigated therapeutic potential of five quinonoids, viz. emodin, diospyrin, plumbagin, menadione and thymoquinone, derived from natural products. The antimicrobial activity of quinonoids was evaluated against a broad panel of multi-drug and extensively drug-resistant tuberculosis (M/XDR-TB) strains, rapid growing mycobacteria and other bacterial isolates, some of which were producers of ß-lactamase, Extended-spectrum ß-lactamase (ESBL), AmpC ß-lactamase, metallo-beta-lactamase (MBL) enzymes, as well as their drug-sensitive ATCC counterparts. All the tested quinones exhibited antimycobacterial and broad spectrum antibacterial activity, particularly against M. tuberculosis (lowest MIC 0.25 µg/mL) and Gram-positive bacteria (lowest MIC <4 µg/mL) of clinical origin. The order of antitubercular activity of the tested quinonoids was plumbagin > emodin ~ menadione ~ thymoquinone > diospyrin, whereas their antibacterial efficacy was plumbagin > menadione ~ thymoquinone > diospyrin > emodin. Furthermore, this is the first evaluation performed on these quinonoids against a broad panel of drug-resistant and drug-sensitive clinical isolates, to the best of our knowledge.

Pomegranate pericarp extract enhances the antibacterial activity of ciprofloxacin against extended-spectrum ß-lactamase (ESBL) and metallo-ß-lactamase (MBL) producing Gram-negative bacilli.

A methanolic extract of Punica granatum (pomegranate) fruit pericarp (PGME) was tested in combination with ciprofloxacin against extended-spectrum ß-lactamase (ESBL) producing Escherichia coli, Klebsiella pneumoniae, and metallo-ß-lactamase (MBL) producing Pseudomonas aeruginosa, which were screened for their resistance profile against fluoroquinolone antibiotics. The minimum inhibitory concentrations (MIC) of ciprofloxacin and PGME, alone, were determined, and synergy of ciprofloxacin-PGME combinations evaluated by checkerboard assay and fractional inhibitory concentration (FIC). Nineteen out of forty-nine strains exhibited synergy with ciprofloxacin (FIC of 0.125-0.5 for ciprofloxacin) further verified by agar-well assay. This could be due to the bacterial efflux pump inhibitor (EPI) activity of the polyphenolic constituents of PGME. However, the isolates exhibiting a high level of ciprofloxacin resistance did not respond to ciprofloxacin-PGME combinations, which could be due to target site modification not influenced further by EPI activity of PGME. Again, some strains were sensitive or weakly resistant to ciprofloxacin, which exhibited 'indifference' to the combination, probably due to a lack of over-expressed efflux mechanism. Thus, a synergy of a ciprofloxacin-PGME combination was demonstrated for the first time against ESBL- and MBL-producing Gram-negative bacilli, and the efficacy of an existing drug improved with the help of an inexpensive alternative therapy.