Antimicrobial properties of Kalanchoe blossfeldiana: a focus on drug resistance with particular reference to quorum sensing-mediated bacterial biofilm formation.

OBJECTIVES: This study attempts to investigate the antimicrobial properties of Kalanchoe blossfeldiana with a particular reference to quorum sensing (QS)-mediated biofilm formation. METHODS: The methanol extract of K. blossfeldiana leaves (MEKB) was evaluated for antimicrobial properties including QS-controlled production of biofilm (including virulence factor, motility and lactone formation) in Pseudomonas aeruginosa. Methanol extract of K. blossfeldiana was also evaluated for anti-cytokine (tumour necrosis factor-alpha, interleukin-6 and interleukin-1 beta) properties in peripheral blood mononuclear cells (PBMC). KEY FINDINGS: Methanol extract of K. blossfeldiana exhibited antimicrobial effect on clinical isolates, as well as standard reference strains. Pseudomonas aeruginosa exposed to MEKB (subminimum inhibitory concentration (MIC)) displayed reduced biofilm formation, whereas supra-MIC produced destruction of preformed biofilms. Methanol extract of K. blossfeldiana reduced the secretion of virulence factors (protease and pyoverdin) along with generation of acyl homoserine lactone (AHL). Confocal laser scanning microscopy images indicate reduction of biofilm thickness. The extract also reduced cytokine formation in lipopolysaccharide-stimulated PBMC. CONCLUSIONS: Kalanchoe blossfeldiana was found to interfere with AHL production, which in turn may be responsible for downregulating QS-mediated production of biofilm and virulence. This first report on the antibiofilm and anticytokine properties of this plant may open up new vistas for future exploration of this plant for combating biofilm-related resistant infections.

Anti-biofilm activity of Marula - a study with the standardized bark extract.

ETHNOPHARMACOLOGICAL RELEVANCE: Marula (Sclerocarya birrea; family - Anacardiaceae) is an African plant, which enjoys wide socio-economic importance particularly in southern part of Africa. The fruits are consumed as food and also as alcoholic beverage (cream liquor). In different parts of Africa, the decoction of the bark is traditionally used for the treatment of dysentery, diarrhoea, and various other infectious conditions. The aim of the study was to investigate the anti-biofilm properties of the methanol extract of Marula bark (stem bark of Sclerocarya birrea), with a view towards combating the emergence of antimicrobial resistance often associated with bacterial biofilms. MATERIALS AND METHODS: The standardized methanol extract was initially tested for its antimicrobial property. The crystal violet assay was used for evaluating anti-biofilm (biofilm formation by Pseudomonas aeuginosa) activity. Further in order to study the mechanism of anti-biofilm activity, the same was evaluated for understanding its role on various quorums sensing mediated phenomenon (swarming motility assay, protease and pyoverdin assay) that are known to be associated with the formation of biofilms and pathogenicity. RESULTS: The methanol extract showed no inhibition of bacterial growth up to a concentration of 200 µg/ml. Interestingly, the sample produced anti-biofilm activity (around 75% decrease; 100 µg/ml) at sub-lethal concentration. Further it also significantly reduced the QS mediated swarming motility. The release of various virulent factors (protease and pyoverdin) was found to be lowered when pre-treated with the extract. CONCLUSION: The present study illustrates the anti-biofilm property Sclerocarya birrea. The standardized extract significantly disrupted the quorum sensing mediated production of biofilm formation and also inhibited swarming ability of the cells. The extract displayed a regulatory role on the secretion of protease and pyoverdin, two QS dependent pathogenic factors found in Pseudomonas aeruginosa. This study also validates the ethnobotanical use of Marula.