Inhibitory efficacy of geraniol on biofilm formation and development of adaptive resistance in Staphylococcus epidermidis RP62A.

PURPOSE: The current study has been designed to delineate the efficacy of geraniol (GE) on biofilm formation in Staphylococcus epidermidis as well as the effect of subinhibitory concentrations of GE on the development of adaptive resistance. METHODOLOGY: Biofilm biomass quantification assay was performed to evaluate the antibiofilm activity of GE against S. epidermidis. Microscopic observation of biofilms and extracellular polymeric substance (EPS), slime and cell surface hydrophobicity (CSH) production were also studied to support the antibiofilm potential of GE. In addition, S. epidermidis was examined for its adaptive resistance development upon continuous exposure of GE at its subinhibitory concentrations.Results/Key findings. The MIC of GE against S. epidermidis was 512 µg ml-1. Without hampering the growth of the pathogen, GE at its sub-MICs (50, 100, 150 and 200 µg ml-1) exhibited a dose-dependent increase in antibiofilm activity. The minimal biofilm inhibitory concentration (MBIC) of GE was found to be 200 µg ml-1 with a maximum biofilm inhibition of 85 %. Disintegrated biofilm architecture, reduced EPS, slime and CSH production validated the antibiofilm efficacy of GE. Although the action of GE on preformed biofilm is limited, a 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide (XTT) reduction assay and live/dead cell staining method revealed reduction in the viability (47 %) of biofilm inhabitants at 2×MIC concentration. Sequential exposure of S. epidermidis to the sub-MICs of GE resulted in poor development of adaptive resistance with diminished biofilm formation. CONCLUSION: The present study highlights the potential of GE as a suitable candidate for the control of biofilm-mediated S. epidermidis infections.

In vitro activity of alpha-mangostin in killing and eradicating Staphylococcus epidermidis RP62A biofilms.

Alpha-mangostin (α-MG) has been reported to be an effective antibacterial agent against planktonic cells of many Gram-positive bacteria. However, the antibiofilm potency of α-MG remains unexplored till date. In this study, the antibiofilm and mature biofilm eradication ability of α-MG against Staphylococcus epidermidis RP62A (ATCC 35984) biofilms were evaluated. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of α-MG against S. epidermidis RP62A were found to be 1.25 and 5 µg/mL, respectively. α-MG exhibited a phenomenal concentration dependent rapid bactericidal activity (>4-log reduction within 5 min). In a multi-passage resistance analysis using S. epidermidis, no development of resistance to α-MG as well as antibiotics was observed in its habituation. α-MG at its 1/2 MIC effectively inhibited the initial biofilm formation of S. epidermidis, which was further confirmed through scanning electron microscopic (SEM) analysis that portrayed a lucid reduction in the aggregation and the spread of biofilm. The crystal violet staining and viable cell quantification results confirmed the eradication of preformed immature and mature biofilms of S. epidermidis by α-MG in a concentration dependent manner. Besides, the biofilm eradication ability was also confirmed through SEM and live/dead BacLight staining using confocal laser scanning microscopy (CLSM). Thus, the present study exemplifies that α-MG could plausibly assist to eliminate biofilm infections associated with multidrug-resistance staphylococci.

Anti-biofilm mechanisms of 3,5-di-tert-butylphenol against clinically relevant fungal pathogens.

The methanolic extract (PFME) of Pleurotus florida was assessed for anti-biofilm activity against Candida species. 3,5-Di-tert-butylphenol (3,5-DTB) was identified as the major antifungal constituent in PFME. In its pure form 3,5-DTB inhibits, disrupts, and reduces the viability of biofilm cells as seen from scanning electron and confocal microscopy studies. Microscopic studies and propidium iodide uptake assays confirmed that 3,5-DTB damages the cell membrane of Candida cells. In addition, 3,5-DTB induces accumulation of reactive oxygen species (ROS) which contribute to its pronounced anti-biofilm activity. The results of the present study show that 3,5-DTB exhibits combined anti-biofilm and conventional fungicidal activity against Candida species and elucidate the underlying mechanisms.

Production of naphthoquinones and phenolics by a novel isolate Fusarium solani PSC-R of Palk Bay and their industrial applications.

The present study was attempted to enhance the production of naphthoquinones and phenolics by Fusarium solani PSC-R of Palk Bay origin, which exhibited potent antibacterial, antioxidant and dyeing activity. Maximum productivity of naphthoquinones and phenolics was achieved in potato infusion medium supplemented with 2% sucrose. Addition of nitrogen sources to the medium adversely affected the production of both naphthoquinones and phenolics. An initial pH of 5 and incubation at 31°C for six days at 140rpm was found to increase the yield (123.65mg/g of DW), concentration (867.33mg/l) and total naphthoquinones (602.8µM/g DW) by 7.58, 10.44 and 3.68-fold respectively. Similarly, the antioxidant and antibacterial activity associated with the phenolics of PSC-R increased by 1.5-fold in the optimized medium. The obtained results document the effective means of enhanced production of naphthoquinones and phenolics in the suspension culture of F. solani PSC-R at bioreactor level.

Inhibition of Streptococcus pyogenes biofilm formation by coral-associated actinomycetes.

Streptococcus pyogenes biofilms tend to exhibit significant tolerance to antimicrobials during infections. We screened coral-associated actinomycetes (CAA) for antibiofilm activity against different biofilm forming M serotype of Streptococcus pyogenes. Actinomycetes isolated from the mucus of the coral Acropora digitifera were screened for antibiofilm activity against S. pyogenes biofilms wherein several isolates clearly demonstrated antibiofilm activity. The biofilm inhibitory concentrations (BICs) and the sub-BICs (1/2 and 1/4 BIC) of the extracts significantly prevented biofilm formation up to 60-80%. The extract of Streptomyces akiyoshinensis (A3) displayed efficient antibiofilm activity against all the biofilm forming M serotypes. All the five extracts efficiently reduced the cell surface hydrophobicity (a crucial factor for biofilm formation in S. pyogenes) of three M types and thus may inhibit biofilm formation. CAA represent an interesting source of marine invertebrates-derived antibiofilm agents in the development of new strategies to combat Streptococcal biofilms.

Antibiofilm activity of coral-associated bacteria against different clinical M serotypes of Streptococcus pyogenes.

Streptococcus pyogenes is the frequent cause of purulent infections in humans. Formation of a biofilm is one of the important aspects of its pathogenicity. Streptococcus pyogenes biofilm communities tend to exhibit significant tolerance to antimicrobial challenge during infections. Exploring novel targets against biofilm-forming pathogens is therefore an important alternative treatment measure. We attempted to screen marine bacteria, especially coral-associated bacteria (CAB), for antibiofilm activity against streptococcal biofilm formation. The bacterial biofilms were quantified by crystal violet staining. Of 43 CAB isolates, nine clearly demonstrated antibiofilm activity. At biofilm inhibitory concentrations (BIC), biofilm formation was reduced up to 80%, and sub-BIC (0.5 and 0.25 BIC) significantly reduced biofilm formation by up to 60% and 40-60%, respectively. Extracts of Bacillus horikoshii (E6) displayed efficient antibiofilm activity. As quorum sensing (QS) and cell surface hydrophobicity (CSH) are crucial factors for biofilm formation in S. pyogenes, the CAB were further screened for QS inhibition properties and CSH reduction properties. This study reveals the antibiofilm and QS inhibition property of CAB.