In vitro antibacterial and early stage biofilm inhibitory potential of an edible chitosan and its phenolic conjugates against Pseudomonas aeruginosa and Listeria monocytogenes.

In the present study, the antibacterial potential of chitosan grafted with phenolics (CPCs) such as caffeic acid (CCA), ferulic (CFA), and sinapic acid (CSA) were evaluated against foodborne pathogens like Pseudomonas aeruginosa (PA) and Listeria monocytogenes (LM). The geometric means of minimum inhibitory concentration (MIC range 0.05-0.33 mg/ml), bactericidal concentration (MBC range 0.30-0.45 mg/ml), biofilm inhibitory concentration (BIC range 0.42-0.83 mg/ml), and biofilm eradication concentration (BEC range 1.71-3.70 mg/ml) of CPCs were found to be lower than the MIC (0.12-1.08 mg/ml), MBC (0.17-1.84 mg/ml), BIC (4.0-4.50 mg/ml), and BEC (17.4-23.0 mg/ml) of unmodified chitosan against PA and LM. CPCs attenuated the biofilms of PA and LM by increasing the membrane permeability of bacteria embedded within the biofilms. Further, sub MIC of CPCs (0.5 × MIC) significantly reduced the biofilm adhesion (p < 0.001) by representative strains of LM (CCA: 72.2 ± 3.5, CFA: 79.3 ± 0.9, and CSA: 74.9 ± 1.5%) and PA (CCA: 64 ± 1.1, CFA: 67.8 ± 0.8, and CSA: 65.7 ± 4.9%). These results suggested the antibacterial and anti-biofilm potential of CPCs that can be exploited to control foodborne pathogenic infections.

Antibacterial activity of Staphylococcus aureus biofilm under combined exposure of glutaraldehyde, near-infrared light, and 405-nm laser.

Healthcare-associated infections have increasingly become problematic in the endoscopic procedures resulting in several severe diseases such as carbapenem-resistant Enterobacteriaceae (CRE)-related infections, pneumonia, and bacteremia. Especially, some bacterial strains are resistant to traditional antimicrobials. Therefore, the necessity of developing new antibiotics or management to deal with bacterial infections has been increasing. The current study combined a low concentration of glutaraldehyde (GTA) with near-infrared (NIR) light and 405-nm laser to entail antibacterial activity on Staphylococcus aureus biofilm. MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay and colony forming unit (CFU) counting were used to quantify the viable cells while fluorescent and scanning electron microscopic images were used to qualitatively evaluate the cell membrane integrity and structural deformation, respectively. Practically, S. aureus biofilm was highly susceptible (7% cell viability and 6.8-log CFU/cm2 bacterial reduction for MTT assay and CFU analysis, respectively) to the combination of GTA (0.1%), NIR light (270 J/cm2), and 405-nm laser (288 J/cm2) exposure. GTA could form either DNA-protein or protein-protein crosslinks to inhibit DNA and protein synthesis. The NIR light induced the thermal damage on protein/enzymes while 405-nm laser could induce reactive oxygen species (ROS) to damage the bacterial membrane. Thus, the proposed technique may be a feasible modality for endoscope cleaning to prevent any secondary infection in the healthcare industry.

Antibacterial and Biofilm Modulating Potential of Ferulic Acid-Grafted Chitosan against Human Pathogenic Bacteria.

The emergence of more virulent forms of human pathogenic bacteria with multi-drug resistance is a serious global issue and requires alternative control strategies. The current study focused on investigating the antibacterial and antibiofilm potential of ferulic acid-grafted chitosan (CFA) against Listeria monocytogenes (LM), Pseudomonas aeruginosa (PA), and Staphylococcus aureus (SA). The result showed that CFA at 64 µg/mL concentration exhibits bactericidal action against LM and SA (>4 log reduction) and bacteriostatic action against PA (<2 log colony forming units/mL reduction) within 24 h of incubation. Further studies based on propidium iodide uptake assay, measurement of material released from the cell, and electron microscopic analysis revealed that the bactericidal action of CFA was due to altered membrane integrity and permeability. CFA dose dependently inhibited biofilm formation (52⁻89% range), metabolic activity (30.8⁻75.1% range) and eradicated mature biofilms, and reduced viability (71⁻82% range) of the test bacteria. Also, the swarming motility of LM was differentially affected at sub-minimum inhibitory concentration (MIC) concentrations of CFA. In the present study, the ability of CFA to kill and alter the virulence production in human pathogenic bacteria will offer insights into a new scope for the application of these biomaterials in healthcare to effectively treat bacterial infections.

In Vitro Antibacterial Activity of Phlorotannins from Edible Brown Algae, Eisenia bicyclis Against Streptomycin-Resistant Listeria monocytogenes.

Listeria monocytogenes (LM) is an important food borne pathogen responsible for listeriosis. Further, LM is an etiological agent associated with life threatening conditions like meningitis and encephalitis. Biofilm forming and drug resistant LM may potentially become difficult to treat infections and hence effective controlling measures are required to prevent LM infections. In view of this, the present study evaluated an anti-listerial potential of edible brown seaweed, Eisenia bicyclis, by disc diffusion and micro-dilution methods. The results of the present study suggested that the anti-listerial activity of various phlorotannins isolated form E. bicyclis were in the range of 16-256 µg/ml. Among the phlorotannins isolated, fucofuroeckol-A (FAA) exhibited the highest anti-listerial potential (MIC range 16-32 µg/ml) against LM strains tested. Further, in checker board synergy assays, FFA-streptomycin combination exhibited significant synergy (fractional inhibitory concentration index, ∑FIC < 0.5) against aminoglycoside resistant clinical strains of LM. The results of the present study suggested the potential use of edible seaweed E. bicyclis as a source of natural phlorotannins to control food borne pathogenic infections.

7,10-Epoxyoctadeca-7,9-dienoic Acid: A Small Molecule Adjuvant That Potentiates ß-Lactam Antibiotics Against Multidrug-Resistant Staphylococcus aureus.

The emergence of methicillin-resistant Staphylococcus aureus (MRSA) infections with multi-drug resistance needs effective and alternative control strategies. In this study we investigated the adjuvant effect of a novel furan fatty acid, 7,10-epoxyoctadeca-7,9-dienoic acid (7,10-EODA) against multidrug-resistant S. aureus (MDRSA) strain 01ST001 by disc diffusion, checker board and time kill assays. Further the membrane targeting action of 7,10-EODA was investigated by spectroscopic and confocal microscopic studies. 7,10-EODA exerted synergistic activity along with ß-lactam antibiotics against all clinical MRSA strains, with a mean fractional inhibitory concentration index below 0.5. In time-kill kinetic study, combination of 7,10-EODA with oxacillin, ampicillin, and penicillin resulted in 3.8-4.2 log10 reduction in the viable counts of MDRSA 01ST001. Further, 7,10-EODA dose dependently altered the membrane integrity (p < 0.001) and increased the binding of fluorescent analog of penicillin, Bocillin-FL to the MDRSA cells. The membrane action of 7,10-EODA further facilitated the uptake of several other antibiotics in MDRSA. The results of the present study suggested that 7,10-EODA could be a novel antibiotic adjuvant, especially useful in repurposing ß-lactam antibiotics against multidrug-resistant MRSA.

Antimicrobial activity of a novel furan fatty acid, 7,10-epoxyoctadeca-7,9-dienoic acid against methicillin-resistant Staphylococcus aureus.

We analyzed the antimicrobial potential of a novel furan fatty acid, 7,10-epoxyoctadeca-7,9-dienoic acid (7,10-EODA) against methicillin-resistant and -sensitive S. aureus (MRSA and MSSA). The anti-staphylococcal activity of 7,10-EODA and its consequences on cell physiology was determined by disc diffusion, broth microdilution, and flow cytometry. Anti-virulence activity of 7,10-EODA was evaluated by bioassays. 7,10-EODA was anti-staphylococcal with minimum inhibitory concentration (MIC) range of 125-250 mg/L. 7,10-EODA exhibited a dose response and inhibited MRSA 01ST001 by 90.5% and ATCC 29213 (MSSA) by 85.3% at 125 mg/L. MIC of 7,10-EODA permeabilized >95 % of MRSA 01ST001 cells to small molecules. Sublethal dose of 7,10-EODA was non-toxic but markedly reduced the hemolytic, coagulase, and autolytic activities of MRSA and MSSA at 15.6 mg/L. The results provide a lead for the utilization of natural furan fatty acids as novel anti-MRSA agents.