title: Synergistic action of cinnamaldehyde with silver nanoparticles against spore-forming bacteria: a case for judicious use of silver nanoparticles for antibacterial applications.
abstract: Silver has long been advocated as an effective antimicrobial. However, toxicity issues with silver have led to limited use of silver in nanoform, especially for food preservation. With the aim of exploring combinatorial options that could increase the antibacterial potency of silver nanoparticles and reduce the effective dosage of silver, we evaluated the extent of synergy that a combination of silver nanoparticles and an essential oil representative (cinnamaldehyde) could offer. A battery of gram-positive and gram-negative bacterial strains was utilized for antibacterial assays, and extents of synergism were calculated from fractional inhibitory concentration indices. The activity of nanoparticles was greatly enhanced when utilized in the presence of cinnamaldehyde. We observed combinatorial effects that were strongly additive against all the bacterial strains tested, and genuine synergy was found against spore forming Bacillus cereus and Clostridium perfringens - bacterial strains associated with release of cytotoxins in contaminated food and known for their persistence. Bacterial kill curve analysis revealed a very fast bactericidal action when a combination of two agents was used. The electron and atomic force microscopy also revealed extensive damage to the bacterial cell envelop in the presence of both agents. We also performed hemolysis assays to investigate and approximate the extent of toxicity exhibited by the two agents, and observed no adverse effect at the concentrations required for synergy. This study shows that safe levels of silver in nanoform in combination with essential oil component cinnamaldehyde can be effectively used for controlling the spore-forming bacterial species.
authors.affiliation: Department of Biotechnology, Indian Institute of Technology Roorkee, Roorkee, Uttarakhand, India.
authors.forename: Indro Neil
authors.initials: IN
authors.lastname: Ghosh
authors.affiliation: Department of Biotechnology, Indian Institute of Technology Roorkee, Roorkee, Uttarakhand, India.
authors.forename: Supriya Deepak
authors.initials: SD
authors.lastname: Patil
authors.affiliation: Department of Biotechnology, Indian Institute of Technology Roorkee, Roorkee, Uttarakhand, India ; Center for Biodesign and Diagnostics, Translational Health Science and Technology Institute, Gurgaon Haryana, India.
authors.forename: Tarun Kumar
authors.initials: TK
authors.lastname: Sharma
authors.affiliation: Department of Biotechnology, Indian Institute of Technology Roorkee, Roorkee, Uttarakhand, India.
authors.forename: Santosh Kumar
authors.initials: SK
authors.lastname: Srivastava
authors.affiliation: Department of Biotechnology, Indian Institute of Technology Roorkee, Roorkee, Uttarakhand, India.
authors.forename: Ranjana
authors.initials: R
authors.lastname: Pathania
authors.affiliation: Department of Biotechnology, Indian Institute of Technology Roorkee, Roorkee, Uttarakhand, India.
authors.forename: Naveen Kumar
authors.initials: NK
authors.lastname: Navani
mesh_terms: D000171:Acrolein / Q000031:analogs & derivatives* / Q000737:chemistry / Q000494:pharmacology; D000900:Anti-Bacterial Agents / Q000737:chemistry / Q000494:pharmacology*; D001419:Bacteria / Q000187:drug effects*; D004357:Drug Synergism; D004912:Erythrocytes; D006461:Hemolysis / Q000187:drug effects; D006801:Humans; D053768:Metal Nanoparticles / Q000737:chemistry*; D008826:Microbial Sensitivity Tests; D050296:Microbial Viability / Q000187:drug effects; D012834:Silver / Q000737:chemistry / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; D012834:Silver; D000171:Acrolein; C012843:cinnamaldehyde
keywords: antibacterial activity; bacterial food spoilage; erythrocyte toxicity; essential oil; in vitro; synergy; toxin producing spore-forming bacteria