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Plates were incubated at 370.5C for 24 h. Microbial inhibition was visually evaluated as the diameter of the inhibition zones surrounding the disks, including them, and recorded in millimeters according to NCCLS ( 2015 ).Published online 2016 Dec 1.PMCID: PMC5178834 PMID: 28058251 Evaluation of the Antibacterial Activity of Bergamot Essential Oils on Different Listeria Monocytogenes Strains Stefania M.
Essential Oil University Database License Information DisclaimerMarotta, Filippo Giarratana, Alessio Parco, Domenico Neri, Graziella Ziino, Alessandro Giuffrida, and Antonio Panebianco Author information Article notes Copyright and License information Disclaimer Department of Veterinary Sciences, University of Messina, Messina, Italy Department of Veterinary Sciences, University of Messina, Polo Universitario della Annunziata, 98168 Messina, Italy. Conflict of interest: the authors declare no potential conflict of interest. Received 2016 Jul 19; Revised 2016 Sep 22; Accepted 2016 Sep 22. Copyright S.M. Marotta et al., 2016 This work is licensed under a Creative Commons Attribution 3.0 License (by-nc 3.0). This article has been cited by other articles in PMC. Abstract Essential oils are aromatic and volatile substances extracted from plants and characterized by antimicrobial activity. The aim of the present study was to evaluate the antibacterial activity (agar disc-diffusion method) of seven different bergamot essential oils (BEOs) on eight Listeria monocytogenes strains. Minimal inhibitory concentration (MIC) of most efficient BEOs was estimated. ![]() One of the tested microorganisms resulted insensible to all the BEOs; 3 strains showed an inhibition from weak to null and the remaining 4 a variable susceptibility. Among the BEOs tested, one showed a strong activity against four pathogenic strains. Four BEOs revealed weak, moderate or null activity in all the 7 sensitive strains, while for two oils only a weak or no activity was reported. MIC values were 0.625 LmL for the most efficient BEO, 2.5 and 5 LmL for the other samples that showed moderate inhibition. Experiment results are significantly related to the strains tested (P 0.01). In conclusion, we can consider BEO as a natural technological hurdle for Listeria monocytogenes in combination with other preservation strategies. Finally, this study underlines the necessity to evaluate the antimicrobial activity of EOs on a significant strains number of the same bacteria. Key words: Listeria monocytogenes, Bergamot, Essential oils, Antibacterial activity Introduction The interest in natural methods that can make food safer, avoiding the use of chemical preservatives or additives, has increased the study on these products (Giarratana et al., 2013, 2016; Klein et al., 2013; Moreira et al., 2005; Muscolino et al., 2016 ). ![]() The aim of this study was to evaluate the in vitro antimicrobial activity of different BEOs against several Listeria monocytogenes strains. Materials and Methods Essential oils collection For this study, seven different samples of Citrus bergamia Risso essential oil (BEO) were tested. Among these, five were collected from local producers from Reggio Calabria district (BEOa-e), while, the remaining two from commercial products (BEOf: Mystic moments, Fordingbridge, UK; BEOg: Erboristeria magentina, Poirino, Italy). Bacterial cultures Eight Listeria monocytogenes strains were tested: five from seafood samples (wild types) and three from American Type Culture Collection (ATCC) ( Table 1 ). Working cultures were prepared by inoculating a loopful from the frozen stock (-80C), on tryptic soy broth (Biolife, Milan, Italy) 0.6 yeast extract (YE) (Biolife) and then incubated at 370.5C for 24 h, in order to achieve an OD 600 of 1.2, corresponding to 10 9 colony forming unitmL (SmartSpec Plus; Bio-Rad, Milan, Italy). Table 1. Listeria monocytogenes strains. ID strains Serotype Origin 94me - Wild type - smoked salmon fillets 115me - Wild type - smoked salmon fillets 157me - Wild type - smoked salmon fillets 163me - Wild type - fresh salmon fillets 168me - Wild type - fresh salmon fillets ATCC 13932 4b Human ATCC 19111 12 Poultry ATCC 7644 12c Human Open in a separate window ATCC, American Type Culture Collection. ![]() Broth cultures strains were spread with a sterile swab on the surface of TSA (Biolife) 0.6 YE agar plates. Sterile 6-mm paper disc impregnated with 15 L of each tested BEOa-g were placed on the surface of inoculated plates. Two disks impregnated one with 15 L of Streptomycin (50 pgmL) (Biolife) and one with 15 L of sterile distilled water as positive and negative control were used respectively. Plates were incubated at 370.5C for 24 h. Microbial inhibition was visually evaluated as the diameter of the inhibition zones surrounding the disks, including them, and recorded in millimeters according to NCCLS ( 2015 ).
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