Listeria Innocculosis

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The aims of this experiment were to investigate the inhibitory power of nisin on Listeria innocua and determine the minimum inhibitory concentration (MIC) of nisin on this bacterium. This was evaluated by inoculating a sterilized slice of mozzarella cheese with a known concentration of L. innocua and nisin. Then after incubation at 7°C for 5 days, the log10 reduction value was calculated. Nisin’s effect on L. innocua’s growth was also evaluated via microdilution, with the goal of determining the MIC. The bacteria grew to a much higher concentration on the mozzarella cheese after being exposed to nisin and incubated at 7°C for 5 days and the microdilution procedure was unable to confidently determine the MIC of nisin on L. innocua. These results …show more content…

This efficacy can be analyzed via various antimicrobial tests such as E-tests, disc diffusion, agar dilution, and microdilution. E-tests assess antimicrobial properties by applying a concentration gradient using strips on an agar plate inoculated with the microorganism of interest. The inhibition zones can then be assessed surrounding each strip of known antimicrobial concentrations. Disc diffusion uses this same procedure; however, the antimicrobial is applied to small discs rather than a strip. Agar dilution quantifies an effective antimicrobial concentration by using multiple agar pour plates containing increasing concentrations of the inhibitory compound. The minimum inhibitory concentration (MIC) can then be determined by identifying the agar plate with the lowest concentration that did not support growth. Microdilution – the antimicrobial test conducted in this experiment – determines the MIC by filling the wells of a microtiter plate with decreasing concentrations of the antimicrobial. Micrograms are then added to the wells at a standardized concentration and the plate is incubated for 24-49 hours and the optimal temperature. Growth in these wells is then determined by measuring the turbidity (OD600) of the broths. Thus, the MIC identified as the well with the lowest concentration of the antimicrobial that inhibits …show more content…

Listeria innocua is a surrogate microorganism for Listeria monocytogenes, for it is a relatively harmless microorganism that has similar resistance properties to its pathogenic relative. The aims of this experiment were to determine the MIC of nisin on Listeria innocua and to examine the growth inhibition effectiveness of this compound when combined with Listeria innocua on a slice of sterilized mozzarella cheese. The hypotheses of this experiment were that nisin would act to decrease the concentration of Listeria innocua bacteria on the mozzarella slice and that the MIC would be quantified via microdilution. The expected results were that the CFU/ml of Listeria innocua after treatment of nisin on mozzarella cheese would be lower than the initial concentration and that a distinct increase in turbidity of a set of wells would be apparent in the microtiter after incubation, providing the MIC of nisin on Listeria

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