I am trying to test for the efficacy of essential oils as antimicrobials against Listeria and Salmonella in soft cheese. I will be working with inoculum levels of 100cfu/ml and 10000cfu/ml because they are levels of detection. my question is how I can achieve these two levels of inoculum accurately.
You have to use the spectrophotometer. For essential oils, if you want to check the MIC and MBC, you can make the con according to McFarlands standard and proceed with 96 well plates.
Has anyone used the Rapid automated bacteria impedance technique to assess antimicrobial effects of essential oils?
As Dr Druggan suggested, absorbance is very useful, nevetheless it is necessary to standardize each single strain that you are going to test, as within the same species, different strains could have different cell size and different growth dynamics.
You can avoid spectrophotometer at the following procedure - concider that photometer messures also all your dead cells!
Take an fresh overnight culture and make a decimal dilution line in a broth. Incubate the whole dilution line at 37°C for 3-4 h. Than choose the tube lower than the one with slightest turbidity - this should be 107 cfu/ml. Now it is easy to achieve a 102 and a 104 inoculum, which additionally can be confirmed by plating on agar. Works very good with Listeria and Salmonella. That´s how a microbiologist would do.
Dear Bruno, I recomend you M26-A, M07-A8 and M100_S21 NCCLS - CLSI protocols.