Can I first measure the OD of 0.5Mc farland by spectrophotometer, then I dilute the bacteria (E.coli & S.aereus) until I get the same OD value as Mc Farland by spectrophotometer in order to obtain 1.5x10^8 ?
Yes, and note that this is a standard microbiological method for estimating / quantifying microbial number in saline. For best accuracy you should first quantify your bacterial cell suspension by plate count and correlate results with measurements against your McFarland standards. Absolute bacterial counts vary when correlated with McFarland scale readings and are influence by microbe size and shape as well as number. Bacterial number, size and shape influence McFarland measurement. Once you determine the correlation between bacterial number (specific isolate) with McFarland value you can use the McFarland reading to calculate bacterial number in future experiments. The typical and well published correlations between bacteria and McFarland values are estimates only.
Thank you for Dr.Frank and Dr.Singh. Your explaination was really helpful for me.
Thank you for Dr.Shweta and Shervin too.
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