I prepared Salmonella Typhimurium and Salmonella Enteritidis cocktail. I measured the OD value of each single species and also the cocktail. OD value for the cocktail (mixture of both) is slightly lower than each single species. Why could it be?
Hello,
It is only a guess, but , could it be that when mixing the two strains there has been an aggregation? If lumps have formed or the mixture have precipitated you could obtain lower OD values.
the OD was measured at 0 hour or after incubation?
the initial inoculate size was equal for the single strains and the mixture?
if one of the strains has antagonistic activity against the other strain, it is possible to give lower OD.
It is possible that OD of single strain is more than of mixed culture, because of competitive and possible antagonism or commonsalism obtained between mixed cultures.
There is also possibility that both species have different incubation time. And they are not the strains, they are the different species of Salmonella
One important phenomenon is competition among different strains. Competition for space and food, by simple example if you see a bus overloaded where there are either only males or only females the count will always be much higher than the bus where both both male and female subjects are there, i.e., a minimum distance is to be maintained among individuals of two strains.
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