Additionally to contamination (investigatable pre-usage), I anticipate that spreaders are likely to be more (or less) common depending on the specific product / microbial profile.
(IMEX of seafood/coated seafood some spreading is inevitable but frequent is not.)
I anticipate that also more likely for high bacterial levels on plate, eg NRTE, PHF foods.
As per my link, Bacillus group appears common for milk. i suspect for various other product also (haven't looked up book details as yet).
Hence my queries.
Thank you for the clarification! :) I highly agree that high bacterial levels on plate will most likely result in spreader "spr" colony formation as this is the result of using low dilutions when you have high microbial load.
And to address some of your questions
-food products that are likely to have mold contamination are best candidates for spr formation. This is due to the filamentous characteristic of mold colonies.
-As for plating method, when using conventional agar media, it is easier to have spr in pour plating method compared to spread plate. But when using 3M petri plates, it is almost close to impossible to have spr formation except when there is excess liquid plated
-lastly, spr colonies may persist in spread plate method if agar plates used during testing were not allowed to dry and age for atleast 24 h
Btw, I would like to clarify that I am referring to spr colonies that are considered as "laboratory accidents" where you can no longer obtain a plate count because of the obstruction because it covers half or more than half of the area of the plate.
The difference in colony size as depicted in some of the pictures earlier posted are due to inherent characteristics of a particular organism. It is also a must to have knowledge of the general microflora of the product and its morphology when evaluating plate count tests. This will allow the experimenter to differentiate target microflora from unwanted contamination, in this case, spr colonies
Hope I was able to attend to your queries,
Many thanks and regards,