Question

After performing a spread plate method on a bacterial specimen, the culture was incubated for 48 hours at 37°C. Upon viewing the plate, there was heavy growth with no isolated colonies. Please discuss the errors in the procedure that could have produced this result.

Answer 1

there are possibly three things that might have resulted in this kind of error.

1) the amount of sample used for spreading plays a crucial role here. generally for a 25ml plate, we spread a 100uL of bacterial culture. If it is a lot more than that, it might result in a formation of a lawn rather than an individual colony.

2) second thing that can do this is the dilution that was performed before spreading the bacterial culture. The bacterial cells are present in a huge number in a solution so directly plating them would also result in the formation of lawn. A sample from natural sources is serially diluted to the power of 8-9 to observe seperate colonies.

3) Last and what seems to be the problem is the incubation time for the plates. We generally grow a bacteria at temperature of 37, but most of the bacteria are very quickly growing and a visible colony is obtained just after 12-16 hrs. So, incubating it 48 hrs would always show an overgrowth and this seems to be the issue from experiment.

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