In order to be sure about contamination on my work desk, I prepared Nutrient Agar plates on the desk and then put some of them in incubator at 37C for 48hrs. There were not any contamination when I examined the petries visually. Now, I want to know that whether I can use the incubated petries for culture of bacteria? If so, will it be safer to culture bacteria in incubated petries?
Ideally no. If something already started growing by the end of the first experiment and if it shows up in your actual experiment it may be a false positive!
Hi Hamed,
Yes you can use the agar plates that are incubated and it is one of the best methods to remove any contamination issues in your experiments. Ideally after poring the nutrient agar into the petri plates you can incubate them at 37 degrees for 18 - 24 hrs, observe the plates for visual growth of the bacteria i.e. contamination if any. Then these plates can be kept in normal refrigerator until used. This procedure helps the microbiologist in discarding the contaminated plates and using only the good ones.
I would suggest this procedure if your are planning to carry out a big experiment involving a large number of plates and there is nothing wrong in this procedure.....
All the best in your work..
Amarnath Pisipati
Icubation is essential but when culture plates are fully dry then there are minimum chance of contamination but not always. So Plates should be incubate in order to dry plates in incubater rather than opn dry.
U can not use the same plate as u cant be confident about spores with 24h/ 48h observation
You can use it, but ensure that your plate previously not contaminated with any organisms.......
Yes you can use this plate provided you are not growing any moisture loving bacteria such as B.pertussis.
If you are working with aerobic and "fast" growing microorganisms, there should not be a problem, however if you are working with slow growing bacteria I would leave the plates a further 24h at 37ºC... If no bacteria grew in the plates, the nutrients present have not been spent and an be used for you experiment
Just make sure they don't dry out at all. I presume you have wrapped them in parafilm?
You incubated 2-3 plates as control to be sure that the batch of plates are not pre-contaminated, and you like to re-use the control plates that are free from any sign of growth, is that wright? If it's Ok, the answer is you can not use the incubated plates even it is free from any growth. Incubation usually carried out at 35-37 C for 24-48 hrs, during incubation the media loose water by evaporation, then the nutrients in the media increased in concentration than the original media and so it become not the same as the freshly prepared standard media. Moisture content is essential for cell viability and nutrient diffusion into the cell to multiply and giving colonies. Please kindly check the part on quality control/quality insurance in Standard Methods.
Dear sir, u can do but when you use many Nutrient agar plates pls keep one plate as a control and use all other plates for contamination test because that control is used to identify the plate contamination.
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