Problems with bacterial growth! help! - (Jan/08/2007 )
Hi all,
I'm currently working on a project on enumeration of bacteria from water samples. I'm facing a problem now. I've actually performed serial dilution on the samples collected. Results turned out to be problematic.
The colonies appearance is not as expected (Diluted tubes having no growth). Instead, some of the more diluted tubes turned out to have colonies. this becomes pretty hard for me to draw significant impact or conclusions from the results obtained. I'm writing to ask what may have gone wrong? Has someone encountered similar problems?
Thank you! anyone with solutions can email shilinchen@hotmail.com. thanks alot:)
Mameemoo
How did you do your dilutions? serial?
maybe you have contamination, that's why you see some bacteria growing in the highly diluted samples, not coming from the dilution, but rather from a contamination.
maybe you have contamination, that's why you see some bacteria growing in the highly diluted samples, not coming from the dilution, but rather from a contamination.
Hi,
thank you for your reply! I did serial dilution. Such observations occur all the time. Any suggestions? I did serial dilution under aseptic conditions. thank you!
mameemoo
but are you plates, tips and dilution water sterile?
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Hi Friend,
Seems u have some problem with ur tips or mixing. Ensure that u use different sterile tips for each dilution... While transferring from one tube to another tube, generally we pipette out the sample into the next tube and mix the contents with the same tips. Avoid this. Discard the tips after u transfer the sample and use a fresh sterile tip for mixing the content. If we mix with the same tip, the organisms adhering to the outer side of the tips (which we think is negligible) cause a great deal of confusion while we analise the results. Also ensure u mix the dilutions evenly after each tansfer. Try this... May work out...
First off I'm wondering why, if you expect the diluted tubes to have no growth, you are doing dilutions at all?
How many dilutions are you doing? Do you get similar levels of growth at each dilution? Do you get the growth in some tubes, but not others?
Run some negative controls on your dilution medium. If you get growth there, whatever you are using for diluting the samples is probably contaminated. If you don't then it is probably either tips or technique.