Hi Nidhi,

Can you be a little descriptive? Since I am unable to understand you properly. I do have a question, though. When you say bacterial culture, do you mean that it already has the inoculum and then you have detected a contamination or you've prepared the media and it got contaminated somehow?

I have prepared nutrient broth and inoculated 3 isolated bacterium from nutrient agar plates with the help of loop and one test tube was taken as control. After 24 hrs all the 4 tubes were found with some turbidity. so I thought that the control which was not inoculated with any sample got contaminated means all the cultures might have that contamination.

Hi Nidhi,

You can check the following:

1. Check the autoclave. The simplest would be to use autoclave tapes. See if the pressure is proper when using it next time.

2. Check the BSL hood where you're working. You can simply put a plate in there for some time and then incubate it. See if something is growing there.

3. If you're using screw cap tubes, make sure you tighten them up properly. If you're using cotton plugs, be careful while handling them. Good handling and use of good aseptic technique is a must.

4. If you've selective media available, then you can check the 'purity' of your culture by streaking or spreading (after serial dilution). Check the 'control' tube too to see the nature of the possible contaminant.

5. You could've had them checked by measuring the OD in a spectrophotometer. That would've given you a rough idea of the time when the purity of the control tube was compromised. But a 24 hours old tube would've hardly given you that idea anyway.

These are some general tips. Best of luck with your experiment.

Cheers.

Actually autoclave tape is far from being guaranteeing that your items were sterilised, it merely show they were exposed to high temp and steam for some time. Indeed in some cases colour will change after 10 min at 121C. Bacillus spores are much better indicator though an expensive one. Also keep in mind that large volumes (>1L) of liquid will need longer then 20 min-121C, a simple issue of heat capacity.

Yoram

Thank you Sir Debaki Ranjan and sir Yoram Gerchman for your valuable suggestions.

yes I keep the plugs of tube very tight next time I will try to do according to your suggestions. Thanks a lot for such a valuable information.