Due to CLSI and EUCAST Guidelines the answer is NO
The Clinical And Laboratory Standard Institute (CLSI) recommends in its guideline M7 to "prepare the inoculum by making a direct broth or saline suspension of isolated colonies selected from an 18-24 hrs agar plate (a nonselective medium, such as blood agar, should be used)".
Citing this, I would answer your question with "No". You should keep in mind that susceptibility testing procedures are adapted for bacteria in their logarithmic growth phase. If you store a culture, already grown, at 4C overnight, the bacteria are no longer in logarithmic growth phase. But, why storing overnight and not adjusting your schedule to have the 18-24 hrs incubation finished at the time you start your sensitivity test?
Hello Mac,
In my lab, antibiotic disc diffusion assays are quite frequent and one thing I can tell is that the cultures should in log phase for the assay to be done. culture plates are kept in 4OC only for storage and if you want to do any experiment then try to use fresh inoculum in any desired media that should be about 16-20 hrs old.
I would not recommend to do so. Several bacteria are sensitive to such a low temperature and may be stressed. They mayweed time to recover a normal growth rate.
No this will not work as temperature sensitive groups may die.
No , you should Prepare the inoculum for seeding the antimicrobial susceptibility media from fresh cultures of bacteria
I would not recommend to use that. In general, it would be ideal to use bacteria in logarithmic growth phase for such a sensitivity test. I would encourage you to reschedule so that you can assay in moderate timing. Also, international standard methods such as CLSI will be helpful for you.
For all the reasons indicated above, not the best choice. Unless you do parallel testing you probably won't notice the difference. I experienced the loss of ESBL encoding plasmid in Klebsiella pneumoniae ATCC 70063 when the BA plate is kept over the weekend in the fridge.
I think it is not a good choice, BUT we have colleague, that they do a special work on Friday, after doing a regular procedure as CLSI; then inoculated plate plus disc antibiotic store at 4 C until sunday, and then Sunday afternoon, put it in Incubator overnight, for identify the result the next day (Monday).
I never read any publication accordingly about this
I would doubt that. The idea behind the standardization of the disc susceptibility test is to have the same conditions every time we perform it. When you keep a plate in the refrigerator overnight there is a number of unknown possible changes the may have an impact on the results of the tests. Among these, the influence of the refrigeration on the bacteria (some may be weakened by it while others may not, metabolism rate may vary etc). I did not understand from your question if you intend to store the cultures with the discs. If you do, diffusion of the drug under refrigeration may vary causing alterations in the drug/bacterium interaction. For example if you to the test normally, drug diffusion and bacterium replication will start more or less (after the lag phase) at the same time. Under refrigeration you may have drug diffusion but no bacterium multiplication. When the latter starts, it will be inhibited by drug, resulting in false susceptibility.
I think it is not a good idea. You will not know what influence this will have on the results you will get. This will also affect the reliability of your susceptibility findings .
I think it is not a good idea also because the results will be altered because the growth of the cultured microorganisms is slowered.
No, its not good idea. This will affect the microbial growth as well as the drug diffusion rate
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