I am trying to grow S.aureus NCTC 6571 in Cation-adjusted Mueller Hinton Broth. I need this to be at a starting inoculum of 10^5CFU/ml for antimicrobial susceptibility testing. I am diluting this from an overnight culture to 10^8CFU/ml by using a 0.5 McFarland Standard, then to 10^5CFU/ml in 3 1 in 10 serial dilutions. However, I am not getting any growth what-so-ever. Has anyone had a smiliar issue or is there anything you can suggest?
Thank you!
I assume these are being diluted into a final concentration of 10^5 cfu/ml in the same solution as your antimicrobial treatment. Have you checked the literature to see what sort of concentration you might expect for the MIC of your antimicrobial treatment? It may be that you simply haven't gone to a low enough treatment concentration to allow for any growth of S. aureus. However, if you're not getting any growth in your treatment-free control then it must be another issue. It may also be something easily overlooked like the temperature of your plate reader during incubation.
For each strain, five tenfold dilutions were prepared to achieve concentrations ranging fom 0 to 10^4 CFU/ml.
Do check the temperature of the incubator.
Sometimes the internal temperature of incubator
can be warmer than set. Or the temperature may
not evenly distributed as expected.
Also, you may take a cross examination of
your medium. Perhaps you get a control which
will give a better idea of your result.
Growth and Laboratory Maintenance of Staphylococcus aureus
www.ncbi.nlm.nih.gov › pmc › articles › PMC6211185
S. aureus is also the etiological agent of suppurative abscesses, as first described by ... All manipulations with S. aureus strains must be performed following ... drug targets and the development of new antibiotics (van Hal and Paterson, 2011). ... Using a sterile pipet transfer 0.9 ml of a culture into a 2-ml sterile cryogenic vial ...by DM Missiakas · 2013
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