determining amount of gentamycin to use - (Jun/07/2011 )

Hi there,
I am new to the lab and am working with campylobacter jejuni. I wish to add gentamycin to kill off extracellular bacteria and need to use 100ug/mL in 10 mL mueller hinton broth. Do I need to take into consideration the activity of the gentamycin when weighing it out? Or should I just multiply the ug/mL by 10 mL?

The real answer is to infect culture medium and then do a serial 2x dilution of gentamicin into wells on a plate, so you can quantify the amount necessary to inhibit growth. This tells you how sensitive the strain is, and how potent the gentimicin stock is. Inhibition of growth is not necessarily the same as killing, so you might need to test for cell death, if that is what you need. I would use 4-8x more than the minimum amount in a final experiment.