Problem Testing Antibiotic Sensitivity of Clumping Bacteria - And to do so without vigorous shaking.... (Oct/11/2004 )

Greetings to all,

I have this bacteria that tends to clump together during growth in liquid media (despite with gentle shaking, vigorous shaking is harmful to the cells) so I have difficulty getting a nice lawn of growth to test it's sensitivity to certain antibiotics in agar diffusion test.

Short of plating them on agar containing the different antibiotics as a last resort, are there any other ways to test for antibiotic sensitivity?

Thanks to all in advance.

Have you tried adding a detergent to the culture, e.g. 0.1% Tween 80?

You can test for antibiotic sensitivity in liquid growth (MIC - Mininmal Inhibitory Concentration mehod). Simply prepare a range of of growth vessels (10 ml tubes with a ml of media in them will do just fine for most bacteria) with different concentrations of your antibiotic and a small cmount of cells for each - then leave to grow at optimal conditions and check next day. Tubes that show no growth have been inhibited by the antibiotic. don't forget to prepare one with no antibiotic as control.

the determination of the MIC is routinely done around here in 96 well multiwell plates with 100µl medium and a minimal inoclumum of cells. the good thing is that you don't need a lot of vessels and you can read the plate at 600nm in an ELISA reader do determine growth of the cells.

mike

Alternatively, depending on how sticky they are, you can try to incorporate them into soft agar and pour them on your plate. Add antibiotics discs after hardening.