Ampicillin as positive control - (Apr/03/2014 )

Hello!

can anyone suggest why the ampicillin when used as a positive control didnt make a change against bacteria such as pseudo.aerog. and others like listeria? i used it in 48 well plate with broth culture, not agar plate. so i was applying it at RT and there is no hot media or agar that may have degraded the product.

I used 0.2 mg/1ml

do i need to increase the concentration? any reference or guidelines are available and could be helpful on the optimum usage of ampicillin salt??

Always greatly appreciated your help!!

Pseudomonas aeruginosa is resistant to ampicillin, and this antibiotic is only bacteriostatic vs. Listeria.

what is the positive control i should use against those bac?

i have five bacteria: staph aureus, e.coli, listeria monocytogenes, salmonella and pseudomons.

In that case i need to use different antibiotic that act on each specifically?

What are you trying to accomplish - your hypothesis?