Dear Ahmed Fakhr;

This may be the case, that is, bacteria may be sensitive to gentamicin, while amikacin may become resistant. Of course bacteria have various resistance mechanisms.I will only comment on the efflux pump, which is the resistance mechanism I have been working on. Efflux pumps are a system that effluxed drug from inside the cell and out of the cell. It is also active in most gram negative bacteria.

Thank you

Best Wishes

Thanks Eda for your answer.. So you mean the efflux pump could affect amikacin selectively and not affect gentamycin.. In this case, is it safe to use gentamycin for the patient or is it probable to develop resisance for gentamycin as well

You're welcome.

I'm not sure if it might be selective, but it may develop resistance.

Thanks Eda

I was searching and I found this reference.

A plasmid-mediated acetyltransferase, now known as AAC(6′)-Ib or AacA4 [26,27,34,161], was first reported in P. aeruginosa that conferred resistance to amikacin besides other aminoglycosides but not gentamicin C1 [160,162,163].

Article Amikacin: Uses, Resistance, and Prospects for Inhibition

Yes it is possible that an organism is sensitive to gentamycin and resistant to amikacin. Not every case of resistance is plasmid related related however there is a greater chance of cross resistance. Nearly 50 years ago, I isolated a Gram negative rod Classed as Pseudomonas species using one method and Alkaligenes faecalis using another, which was growing in a batch of disinfectant. As a matter of course I checked and it was resistant to both Gentamycin and Neomycin sulphate. I stored it in liquid nitrogen and re-tested and found it had become sensitive to both which suggested in that case it was plasmid related. I also found that gram negative bacteria growing in the cooling water carried the same resistance pattern.

Yes, this is possible. I have observed on Pseudomonas cultures