MIC values much higher than expected

[Silvia_84]

Hi all,

 

I am new with Microbiology laboratory stuff and I am doing some MICs with microbroth dilution method. I have a problem with that because I obtain MIC values for my control strains higher than expected (2-3 fold higher) and I can't understand what does not work in my experiment. I thought that it could be a diminished antibiotic potency but the drug is not out of date. I thought that it could depend on the solvent I use to make the antibiotic dilutions..I am doing them in Iso Sensitest broth. The procedure I used so far for my MIC is always the same and it worked with antibiotics like Ampicillin and Meropenem. Now I changed antibiotic and I am using Amikacin and Gentamicin and for both the drugs I always have MIC higher than expected.

Could you suggest me what might be the problem?

 

Thank you very much in advance.

 

Best,

 

Silvia