Antibiotic sensitivity testing of colistin was done by Kirby Bauer method.I have isolated DNA by boiling method.
Colistin antibiotic sensitivity not recommended by kbddm since it is a large molecule.... Certainly there could b other reasons for resistance
Might have different mechanisms of resistance or check the PCR conditions by adding DMSO...for amplification
Use microdilution method for checking sensitivity you will get what you want. like either the strain is sensitive or resistant.?.
As per your protocol of DDM, the colistin shows the false positive results on your method. This method is not recommended by CLSI Because of the hydrophobic and large molecule of colistin it can't diffuse in agar. CLSI recommends broth microdilution method. However, agar microdilution also gives good results. Secondly, your DNA extraction is done by boiling method. by this method, you will get both plasmid and genomic DNA along with some other cell derbies. which may inhibit amplicon formation by PCR.. instead of the boiling method use alkaline lysis method which is the recommended method for plasmid DNA isolation only.
It's depends on bacteria also. Like Proteus which is intrinsic resistance to colistin.
Please can you determine the MIC, to confirm the isolates are colistin resistant, if they are negative for mcr-1- gene after MIC, then there is possibility of existence of other mechanisms of resistance such as efflux and chromosomal resistance mechanism
Most of the answers are relevant, neither all colistin resistant bacteria have the same mechanism of resistance, nor all bacteria need mcr-1 gene, it is mcr-2 also, and there may be many more, yet unknown.
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