I screened 300 isolates, out of which i got 80 phenotypically ESBL positive isolates through antibiotic disk method. And when i tried to detect molecularly through PCR, for blaTEM gene, i got almost 90% positive for the above said gene which means phenotypically ESBL negative isolates also showed to have blaTEM gene ...
So is it possible ?? that phenotypically only few isolates showed ESBL positive but however when pcr is done, almost 90% showed the presence of blaTEM gene ????
Some TEM enzymes (e.g. TEM-1) are “normal” beta-lactamases and not ESBL, thus conferring only resistance against penicillin and 1st-generation cephalosporins. You could define the exact TEM type to confirm the genotype! The classic ESBL phenotype is mostly due to plasmid carriage encoding for CTX genes.
Not all blaTEM genes produce ESBL. You need to sequence your PCR products of blaTEM in order to find out the point mutations. Kindly refer to www.bldb.eu. This beta lactamase database gives a comprehensive list of all the beta lactamases and their functional information.
Yes it is possible to detect the gene by pcr. As not all genes a|e expressed the phenotypic study could show a negative result
There are other genes responsible to produce ESBL rather than TEM. Which means that it is OK to have isolates have phenotypically ESBL and you can not detect TEM gene in it. In addition, the TEM gene have different types as bleTEM-1, TEM-2, TEM20...TEM135. I mean that may be the gene which is responsible to produce ESBL in your isolates could be another allele of TEM gene
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