University Journal of Pre and Paraclinical Sciences
Genotypic characterisation of carbapenem resistant Escherichia coli isolates from blood stream infection and fallacies associated with Modified Hodge Test to detect production of carbapenemases
Abstract
Gram negative enteric bacilli are a leading
cause for sepsis in children and adults.
Emergence of drug resistance is a major
problem which limits the options available
for therapy. Carbapenemase is one of the
beta lactamases conferring resistance to
carbapenem group of drugs making it difficult
to treat since the treatment options are
lesser. Detection of carbapenem resistance
plays an important role in understanding
the epidemiology and spread of
resistance. This pilot study was done to
characterise Escherichia coli isolates from
blood stream infection and identify genes
responsible for carbapenemase production
and correlate the results with MHT.Twenty
consecutive isolates of E.coli resistant to
imipenemmeropenem by disk diffusion
were characterised. Multiplex PCR was
performed to detect various genes responsible
for carbapenemase production that
are NDM, KPC, SPM, VIM, OXA-48, IMP
and GES and compared with the MHT results.
It was observed that NDM
was the common gene conferring resistance.
However, we found that among a
total of 6 isolates positive for the NDM
gene, 4 of them gave a false negative result
with MHT. Among the 20 isolates, 3
gave a false positive result with MHT. The
reasons could be excess production of
ESBLs. We found that a majority of isolates
(9 out of 20) were negative with PCR
and MHT though they had a resistant
zone of inhibition with carbapenems. The
reasons for this could be due to other resistant
mechanisms such as porin loss
(OMP defects), efflux pumps and Amp C
beta lactamase production. In conclusion
conventional multiplex PCR is a sensitive
technique to detect multiple genes. Phenotypic
tests can serve as an inexpensive
alternative. However, MHT results should
be interpreted with caution as it is well
known that it has a sensitivity of only 11 in
detecting NDM though it picks up KPC
and OXA-48 well.
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