Using
a small molecule screened from a synthetic library of 8,000 molecules,
researchers at the Indian Institute of Technology (IIT) Roorkee have been able
to reverse drug resistance and restore the efficacy of fluoroquinolone-group of
antibiotics by inhibiting the proton gradient which drives the efflux pump.
Antibiotic-resistant bacteria use the efflux pumps to expel antibiotics from
the intracellular environment thus preventing antibiotics from reaching the
target thus helping the bacteria to survive.
By
inhibiting the proton gradient using the small molecule, the team led by Prof.
Ranjana Pathania from the Department of Biotechnology at IIT Roorkee was able
to inactivate the efflux, leading to an effective build-up of antibiotic inside
the bacteria and subsequent bacterial death. The results were published in
the International Journal of Antimicrobial Agents.
The
team studied the efficiency of the small molecule in multidrug-resistant
bacteria Acinetobacter baumannii. While the small molecule did
not inhibit the growth of the bacteria per se, it was able to
enhance the activity of a few antibiotics such as ciprofloxacin and norfloxacin
in fluoroquinolone-resistant clinical isolates of A. baumannii. A.
baumannii causes pneumonia, meningitis and urinary tract infections
and is one of the most prevalent hospital-acquired infections across the world.
ESKAPE pathogen
“The
reason for using small molecule to target A. baumannii is
because it is among the six ESKAPE pathogens (Enterococcus faecium,
Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii,
Pseudomonas aeruginosa, and Enterobacter species)
that cause the most hospital-acquired infections,” says Atin Sharma from the
Department of Biotechnology at IIT Roorkee and one first author of the paper.
“Since
discovering new antibiotics takes a long time, boosting the activity of
existing antibiotics by inhibiting the mechanism that prevents the drugs from
acting will be a viable alternative,” Sharma says.
“Since
the molecule inhibits the proton gradient, it and can potentially inhibit a
wide variety of proton-driven efflux pumps in many multidrug-resistant
pathogens,” says Prof. Pathania.
They
found that lower dosage of antibiotics were sufficient to kill the bacteria
when used along with the small molecule. In the case of clinical isolates
of A. baumannii, when 25 micromolar of the inhibitor was used
along with the antibiotic, there was a 64-fold reduction in the minimum
inhibitory concentration (MIC) (the lowest concentration of the compound
required to inhibit the visible growth of a pathogen) of both ciprofloxacin and
norfloxacin.
“The
use of small molecule inhibitor not only restores the efficacy of antibiotics
but also decreases the frequency of resistant bacteria,” she says.
Ciprofloxacin in combination with 50 micromolar of the inhibitor exhibited
“significantly lower” mutation selection frequency compared with ciprofloxacin
used alone at the same concentration.
The
molecule appears safe to mammalian cells at minimum effective concentration of
16 micromolar and 32 micromolar for ciprofloxacin and norfloxacin respectively.
The IC50 (a measure of toxicity) of the small molecule for human embryonic
kidney cells is about 133 micromolar, which is about ten times more than the
effective concentration.
“Most
of the PMF [proton-motive force] inhibitors are associated with high toxicity.
But the small molecule is not an inhibitor of PMF as it targets only the proton
gradient and hence is not toxic to mammalian cells,” says Prof. Pathania.
The molecule has also been tested in mice models for safety
and efficacy. “We could revive the activity of ciprofloxacin and norfloxacin on
mice model of A. baumannii,” she says.
Source: THE HINDU-5th November,2017
