d their experiments using a drug called cephalexin, a member of the widely-prescribed cephalosporin class of antibiotics. These drugs and the penicillins, which share a common chemical backbone called the -lactam ring, work by disrupting the bacterial cell wall. Bacteria have evolved enzymes called -lactamases, which chop the -lactam ring in half, inactivating the drugs. An inhibitor for one type of lactamase has already been marketed as part of a 'package drug' with amoxicillin to fight resistance.
But the lactamase enzyme that Vila's group studied is in a different class that is causing an emerging problem around the world. This class, the metallo--lactamases, is more threatening, said Vila, because it is effective against a broader spectrum of antibiotics, such as carbapenems. However, it also represents a younger set of enzymes that are still evolving, and that enabled the scientists to observe that evolution in fast-forward.
The group used a lactamase gene from the Bacillus cereus soil bacteria and tested it in the laboratory strain E. coli. The gene is very similar to lactamase genes found in disease-causing bacteria such as Pseudomonas and Acinetobacter -- common culprits in resistant, hard-to-treat hospital infections. And it is almost identical to a lactamase gene found in Bacillus anthracis, which causes anthrax.
Together, the four mutations identified by the group increased the enzyme's efficiency at inactivating cephalexin seven-fold. The mutations influenced the enzyme's active site, where the chopping of antibiotic molecules takes place. One of the mutations has already been found in nature, in a lactamase from Pseudomonas.
In some cases, there is a tradeoff associated with antibiotic resistance: the bacteria's success in fighting a particular antibiotic can cause it to lose efficiency in inactivating other antibiotics. But that was not the case here.
"This evolved enzyme works better against cephalexin andPage: 1 2 3 Related biology news :1
Contact: Jennifer Donovan
Howard Hughes Medical Institute
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