Understanding Antibiotic Resistance

Scientists at the University of Bristol, together with collaborators at the University of Aveiro, Portugal, have solved the structure of an enzyme that breaks down carbapenems, antibiotics ‘of last resort’ which, until recently, were kept in reserve for serious infections that failed to respond to other treatments.

Increasingly, bacteria such as E. coli are resisting the action of carbapenems by producing enzymes (carbapenemases) that break a specific chemical bond in the antibiotic, destroying its antimicrobial activity.

Carbapenemases are members of the group of enzymes called beta-lactamases that break down penicillins and related antibiotics, but it has not been clear why carbapenemases can destroy carbapenems while other beta-lactamases cannot.

Using molecular dynamics simulations, Professor Adrian Mulholland in the School of Chemistry and Dr Jim Spencer in the School of Cellular and Molecular Medicine, showed how a particular type of carbapenemase enzyme reorients bound antibiotic to promote its breakdown and render it ineffective.

“The recent appearance and spread of bacteria that resist carbapenems is a serious and growing problem: potentially, we could be left with no effective antibiotic treatments for these infections. The emergence of bacteria that resist carbapenems is therefore very worrying.”

In a study published in the Journal of the American Chemical Society (JACS), the scientists combined laboratory experiments with computer simulations to investigate how one particular type of carbapenemase recognises and breaks down antibiotics. In beta-lactamase (the CAS number is 9073-60-3 or 9001-74-5) that cannot break down carbapenems, this rearrangement cannot happen, and so the enzyme cannot break down the antibiotic. Knowing this should help in designing new drugs that can resist being broken down.

Dr Spencer said: “Combining laboratory and computational techniques in this way gave us a full picture of the origins of antibiotic resistance. Our crystallographic results provided structures which were the essential starting point for the simulations and the simulations were key to understanding the dynamic behaviour of the enzyme-bound drug.

“Identifying the molecular interactions that make an enzyme able to break down the drug, as we have done here, is an important first step towards modifying the drug to overcome bacterial antibiotic resistance.”

Researchers Devise Simple and Cheap Method to Detect TB

Tuberculosis or TB as it’s become more commonly known, is a horrible disease by all accounts, it slowly kills many of its victims, particularly those living in the developing world. In 2010, it killed an estimated four thousand people every single day, which is particularly horrendous when noting that many of those who succumb to its effects could be have been saved were they to be diagnosed and treated in a timely manner.

Unfortunately, in many areas of the world neither is available, thus the news that a team of researchers working together from several universities in the US has developed a new kind of test that reveals the presence of TB in patients, both quickly and cheaply, is truly exciting. The new probe, as the team describes in their paper published in Nature Chemistry, can allow for TB detection using nothing more than a simple box housing light emitting diodes and some filters.

Up till now, the only way to test for TB in remote patients was to collect a sputum sample and send it to a location that had a microscope, where trained clinicians looked for the TB bacteria. Sadly, this method is not only slow, it’s also relatively inaccurate when there are few bacteria to be seen, such as is the case with infected children. With the new probe, test times can be reduced to mere minutes and accuracy is improved dramatically.

Reducing the amount of time it takes to test for TB not only helps the patient, it helps those around them too because TB is of course, communicable, with some estimating that one infected, untreated person may account for as many as ten or fifteen new infections in others in just one year.

Early diagnosis of tuberculosis can dramatically reduce both its transmission and the associated death rate. The extremely slow growth rate of the causative pathogen, Mycobacterium tuberculosis (Mtb), however, makes this challenging at the point of care, particularly in resource-limited settings. Here we report the use of BlaC (an enzyme naturally expressed/secreted by tubercle bacilli) as a marker and the design of BlaC-specific fluorogenic substrates as probes for Mtb detection. These probes showed an enhancement by 100–200 times in fluorescence emission on BlaC activation and a greater than 1,000-fold selectivity for BlaC over TEM-1 beta-lactamase, an important factor in reducing false-positive diagnoses.

Insight into the BlaC specificity was revealed by successful co-crystallization of the probe/enzyme mutant complex. A refined green fluorescent probe (CDG-OMe) enabled the successful detection of live pathogen in less than ten minutes, even in unprocessed human sputum. This system offers the opportunity for the rapid, accurate detection of very low numbers of Mtb for the clinical diagnosis of tuberculosis in sputum and other specimens.