Rapid drug resistance testing
I came across this news alert via Microbe World, which very briefly summarizes some research at St. George’s University of London investigating a hand held device to rapidly determine whether patient isolates of M. tuberculosis are antibiotic resistance. This new technology will use a cartridge based format to test sputum samples, and report in 15 minutes what antibiotics might be effective in patient treatment. Currently, the standard for antibiotic susceptibility are variations of disk diffusion or use dilution tests, both of which require incubation of an organism in the presence of control agents to assess susceptibility. Accurate determinations of susceptibility may require an extended incubation time, however good indications susceptibility can frequently be determined in a shorter amount of time, and better patient outcomes will be obtained by starting effective antibiotic treatment sooner rather than later. Susceptibility testing can also be accomplished using molecular genetic approaches, typically using a polymerase chain reaction based approach to directly detect genes that are involved in antibiotic resistance. Even still, this approach requires some time to complete, as DNA from a microbe of interest needs to be extracted prior to performing and analyzing the sample by PCR. So this new approach that suggests meaningful results in 15 minutes looks very interesting.
The original press release at the St. George’s website gives a little bit more information. This report indicates that the device uses a combination of DNA analysis (almost certainly PCR-based) and a TB identification system (probably a serological detection method) in a single unit. Polymerase chain reaction can be extremely rapid, and the procedure can actually be accomplished in a few minutes using conditions optimized for very specific conditions. Analysis would likely use a spectrophotometer based approach, which has been used to measure DNA concentration for years and can be scaled down into a remarkably small unit. The drawback of this type of approach would likely be one of specificity. If a patient has a M. tuberculosis infection, and if that isolate exhibits one of the standard forms of antibiotic resistance, the device would report back a meaningful result. However, if the patient has another infection, or if the patient isolate is resistant to another antibiotic, this machine might report back a “negative” result which in fact would not be a helpful diagnosis.
Although this is an intriguing approach in clinical diagnostics, and may have in specific clinical settings a very clear benefit, the headline of the report worries me a bit– “Unnecessary TB deaths to be thing of the past”–the overt implication being that we have solved the issue of antibiotic resistance with this very troubling pathogen. M. tuberculosis infection are becoming notoriously difficult to treat due to growing acquisition of antibiotic resistance. New patient isolates are arising that are resistant to many first and second line antibiotics. The article equates very early detection of infection with clear patient outcomes, and although this is true to some extent, it does not address those infection which are already resistant to antibiotic treatments. In these cases, the clearest benefit of detection is to the community at large, where the further spread of antibiotic resistance from undiagnosed cases can be prevented.