More Clues Revealed as to How Microbes Confer Resistance

The issue of antibiotic resistance may have just gotten more complex as researchers from the University of Groningen and San Diego took a look at the resistant cells’ ability to express an antibiotic-deactivating factor. The full study and a video clip of an experiment completed in the study is published in PLOS Biology.

In the video clip of the experiment, Staphylococci bacteria are seen “expressing a resistance gene for the antibiotic chloramphenicol. Next to them are black Streptococcus pneumoniae bacteria that do not have the resistance gene. In a medium containing the antibiotic, the green cells begin to grow and divide whereas the non-resistant black cells don't. After a time, individual black cells begin to divide and they even outgrow their green companions.”

Of this video clip, Robin Sorg, first author on the paper explained in a recent press release, “'The resistant cells take up the chloramphenicol and deactivate it. At a certain point, the concentration in the growth medium drops below a critical level and the non-resistant cells start growing.” According to Dr. Sorg, this process is similar to what has been seen with cells that are resistant to penicillin, which secrete β-lactamase enzymes that break down the antibiotic. In the case of the Staphylococci bacteria, the antibiotic “is deactivated inside the resistant cells.”

Dr. Sorg states that this breakthrough, which was discovered using time-lapse microscopy, shows that “susceptible bacteria can survive longer when resistant bacteria are present, and in the end even outcompete them.” Interestingly, the researchers noted in the experiment that although the susceptible cells stopped growing, they did not die. “'Many antibiotic-induced killing mechanisms rely on dividing cells, or at least on cells with an active metabolism.' What doesn't kill the cells will perhaps not make them stronger, but certainly gives them time to pick up resistance genes from their environment.”

Dr. Sorg feels that the knowledge learned from their experiment highlights the need for further discretion when prescribing antibiotics. Perhaps in the future, individuals would need to be scanned for non-pathogenic microbes that can confer resistance to the pathogenic microbes, prior to starting an antibiotic, in order to make a better informed decision about the types of antibiotics to prescribe and the future implications.

Another recent study from the University of Copenhagen has also shed some light on how bacterial pathogens are able to evade antibiotics. The researchers found that cells called persister cells helps pathogens avoid the effects of antibiotics by lying dormant for the duration of the antibiotic therapy, and then reactivating once the course of antibiotics is complete. More research is needed to fully understand how these persister cells work, but the study brings researchers one step closer to understanding the problem of antibiotic resistance.