Battling Antimicrobial Resistance

When an antibiotic treatment regimen is not successfully completed by a patient, the surviving bacteria have encountered the evolutionary pressure of the antibiotics that killed off a majority of their weaker population. These surviving, stronger bacteria are able to persist and continue growing inside the patient, eventually becoming strong enough to again cause symptoms. Because they’ve already encountered these antibiotics, the same prescription may not be able to eradicate the disease. The bacteria that end up evading a round of improperly prescribed or improperly taken antibiotics are able to do so through random mutations in their genomes. These mutations stem from imperfect replication when bacterial cells divide and create two copies from the parent cell. A genetic mutation in the genome often presents as an altered protein. Sometimes, these mutations impart a benefit to the bacterium, enabling it to not be affected by an antibiotic as designed. In the end, this mutated bacterium is able to persist, continue growing and dividing, and ultimately become the majority of an infection that is now classified as “resistant.” Bacteria can also transfer resistance genes between one another on plasmids. The resulting resistant strain of the bacteria then becomes increasingly difficult to address. Hear more about bacteria and the overuse of antibiotics on our Science Diction podcast episode, “Antimicrobial Resistance.”

In the mid-20th century, Mycobacterium tuberculosis (Mtb) was treatable with just one or two antibiotics. As antibiotic use and overuse has increased in the past several decades, and perhaps as a function of Mtb incidence globally, resistance to these antibiotics has risen quickly. Today, there are roughly 15 different potential antibiotics that can be used in a Mtb treatment regimen, though the most common regimens use a four-drug combination. By including multiple antibiotics in Mtb treatment, doctors can reduce the overall treatment time, increase effectiveness, and reduce the chance of relapse.

For instance, in multi-drug resistant Mtb, a treatment using Bedaquiline, Pretomanid, Linezolid, and Moxifloxacin (BPaLM) has been shown to be effective while also reducing treatment down to six months compared to the previous treatments, which would last up to 20 months and included other antibiotics that have much more severe side effects. With respect to AMR, using four drugs helps make sure that the bacteria causing the disease is eradicated. Read about a current outbreak of tuberculosis in the United States and why it prompts concern for antimicrobial resistance at “Should I Be Concerned About Tuberculosis?”.