Multi-Drug Regimen Effective at Eradicating Disease
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. Read more about bacteria and the overuse of antibiotics at “The Threat of 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.
