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Strains of Streptococcus pneumoniae resistant to penicillin — and often several other drugs — have emerged in the United States primarily via person-to-person transmission of relatively few distinct strains or "clones," says Sandra Richter, MD, a researcher at University of Iowa College of Medicine in Iowa City. "It’s clear that certain genetic lines have become dominant," she says. "It seems clear that multidrug-resistant puemococci are increasing in prevalence and you can trace the majority to 12 different [clones]."
In addition, the resistant strains appear to be transferring genes encoding resistance to susceptible varieties of pneumococci, Richter says. "We concluded both things were happening. Clones were being passed around [person to person], but also there were new strains acquiring resistance."
The most serious clinical therapy problem is primarily with meningitis, but there is concern the trend will make a variety of infections more difficult to treat. "The concern is that [resistance] is going to continue to grow," Richter says. "This has emerged so recently — in the ’90s. It could continue to gain resistance to other classes, like the fluoroquinolones, which has started to occur in Canada."
Because of the emergence of antimicrobial resistance in pneumococci, some clinicians now recommend fluoroquinolones for the treatment of pneumonia in adults. However, fluoroquinolones are not licensed for use in children, a factor that may be helping to slow the rate of emerging resistance to the drug.