The focus of his team was also on samples, in which the bacteria failed to respond to the agent. They discovered two types of resistance. "Spontaneous mutations can occur in the gene for dihydrofolate reductase rendering trimethoprim no longer able to attack the changed enzyme, which means it becomes ineffective," Nitsche-Schmitz explained. The team from Braunschweig detected a specific mutation in this gene in many samples, which renders streptococci resistant. In addition, bacteria can transfer copies of changed variants of the dihydrofolate reductase gene to other bacteria. This process called horizontal gene transfer allows resistance to spread very rapidly. The scientists found two genes of this type to be further causes of insensitivity.
The study shows that the antibiotic trimethoprim is a therapeutic option for Streptococcus pyogenes infections in some geographical regions of the world. The frequency of resistance is much lower than previously believed and the medication is inexpensive, stable and effective in Staphylococcus aureus co-infections. "However, it is like a sword that can loose its sharpness quickly," Nitsche-Schmitz said. "We found three causes for the rapid spread of resistance. It is important that trimethoprim, like all antibiotics, is not prescribed without need and that patients take the agent in accordance with the instructions given."