Non-resistant germs resist antibiotics

Slow growth makes pathogens less susceptible to antibiotics

08/15/2014

Multidrug-resistant pathogens are considered to be a significant problem in the medical community, as bacterial infectious diseases are treated correspondingly worse. „But even without resistance, pathogens can survive antibiotics for some time, which is why the treatment takes several days to weeks or even months“, reports the University of Basel. So far, many researchers worldwide were of the view here, „that these germs are in a kind of sleep state“, in which they do not grow and therefore are not vulnerable to antibiotics, so the message from the university.

However, the research team led by infection biologist Professor Dirk Bumann from the Biozentrum of the University of Basel has now shown that the „sleep state“ Salmonella infection has little significance for resistance to antibiotics. Rather, here are the „numerous slow-growing germs“ Cause of the delayed effect of the therapy. Since slow and fast-growing pathogens of the same genus can be found in the same tissue, a completely different antibiotic susceptibility is to be expected, which should be taken into account in the treatment. Their results have the researchers in the specialist magazine „Cell“ released.

Growth rate of Salmonella determined
According to information from the University of Basel, it was already known from previous studies that completely identical bacteria in the test tube can grow side by side at very different speeds. „However, it was still unclear whether bacterial communities are actually so different even in the infected host“, The researchers continue to report. With help „fluorescent proteins“ the team around Professor Bumann now claims to have succeeded, „to measure the proliferation of individual Salmonella in infected tissues.“ It was shown, „that part of the Salmonella grows very fast with many offspring, which aggravate the disease symptoms.“ However, most bacteria would „get into tissue regions with only a few nutrients where they can grow slowly.“

Slowly growing pathogens are less sensitive to antibiotics
After the researchers had determined the different growth rate of the bacteria, they then checked in a next step, how this different growth behavior affects the success of therapy. In infected mice, Professor Bumann and colleagues examined the response to antibiotic therapy. The symptoms of the disease have improved very quickly, „but even after five days of therapy, pathogens were still detectable, which could cause a relapse“, reports the University of Basel. „We were able to kill around 90 percent of salmonella with the first antibiotic dose, especially the fast-growing ones“, but „in contrast, non-growing Salmonella survived much better“, explained Professor Dirk Bumann. The success of the treatment clearly depends on the rate of reproduction.

Sleeping and slow growing germs complicate the therapy
According to the results of the Swiss researchers, sleeping germs are not the main problem in the resistance of non-resistant antibiotic pathogens, but in fact slow-growing pathogens are a much bigger problem. Because these could tolerate antibiotics a little worse than sleeping germs, but they were much more numerous and could also boost their growth anytime again, as soon as the antibiotic level drops again. This threatens after discontinuation of the drugs, a renewed outbreak of infection. „If we better understand such bacteria, one could perhaps significantly shorten the treatment period with targeted antibiotic therapy“, so the hope of the researchers. This is „especially interesting for infections in which patients have to take their medication over many days and weeks to prevent a relapse“, reports the University of Basel. (Fp)