Varying levels of antibiotic resistances in tissue can hamper treatment
Bacteria with different levels of antibiotic sensitivity can coexist within the same tissue. This makes infectious diseases increasingly difficult to treat, as particularly slowly growing pathogens hamper treatment, researchers at the University of Basel report in "Cell".
Many bacteria are principally susceptible to treatment, but can still survive for some hours to days in adverse environmental conditions, such as exposure to antibiotics. Scientists commonly assume that these pathogens are in a type of "dormancy" state. They don't grow and thus become invulnerable against the effects of many antibiotics. However, Dirk Bumann and his team at the University of Basel demonstrated that dormant pathogens play only a minor role in Salmonella-infected tissue. Instead, abundant slowly growing bacteria are the biggest challenge for treatment.
The researchers used fluorescent proteins to measure the proliferation of individual Salmonella. The results revealed that in host tissues some Salmonella grow very rapidly, producing many daughter cells. Most bacteria, however, reside in tissue regions with limited nutrient supply, in which they grow only slowly. These are the bacteria that hamper the treatment.
The mouse trials confirmed this. Therapy of infected mice quickly ameliorated disease signs, but even after five days of treatment, some bacteria still survived in the tissues, posing a risk for relapse. "We could kill already 90 percent of the Salmonella with the first antibiotic dose, particularly those that grew rapidly", reports Bumann, "but non-growing Salmonella survived much better. Treatment success thus depended on the Salmonella replication rate."
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