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Researchers at Uppsala University and Emory University in the United States demonstrate this in a study published in the leading journal of microbiology Nature Microbiology.
“Our results indicate that a common reason antibiotic treatment fails is that a common test method has not found that among a large number of antibiotic-sensitive bacteria there is also a small amount that is resistant to the tested antibiotic. “says Dan Andersson, professor of medical bacteriology at Uppsala University.
The phenomenon that, in addition to antibiotic-sensitive bacteria, there may also be a very small number of resistant bacteria, less than one percent of the total, in a sample is called heteroresistance.
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The most common test method often does not find that, in addition to antibiotic-sensitive bacteria, there are also a small number of resistant bacteria in the sample.
– If such resistance is not detected, there is an obvious risk that the chosen antibiotic treatment will not work. It kills antibiotic-sensitive bacteria, but at the same time gives free play for resistant bacteria to reproduce, explains Dan Andersson.
The researchers studied the prevalence of heteroresistance against any of the 28 different types of antibiotics in four different bacterial species. The samples came from patients with different types of serious infections.
For more than a fourth proven combination of bacteria and antibiotics, heteroresistance was detected.
– This surprisingly high number indicates that heterresistance is a seriously underrated problem in healthcare, says Dan Andersson.
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Dan Andersson
The resistant bacteria had many copies of various so-called resistance genes. However, when these bacteria were grown without antibiotics, in most cases they were so unstable that they quickly lost excess resistance genes.
– Actually, it may mean that bacteria that are resistant when the patient sample is taken may have become sensitive to antibiotics when examined in the laboratory. Of course, this makes diagnosis difficult and emphasizes the importance of developing and introducing methods that can quickly detect heteroresistance in bacterial samples, says Dan Andersson.
The researchers will continue other studies to get a better idea of how big the heteresistance problem is in healthcare.
– Among other things, we are planning a study in which we examine preserved samples from patients with blood poisoning to see if there is any connection between the incidence of heteroresistance and mortality in the disease, says Dan Andersson.
Footnote: The scientific article in Nature Microbiology can be read here.
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