In recent years we have all become familiar with the concept of spillover, the leap of species by which an animal pathogen becomes capable of infecting, reproducing and also transmitting itself to humans. But if this leakage from a “reservoir” species is quite frequent for viruses, thanks to human penetration into ecosystems, how widespread is it instead among superbugs? Based on a new analysis published in Nature Microbiologyit is not so easy for antibiotic resistant bacteria to change their ecological niche and be transmitted from nature to humans.
Superbatteri lombardi. A research group which also includes scientists from the Policlinico San Matteo in Pavia and the Department of Biomedical and Clinical Sciences of the University of Milan at the Luigi Sacco Hospital, has sequenced almost 3,500 genomes of bacteria of the genus Klebsiella collected in just under 18 months in different contexts (hospital, veterinary, community, agricultural, from wild animals and from environmental sources), around the city of Pavia.
Half of the cases were bacteria Klebsiella pneumoniaepathogens particularly resistant to antibiotics that attack immunosuppressed patients and cause pneumonia, meningitis, blood or urinary tract infections.
Which guests? The premise, explain the authors of the work on The Conversationis that the transmission of superbugs between two hosts or contexts (for example, between man and man or between animals and man) results in two samples of bacteria with identical genome even if extracted from different sources.
By comparing the DNA of superbugs collected in a short period of time and in a limited area of Northern Italy, the scientists attempted to analyze the type of transmission in progressand also to understand if the K. pneumoniaea hospital bacterium that has developed resistance to carbapenems, among antibiotics of last resort, is capable of spreading outside the clinical context.
Two comforting facts. The first reassuring news is that the authors have found no evidence of the spread of Klebsiella resistant to carbapenems outside the hospital setting. Probably, the ability to wear a permanent shield against antibiotics comes at a cost, i.e. the reduced ability to compete with other bacteria spread outside hospitals.
The second is that humans almost always get superbug infections from other humans rather than from animals or environmental sources. Similarly, animals usually infect other animals, plants other plants. It does not mean that kingdom and species transition is impossible, but rather that superbugs are very well adapted to their ecological context and that this acts as a barrier when they try to change it.
A strain of superbug may be well adapted to a cow and potentially capable of temporarily colonizing a human, but it would not last long among new rival bacteria that know their host well, and would not be able to continue along the chain. of human-to-human transmission.
Stay alert. It is possible that for other families of superbugs or in other geographical contexts where the proximity between man and animals is greater, things go differently.
The study must not persuade us to let our guard down about the threat of antibiotic resistance, considered by the WHO to be one of the greatest risks to public health. First, because humans represent the greatest threat of transmission to other humans and therefore the risk remains, especially within hospitals. And also because the passage of species, although more difficult, is not impossible, and the risks when this happens are there for all to see.