‘Extremely deadly Salmonella variants in Africa are still barely treatable with antibiotics’
University of Antwerp researchers unravel genetic code of new and more dangerous salmonella variants in Africa
University of Antwerp researchers have genetically mapped new and more dangerous salmonella variants from Africa. These salmonella variants are under-reported, but they often cause very severe infections. Moreover, high degrees of antibiotic resistance have been observed in some cases, making such infections virtually untreatable in sub-Saharan Africa.
An international network of researchers has done an enormous amount of work to prepare an inventory of the global genetic overview of the spread of these salmonella bacteria. The scientists have published two global genetic studies in the journal Nature Communications, each mapping a different, new salmonella variant.
Drawing on more than a thousand bacterial samples from around the world, they read out the complete genetic sequence of all those bacteria. ‘This was truly a feat, involving collaboration with colleagues from all over the world, including dozens of scientists from Africa, and bringing together a tremendous amount of genetic information’, notes Professor Sandra Van Puyvelde (University of Antwerp and the University of Cambridge).
‘We also delved into historical bio-banks, which allowed us to include a wide range of samples, including some that were collected in the 1980s in what was then Zaire or that date from 1940 and have up to now been kept in the cellars of the Pasteur Institute in Paris. This wealth of genetic information made it possible to unravel the genetic lineage of these bacteria’.
Mysterious infections due to Salmonella Concord
The scientists started by investigating the mysterious case of Salmonella Concord. This bacterial variant surfaced around the world in the early 2000s, linked to adoptions from Ethiopian orphanages. ‘The adopted children carried the bacteria, which suddenly led to the identification of such salmonella infections worldwide’, explains Wim Cuypers (a researcher at the University of Antwerp and the Institute of Tropical Medicine). ‘Those cases were quickly under control, but it is remarkable how the variant managed to spread, in Ethiopia and throughout the world’.
Particularly disturbing is the incredibly high level of antibiotic resistance found in salmonella samples from Ethiopia. Cuypers continues, ‘For this reason, we must also remain vigilant. Contained in “mobile DNA”, such resistance can be passed on to other, related bacteria. Incidentally, we are increasingly seeing such extreme forms of antibiotic resistance worldwide. Because that type of resistance is mobile, there is a high threat of more untreatable bacterial infections’.
One of the most important causes in Africa?
In addition, the researchers delved into cases of ‘invasive’ non-typhoidal Salmonella. Such non-typhoidal Salmonella are variants also known to us for causing relatively mild gastrointestinal infections. In Africa, however, a new branch in the salmonella lineage has emerged that causes ‘invasive’ infections, or severe life-threatening infections of the otherwise sterile blood. Such infections with invasive non-typhoidal Salmonella are seen primarily in children under five years of age who are living in poor hygienic conditions, and who are also often malnourished or infected with malaria. Those salmonella infections are associated with hallucinatory mortality rates of up to 20% in some cases. For example, up to hundreds of young children would die daily in Africa, and those invasive non-typhoidal Salmonella also appear to be particularly resistant to available antibiotics.
‘The DNA code of more than a thousand salmonella bacteria originating from across Africa was examined to reconstruct the genetic evolution’, recounts Professor Kris Laukens (University of Antwerp). ‘To do this, we are using very powerful computer applications for diverse purposes, including to map how those salmonella bacteria have spread across the continent and to characterise antibiotic resistance’.
These studies provide a breakthrough in the genetics of this type of infection, and they provide a helicopter perspective on its spread. This information is crucial for monitoring and the associated antibiotic resistance, and it can be used in the implementation and development of accurate strategies, including new vaccines.
Read the papers here:
Contact information Prof. Sandra Van Puyvelde
E-mail: sandra.vanpuyvelde@uantwerpen.be