The first global-scale genetic study of Salmonella Enteritidis bacteria, which is a major cause of blood poisoning and death in Africa and food poisoning in the Western World, has discovered that there are in fact three separate types of the bacteria. The study also showed the African types have developed resistance to many antibiotics and behave differently to the type commonly found in the West.
Because routine microbiological testing is not able to distinguish between the S. Enteritidis circulating in Africa and the rest of the world, the scientists involved in the study sequenced 675 isolates of S. Enteritidis from 45 different countries and six continents. Analysis of the Salmonella genomes revealed the three major types they discovered — a common global type and two novel African types.
As stated in the research, once Salmonella reaches the bloodstream it’s known as invasive non-typhoidal Salmonella (iNTS) disease, a serious and neglected tropical disease. Last year, it was estimated to cause 680,000 deaths per year worldwide, more than half of which were in Africa.
Based on those statistics, the article explains there is a definite need to understand where in the African environment the bacteria live, in order to prevent this disease.
The common global type of S. Enteritidis is normally associated with poultry and predominantly infects the intestine, causing diarrhea. However, in Africa the two newly identified types are a major cause of blood poisoning and death, because in people with weak immune systems, the pathogens are able to pass with greater ease from the gut into the bloodstream.
The study also showed that the two African types carried more of the genes that give them resistance to common antibiotics. These strains do not respond to the antibiotics commonly available, and have to be treated with cephalosporin or ciprofloxacin, antibiotics of last resort in many African settings.
“This study highlights a very important issue; that a relatively mild version of a bacterium can evolve into a more dangerous pathogen under the right conditions,” researcher Nick Thomson, said in the article. “A combination of HIV, antibiotic resistance and lack of health care and sanitation has facilitated the emergence of Salmonella as a deadly disease in Africa and its importance was not originally recognized,” he continued.
While it is not yet clear if the African varieties have infected people overseas, concern in the U.K. is increasing due to the growing illegal trade in bush meat products, which have been smuggled into the country. Bush meat is considered a delicacy in some African cultures, but is illegal in the U.K. due to the high chance of it being bacteria laden with Salmonella, Campylobacter, pseudotuberculosis, and a host of other bacteria and parasites, another article explains.
“The more we look, the more we understand the potential for bacteria which cause mild disease in rich settings to emerge as causes of highly deadly disease in Africa. Hence a critical first step in tackling diseases such as this is to be able to recognize the different ‘types’, which will in turn allow us to better understand how bacteria can exploit different ecological niches to which the global human population is exposed,” Thomson said.
Researchers said a human vaccine is also under development, but further investigations are urgently needed into where these African types reside in the environment and how they are passed on to or between people.
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