The new research has found three separate types of Salmonella enteritidis bacteria: two novel African types, which appear the same, but are in fact genetically different, from the better characterized Western type.
The organism of concern is a subspecies of Salmonella enterica called Type 1, and the genetic variations relate to serovars called enteritidis. A serotype is strain of Salmonella based on reaction with specific antibodies.
Invasive non-typhoidal Salmonella disease is a disease of the bloodstream (Salmonellosis). It is also a neglected tropical disease, with an estimated 680,000 deaths occurring worldwide each year, with over half of these happening in Africa. Infection usually occurs when a person ingests foods that contain a high concentration of the bacteria.
With the new research, microbiologists sequenced 675 isolates of S. enteritidis from 45 countries and six continents. The analysis showed three major types: a common global one, and two previously uncharacterized African types. Importantly, standard microbiological testing is unable to distinguish between these different types and differentiation is only possible by using molecular biological techniques.
The distinction is, however, important since the common global type infects the intestines and causes diarrhoea, whereas the newly identified African types cause blood borne infections. Blood infections are more serious and carry a higher risk of fatality.
A further important point is that with the two African types, these types contain resistance genes to antibiotics such as amoxicillin and chloramphenicol. These antibiotics, where available, are the common ones used in many parts of Africa. The message here is that such antibiotics would not be effective.
The detection of the two new types does not offer any immediate solutions; however, it does indicate new threats and risk factors and poses an important conundrum for global health services.
The research is a collaborative effort between Wellcome Trust Sanger Institute, Liverpool School of Tropical Medicine and University of Liverpool. The findings have been published in Nature Genetics, in a study headed “Distinct Salmonella Enteritidis lineages associated with enterocolitis in high-income settings and invasive disease in low-income settings.”
