Emergence of Extensively Drug-resistant Shigella Sonnei Strain in France
Published:29 Mar.2023 Source:Institut Pasteur
Shigellosis is a highly contagious diarrheal disease that spreads through fecal-oral transmission. Among the different types of Shigella, Shigella sonnei is the species that mainly circulates in industrialized countries. Shigella sonnei infections can cause short-term diarrhea (3-4 days) that resolves on its own. Antibiotic treatment is, however, necessary for moderate to severe cases (bloody diarrhea, risk of complications) or to prevent person-to-person transmission in epidemic situations. The acquisition of antibiotic resistance mechanisms by Shigella bacteria therefore restricts therapeutic options.
In this study, scientists from the National Reference Center for Escherichia coli, Shigella and Salmonella (CNR-ESS) at the Institut Pasteur demonstrate an increase in antibiotic resistance in S. sonnei isolates collected in France over the past 17 years. The study is based on an analysis of more than 7,000 S. sonnei isolates and epidemiological information gathered in connection with national shigellosis surveillance conducted by the CNR-ESS between 2005 and 2021. The CNR-ESS analyzes all the bacterial isolates sent by its network of private and public partner laboratories throughout France. Over this period, isolates described as "extensively drug resistant" (XDR) were identified for the first time in 2015. The scientists then observed that the proportion of XDR isolates, which are resistant to virtually all the antibiotics recommended for treating shigellosis, increased significantly and reached a peak in 2021, when 22.3% of all S. sonnei isolates (99 cases) were XDR.
Genome sequencing revealed that all these French XDR strains belonged to the same evolutionary lineage, which became resistant to a key antibiotic (ciprofloxacin) in around 2007 in South Asia. In several geographical regions of the world, including France, the strains then acquired different plasmids coding for resistance to other first-line antibiotics (especially third-generation cephalosporins and azithromycin). For severe cases, the only antibiotics that are still effective are carbapenems or colistin, which must be administered intravenously, resulting in more aggressive treatment that requires more complex monitoring in a hospital environment.