A study published late last week in Nature Communications details the evolution and spread of a strain of extensively drug-resistant (XDR) Shigella.
Using genomic epidemiology, a team of researchers led by the United Kingdom Health Security Agency (UKHSA) analyzed a collection of more than 3,000 isolates from a strain of XDR Shigella sonnei that has caused shigellosis outbreaks in the United Kingdom and several other countries (Australia, Belgium, France, and the United States) since late 2021. The analysis revealed an internationally connected outbreak with a most recent common ancestor in 2018 that has been primarily associated with spread among men who have sex with men (MSM).
Although shigellosis is commonly associated with exposure to food or water that has been contaminated by human feces and is known to spread in settings with overcrowding and poor sanitation, oral and anal sex has become a major route of transmission, particularly among MSM.
While earlier versions of the S sonnei strain were resistant to the first-line (ciprofloxacin) and second-line (azithromycin) treatments recommended by the World Health Organization for treatment of shigellosis, the emergent XDR strain carries an additional resistance gene that confers resistance to ceftriaxone and a plasmid that can share the gene with other enteric bacteria. The study authors suggest the resistance to ceftriaxone is likely being driven by bystander resistance resulting from the use of ceftriaxone for treatment of gonorrhea.
"Treatment for ongoing high rates of gonorrhoea in the UK thus likely contributed to the acquisition of resistance to third-generation cephalosporins into this circulating ciprofloxacin resistant lineage of S. sonnei," they wrote. "It is also possible that plasmid fitness cost played a role in the emergence of this XDR strain."
The authors say active surveillance of microbiota among MSM receiving antibiotic treatments for sexually transmitted infections could potentially help mitigate the further development of XDR or pan–drug-resistant strains of Shigella. They also call for open international sharing of genomic surveillance data to help identify early indicators of antimicrobial resistance threats.