Cholera is a severe diarrheal disease typically caused by the O1 strain of the bacterium Vibrio cholerae. All pandemic O1 strains require two critical factors to cause disease: cholera toxin (CT) and toxin coregulated pilus (TCP). However, some nonpandemic strains of V. cholerae do not produce CT or TCP and yet still cause disease.
Researchers from Harvard Medical School, Brigham and Women's Hospital and the Howard Hughes Medical Institute studied one of those strains (AM-19226) which causes a rapidly fatal diarrheal disease in rabbits. Analysis of the genome showed that the bacterium lacked the genes that code for CT and TCP but instead carried a gene encoding a type III secretion system (TTSS), which other bacteria are known to use to infect host cells.
TTSS proved to be essential for AM-19226 virulence in rabbits. An AM-19226 derivative deficient for TTSS did not cause diarrhea or colonize the intestine.
"Our findings provide insight into a new type of diarrheagenic mechanism used by non-O1, non-O139 V. cholerae strains and suggests that TTSS can lead to diarrheal illness," write the researchers.
The research was published in American Society for Microbiology’s journal, mBio.