Multilevel Genome Typing Describes Short- and Long-Term Vibrio cholerae Molecular Epidemiology

Since 1817, cholera, caused by Vibrio cholerae, has been characterized by seven distinct pandemics. The ongoing seventh pandemic (7P) began in 1961. In this study, we developed a Multilevel Genome Typing (MGT) tool for classifying the V. cholerae species with a focus on the 7P. MGT is based on multilocus sequence typing (MLST), but the concept has been expanded to include a series of MLST schemes that compare population structure from broad to fine resolutions. The V. cholerae MGT consists of eight levels, with the lowest, MGT1, composed of 7 loci and the highest, MGT8, consisting of the 7P core genome (3,759 loci). We used MGT to analyze 5,771 V. cholerae genomes. The genetic relationships revealed by lower MGT levels recapitulated previous findings of large-scale 7P transmission across the globe. Furthermore, the higher MGT levels provided an increased discriminatory power to differentiate subgroups within a national outbreak. Additionally, we demonstrated the usefulness of MGT for non-7P classification. In a large non-7P MGT1 type, MGT2 and MGT3 described continental and regional distributions, respectively. Finally, MGT described trends of 7P in virulence, and MGT2 to MGT3 sequence types (STs) grouped isolates of the same ctxB, tcpA, and ctxB-tcpA genotypes and characterized their trends over the pandemic. MGT offers a range of resolutions for typing V. cholerae. The MGT nomenclature is stable, transferable, and directly comparable between investigations. The MGT database (https//mgtdb.unsw.edu.au/) can accept and process newly submitted samples. MGT allows tracking of existing and new isolates and will be useful for understanding future spread of cholera. IMPORTANCE In 2017, the World Health Organization launched the "Ending Cholera" initiative to reduce cholera-related deaths by 90% by 2030. This strategy emphasized the importance of the speed and accessibility of newer technologies to contain outbreaks. Here, we present a new tool named Multilevel Genome Typing (MGT), which classifies isolates of the cholera-causing agent, Vibrio cholerae. MGT is a freely available online database that groups genetically similar V. cholerae isolates to quickly indicate the origins of outbreaks. We validated the MGT database retrospectively in an outbreak setting, showcasing rapid confirmation of the Nepalese origins for the 2010 Haiti outbreak. In the past 5 years, thousands of V. cholerae genomes have been submitted to the NCBI database, which underscores the importance of and need for proper genome data classification for cholera epidemiology. The V. cholerae MGT database can assist in early decision making that directly impacts controlling both the local and global spread of cholera.