Global and regional landscape of biogeographical diversity of Streptococcus mutans: Epidemiological insight from multilocus sequence typing

Streptococcus mutans (S. mutans) is a major cariogenic bacterium. However, its geographic population structure remains poorly characterized. This study included 728 clinical strains collected by our team (339 from Bengbu and 389 from Guangzhou), of which 648 were newly isolated. Following sequence typing, 137 strains could not be assigned a sequence type (ST) due to genetic variations, whereas the remaining 591 strains were categorized into 153 STs, including 100 novel STs. These 591 strains (305 from Bengbu and 286 from Guangzhou isolates), together with 467 strains retrieved from the PubMLST database (5 Chinese strains with unspecified geographical location and 462 international strains from 13 countries), yielded 1058 strains for genetic analysis. We found that the multilocus sequence typing (MLST) success rate was lower for strains from Guangzhou (73.5%) than for those from Bengbu (90.0%), with 27 STs shared between the two regions. The Guangzhou isolates exhibited significantly greater genetic diversity. Among the 462 international strains, 271 STs were identified. Although 23 STs were shared between Chinese and international isolates, considerable population stratification was observed. ST2 was the most prevalent ST. However, it was detected in only 35 of 1058 strains (3.3%). Genetic variation was significantly associated with isolation site (plaque vs. saliva) and serotype (c/e vs. f/k), but not with caries status. Overall, the findings indicate a high level of population diversity in S. mutans, the absence of dominant global epidemic strains, and no association between ST and caries status.