Materials and methods: The antimicrobial effects of vitamin D3 were evaluated against Strep. sobrinus and Strep mutans using the agar disc diffusion method. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of vitamin D3 were determined using a microdilution method following the guidelines by the Clinical Laboratory Standards Institute (CLSI). Scanning electron microscope (SEM) was used to evaluate the morphological changes of bacterial cells following exposure to vitamin D3.
Results: Strep. sobrinus was more sensitive to vitamin D3 compared to Strep. mutans bacteria. The MIC values of vitamin D3 against Strep. sobrinus and Strep. mutans were 60 μg/ mL and 250 μg/mL respectively whereas the MBC values were 120 μg/mL and 500 μg/mL, respectively. Moreover, significant changes in the bacterial morphology were observed in treated bacterial cells with vitamin D3 as compared to the untreated control bacteria using SEM.
Conclusion: These findings suggested that vitamin D3 has excellent antimicrobial effects against Strep. sobrinus and Strep. mutans and may be considered as a promising compound in the prevention of dental caries in the future. Further research is recommended to elucidate the mechanism of vitamin D3 on these bacteria.
METHODOLOGY/PRINCIPAL FINDINGS: We performed a literature review, whole genome sequencing on 145 GBS isolates collected from six Southeast Asian countries, and phylogenetic analysis on 7,468 GBS sequences including 227 variants of ST283 from humans and animals. Although almost absent outside Asia, ST283 was found in all invasive Asian collections analysed, from 1995 to 2017. It accounted for 29/38 (76%) human isolates in Lao PDR, 102/139 (73%) in Thailand, 4/13 (31%) in Vietnam, and 167/739 (23%) in Singapore. ST283 and its variants were found in 62/62 (100%) tilapia from 14 outbreak sites in Malaysia and Vietnam, in seven fish species in Singapore markets, and a diseased frog in China.
CONCLUSIONS: GBS ST283 is widespread in Southeast Asia, where it accounts for a large proportion of bacteraemic GBS, and causes disease and economic loss in aquaculture. If human ST283 is fishborne, as in the Singapore outbreak, then GBS sepsis in Thailand and Lao PDR is predominantly a foodborne disease. However, whether transmission is from aquaculture to humans, or vice versa, or involves an unidentified reservoir remains unknown. Creation of cross-border collaborations in human and animal health are needed to complete the epidemiological picture.