Acid shock triggers virulence surge accompanied by bacterial elongation in streptococcus mutans

Abstract Pediatric caries is a major global oral health burden, children are particularly susceptible due to immature oral defense mechanisms, underdeveloped immune responses, and frequent exposure to sugar-rich diets that promote cariogenic bacterial activity. Streptococcus mutans ( S. mutans ) is widely recognized as a primary cariogenic pathogen, responsible for key virulence factors such as acid production, acid tolerance and exopolysaccharide (EPS) synthesis. Given that S. mutans can adapt to acidic environments through mechanisms such as the acid tolerance response (ATR), we cultured S. mutans in a medium supplemented with hydrochloric acid or lactic acid at pH gradients of 6, 5 and 4 to observe how its virulence changed in response to early low pH shock. S. mutans was found to exhibit delayed growth, increased biofilm biomass, and up-regulated expression of virulence-associated genes, accompanied by bacterial elongation under early low pH shock. It is noteworthy that the morphological changes in bacteria have a substantial impact on biofilm formation and stability. We propose that early acid shock may trigger a virulence surge through bacterial elongation, thus conferring a stronger cariogenic capacity. This finding provides critical insights into the pathogenic mechanisms of pediatric caries and offers potential targets for developing tailored preventive strategies for children.