关键词: 栖组织普雷沃菌, 栖牙普雷沃菌, 小斑点普雷沃菌, 牙釉质龋, 生物膜, 脱矿

Abstract: Objective    To investigate and compare the cariogenic effects of three Prevotella species ［Prevotella histicola（P.h），Prevotella denticola（P.d）and Prevotella maculosa（P.m）］ and provide a reference basis for the prevention and treatment of dental caries. Methods    Three Prevotella species and Streptococcus mutans（S.m）were cultured for 24 h. The pH of the bacterial supernatant was then measured，and high-performance liquid chromatography was employed to detect acid production in the supernatant. The four bacterial cultures were incubated at pH levels of 4.5，5.5，and 6.5 for 24 h，and the optical density（OD）was measured to evaluate bacterial acid resistance. Crystal violet staining was used to detect the biofilm formation of the four bacterial cultures after 48 h of incubation. The morphology and structure of the biofilm were observed using scanning electron microscopy and laser confocal microscopy. The content of water-insoluble extracellular polysaccharides in the biofilm was determined using the anthrone method. Twenty impacted third molars were collected from patients who visited the Department of Stomatology at Qingdao Municipal Hospital between July and August 2024. Forty enamel blocks were prepared and randomly divided into five groups，each containing eight blocks. The groups were incubated in TSBS culture medium with bacterial solutions of P.h（P.h group），P.d（P.d group），P.m（P.m group），and S.m（S.m group），and a sterile control group was set. After two weeks of culture，the enamel surface morphology was examined using scanning electron microscope，and the difference in Vickers hardness（HV）of the enamel blocks before and after culturing was measured with a micro Vickers hardness tester. Results    ①After 24 h of incubation，compared with the three Prevotella species，the pH of the supernatant from S.m was lower，and the concentrations of lactic acid and total acid were higher. The pH of the supernatant from P.h was significantly lower than that from P.d and P.m，and the concentrations of succinic acid，lactic acid，acetic acid，and total acid were all greater than those of P.d and P.m，with all differences being statistically significant（P < 0.05）. The differences between P.d and P.m were not statistically significant（P > 0.05）. ②After being cultured for 24 h under different pH conditions，the OD of S.m significantly increased compared to the three Prevotella species. At a pH of 6.5，the OD of P.h was greater than that of both P.d and P.m，while the OD of P.d exceeded that of P.m，with all differences being statistically significant（P < 0.05）. As the values of pH decreased，bacterial growth was progressively inhibited. At a pH of 4.5，the OD of S.m increased slowly，while the growth of the three Prevotella species was greatly inhibited. ③After 48 h of cultivation，all three species of Prevotella were capable of forming biofilms. The biofilm formed by P.h exhibited a uniform and dense structure，contaning numerous microbial colonies. Compared to those of P.d and P.m，the concentration of insoluble extracellular polysaccharides in the P.h biofilm ［（1.39 ± 0.23）g/L］ was significantly higher，along with an increased biofilm thickness ［（16.33 ± 2.08）μm］，all the differences being statistically significant（P < 0.05）. The biofilm thicknesses for P.d and P.m were（8.33 ± 1.53）μm and（7.33 ± 1.53）μm，respectively，with corresponding concentrations of water-insoluble extracellular polysaccharides being（0.91 ± 0.04）g/L and（0.72 ± 0.08）g/L. No significant differences were observed between these two species（both P > 0.05）. ④All three species of Prevotella were capable of inducing enamel demineralization. Specifically，the P.h group exhibited a more severe degree of enamel surface demineralization，characterized by a larger HV difference than that of P.d and P.m，the differences being statistically significant（P < 0.05）. There was no statistically significant difference in HV difference between the P.d group and the P.m group（P > 0.05）. Moreover，the HV difference in the S.m group exceeded three Prevotella groups，with statistically significant differences（all P < 0.05）. Conclusion    P.h，P.d and P.m can all lead to dental caries through acid production，acid tolerance，biofilm formation and induction of enamel demineralization，although their cariogenicity is slightly weaker than S.m. The cariogenic effect of P.h is greater than the other two Prevotella species，while no significant differences in cariogenicity are observed between P.d and P.m.

Key words: Prevotella histicola, Prevotella denticola, Prevotella maculosa, enamel caries, biofilm, demineralization