To study the effects of Lactococcus lactis (Ll) on the growth and biofilm formation of 4 kinds of cariogenic bacteria, and to provide the basis for the application in caries prevention and control.

Ll, Streptococcus mutans (Sm) , Actinomyces naeslundii (An) , Actinomyces viscosus (Av) and Lactobacillus acidophilus (La) were cultured under anaerobic conditions. A spot-on-lawn assay was used to evaluate the inhibition of Ll for these 4 kinds of cariogenic bacteria. The antagonistic interaction between Ll and these cariogenic bacteria was detected by plate competition test. The four kinds of cariogenic bacteria cultured separately were the single-cultured group, Ll co-cultured with 4 cariogenic bacteria separately were the co-cultured group. Crystal violet staining (CVS) and scanning electron microscopy (SEM) was used to evaluate the effect of Ll on the biofilm formation of the 4 kinds of cariogenic bacteria. SPSS 20.0 statistical software was used for data analysis. The data from the measurement of the inhibitory-zone diameters (IZD) of Ll against the 4 kinds of cariogenic bacteria were compared and statistically analyzed with One-Way analysis of variance (ANOVA) and tukey′s HSD test, and the amount of bacterial biofilm was compared by Student′s t test.

Spot-on-lawn assay showed that Ll inhibited the growth of the 4 kinds of cariogenic bacteria. Ll had the largest IZD for An, (11.97 ± 0.40) mm, and the smallest for Sm, (4.67 ± 0.32) mm. Ll showed statistically significant difference in the IZD of the 4 kinds of cariogenic bacteria (F = 241.22, P<0.001) . The plate competition test showed that Ll showed competitive inhibition against La, An and Av. CVS showed that the biofilm quantity of Sm and An co-cultured with Ll was (30.66 ± 0.48) and (10.27 ± 0.04) , respectively. The biofilm quantity of Sm and An single-cultured was (80.26 ± 2.55) and (73.98 ± 0.35) , respectively. For Sm and An biofilm, there was statistical difference in the biofilm quantity between co-cultured and single-cultured groups (t_Sm = 19.090, P_Sm<0.001, t_An = 183.3, P_An<0.001) . The SEM showed that Sm and An showed significantly thinner biofilm in coexistence with Ll than in the absence of Ll.

Ll could inhibit the growth of Sm, An, Av, La, and reduce the formation of Sm, An biofilms.