Antibacterial and Antivirulence Effects of Kale (Brassica oleracea var. sabellica) on Streptococcus intermedius

Abstract

Persistent odontogenic infections caused by resistant bacterial species, such as , have consistently been associated with deep-seated infections. This in vitro study aimed to evaluate the antibacterial and antivirulence effects of kale () on . was freshly incubated in tryptic soy broth media. Three experiments per concentration of kale were conducted under aseptic conditions (i.e., disc diffusion, broth microdilution, and reverse-transcription polymerase chain reaction) to evaluate the antibacterial and antivirulence effects. The samples were then treated with 1000, 500, 250, 125, 65, 30, 15, 7, and 3 mg/mL kale; ampicillin (positive control); and tryptic soy broth (negative control). After 24-h incubation, the inhibition zone, minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and relative gene expression of the virulence factor (intermedilysin []) were measured. All assays were conducted in triplicate. The findings were reported and analyzed as means ± standard deviations. The agar disc diffusion and relative gene expression were statistically analyzed using one-way analysis of variance and Tukey’s test, with the significance level set at P < 0.05. Kale showed antibacterial effects on by significantly inhibiting bacterial growth and reducing expression only at a concentration of 1000 mg/mL; it yielded an inhibition zone of 11.12 ± 1.59 mm, which was smaller than that with ampicillin. The MIC and MBC ranged from 15 to 65 mg/mL and from 500 mg/mL, respectively. Conversely, the highest concentration of kale yielded significantly less inhibition than did ampicillin. The antibacterial effects of kale may be dose-dependent. Kale can inhibit bacterial growth and suppress expression under in vitro conditions of , which is mainly involved in deep-seated odontogenic infections.