Inhibitory Effect of Bacillus licheniformis Strains Isolated from Canine Oral Cavity

Abstract

Bacillus licheniformis is used in a broad spectrum of areas, including some probiotic preparations for human and veterinary health. Moreover, B. licheniformis strains are known producers of various bioactive substances with antimicrobial and antibiofilm effects. In searching for new potentially beneficial bacteria for oral health, the inhibitory effect of B. licheniformis strains isolated from canine dental biofilm against pathogenic oral bacteria was evaluated. The antimicrobial effect of neutralized cell-free supernatants (nCFS) was assessed in vitro on polystyrene microtiter plates. Furthermore, molecular and morphological analyses were executed to evaluate the production of bioactive substances. To determine the nature of antimicrobial substance present in nCFS of B. licheniformis A-1-5B-AP, nCFS was exposed to the activity of various enzymes. The nCFS of B. licheniformis A-1-5B-AP significantly (p < 0.0001) reduced the growth of Porphyromonas gulae 3/H, Prevotella intermedia 1/P and Streptococcus mutans ATCC 35668. On the other hand, B. licheniformis A-2-11B-AP only significantly (p < 0.0001) inhibited the growth of P. intermedia 1/P and S. mutans ATCC 35668. However, enzyme-treated nCFS of B. licheniformis A-1-5B-AP did not lose its antimicrobial effect and significantly (p < 0.0001) inhibited the growth of Micrococcus luteus DSM 1790. Further studies are needed for the identification of antimicrobial substances.

Keywords: Bacillus licheniformis; antimicrobial effect; cell-free supernatant; oral pathogens.

Figure 1

Inhibitory activity of nCFS of Bacillus licheniformis strains against the growth of oral pathogens; data are presented as the arithmetic means ± standard deviation; **** (p < 0.0001)—significant difference compared to the non-treated control.

Figure 2

Forming of viscous filament known as ropy phenotype in B. licheniformis A-1-5B-AP.

Figure 3

Enzymatic treatment of neutralized cell-free supernatants of B. licheniformis A-1-5B-AP and its activity against indicator strain of Micrococcus luteus DSM 1790; data are presented as the arithmetic means ± standard deviation; **** p < 0.0001—significant difference compared to the non-treated control.