Background. Chronic periodontitis is one of the most common infectious diseases of the oral cavity. Dental plaque contains a mix of oral bacteria, and grows as biofilm on tooth surfaces. One of the bacterial species associated with periodontitis is Porphyromonas gingivalis, a Gram-negative anaerobic rod. Lactobacilli are used in probiotic products and are known to play an important role in the management of health by stimulating the immune system and contributing to the balance of the normal microflora. The knowledge of probiotic effects on oral bacteria is at present limited.
Purpose. Lactobacillus reuteri, and Lactobacillus acidophilus are two species used in different probiotic products. In the presence of glycerol L. reuteri produces an antimicrobial product, 3-hydroxypropionaldehyd, also called reuterin. The purpose of the study was to examine the impact of L. reuteri and L. acidophilus on biofilm formed by P. gingivalis.
Methods. To study whether L. reuteri and L. acidophilus had ability to alter the biofilm formation of P. gingivalis, 108 CFU/mL P. gingivalis and 108 CFU/mL of one of the lactobacilli were co-cultured in Brucella broth using cell-culture plates. After 48 h incubation the broth was removed and the biofilm studied by microscopy, crystal violet staining with subsequent absorbance measurements at 590 nm. Viable bacterial cells were determined in the biofilm and in the removed growth medium.
Results. P. gingivalis and L. reuteri cultured individually formed heavy layers of biofilm (A590=2.1-3.1), whereas L. acidophilus gave a very thin layer (A590=0.21-0.35). In the biofilm competition assay, the level of viable P. gingivalis cells were reduced by at least 3 logs regardless the addition of glycerol when co-cultured with L. reuteri or L. acidophilus. In presence of glycerol, both P. gingivalis and L. reuteri were reduced below the detection level after 48 h incubation.
Even though P. gingivalis cultured as single species formed a dense biofilm this was strongly reduced when co-cultured with L. acidophilus.
Conclusion. In summary, the observed glycerol-dependent growth inhibition of P. gingivalis by L. reuteri seemed to be due to reuterin production. Competition in the biofilm model appeared to favor both lactobacillus species tested at the expense of P. gingivalis. The lactobacilli were able to strongly inhibit or suppress the growth of a major periodontal pathogen in the biofilm-competition assay.
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