Lactobacilli
Kingdom: Bacteria Phylum: Firmicutes Class: Bacilli Family: Lactobacillacea Genus: LactobacillusGeneral Characteristics
Lactobacillus species from the family Lactobacillaceae. G+ bacilli . Arranged in pairs of short chain and straight rod. Facultative anaerobes.Non motile . Non spore forming . Catalase (-) . Fermentation of many carbohydrates and forming acids.
Habitation 1- Oral cavity . 2- Gastrointestinal tract . 3- Female genital tract .
Species :-Lactobacillus acidophilus Lactobacillus casei Lactobacillus fermentum Lactobacillus brevis
Taxonomy
Lactobacilli are classified into two groups based on glucose fermentation :- 1- Homo Fermenters :- Produce lactic acid from glucose fermentation . ex :- Lactobacillus casei Lactobacillus acidophilus 2- Hetero Fermenters :- Produce 50% lactic acid as well as acetate , ethanol and carbon dioxide. ex :- Lactobacillus Fermentum Lactobacillus brevis* Culture:-
A- Tomato juice agar (pH 5) .
B- Rogosa agar Fatty acids. Magnesium, pH (6 – 6.5). Purine , pyrimidine.Vitamins and amino acids. Sodium acetate and ammonium citrate is used to inhibit the growth of normal oral flora and fungi. This medium is selective medium specially for lactobacilli.
The Role of Lactobacilli in Dental Caries
At birth oral cavity is sterile. Infant during passage through the birth canal the oral cavity may be contaminated with lactobacilli from the female vagina. After that and during first 2 years of life Lactobacillus species occur in very low numbers: Lactobacillus species and Streptococcus mutans are cariogenic (bacteria which cause dental caries).Oral ecology
Steps of Dental Caries :-1- Streptococcus mutans is the most important species in the forming of caries which found in the mouth when a solid surface such as teeth are present and the first step is the colonization on tooth surface . 2- When sugar is ingested , sucrose is broken down to monosaccharides (Glucose and Fructose), and the presence of sucrose stimulates Streptococcus mutans to synthesis sticky polymers and this allow for adhesions to smooth surface (tooth).
3- Then they ferment sucrose to the strong acid (lactic acid). 4-This acid destroy the tooth structure by demineralization of Ca (OH)2 and calcium phosphate mostly hydroxyapatite {Ca5(PO4)3(OH)}. 5- Lactobacillus species will continue to form lactic acid and produce the cavity of dental caries.
Steps of Dental Caries
Dental Caries Activity Tests :-1. Counting of Streptococcus mutans and lactobacillus spp. in the saliva . * High caries activity:- If the counting is >106 CFU/ml of Streptococcus mutans and > 105 CFU/ ml of Lactobacillus species. * Low caries activity:- Low caries activity:- If the counting is < 105 CFU/ ml of Streptococcus mutans and < 104 CFU/ ml of Lactobacillus species.
1. Counting of Streptococcus mutans and lactobacillus spp. in the saliva
2. Snyder test:
Is used to determine a person’s susceptibility to dental caries Acid production from cariogenic Lactobacillus species on the teeth or in other areas of the mouth.Contains 2% glucose pH indicator bromocresol green.4.8 inhibits the growth of most organisms (ideal for Lactobacilli)Saliva samples are inoculated into the tubes and allowed to incubate.Lactobacillus glucose lactic acid 4.8_4.4. green yellow dental caries.
3- REDUCTASE TEST This test measures the activity of reductase enzyme present in salivary bacteria. The sample is mixed with nitrate broth and a fixed amount of diazoresorcinol (indicator). The change in color immediately and after 15 min is taken as a measure of caries activity. Nitrate/nitrite reductase enzyme caries activity