Download Lactobacilli Lactobacillus species General Characteristics

Lactobacilli
Lactobacillus species
General Characteristics:
* Lactobacillus species derived from the family Lactobacillaceae Gram positive
bacilli.
* Arranged in pairs of short chains.
* Grow in facultative anaerobic conditions.
* 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
Gram positive lactobacilli
Lactobacilli under electron microscope
*Taxonomy:Lactobacilli are classified into two groups based on glucose fermentation:1- Homo Fermenters:Produce lactic acid from glucose fermentation.
e.g. Lactobacillus casei
Lactobacillus acidophilus
2- Hetero Fermenters:Produce 50% lactic acid as well as acetate, ethanol, and carbon dioxide.
e.g. Lactobacillus Fermentum
Lactobacillus brevis
*Cultures:Lactobacilli need complex nutritional requirements. They
microaerophilic or facultative anaerobic condition and acidic pH.
grow
Lactobacilli can grow on many media:1- Blood and chocolate agar (enriched media). Incubate at 37C° 2-4 days.
2- Special Selective medium.
under
A- Tomato juice agar (pH 5): which contain peptone, casein, tomato juice and
agar.
Tomato juice agar
B- Rogosa agar: This medium contains fatty acids, magnesium, purines,
pyrimidine, vitamins, and amino acids and the pH is (6-6.5). It also contains
sodium acetate and ammonium citrate which is used to inhibition the growth of
normal flora and fungi and made this medium selective especially for lactobacilli.
Rogosa agar
*Oral Ecology:At birth oral cavity is sterile and during infant passage through the birth canal, his
oral cavity may be contaminated with lactobacillus species from the female
vagina, after that and during the first 2 years of his/her life, lactobacilli occur only
in a very low numbers. In oral cavity they constitute less than 1% of the total oral
flora.
Lactobacillus species and Streptococcus mutans are cariogenic bacteria which
cause dental caries.
*Steps of Dental Caries:1-Streptococcus mutans is the most important species in the forming of dental
caries 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 into monosaccharides (glucose
and fructose), and the presence of sucrose stimulates Streptococcus mutans to
synthesis sticky polymers and this allow for adhesions on smooth surface (tooth).
3-Then they ferment sucrose to form a strong acid (lactic acid), which destroys the
tooth structure by demineralization of Ca (OH)2 and calcium phosphate mostly
hydroxyapatite {Ca5(PO4)3(OH)}.
4-Lactobacillus species will continue to form lactic acid and produce the cavity of
dental caries.
*Dental Caries Activity Tests:1-Counting of streptococcus mutans and lactobacillus species 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: If the counting is < 105 CFU/ ml of Streptococcus mutans
and < 104 CFU/ ml of Lactobacillus species.
2. Snyder test: is used to determine a person’s susceptibility to dental caries. The
susceptibility is correlated with acid production that is assumed to result from
fermentation by cariogenic Lactobacillus species on the teeth or other areas of the
mouth.
The Snyder test agar contains 2% glucose and a pH indicator bromocresol
green. The pH of the agar is about 4.8, which inhibits the growth of most
organisms, but it is ideal for acidophiles such as Lactobacillus species. Saliva
samples are inoculated into the tubes and allowed to incubate. If lactobacilli are
present in the saliva, it will ferment the glucose and produce lactic acid, causing
the pH to drop to about 4.4. This causes the bromocresol green to change from
green to yellow. A culture demonstrating a yellow color indicates a person is
susceptible to the formation of dental caries.
Snyder test
3. Reductase Test:
Salivary reductase test measures the activity of reductase enzyme present in
salivary bacteria. Paraffin-stimulated saliva is collected in a plastic container
and an indicator dye "diazoresorcinol" is added to nitrate broth, which
colors the saliva blue.
The reductase enzyme liberated by the salivary bacteria cause changes in the
medium from blue to other colors, which indicate the caries conduciveness
of the patients.
Color
Time
Score
Conduciveness on
caries
Blue
15 min
1
Non-conducive
Orchid
15 min
2
Slightly conducive
Red
15 min
3
Moderately
conducive
Red
30 sec
4
Highly conducive
Pink/White
30 sec
5
Extremely
conducive