Lactobacilli

Lab Twenty Tow:- ________________ Medical Microbiology
Prepared by: Luma J. Witwit

Lactobacilli

Lactobacilli, gram positive rod shaped bacteria that are non-sporing, non motile, non capsulated either facultative anaerobic or strictly anaerobic strongly acid producing (acidogenic) by fermentation of carbohydrates and exceptionally capable of survival and growth under acid conditions (aciduric ) Lactobacilli are divided in to tow groups on the basis of glucose fermentation:-

1- Hetero fermentative Lactobacilli (ferment glucose to mixed organic acid + CO2 + ethanol ).

2- Homo fermentative Lactobacilli (ferment glucose to lactic acid).


Lactobacilli and Dental Caries:-

Dental caries is the destruction of the enamel dentin or cementum of teeth due to bacterial activities.
Caries are initiated by direct demineralization of the enamel of teeth due to lactic acid and other organic acids which accumulate in dental plaque.
Lactic acid bacteria in the plaque produce lactic acid from the fermentation of sugars and carbohydrates in the diet of the host . Together with certain Streptococci , The commensally Lactobacilli of the mouth probably play an important part in the causation of dental caries. The bacteria are thought to ferment dietary carbohydrates, such as sucrose, with the production of acid which dissolves the mineral component (calcium phosphate, hydroxidel of the enamel and dentine. The Lactobacilli are more aciduric than the Streptococci and other oral bacteria and therefore survive and continue to ferment carbohydrate under more strongly acidic conditions. e.g. at pH 3.0 to 4.0. There are often significantly relate to the salivary levels of caries associated microorganisms including Lactobacilli and the number of eating events per day.
Lactobacilli comprised 2% to 3% of the total cultivable micro flora at (normal sites) but 18% at those enamel sites experiencing the most extensive mineral loss.

Diagnosis

1- Gram stain: gram positive rods.
2- Media containing glucose, yeast extract or blood, incubated for 2 to 4 days at 37Co under anaerobic conditions (5% CO2).

3- Selective media.
a) Tomato juice agar (pH = 5) for Lactobacilli .
b) Trypsin Digest agar for L. acidophilus.
c) Regosa agar (2.5% sodium acetate); For Lactobacilli.
d) Tomato juice agar special (pH =5 ).

This media encourage the growth of Lactobacilli and at the same time inhibit the growth of many commensal bacteria they may be encountered in saliva.

Synder test
Synder test is prepared for the colorimetric diagnosis of caries activity, this method is based on acid production in carbohydrates medium by acidogenic microorganism from the buccal cavity and is evidenced by a change in color of the indicator, bromocresol green from a blue green to a yellow color.
This test gives excellent correlation with the Lactobacillus plate count and with the clinical picture and provides a simple reliable method for ordinary clinical use in the diagnosis of caries activity.

Procedure
Mix 0.2 saliva with synder test agar (dextrose, tryptone, sodium chloride, Indicator bromcresol green) and incubated at 37Co for 72 hours.

Interpretation Incubation hours

Caries Activity 24 48 72
Marked positive positive positive
Moderates negative positive positive
Slight negative negative positive
Negative negative negative negative

* Positive: change in color (bluish-green to yellow)
Negative: no change in color (green still)