1. Lactobacillus
Dr Alex Owusu-Ofori

2. Lactobacillus species
L. brevis
L. acidophilus
L. sanfranciscensis
L. casei

3. Lactobacillus species Characteristics
Gram positive,
Rod-shaped
Non-sporulating
Non motile
Survive both aerobic and anaerobic
Occur singly or in chains

4. Lactobacillus species Gram Stain
Two types
Long slender GPR in chains
Short GPCB

5. Lactobacillus species Colony Morphology
Grows on sheep blood
Multiple colony morphologies
Nonhemolytic or alpha hemolytic

6. Lactobacillus species
Lactobacillus acidophilus produces vitamin K and lactase
L. acidophilus cannot make other vitamins and amino acids
They generate ATP by non-oxidative substrate-level phosphorylation

7. Lactobacillus species Clinical Significance
Normal flora
Mouth
GI tract
Female vaginal tract
Rarely pathogenic
Endocarditis
Meningitis

8. What is the clinical significance of Lactobacillus species?
It is considered normal flora of the mouth, gastrointestinal tract, and female genital tract

9. Lactobacillus in humans
Vagina has flora that varies according to hormonal influences at different ages.
Before puberty and after menopause it is mixed, nonspecific and scanty – mainly normal skin and colon flora.
During childbearing years – predominantly anaerobic and microaerophilic members of the genus lactobacillus with a few anaerobic G-ve rods, G +ve cocci and yeast that can survice the acidic conditions produced by lactobacilli.

10. Lactobacillus in humans
These conditions develop because glycogen is deposited in vaginal epithelial cells under the influence of oestrogenic hormones and metablised to lactic acid by lactobacilli.
This process results in a vaginal pH of 4-5, which is optimal for growth and survival of lactobacilli but inhibits many other organisms.

11. Industrial use Used for sour bread, milk,yogourt, sausages
Lactobacilli need maltose, then produce ethyl alcohol and CO2
Lactobacilli produce lactic and acetic acids giving the sour flavor, pH inhibits microbial growth
Milk is Soured by Streptococcus lactis, Lactobacillus
Yogurt- Streptococcus and Lactobacillus added to milk

12. Bacteria in Yogurt lactic acid bacteria are found in yogurt
Streptococcus thermophillus
lactic acid bacteria are found in yogurt
lactic acid lowers the pH in milk causing
casein (milk protein) to denature and the milk to curdle
Lactobacillus bulgaricus
Lactobacillus acidophilus
Lactobacillus casei
Bifidobacterium Bifidum
lactose pyruvic acid lactic acid

13. MICROBIOLOGY OF DENTAL CARIES
Specific plaque hypothesis:
mutans streptococci are important in caries
initiation
Non-specific plaque hypothesis:
Heterogeneous groups of bacteria are involved
in caries initiation

14. A recent model of caries

15. The caries culprits
The main microorganism involved in the initial caries process is S. mutans.
S. sobrunis and lactobacillus are also involved, but must have s. mutans present to colonize.
Lactobacillus produces lactic acid at higher concentrations than “helpful” bugs

16. CARIOGENICITY OF LACTOBACILLUS SPECIES
Present consensus:
Lactobacilli are not involved in the initiation of
dental caries
They are involved in the progression of the
lesion deep into enamel and dentine
They are pioneer organisms in the advancing
carious process

17. CARIOGENICITY OF LACTOBACILLUS SPECIES
Present in increased numbers in most carious
cavities affecting enamel & root surfaces
Numbers in saliva correlate with caries activity
Some strains produce caries in some rat species
Initiate and maintain growth at low pH (aciduric)