Lactobacillus Dr Alex Owusu-Ofori

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

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

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

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

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

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

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

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.

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.

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 3.6 - 4.0 inhibits microbial growth Milk is Soured by Streptococcus lactis, Lactobacillus Yogurt- Streptococcus and Lactobacillus added to milk

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

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

A recent model of caries

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

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

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)