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Lactic Acid Bacteria (LAB)

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Taxonomy

The classical approach to bacterial taxonomy was based on morphology and physiology. Currently, molecular characteristics, such as mol% G+C content of the DNA, electrophoretic properties of the gene products, DNA:DNA hybridization studies and sequences of ribosomal RNA (rRNA), have become important taxonomic tools. This has resulted in dramatic changes in taxonomy of the LAB. The classification of LAB remains the focus of intense taxonomic studies.

Phylogenetically the LAB belong to the clostridial branch of the Gram-positive bacteria. They are catalase-negative, non-sporeforming cocci, coccobacilli or rods that have less than 55 mol% G+C content in their DNA.

The bifidobacteria were discovered in 1900 and were included in the genus Lactobacillus as L. bifidus. Only in 1986 they were transfered to the genus Bifidobacterium (Actinomyces subdivision of the Gram-positive bacteria). They are not true lactics because they produce lactic and acetic acids in the ratio of 2:3, they differ from other LAB in the key enzyme of hexose fermentation, and most importantly, they have high (55-57 mol%) G+C content in their DNA.

cellular organisms - Bacteria - Firmicutes - Bacilli - Lactobacillales


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Brief facts

 

Fermentation leading to exretion of lactate

 


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Families of order Lactobacillales


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About probiotics


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Probiotics and health

Based on Lomax AR, Calder PC. 2009.

Immune function
Function Description Findings
Phagocytosis The process by which phagocytic cells (for example, neutrophils and monocytes) engulf foreign cells and debris; this can lead to presentation of antigens on the phagocyte surface and facilitation a cell-mediated immune response. L. rhamnosus and L. coryniformis enhanced, other probiotics shown mixed results.
Natural Killer (NK) Cell Activity NK cells are involved in killing infected or tumor cells by causing apoptosis or necrosis. L. rhamnosus and L. lactis enhanced NK activity.
Cytokine Production by T Lymphocytes Cytokines, such as Inteferon, Tumor Necrosis Factor alpha, Interleukins, etc. modulate the function of various cell types. Probiotics appear to have very little effect on the majority of cytokines measured.
Antibody production in response to vaccination Antibodies are used by the immune system to identify and neutralize foreign objects, such as bacteria and viruses. Antibody responses have been increased by probiotics in some, but not all, studies.
Probiotics and infection
Condition Findings
Enterocolitis and sepsis in very low birth weight infants L. acidophilis reduced the incidence of necrotizing enterocolitis, sepsis and death.
Antibiotic-Associated Diarrhoea Some Lactobacilli have been shown to reduce risk of developing the diarrhoea in infants and children.
Helicobacter pylori infection Although there was no significant effect on H. pylori eradication, severity and frequency of overall symptoms were reduced.
Acute Common Childhood Diarrhoea Probiotic supplementation was reported to reduce the duration of non-rotavirus diarrhoea. L. casei, L. acidophilus, L. helveticus, and S. thermophilus redused incidence of diarrhoea in healthy children.
Travellers' Diarrhoea A mostly beneficial effect has been observed regarding incidence, risk of frequency of the diarrhoea.
Probiotics and inflammatory condition
Condition Findings
Irritable Bowel Syndrome (IBS) Supplementation with Lactobacillus GG decreased abdominal distention, but other gastrointestinal symptoms and abdominal pain were not altered.
Ulcerative Colitis in Adults L. acidophilus and L. reuteri alleviated symptoms and decreased exacebrations. Other non-LAB probiotics also had some beneficial effects.
Rheumatoid Arthritis No significan effects were shown.
Allergies (nasal and food allergies, atopic dermatitis) Neutral and some beneficial results were achieved in various clinical studies in adults and children.


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Possible mechanisms of action of probiotics


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Potential probiotic traditional fermented foods

Modified from Rivera-Espinoza Y, Gallardo-Navarro Y. 2010.

Product Microorganisms Description
Ben-saalga LAB A traditional gruel from Burkina Faso (E.H. Tou et al. 2007).
Boza Lactobacillus plantarum, L. brevis, L. rhamnosus, L. fermentum, Leuconostoc mesenteroides subsp. dextranium A popular fermented beverage in Turkey, Albania, Bulgaria, Kyrgyzstan, Macedonia, Montenegro, Bosnia and Herzegovina (Todorov SD et al. 2007).
Ilambazi lokubilisa LAB Fermented maize porridge, traditional in Zimbabwe (Gadaga TH et al. 1999).
Kenkey Lactobacillus plantarum, Pediococcus pentosaceus, Lactobacillus fermentum/reuteri and Lactobacillus brevis Fermented maize (Olsen A et al. 1995).
Kimmchi LAB Korean traditional Baechu (Chinese cabbage) kimchi (health benefits).
Kishk LAB Egyptian traditional porrige prepared from a powdery cereal of burghul (cracked wheat) fermented with milk and laban (yoghurt) (Morcos SR et al. 1973).
Koko W. confusa and Lact. fermentum African spontaneously fermented millet porridge and drink (Lei V, Jakobsen M. 2004).
Sauerkraut LAB Fermented cabbage products in several European countries (health benefits).
Tarhana Streptococcus thermophilus, Lactobacillus fermentum, Enterococcus faecium, Pediococcus pentosaceus, Leuconostoc pseudomesenteroides, Weissella cibaria, Lactobacillus plantarum, Lactobacillus delbrueckii spp. bulgaricus, Leuconostoc citreum, Lactobacillus paraplantarum and Lactobacillus casei A traditional Turkish fermented cereal food (Sengun IY 2009).
Tempeh LAB A traditional fermented Malay soy product (health benefits).


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References


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