Lactobacillus characteristics, morphology, benefits

3947
Sherman Hoover

Lactobacillus It is a genus of bacteria made up of a series of beneficial species of particular interest in the industry. The word Lactobacillus comes from "lactis", which means milk, and "bacillus", which means small bacilli.

The genus was classified according to the phenotypic characteristic of the type of fermentation carried out. The physiological basis of this classification is the presence of the enzymes fructose 1 & 6 diphosphate aldolase and phosphoketolase, which are key in the homo or hetero fermentative metabolism of hexoses and pentoses respectively..

Its fermentative properties and metabolic products make bacteria of the genus Lactobacillus are among the first organisms used by man for food production.

They are also used for their preservation, by inhibiting the invasion by other microorganisms that cause food-borne diseases..

The gender Lactobacillus it has become an essential element for modern food and new industrial technologies, due to the interest in its beneficial effects and functional properties.

Article index

  • 1 Features
  • 2 Taxonomy
  • 3 Morphology
    • 3.1 Microscopic characteristics
    • 3.2 Macroscopic characteristics 
  • 4 Benefits
  • 5 References

Characteristics

These bacilli are generally non-motile, but some species are motile due to peritric flagella. They are Gram positive, however, if there are dead bacteria, they stain red, giving a variable Gram image in the presence of Gram staining..

They do not sporulate and some strains have bipolar bodies that probably contain polyphosphate.

Homofermentative Lactobacillus have internal granules revealed by Gram stain or methylene blue staining..

For the diagnosis and identification of the species, the most useful method is the Polymerase Chain Reaction (PCR)..

Cell wall and ultrastructure

The cell wall of the genus Lactobacillus, observed under an electron microscope, is typically Gram positive, it contains peptidoglycans (mureins) of the Lysine-D-Asparagine type of various chemotypes..

This wall also contains polysaccharides linked to the peptidoglycan through phosphodiester bonds, but only has teichoic acids related to it in some species.

It also contains large mesosomes that characterize this genus.

Biochemical characteristics

Most do not have proteolytic or lipolytic activity in media containing proteins or fats..

However, some strains may show slight proteolytic activity due to proteases and peptidases bound to or released by the cell wall, as well as weak lipolytic activity due to the action of intracellular lipases..

They do not normally reduce nitrates, but certain species do when the pH is above 6.0.

Lactobacilli do not liquefy gelatin, nor do they digest casein. They also do not produce indole or hydrogen sulfide (HtwoS), but most produce small amounts of soluble nitrogen.

They are catalase negative, although some strains produce the enzyme pseudocatalase that breaks down hydrogen peroxide.

They are cytochrome negative, due to the absence of porphyrins and present a negative benzidine reaction.

They grow well in a liquid medium, where they precipitate rapidly after growth ceases, giving rise to a soft, granular or viscous sediment, without the formation of biofilms..

Lactobacillus do not develop typical odors when growing in common media, however they contribute to modify the taste of fermented foods, producing volatile compounds such as diacetyl and its derivatives, and even hydrogen sulfide (HtwoS) and amines in cheese.

Nutrition and growing conditions

Lactobacilli require carbohydrates as sources of carbon and energy. Also amino acids, vitamins and nucleotides.

Lactobacilli culture media must contain fermentable carbohydrates, peptone, meat extract and yeast extract.

Better still if they are supplemented with tomato juice, manganese, acetate and oleic acid esters, especially Tween 80, as this is stimulating and even essential for many species.

The species of the Genus Lactobacillus grow well in slightly acidic media, with an initial pH of 6.4-4.5 and with an optimal development between 5.5 and 6.2. and noticeably decreases in neutral or slightly alkaline media.

Lactobacillus are able to lower the pH of the substrate where they are below 4 through the formation of lactic acid.

In this way, they avoid or at least considerably reduce the growth of almost all other competing microorganisms, except that of other lactic acid bacteria and yeast..

Oxygen needs

Most strains of Lactobacillus they are mainly aerotolerant; optimal growth is achieved under microaerophilic or anaerobic conditions.

It is known that an increase in the concentration of COtwo (approximately 5% or up to 10%) can stimulate growth, especially on the surface of the media.

Growth temperature

Most lactobacilli are mesophilic (30-40 ° C), with an upper limit of 40 ° C. Although their temperature range for growth is between 2 and 53 ° C, some grow below 15ºC or 5ºC and there are strains that grow at low temperatures, close to freezing (for example, those that inhabit frozen meat and fish ).

On the other hand, there are the "thermophilic" lactobacilli, which can have an upper temperature limit of 55ºC and do not grow below 15ºC..

Metabolism

These microorganisms lack cytochrome systems to carry out oxidative phosphorylation and do not have superoxide dismutases or catalases..

Members of this genus transform glucose and similar aldehyde hexoses into lactic acid by homofermentation or into lactic acid and other additional end products such as acetic acid, ethanol, carbon dioxide, formic acid, and succinic acid by heterofermentation..

Sensitivity to antibiotics and drugs

Lactobacilli are sensitive to most antibiotics active against Gram-positive bacteria. It has been possible to study the sensitivity of intestinal lactobacilli to antibiotics used as food additives.

Habitat

Lactobacilli can be found in dairy products, cheeses, grains, meat or fish products, water sources, sewage, beers, wines, fruits and fruit juices, cabbage and other fermented vegetables such as: silage, sour masses and pulps.

They are also part of the normal flora of the mouth, gastrointestinal tract, and vagina of many temperature-stable animals, including man..

They can also be found in secondary habitats such as organic fertilizers..

Taxonomy

Domain: Bacteria

Division: Firmicutes

Class: Bacilli

Order: Lactobacillales

Family: Lactobacillaceae

Genus: Lactobacillus.

Morphology

Microscopic characteristics

The bacilli are approximately 2 - 6 μ long. They can sometimes be seen with rounded ends. Its distribution in space can be isolated or in short chains. Some form palisades.

They are Gram positive when stained with the Gram stain.

The Lactobacillus have peptidoglycan in their cell wall and alsocontain a secondary polymer layer (SCWP), consisting of teichoic, lipoteichoic, lipoglycan, teicuronic acids.

Many species of the genus Lactobacillus have in their envelopes an additional layer of proteins called the S layer or surface layer (S & layer).

Within this genus are species such as L. acidophilus, L. brevis, L. crispatus, L. gasseari, L. helveticus, L. kefir among others.

Macroscopic characteristics 

The colonies of Lactobacillus on solid media they are small (2-5 mm), convex, smooth, with entire margins, opaque and without pigments.

Some strains may show yellowish or reddish coloration. Most have rough colonies, while others, like Lactobacillus confusus, have slimy colonies.

Profits

The gender Lactobacillusit is beneficial for human and animal health.

The benefits are listed below:

Stabilizes the intestinal flora by increasing resistance to infections at this site

For example, Lactobacillus GG, appear to produce antimicrobial substances that are active against various bacteria such as E. coli, Streptococcus, Clostridium difficile, Bacteroides fragilis Y Salmonella.

These substances are aromatic compounds such as diacetyl, acetaldehyde, reuterin, bacteriolytic enzymes, bacteriocins, among others..

  • Prevents and controls some diseases, such as colon cancer.
  • They improve the quality of preservation of certain foods.
  • They are used as a starting point by the industry to obtain biotechnological products applicable to the solution of both human and animal health problems..
  • They influence the bioavailability of nutrients by facilitating a breakdown of whole milk proteins, releasing calcium and magnesium in large quantities.
  • They are also involved in the synthesis of B vitamins and phosphates..

Pathogenicity

The pathogenicity of lactobacilli is rare, although recently some infectious processes have been reported in humans where these microorganisms have been involved..

These include dental caries, rheumatic vascular disease, abscesses, septicemia, and infective endocarditis, caused by L. casei subsp. rhamnosus, L. acidophilus, L. plantarum and occasionally Lactobacillus salivarius.

However, the biochemical bases of such pathogenicity are still unknown..

Table: Types of infection caused by various species of the Genus Lactobacillus

References

  1. Kale-Pradhan PB, Jassal HK, Wilhelm SM. Role of Lactobacillus in the prevention of antibiotic-associated diarrhea: a meta-analysis. Pharmacotherapy. 2010; 30 (2): 119-26.
  2. Reid G. The Scientific Basis for Probiotic Strains of LactobacillusApplied and Environmental Microbiology. 1999; 65 (9): 3763-3766.
  3. Harty DW, Oakey HJ, Patrikakis M, Hume EB, Knox KW. Pathogenic potential of Lactobacilli. Int J Food Microbiol. 1994; 24 (1-2): 179-89.
  4. Koneman E, Allen S, Janda W, Schreckenberger P, Winn W. (2004). Microbiological Diagnosis. (5th ed). Argentina, Editorial Panamericana S.A.
  5. Ellie Goldstein, Tyrrell K, Citron D. Lactobacillus Species: Taxonomic Complexity and Controversial Susceptibilities Clinical Infectious Diseases, 2015; 60 (2): 98-107

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