A Friend Among Foes: Lactobacillus
Author: Vipin Chandra Kalia
Bacteria are perceived as something dangerous to interact with. It is true to some extent but not to its fullest limits. In fact, our body harbours a lot of bacteria and most of them are useful and important for proper functioning of our metabolisms. Human skin is harboured by bacteria belonging to Bacteriodetes, Proteobacteria, Propionibacterium, Staphylococcus, Corynebacterium, etc. Human gut carries more than 160 species of bacteria. Bacteriodetes, and Fermicutes dominate the gut microbiome and ensure good health. The group, which we all dread is constituted by bacteria belonging to: Vibrio, Pseudomonas aeruginosa, Shigella, Salmonella typhi, Escherichia coli, Serratia, Klebsiella, Mycobacterium, Burkholderia, etc. The organisms which we love and hate are the ones belonging to the genus: Lactobacillus. Certain species of Lactobacillus are dangerous and cause infectious diseases, whereas there are others which we wish should stay within our body. Probiotic bacteria range from Lactobacillus reuteri , L. bulgaricus, Lactobacillus GG, L. casei, Bifidobacterium longum, B. bifidum, Streptococcus thermophiles, and a yeast, Saccharomyces boulardii.
Human gastrointestinal microbiota
It is represented by: L. gasseri, L. mali, L. crispatus, L. reuteri, L. delbrueckii, L. ruminis,L. animalis. and L. rhamnosus, The oral cavity of the human beings is dominated by: L. salivarius, L. brevis, L. acidophilus, L. paracasei, L. crispatus, L. plantarum, L. rhamnosus, L. vaginalis, and L. gasseri.
Animal gastrointestinal microbiota
Most common representative are: L. reuteri, and L. johnsonii.
The Friend: Lactobacillus acidophilus
A small population of L. acidophilus is needed for body. It is distributed in the intestine, mouth, urinary system and female genitals. It is important for the metabolism of lactose present in milk products through the enzyme lactase produced by this bacterium. It is well known as probiotic, which supports the body to absorb nutrients. The most effective usage of this bacterial species is to treat unhealthy conditions arising during diarrhea, asthamatic attacks, vaginal (yeast) infections, ulcers (caused by Helicobacter pylori), lactose intolerance, irritable bowel syndrome, common cold in adults, skin disorders (blisters, eczema and acne). The presence of Lactobacillus spp. such as L. crispatus, L. iners, L. gasseri, and L. jensenii in the vaginal region is very helpful in preventing the invasion of viruses and pathogenic bacteria. This bacterium is used as supplement in a few fermented foods: yogurt, pickles, kefir and soy products. Food Industries are always worried about contamination with harmful bacteria or the population of the probiotic bacteria getting declined. This obviously reduces the quality of the product and affects its sales. The consumers are also concerned about the fact that some of the products may not contain L. acidophilus at all or may have more of bad bacteria. Under these scenarios, the need is to verify the claims by identifying the bacteria.
Conventional and Spectroscopic methods
Morphological and biochemical assays are the first step towards bacterial identification. MALDI mass spectrometry of ribosomal proteins is a sophisticated process to identify L. plantarum and related species.
Molecular biology techniques
The rapid progress in molecular biology has made the identification more precise. The techniques employed for searching Lactobacillus include: PCR, RFLP, PFGE, RAPD, repetitive element PCR, etc. PCR of region between rrs gene and 23S rDNA has been quite effective in this respect. A large number of Lactobacillus strains could be identified using restriction enzymes (REs) for digesting: (i) rrs gene -ApaI, DdeI, HaeIII, HinfI, MspI, NcoI, NheI, NotI and SmaI, SphI, and (ii) the region between rrs gene and 23S rDNA - EcoRI, DraI, SfuI, VspI, SspI, and HincII. Other genes which assist in identifying Lactobacillus species –L. gasseri, L. johnsonii, L. plantarum, L. paraplantarum, L. pentosus, L. rhamnosus, L. taiwanensis, are: bsh, fbp, ftsZ, metRS, minD, mub, mutL, nrdD, pgm, pheS, polA, pyrG, recA, rpoA, and tuf. A major limitation with the use of rrs genes for identifying Lactobacillus is that, each genome harbours 4-9 copies of this gene. rrs gene copies from different Lactobacillus species show very high homology, which can lead to mis-interpretation. In a study involving 19 species of Lactobacillus (50 strains), the only organism, which could be distinguished on the basis of rrs was L. sanfranciscensis. Digestion of 268 copies ofrrs representing 50 strains with 10 different REs enabled identification of a 1-2 strains of the following species: L. acidophilus, L. sanfranciscensis, L. brevis, L. casei, L. fermentum, L. johnsonii, L. paracasei, L. gasseri, L. plantarum, L. amylovorus, L. keﬁranofaciens, L. buchneri, L. reuteri, L. sakei, L. ruminis, L. salivarius, and L. rhamnosus. In the various studies using different genes of Lactobacillus and their digestion with REs, there has been no consensus so far. The need is to look for biomarkers, which can be used by all researchers.
The consensus genes
A genome wide screening of 50 strains of Lactobacillus representing 19 species, revealed that around 9 genes were present in all of them:gyrB, pyrB, recA, dnaJ, cysS, dnaA, pyrG, polA, and dnaK. recA in combination with REs: BfuCI, RsaI, HpyCH4V, andCviAII was the most effective. The other genes whose digestion patterns can be exploited for identifying Lactobacillus were - ruvB, purA, dnaA, dnaJ, and gyrB with REs- BfuI, AluI, Tru9I, CviAI and TaqI.
Although, Lactobacillus strains acting as probiotics are unlikely to persist within the human gut for a long period. However, in light of the fact that these bacteria are excellent for activating the human immune system, they must be monitored for their health benefits. Their benefits during antibiotic treatment is important, because antibiotics may be indiscriminate it their action and may kill good bacteria as well. Probiotics support the growth of beneficial bacteria and thus help human being.
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About Author / Additional Info:
Researcher in Microbial Biotechnology and Genomics at CSIR-IGIB, Delhi.