LACTOBACILLUS RHAMNOSUS: CHARACTERISTICS, MORPHOLOGY - BIOLOGY - 2025

Lactobacillus rhamnosus is a Gram-positive, rod-shaped, microaerophilic, and facultatively anaerobic bacterium. It can grow singly or in short chains. It is not spore-forming, mobile, and catalase-negative. It is mesophilic, but some strains can grow at temperatures below 15 ° C or above 40 ° C.

Some strains of L. rhamnosus are used in the food industry due to their probiotic and antimicrobial activities. Its uses include, not only as probiotics, but also as protectants for fermented and non-fermented dairy products, beverages, ready-to-eat foods, sausages, and in salads.

Lactobacillus rhamnosus. Taken and edited from

characteristics

Lactobacillus rhamnosus is a very demanding bacterium in terms of its nutritional requirements. To grow, you need folic acid and other vitamins like riboflavin, niacin, or pantothenic acid. It also requires mineral calcium. Its initial growth requires acidic media, with a pH between 4.5 and 6.4.

Its metabolism is facultative heterofermentative. Convert hexoses to L (+) - lactic acid, according to the Embden-Meyerhof pathway. It also ferments the pentoses. In the absence of glucose, it produces lactic acid, acetic acid, formic acid, and ethanol.

Taxonomy

Lactobacillus is the most diverse of the three genera within the family Lactobacillaceae, belonging to the phylum Firmicutes, class Bacilli, order Lactobacillales.

This genus is divided into three groups (A, B and C) according to their type of fermentation: A) includes obligate homofermentative species, B) facultatively heterofermentative species and C) obligate heterofermentative species.

Lactobacillus rhamnosus belongs to group B of this division. It is also included in the functional group of Lactic Acid Bacteria (LAB). LABs are bacteria that, by carbohydrate fermentation, mainly produce lactic acid as the final metabolite.

This species was originally considered a subspecies of L. casei, later it was elevated to the species level thanks to genetic investigations, due to the great morphological and characteristic similarities.

This and two other species make up the Lactobacillus casei complex, a functional group without taxonomic validity. One of the most studied strains of this species, L. rhamnosus GG, is isolated from the human intestine.

Morphology

Lactobacillus rhamnosus is a rod-shaped bacterium, with measurements ranging from 0.8 to 1.0 μm in width and from 2.0 to 4.0 μm in length. It can grow singly or in short chains. It does not have a flagellum, therefore it lacks movement. It can have pilis and plasmids.

Lactobacillus rhamnosus has a wide variety of strains that grow in different environments, including the vagina and gastrointestinal tract of humans. Each strain has the ability to adapt to a wide range of environments.

Its central genome contains 2,164 genes, out of 4,711 genes in all. The L. rhamnosus LRB strain has a circular chromosome of 2,934,954 bp with a GC content of 46.78%.

Cellular wall

The cell wall consists primarily of a thick layer of peptidoglycan (PG), an amino-sugar polymer cross-linked with peptide bridges. The cell wall is responsible for maintaining the shape of the cell. It also helps protect bacteria from internal osmotic stresses that can cause cell lysis.

The component sugar of PG consists of N-acetylglucosamine and N-acetyl-muramic acid arranged alternately. The side chain of the peptide, of three to five amino acids, binds to N-acetyl-muramic acid. The exact makeup of the peptide side chain and cross-links is species specific.

Artistic impression of Lactobacillus rhamnosus, Photograph by: Electron Microscopy Unit, Institute of Biotechnology, Helsinki. Taken and edited from

Applications

Lactobacillus rhamnosus is used in the food industry for the production of yogurt, fermented and unpasteurized milk and semi-hard cheese.

Medical applications

Lactobacillus rhamnosus is considered a useful probiotic for the treatment of various diseases. The Lactobacillus rhamnosus GG strain has shown to have multiple current and potential uses in medicine for the treatment of diseases.

Among the diseases positively treated with this strain are: diarrhea of ​​various types, mainly due to rotavirus in children; acute gastroenteritis in children; Gastrointestinal transport of vancomycin-resistant Enterococcus in renal patients; It has also been shown to be helpful in reducing the possibility of developing Asperger's syndrome.

Among the diseases that could potentially be treated or prevented by giving L. rhamnosus GG are respiratory tract infections in children; irritable bowel syndrome; atopic dermatitis, eczema; urogenital tract infections; anxiety and hypertension.

In vitro experiences have shown that it can modulate host immunity by decreasing the production of inflammatory cytokines from different eukaryotes. It also induces the gene expression of intestinal mucin, inhibiting the adherence of pathogens.

Other medical uses include reducing intestinal permeability in children with irritable bowel syndrome. It also helps increase weight loss in dieting patients.

Uses as a probiotic

The L. rhamnosus GG strain also exhibits probiotic and antimicrobial activities, which are used in the food industry. This strain, individually, is capable of inhibiting Clostridium histolyticum, C. difficile and Salmonella enterica.

Combined with other strains of L. rhamnosus or with other non-pathogenic bacterial species, they also inhibit the growth of highly pathogenic bacteria. The L. rhamnosus LC705 strain suppresses the growth of some yeasts and molds.

Pathogenicity

Lactobacillus rhamnosus has been related to various types of infections, mainly of intrahospital origin, that affect patients with weakened immune systems.

In these patients, the underlying diseases have always been malignant or severe gastrointestinal disorders. Among the diseases associated with this species are: bacteremia, endocarditis, meningitis and peritonitis.

Lactobacilli, in general, are resistant to vancomycin. Lactobacillus rhamnosus is susceptible to penicillin and aminoglycosides, with sensitivity rates of up to 70%.

However, some strains are resistant to standard antibiotic regimens. Daptomycin could be used as an alternative to penicillin; sensitivity to cephalosporins is lower. Chromosomal mutations in L. rhamnosus can reduce the affinity of erythromycin for the ribosome.

Lactobacillus endocarditis is considered a difficult disease to eradicate. Relapses can occur, mainly due to the lack of adequate studies on microbial susceptibility.

There are also no standardized treatments, which can increase relapses and even death. Probably the production of lactic acid by lactobacilli could reduce the effective concentrations of antibiotics, reducing their effect.

References

1. LM Lehtoranta, A. Pitkäranta, R. Korpela (2012). Probiotic Lactobacillus rhamnosus GG and respiratory illness in children. Agro Food Industry Hi Tech, 23, 6, Monographic supplement series: Dietary Fibers & Pre / Probiotics.
2. L. Valík, A. Medveďová, D. Liptáková (2008). Characterization of the growth of Lactobacillus rhamnosus GG in milk at suboptimal temperatures. Journal of Food and Nutrition Research.
3. P. Boonma, JK Spinler, X. Qin, C. Jittaprasatsin, DM Muzny, H. Doddapaneni, R. Gibbs, J. Petrosino, S. Tumwasorn, J. Versalovic (2014). Draft genome sequences and description of Lactobacillus rhamnosus strains L31, L34, and L35. Standards in Genomic Sciences.
4. I. Felekos, G. Lazaros, A. Tsiriga, M. Pirounaki, G. Stavropoulos, J. Paraskevas, M. Toutouza, D. Tousoulis (2016). Lactobacillus rhamnosus endocarditis: An unusual culprit in a patient with Barlow's disease. Hellenic Society of Cardiology.
5. KA Nocianitri, NS Antara, IM Sugitha, IDM Sukrama, Y. Ramona, IN Sujaya (2017). The effect of two Lactobacillus rhamnosus strains on the blood lipid profile of rats fed with high fat containing diet. International Food Research Journal.
6. EJC Goldstein, KL Tyrrell, DM Citron (2015). Lactobacillus Species: Taxonomic Complexity and Controversial Susceptibilities. Clinical Infectious Diseases