LACTOCOCCUS: CHARACTERISTICS, MORPHOLOGY, BENEFITS, PATHOGENESIS - BIOLOGY - 2025

Lactococcus is a genus of gram-positive, pleomorphic bacteria that can grow singly, in pairs, or in chains. They are homofermentative chemoorganotrophs, they produce lactic acid by fermentation of glucose.

The food industry uses some species of the genus. They are generally considered non-pathogenic or opportunistic pathogens. However, in recent years, the number of clinical cases associated with infections by these microorganisms has increased, both in animals and in humans.

Lactococcus lactis, Microscopic image. Taken and edited from https://www.openpr.com/news/227665/MoBiTec-GmbH-Introduces-first-Secretion-Vectors-for-the-Lactococcus-lactis-Gene-Expression-System-NICE-developed-by- NIZO-Food-Research.html

characteristics

-Lactococcus are chemoorganotrophic organisms.

-They do not have a flagellum, nor do they form spores. They are facultative anaerobic, catalase negative and non-hemolytic.

-Grow at 10 ° C, but not at 45 ° C. They generally grow in media with 4% (w / v) NaCl. They produce L-lactic acid by fermenting glucose.

-All strains contain phosphatidylglycerol and cardiolipin. Most react with group N antisera.

-Some strains have low levels of menaquinones. The GC content of DNA ranges from 34 to 43% by mole.

Taxonomy

The genus Lactococcus was erected in 1985, to contain a group of bacteria previously included within the genus Streptococcus (lactis) of group N of the Lancefield Classification.

The separation was performed on the basis of nucleic acid hybridization, physiological, comparative immunology, and lipid and lipoteichoic acid composition studies.

Taxonomically it is located in the family Streptococcaceae, of the order Lactobacillales, belonging to the Bacilli class of the phylum Firmicutes.

Currently the genus has 14 valid species, of which nine have been described in the last decade, including Lactococcus reticulitermitis, described in 2018. Lactococcus garviae has two subspecies and Lactococcus lactis has four valid subspecies and one biovar.

Morphology

Bacteria of the genus Lactococcus are shaped like spheres or ovoid cells, which can grow individually, in pairs or in chains. In the case of having a chain shape, the cells are elongated in the same direction of the chain.

They possess numerous plasmids that can vary in size from 2 kb (Kilobase) to more than 100 kb. The cell wall consists of peptidoglycan and a matrix of polysaccharides, teichoic acid, and proteins.

Lactococcus reticulitermitis, cells on agar plates 27, after 2 days of incubation at 30 ° C under anaerobic conditions. Taken and edited from

Benefits

The genus contains 14 species of which only Lactococcus lactis is commonly used for industrial purposes, mainly the subspecies L. lactis subsp. lactis.

Lactococcus lactis has been used historically, both artisan and industrially, in the fermentation of foods, such as cheese, yogurt, sauerkraut and the like.

The United States Food and Drug Administration (FDA) lists it as Generally Recognized As Safe (GRAS). This bacteria, in addition to conferring flavor, also produces acids that preserve food.

Probiotics

Lactic Acid Bacteria (LAB) isolated from natural dairy products are of great interest among correcting probiotics of the normal intestinal microbiota. Many LABs synthesize biologically active peptides or protein complexes.

These compounds are known as bacteriocins. Lactococcus lactis produces bacteriocins such as lacticins, nisins, and lactococcins. Nisin is the best-studied compound in the latter group.

Nisin, produced by some strains of Lactococcus lactis subsp. lactis, is a broad spectrum bacteriocin with enhanced antimicrobial activity. One of the most important properties of nisin is the activity against Gram positive bacteria and bacterial spores of clostridia and bacilli.

It also works against other bacteria that do not form spores, such as many species of pathogenic streptococci and staphylococci. It is also non-toxic, stable at low pH and does not influence the microbiota of the gastrointestinal tract.

All these properties reinforce the role of bacteria in the food industry.

Potential uses

Apart from its important role in the food industry, L. lactis has been used in genetic engineering. Factors such as its completely sequenced genome, small in size (2.3 Megabases or Mbp) and successfully developed cloning system, have made it a working model.

Researchers have obtained, for example, genetically modified Lactococcus lactis strains that produce and release Mycobacterium Hsp65. This substance is a type of heat shock protein (Hsp). Hsps are immunodominant proteins expressed by various immune cells and commensal bacteria.

Orally administered Mycobacterium Hsp65 released by genetically modified bacteria completely prevents induced colitis in mice. These results may open alternative options for the long-term management of inflammatory bowel disease in humans.

Lactococcus garvieae, isolated from cow's milk, has shown its efficacy in inhibiting pathogenic microorganisms in cattle. The inhibitory spectrum of bacteriocin, secreted by Lactococcus garvieae, as an antimicrobial substance has a potential role as an alternative form of antibiotic against bovine mastitis.

Pathogeny

Lactococcus species are considered low virulence organisms, causing opportunistic infections in humans, mainly in people with weakened immune systems.

But, in recent years, the number of clinical cases associated with infections by these microorganisms has increased, both in humans and animals.

The bacteria Lactococcus garvieae, L. piscium and L. lactis subsp. lactis are recognized as the species of this genus with the greatest clinical importance for human and veterinary medicine.

They are often misidentified as enterococci or streptococci. Due to difficulties in correctly identifying them, perhaps their clinical importance has been underestimated.

In humans

Lactococcus garvieae has been associated with various diseases, mainly of the hospital type. These diseases include bacteremia, infective endocarditis, liver abscess, spontaneous septicemia, diverticulitis, urinary tract infection, and peritonitis.

Lactococcus lactis subsp. cremoris has been reported as a causal agent of bacterial endocarditis, septicemia, liver and brain abscesses, necrotizing pneumonitis, purulent pneumonitis, septic arthritis, deep neck infection, peritonitis, ascending cholangitis, and canaliculitis.

Exposure to unpasteurized dairy products is a risk factor for infection with this bacteria. Lactococcus lactis subsp. lactis has been associated with endocarditis, it has also been isolated from clinical samples of blood, skin lesions and urine.

In animals

Lactococcus garvieae and L. piscium are pathogenic for several species of fish, L. garvieae has also been reported as a shrimp pathogen, and causes mastitis in ruminants. Lactococcus lactis subsp. lactis has been reported to cause infections in waterfowl.

Treatments

There is not yet a specific guideline for antimicrobial therapy against Lactococcus infections. For therapy, meanwhile, it is suggested to determine the susceptibility of the pathogen isolated from the cultures.

Penicillin, third-generation cephalosporin, and coamoxiclav have been used based on susceptibility tests.

References

1. S. Hadjisymeou, P. Loizou, P. Kothari (2013). Lactococcus lactis cremoris infection: not rare anymore? BMJ Case Reports.
2. D. Samaržija, N. Antunac, JL Havranek (2001). Taxonomy, physiology and growth of Lactococcus lactis: a review. Mljekarstvo.
3. KH Schleifer, J. Kraus, C. Dvorak, R. Kilpper-Bälz, MD Collins & W. Fischer (1985). Transfer of Streptococcus lactis and Related Streptococci to the Genus Lactococcus gen. Nov. Systematic and Applied Microbiology.
4. TT Choksi, F. Dadani (2017). Reviewing the Emergence of Lactococcus garvieae: A Case of Catheter Associated Urinary Tract Infection Caused by Lactococcus garvieae and Escherichia coli Coinfection. Case Reports in Infectious Diseases.
5. J. Goyache, AI Vela, A. Gibello, MM Blanco, V. Briones, S. González, S. Téllez, C. Ballesteros, L. Domínguez, JF Fernández-Garayzábal (2001). Lactococcus lactis subsp. lactis Infection in Waterfowl: First Confirmation in Animals. Emerging infectious diseases.
6. MZ Nuryshev, LG Stoyanova, AI Netrusov (2016). New Probiotic Culture of Lactococcus lactis ssp. lactis: Effective Opportunities and Prospects. Journal of Microbial and Biochemical Technology.
7. Genus Lactoccocus. In List of Prokaryotic names with Standing in Nomenclature: LPSN. Retrieved from www.bacterio.net/lactococcus.html.
8. AC Gomes-Santos, RP Oliveira, TG Moreira, AB Castro-Junior, BC Horta, L. Lemos, LA Almeida, RM Rezende, DC Cara, SC Oliveira, VAC Azevedo, A. Miyoshi AMC Faria (2017). Hsp65-Producing Lactococcus lactis Prevents Inflammatory Intestinal Disease in Mice by IL-10- and TLR2-Dependent Pathways. Frontiers in Immunology.