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 humans..
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-The Lactococcus are chemoorganotrophic organisms.
-They do not have a flagellum, nor do they form spores. They are facultative anaerobic, catalase negative and non-hemolytic.
-They grow at 10 ° C, but not at 45 ° C. They generally grow in media with 4% (w / v) NaCl. 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.
The gender 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 carried out based on 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 class Bacilli 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 a biovar.
Bacteria of the genus Lactococcus They are shaped like spheres or ovoid cells, which can grow individually, in pairs or in chains. In the case of a chain shape, the cells are elongated in the same direction as 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..
The genus contains 14 species of which only Lactococcus lactis It is commonly used for industrial purposes, mainly the subspecies L. lactis subsp. lactis.
Lactococcus lactis It has been used historically, both artisanal 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 bacterium, in addition to conferring flavor, also produces acids that preserve food.
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 its activity against Gram positive bacteria and bacterial spores of clostridia and bacilli.
It also works against other non-spore-forming bacteria, 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.
Apart from its important role in the food industry, L. lactis it has been used in genetic engineering. Factors such as its completely sequenced genome, small in size (2.3 Megabases or Mbp) and a successfully developed cloning system, have made it a working model..
Researchers have obtained, for example, strains of Lactococcus lactis genetically modified that produce and release Mycobacterium Hsp65. This substance is a type of heat shock protein (Hsp). Hsp 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, it has been shown to be effective in inhibiting pathogenic microorganisms in cattle. The inhibitory spectrum of bacteriocin, secreted by Lactococcus garvieae, as an antimicrobial substance it has a potential role as an alternative form of antibiotic against bovine mastitis.
The species of Lactococcus 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 Y 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.
Lactococcus garvieae It 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 It has been indicated 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 by this bacteria. Lactococcus lactis subsp. lactis has been associated with endocarditis, has also been isolated from clinical blood samples, skin lesions and urine.
Lactococcus garvieae Y L. piscium are pathogenic for various 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.
There is still no specific guideline for antimicrobial therapy against infections caused by Lactococcus. 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..
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