Lactobacillus fermentum is a Gram-positive species of bacterium in the genus Lactobacillus. It is associated with active dental caries lesions. It is also commonly found in fermenting animal and plant material. It has been found in sourdough. A few strains are considered probiotic or "friendly" bacteria in animals  and at least one strain has been applied to treat urogenital infections in women. Some strains of lactobacilli formerly mistakenly classified as Lactobacillus fermentum (such as RC-14) have since been reclassified as Lactobacillus reuteri. Commercialized strains of L. fermentum used as probiotics include PCC, ME-3 and CECT5716
Lactobacillus fermentum belongs to the genus Lactobacillus. Species in this genus are used for a wide variety of applications. These applications include food and feed fermentation. It has been found that some strains for Lactobacillus fermentum have natural resistances to certain antibiotics and chemotherapeutics. They are considered potential vectors of antibiotic resistance genes from the environment to humans or animals to humans.
A microorganism is considered a probiotic by meeting certain characteristics, such as being of human origin, non-pathogenic, having high resistance to passing through the intestine, and being beneficial to the immune system. In general, they are seen as beneficial to the host's body and the human health. Lactobacillus fermentum has been identified as potential probiotic. The use of gut microbes as probiotics in food is aimed towards preventing and treating various health problems. Among these health problems allergies, neoplastic growth, and inflammatory bowel disease are included. Recent areas of study have focused on the influence of probiotics on metabolic functions of their host. One area has been the metabolism of cholesterol by LABs acting as probiotics. Research has shown that Lactobacillus species have been proven to remove cholesterol in vitro through various ways such as assimilation, binding to the surface cells, and incorporation into cellular membranes.
pH and Bile Tolerance
Testing of Lactobacillus fermentum against different pH concentration solutions revealed that it has a strong pH tolerance by its ability to grow and survive a few hours after being incubated in a 3-pH level solution. Strains of Lactobacillus fermentum have also been tested in different bile concentrations and demonstrated to have good bile tolerance when incubated with 3 g L-1 of bile salt. The pH and bile tolerance that L. fermentum demonstrates is significant in terms of its consideration as a probiotic. It has to be strong enough to survive the stresses of the digestive system. The stomach has a pH between 1.5 and 3, and the upper intestine contains 3-5 g L-1 of bile. Lactobacillus fermentum has been found to survive in these conditions further supporting the idea that it can act as a probiotic.
One of the ways in which Lactobacillus fermentum has been seen as a probiotic is by its ability to reduce cholesterol levels. Tests conducted using several strains of Lactobacillus and cholesterol broths demonstrated that lactobacillus fermentum had the largest removal of cholesterol. One of the mechanisms by which L. fermentum may remove cholesterol through in vivo is by the absorption of cholesterol, which as a result accelerates cholesterol metabolism. Another method is by the incorporation of cholesterol in the host body into its cell membrane or walls. This would also increase resistance of the bacterial cell membranes to environmental challenge. A third mechanism is by causing the body to consume more cholesterol. L. fermentum would interfere with the recycling of bile salt and facilitate its elimination, which as a result would increase the demand for bile salt made from cholesterol.
Lactobacillus fermentum ME-3
The strain Lactobacillus fermentum ME-3 has recently been discovered and identified as an antimicrobial and antioxidative probiotic. This strain of Lactobacillus fermentum was discovered from the analysis of human fecal samples in 1994. One of the important characteristics of a probiotic microbe is the tolerance to conditions in the digestive tract. Tests conducted on the ME-3 strain in different bile concentrations found that it was able to survive without large loss in numbers. It has also been found that Lactobacillus fermentum ME-3 has a tolerance to survive drops of pH levels. It can withstand a drop in values from 4.0 to 2.5 without decreasing in numbers. These characteristics of tolerance to bile concentrations and pH levels serve to classify ME-3 as a probiotic.
Lactobacillus fermentum ME-3 has also been found to have the capability to suppress mainly gram-negative bacteria. To a lesser extent, ME-3 has also been observed to be able to suppress Enterococci and Staphylococcus aureus. This would serve a beneficial purpose to the host. ME-3 has several antimicrobial characteristics. These include acetic, lactic and succinic acids, and putrescine. Research on the antioxidant properties of strain ME-3 in soft cheese products revealed that it prevented spoilage. Experimentation has also been conducted on the consumption of the ME-3 strain. The consumption had a positive influence on the microbiota of the gut. Volunteers were given goat milk fermented by strain ME-3 and capsulated ME-3. After three weeks analysis of fecal samples revealed that the ME-3 strain increased the number of beneficial Lactobacilli in comparison to those who were given non-fermented milk. Several human clinical studies performed on ME-3 focused on parameters related to cardiovascular disease development. Consumption of ME-3 indeed results in a reduction of oxidized LDL cholesterol, which is a major contributor to atherosclerosis development. Several mechanisms may contribute to the antioxidant effect of ME-3: the strain modulates the ratio of reduced glutathione/oxidized glutathione in the blood, and increases the levels of paraoxonase, an antioxidant enzyme which protects LDL particles from oxidative modifications.
Properties of the strain ME-3 can serve to classify it as a probiotic that has the ability to protect its host against food-derived infections and also help in the prevention of oxidative damage of food. Its multi-abilities have been tested and proven. Mice treated with a combination of ofloxacin and ME-3 revealed a reduction in liver and spleen granulomas of Salmonella thphimurium. ME-3 is commercialized in the US, in Europe and in Asia in dietary supplement products for cardiovascular health, immune support or detoxification, under the brandname Reg'Activ.
In general, strains of Lactobacillus have been considered safe because of their association with food and because they are normal inhabitants of the human microflora. They have also been identified to have a low pathogenic potential further reinforcing the idea that they are safe microbes.
Recent research in regards to the safety of Lactobacillus fermentum has been carried out on mice. Mice were fed (intragastrically) different concentrations of Lactobacillus fermentum while a control group was also observed. After twenty-eight days blood samples were taken from the mice and analyzed. There was no health difference observed between the control mice and those fed Lactobacillus fermentum in terms of blood biochemistry, protein, albumin, glucose, and cholesterol. Also no negative side effects during the experiment such as change in body weight, feed intake, or clinical signs such as diarrhea and ruffled fur, were observed. The ingestion of Lactobacillus fermentum in mice appeared safe which led to further support that the use of lactobacillus fermentum in food is also safe.
The safety of Lactobacillus Fermentum is called into question in "Lactobacillus fermentum, a pathogen in documented cholecystitis" 
Transferable Resistance Genes
One important consideration to determine the safety of Lactobacillus fermentum is transferable resistant genes. In order for L. fermentum to be considered as a potential probiotic, it must not contain any transferable resistant genes. If a resistance gene is transferable, it could lessen the effect of the use of antibiotics. Out of ten common antibiotic genes that were tested (gatamicin, cefazolin, penicillin, trimethoprim/sulfmethoxazole, ampicillin, carbenicillin, erythromycin, amikacin, chloramphenicol, and norfloxacin), Lactobacillus fermentum was found to only be resistant to amikacin and norfloxacin. [Citation Needed] Others studies have reported that most LABs are also resistant to these antibiotics, which led to the conclusion that it was a common characteristic of LABs. The resistance to these antibiotics can be considered natural or intrinsic. So far no observed Lactobacillus fermentum strains have been observed to have transferable resistance or acquired resistance genes.
Experiments conducted by introducing the strain ME-3 of Lactobacillus fermentum into dairy products as a probiotic ingredient revealed that it was able to suppress the reputed contaminants of food such as pathogenic Salmonella spp., Shigella spp., and urinary tract infections that are caused by E. coli and Staphylococcus spp. Also the introduction of Lactobacillus fermentum strains such as ME-3 in goat milk revealed that it was actually favorable to the host, resulting in an increase in number of beneficial Lactobacilli.
Although LABs have been associated with potential health advantages, they are also responsible for negative outcomes. They are the main organisms involved in the spoilage of tomato products. Species in the genus Lactobacillus have been identified to be the causative organisms. Research was carried out to observe the chemical constituents of tomato juice that stimulate the growth of bacteria that are responsible for the spoilage. These bacteria can resist high temperatures. A strain of Lactobacillus fermentum was extracted from a tomato juice concentrate. Meanwhile, eight different tomato juice mixtures were heated and the survival rate of Lactobacillus fermentum was measured. It was concluded that pectins are the main tomato juice constituents that protect the bacteria cells against destruction from heating. The breakdown of pectin from enzymic action would make the bacteria cells more susceptible to heat. However, it was found in previous research that heating had inactivated natural pectolytic enzymes and therefore Lactobacillus fermentum remained heat resistant. Heat resistance has also been found to correlate with the medium in which the bacteria are cultured, the better the medium used will result in a higher resistance to heat.
Studies have shown that L. fermentum has antibiotic resistances. DNA was isolated from Lactobacillus fermentum and tested for antibiotic resistance against clinically important agents by using broth dilution tests. Different strains of Lactobacillus fermentum demonstrated uniform resistance patterns demonstrating resistance to glycopeptide vancomycin and to tetracycline.
Drug Resistance Plasmids
Sensitivity to Antibiotics
While Lactobacillus fermentum has been found to have antibiotic resistant properties, other studies have demonstrated that lactobacillus fermentum is sensitive to some common antibiotics such as gentamicin, cefazolin, penicillin, trimethoprim/sulfamethoxazole, ampicillin, carbenicillin, erythromycin, amikacin, and cholorampehnicol.
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