a lactic acid bacterium , as described in the invention , can be chosen from among the genera consisting of lactobaccillus , streptococcus , lactococcus , and bifidobacterium . the bacterium is preferably a lactic acid bacterium chosen from among the following : [ 0020 ] lactobacillus acidophilus 9223 ( cncm i - 2274 , deposited on mar . 8 , 1999 ); [ 0021 ] lactobacillus acidophilus 9170 ( cncm i - 2273 , deposited on mar . 8 , 1999 ); [ 0022 ] lactobacillus acidophilus 9173 ( cncm i - 2132 , deposited on feb . 24 , 1999 ); [ 0023 ] lactobacillus helveticus 9343 ( cncm i - 2275 , deposited on mar . 8 , 1999 ); [ 0024 ] streptococcus thermophilus 9340 ( cncm i - 1520 , deposited on dec . 30 , 1994 ); [ 0025 ] streptococcus thermophilus 10090 ( cncm i - 2272 , deposited on mar . 8 , 1999 ). other strains are generally , publically available . cncm i - 2274 , cncm i - 2273 , cncm i - 2132 , cncm i - 2275 , cncm i - 1520 , and cncm i - 2272 have been deposited with the collection nationale de cultures de microorganismes , institut pasteur , 25 rue du docteur roux , 75724 paris cedex 15 , france . these deposits were made pursuant to the budapest treaty conditions . all restrictions on access thereto will be withdrawn upon grant of a u . s . patent on this application . the present invention also includes lactic acid bacteria cultures that associate two or more lactic acid bacteria strains , as described for a single strain in the invention . the present invention also describes dietary supplements or foods containing lactic acid bacteria that improve the quality of sleep . the dietary supplements consist of a milk base , in particular a fermented milk , containing lactic acid bacteria strains whose cell walls are sensitive to the action of mutanolysin . the ingestion of such a dietary supplement or food will improve the quality of sleep . milk is chosen from among the milks of various animal species . the milk might be partially or completely skimmed . the milk base might involve products resulting from the dilution or the concentration of these milks , such as , for example , retentates of ultrafiltration or diafiltration . the milk base might involve media based on milk such as bases for milky foods or milk mixes for yogurt or fermented milks . these milks can be supplemented with lactose , minerals , vitamins , fats , water soluble milk solids , extracts of plants , flavorings , etc . in an alternative approach , this dietary supplement or food can also be obtained from a plant substrate , such as from soy milk , juice or fruit pulp . for example , a dietary supplement or food according to the invention , is obtained by putting in place the following process : a milk base is inoculated with at least one strain of a lactic acid bacterium containing 10 6 to 10 7 colony - forming units per ml . conditions of incubation vary according to the strain or culture of lactic acid bacteria used . for example , if the culture is composed of a strain of streptococcus thermophilus or a mixture containing at least one strain of streptococcus thermophilus , the optimal culture conditions are 25 to 44 ° c . for 3 hr . to 24 hr . if the culture is composed of strains of lactobacillus acidophilus or lactobacillus helveticus , or a mixture containing at least a strain of lactobacillus acidophilus or lactobacillus helveticus , the optimal culture conditions are 37 to 44 ° c . for at least 8 hr . to 16 hr . the milk base inoculated with a culture can be supplemented with peptide n3 , yeast extract , antioxidants such as cysteine , vitamins , soluble fibers such as oligosaccharides or other substrates currently used to encourage the growth of the lactic acid bacteria strains used . the lactic acid bacteria , or the dietary supplements that contain them , permit improved sleep quality by increasing the nrem phase and / or decreasing the rem phase . an increase of the nrem phase of sleep corresponds to an increase of deep sleep . an increase of the deep sleep phase leads to better recuperation from fatigue , greater alertness during the day , and other benefits . further , lactic acid bacteria , being non - pathogenic microorganisms , can be administered to improve the quality of sleep without the risk of triggering an excessive reaction of the immune system . lactic acid bacteria interact positively with the immune system without inducing pathological reactions ( like overproduction of cytokines ) such as those reactions provoked by pathogenic bacteria . in addition , the use of lactic acid bacteria to improve the quality of sleep does not provoke the secondary effects associated with taking barbiturates or benzodiazepines . the present invention will be better understood with the help of the additional information that follows which provides non - restrictive examples illustrating the properties of lactic acid bacteria strains according to the invention . hydrolysis of the different lactic acid bacteria cell walls by mutanolysin cell walls were prepared from lactic acid bacteria cultures in stationary phase . the bacterial cells were broken in a french press . this preparation was treated with sodium dodecyl sulfate detergent and with trypsin to obtain a crude extract of deproteinated cell walls . the cell wall peptidoglycan from the lactic acid bacteria was then digested with mutanolysin from streptomyces globisporus ( sigma - aldrich , st . louis , mo .). peptidoglycan ( 5 - 10 mg / ml ) was incubated with 0 . 1 to 0 . 25 mg of mutanolysin at 37 ° c . in phosphate buffer , ph 5 . 8 , for 24 hours . the resulting hydrolysate was separated by centrifugation , using centrifugal concentrators ( pall filtron microsep ™, northborough , mass .) and a membrane with a cutoff of 10 kda to separate the low molecular weight molecules from the remaining higher molecular weight material . the bacteria tested were lactobacillus gasseri 9221 , lactobacillus acidophilus 9223 , lactobacillus acidophilus 9173 , lactobacillus helveticus 9343 , streptococcus thermophilus 9340 and streptococcus thermophilus 10090 . the cell walls of five of the bacteria tested were partially hydrolyzed by mutanolysin , allowing the recovery of a soluble fraction containing muramylpeptides and an insoluble fraction resistant to the action of mutanolysin . only the cell walls of lactobacillus gasseri 9221 ( cncm i - 2131 , deposited on feb . 24 , 1999 ) was not hydrolyzed by mutanolysin and did not liberate muramylpeptides . induction by lactic acid bacteria of the production of superoxide anion and cytokines in human monocytes monocytes were isolated from healthy human adults . erythrocytes were sedimented with high molecular weight dextran . mononuclear cells were separated from neutrophils by histopaque gradient ( sigma - aldrich ). mononuclear cells , which contained both monocytes and lymphocytes , were cultivated at a density of 1 . 5 × 10 6 cells / ml , which corresponds to approximately 0 . 5 × 10 6 monocytes / ml , in a modified earle &# 39 ; s salt solution medium , in an incubator at 37 ° c ., with 5 % co 2 . in the experiments designed to measure the production of tnfα by monocytes , the monocytes were cultivated in presence of 0 . 2 % heat - inactivated ( 56 ° c ., 30 min .) type ab human serum . the bacteria lactobacillus gasseri 9221 , lactobacillus acidophilus 9223 , lactobacillus acidophilus 9173 , lactobacillus helveticus 9343 , streptococcus thermophilus 9340 and streptococcus thermophilus 10090 . the pellets of lactic acid bacteria were put in suspension to obtain a concentration of bacterial proteins of 1 mg / ml ( determined by the lowry protein assay ). diluted suspensions containing from 0 . 1 to 300 ng / ml of bacterial proteins were tested . the production of superoxide anion ( o 2 ) by monocytes was measured by the cytochrome c method , after having activated the monocytes with phorbol myristate acetate ( pma ) for 40 min at 37 ° c . in an incubator with 5 % co 2 . the reduction of cytochrome by the superoxide anion was measured spectrophotometrically at 550 nm . the extinction coefficient of 0 . 021 μm − 1 was used to calculate the quantity of superoxide anion produced . cytokine production was measured by elisa ( enzyme link immunosorbent assay ) on samples of the monocyte culture medium . elisa kits for il - 1β ( biosource international , carmarillo , calif .) and tnfα ( genzyme diagnostics , cambridge , mass .) were used . [ 0048 ] fig1 shows that lactobacillus acidophilus 9223 , lactobacillus acidophilus 9173 , lactobacillus helveticus 9343 , streptococcus thermophilus 9340 , and streptococcus thermophilus 10090 were capable of strongly activating human monocytes to induce production of superoxide anion and il - 1β . in contrast , lactobacillus gasseri 9221 , whose cell wall is insensitive to the action of mutanolysin , induced only a weak activity in human monocytes . fig2 shows that the production of il - 1β and tnfα were closely correlated ( r 2 = 0 . 95 ). sleep improving activity of lactic acid bacteria cell walls in rabbits sleep experiments were done with rabbits using one of the lactic acid bacteria strains , lactobacillus acidophilus 9223 , that gave a positive response in the in vitro test , and one strain , lactobacillus gasseri 9221 , that was negative in the in vitro test . cell walls of the bacteria tested were administered by intravenous injection . the test animals were adult male new zealand white rabbits ( myrtle rabbitery , thompson station , tenn .) weighing between 3 . 5 and 4 . 5 kg . the rabbits were operated on to implant a system of recording of their electroencephalograms ( eeg ). the system allowed animals to move without constraint . on separate days , each animal received either the vehicle or one of the substances to be tested . therefore , each animal served as its own control . the marginal ear vein was used for the intravenous injection . the volume of injection was 0 . 1 ml / kg . the recordings were interpreted and classified according to three states of wakefulness : awakening phase , nrem phase ( low frequency electroencephalogram , high amplitude electroencephalogram , and no body movement which characterizes deep , heavy sleep ), and rem phase ( high frequency electroencephalogram , low amplitude electroencephalogram , and occasional body movements that characterize paradoxal sleep ). the length of every phase was expressed as a percentage in the recorded time per hour . [ 0055 ] fig3 shows that the cell walls of lactobacillus acidophilus 9223 administered at doses of 0 . 1 mg / kg and 1 . 0 mg / kg influenced sleep by increasing the nrem phase and by decreasing the rem phase . the increase of the nrem phase started during the second hour after injection and persisted throughout the test . in contrast , fig4 shows that the cell walls of lactobacillus gasseri 9221 did not have a significant effect on sleep . the subject matter of this invention is effectively administered to mammals , including humans , orally . effective amounts will vary dramatically , depending on the individual , the state or condition of the individual , the desired result , etc . oral administration is effective to mammals , including humans , because digestion of the lactic acid bacterial cell walls by muramidase - type enzymes naturally occurs throughout the digestive tract , beginning in the oral cavity , and continuing through the stomach and intestines . alternatively , pre - digested muramylpeptides may be administered orally , by injection , or by suppository . the injection may be either iv or im . preferably , for ease of administration and for patient comfort , administration is by an oral route . the active agent , muramylpeptides , are water soluble . lactic acid bacteria , if administered as such , may be provided in any pharmaceutically acceptable carrier , and are preferably provided as an element or additive to a food product , preferably including milk or fermented milk products . in one preferred embodiment , the lactic acid bacteria or pre - digested muramylpeptides are provided in a yogurt product . the yogurt may be flavored or unflavored , and the nature of the yogurt itself , save for the active agent provided herein , does not constitute an aspect of the invention . lactic acid bacteria are advantageously orally administered in an amount ranging from 1 milligram - 1 gram / kilogram of body weight per day . sleep improvement is a complicated mechanism , and the condition of the subject being treated will enormously impact the effective dosage . the vehicle for administration , if the administration is oral , is substantially unlimited provided it does not contain muramylpeptide - digesting enzymes , or otherwise does not block the activity of the active agent of this invention in stimulating superoxide anion production by monocytes , as well as cytokine production . as another method of determining effective amounts , an effective dosage of a 1 mg / ml lactic acid bacteria protein suspension will range from between 0 . 01 - 100 ml / kg . this invention has been described generically , and by reference to specific embodiments . examples are not intended to be , and should not be construed as limiting , unless specifically so indicated . alternatives will occur to those of ordinary skill in the art , particularly with respect to the identification of non - pathogenic lactic acid bacteria , vehicle or carrier , concentration or suspension , or other aspects of preparation . these alternatives remain within the scope of the invention , unless excluded by the recitation of the claims set forth below .
non - pathogenic lactic acid bacteria have cell walls which are susceptible to digestion by muramidase - type enzymes , which produce fragments referred to as muramylpeptides . the ingestion of muramylpeptides , either directly , or by digestion of non - pathogenic lactic acid bacteria , promote sleep and improves the quality of sleep . in particular , non - rapid eye movement sleep phase is enhanced . the muramylpeptide digestion - products of non - pathogenic lactic acid bacteria promote monocyte production of superoxide anion and the cytokines of il - 1β and tnfα .