259 Journal ofFood Protection Vol. 42, No.3, Pages 259-262 (March,1979) Copyright © 1979, International Association of Milk, Food, and Environmental Sanitarians Roles of Lactobacillus in the Intestinal Tracf1 WILLIAM E. SANDINE Department ofMicrobiology, Oregon State University. Corvallis, Oregon 97331 (Received for publication August 14, 1978) ABSTRACT billion per gram. Their absence in certain "healthy" Despite the opinion of many scientists and laymen that lactobacilli persons would suggest that while their function may be Downloaded from http://meridian.allenpress.com/jfp/article-pdf/42/3/259/1649905/0362-028x-42_3_259.pdf by guest on 27 September 2021 benefit adult intestinal health, the medical and scientific communities desirable, it may also be dispensible. Lactobacilli are not do not accept this as fact. This paper offers possible beneficial and the most numerous bacteria in the Gl tract as illustrated detrimental roles which lactobacilli could play; relevant literature citations also are made. Healthful roles include those exerted as a result in Table 2. This would suggest that if their intestinal of their presence as members of the intestinal flora as well as their metabolic activities are beneficial to man they would be benefits as culture or enzyme preparations. Speculative detrimental useful because of what a relatively few, that is from a effects discussed are nutrient competition, carcinogen activation and hundred per gram to 500 million per gram, could do. But detoxification interference (glucuronide hydrolysis). all food microbiologists are aware that it isn't always the total number of bacteria present that is important, but In moving from the stomach through the intestinal the type. In this regard it is of interest that certain tract, food passes through the duodenum, jejunum and individuals lack or have low numbers of coliforms in ileum of the small intestine and the ascending, transverse stool samples due to antibiotic production by a and descending colon of the large intestine. For many TABLE 1. Number of lactobacilli in the human stomach, intestinal microorganisms. this is a hostile environment where a tract number of factors or compounds, contributed in part by lactobacilli, discourage growth and in some instances Sample Source Viable count (rangle log10/g) survival of undesirable bacteria. These factors include gastric juice, bile, fatty acids, organic acids, hydrogen Upper small intestine N-6 sulfide, lysozyme, lysolecithin, antibiotics and peristalsis. Lower small intestine N-8 Large intestine N-9 In this discussion we will be concerned with bacteria of Feces 3.6-9.3 the Lactobacillus genus and consider the roles these a Adopted from Drasar (6) and Drasar and Hill (8). bacteria might have in the intestinal tract. If they play bN =less than 10 per gram. any role at all, it follows that they would be present in a reasonable number in most humans. Savage (26) and non-sporeforming variant of Bacillus subtilis (18). In others have indicated that this is the case. Table 1 these situations, the population of these bacteria do not summarizes data indicating the approximate number of exceed 104 per gram of feces (Gerhardt. personal lactobacilli present in the intestinal tract. Here it may be communication) but lactobacilli are increased. seen that they range from not detectable in some individuals, except for the feces, to from a million to a FUNCTIONS OF LACTOBACILLI We might speculate about functions the lactobacilli 'Paper presented at 1978 annual meeting of American Society for Microbiology, May 14-19. Las Vegas, Nevada, Technical Paper No. could play in the human intestinal tract and some 4932. Oregon Agricultural Experiment Station. suggested roles are shown in Table 3. Three possible Table 2. Approximate numbers Genus Bif!dobacterium N 2.0 4.0 7.0 10.5 Clostridium N N N N 3.0 Enterobacteria N N 3.3 7.0 6.0 Enterococci N N 2.3 7.0 3.5 Lactobacillus N 1.0 N 6.5 4.0 Veillonella N N N 3.0 3.0 Yeasts N 1.0 2.3 N 1.0 14 x w-6 260 SAN DINE detrimental roles, nutrient competition, carcinogen acids (40 o/o each) and deoxycholic acid (10 o/o) (2). They aid activation, and glucuronide hydrolysis are suggested in digestion by forming polymolecular aggregates while nine beneficial attributes are listed. Published (micelles) with water-insoluble lipids and fat-soluble research reports will support some of these roles for vitamins (19) and are recycled as conjugates of glycine lactobacilli while others are speculative. and taurine (3: 1 ratio). Deconjugated bile acids are more Since 1947 (15) a number of reports reviewed recently inhibitory for bacteria than the conjugated acids (9) and (20,27,28) have been made concerning antibiotic deconjugation is one of the main microbial reactions production by lactobacilli. These have been called by which alter the bile acids. The small intestine contains various names including acidophilin, acidolin, lacto­ little free bile acids but significant quantities appear in bacillin and lactocidin. Strains vary in their ability to the large bowel. They may function here to control the produce these substances and cultural conditions microbial composition but no evidence proves that this is influence the amount produced within strains. In vitro so (26). If this is important, it would be worthwhile to inhibitory activity has been reported against salmonellae, examine lactobacilli for their ability in this regard. Downloaded from http://meridian.allenpress.com/jfp/article-pdf/42/3/259/1649905/0362-028x-42_3_259.pdf by guest on 27 September 2021 shigellae, staphylococci, Proteus. Klebsiella, pseudo­ Gilliland and Speck (I I) have tested human fecal monads, enteropathogenic Escherichia coli, bacilli and lactobacilli (L. acidophilus, L. buchneri, L. casei, L. Vibrio organisms. In vivo studies with human medical fermentum, L. leichmannii, L. plantarum, L. salivarius) and intestinal surgery patients are needed to determine for deconjugation of glycocholate and taurocholate. Only if these antibiotic substances benefit intestinal health. L. buchneri strains were inactive on both conjugates and Organic acids such as acetic and lactic which are all of six L. acidophilus isolates tested deconjugated produced by lactic acid bacteria will inhibit growth taurocholate (Table 4). Thus lactobacilli can liberate free of many bacteria, especially pathogenic gram-negative bile acids in the intestinal tract and thereby could exert types. A number of literature reports have dealt with an influence on the balance of bacteria present. this phenomenon (5,13,29) and have shown that while pH per se is a factor, lower pH values also potentiate the TABLE 4. Ability of lactobacilli from human feces to deconjugate bile acidsa. activity of these acids since the undissociated forms are most destructive. Also these volatile acids are especially Species Taurocholate Glycocholate antimicrobial under the low oxidation-reduction po­ L. acidophilus 6/6 116 tentials (26) which lactic acid bacteria help maintain in L. buchneri 0/3 0/3 9/13 the intestines. Diet may be a factor determining the L. casei 0/13 L.fermentum 115 3/5 amount of these acids produced as, for example, with L. leichmannii 3/4 314 breast-fed human infants (3,4). Here, bifidobacteria, L. plantarum 0/3 2/3 1/2 1/2 which derive growth-promoting oligosaccharides from L. salivarius human milk, produce acetate and lactate homofermen­ a Data of Gilliland and Speck (11). No. positive/No. strains. tatively resulting in a fecal pH of about 5.0. Apart from the growth-products influence lactobacilli COLON CANCER likely have in suppressing undesirable bacteria in the Interactive effects between food constituents and intestinal tract, they may also out-compete other bacteria bacteria in the intestine are believed involved in the for nutrients and occupy sites as gut colonizers and make etiology of colon cancer (7,1 7). Glucuronide formation in these sites unavailable to other microorganisms (10). the liver is an important detoxification mechanism in Data supporting these possibilities are not available from humans; the glucuronides formed are excreted with bile research involving humans but hopefully will be and may be hydrolyzed by certain intestinal bacteria to forthcoming. Recent studies in animals, however, release a potential carcinogen. Other enzymatic capabil­ support such a model (21,23). ities of the intestinal microflora may also be involved in carcinogen production such as reduction of azo and BILE SALTS aromatic nitrogen compounds through azoreductase and Bile salts are surface-active chemicals produced in the nitroreductase activities. Steroid and protein metabolites liver from the catabolism of cholesterol. The bile acids produced by bacteria have also been shown to yield produced in humans are chenodeoxycholic and cholic carcinogens or co-carcinogens (7). The role that TABLE 3. Possible functions for lactobacilli in the intestinal tract. Beneficial Nat ural flora Adjunct Detrimental 1. Antibiotic production 1. Disease therapy 1. Nutrient com petition 2. Organic acid production 2. Preventative therapy 2. Carcinogen activation 3. Lower pH and 0/R 3. Enzyme source 3. Glucuronide hydrolysis 4. Competitive antagonists 5. Bile deconjugation 6. Carcinogen suppression ROLES OF INTESTINAL LACTOBACILLI 261 lactobacilli play in these processes in the human intestine and clinically, that the use of "sour milk" as an article of is difficult to access. In the rat, Lactobacillus species diet checks or altogether arrests this unhealthy have been ranked third in