Much research has been carried out in the field of human probiotics in the last decade (see review Huis in't Veld et al. (1994) Tibtech 12, 6–8). This research has been prompted by the rising interest by the public in their health and well-being. Many probiotic products are now available on the market and some of the beneficial effects derived from these products range from alleviation of lactose intolerance (Gilliland, S. E. (1990) FEMS Microbiol. Rev. 87, 175–188) to prevention of diarrheal diseases (Marteau, P. et al. (1993) FEMS Microbiol. Rev. 12, 207–220) and possible prevention of carcinogenesis (Adachi, S. (1992) In “The Lactic Acid Bacteria in Health and Disease”. (Wood, Ed.), 233–262, Elsevier, Barking). Controversy exists over many of these beneficial effects as no standardised procedures are available and contradictory results have been published with regard to the possible beneficial effects of cultured products containing ‘probiotic’ bacteria.
Poor choice of strain has been cited as one of the contributing factors to the inconsistency and variability of results (Marteau, P. et al. (1993) supra) (Kim, H. S. (1988) Cult. Dairy Prod. J. 23, 6–9) and Fuller, R. ((1989) J. Appl. Bact. 66, 365–378) outlined criteria pertaining to the successful isolation of probiotic strains. The strains should be indigenous to the intended host species and also have the ability to (i) survive and grow within that host; (ii) exert a beneficial effect at the target site and (iii) be maintainable in the carrier food or system throughout product manufacture and storage.
There is a fast growing market for health-promoting products including probiotics. Many such products are now available (Jong, S. C. and Birmingham, J. M., (1993) ATCC Quart. Newslett. 13(1), 1–11). One of the more important components of these products is the microorganisms used. The most frequently utilised species include Bifidobacterium sp., Lactobacillus sp., and Propionibacterium sp. (O'Sullivan, M. G., et al. (1992) Trends in Food Sci. and Tech. 3(12), 309–314). There is a lack of substantiated evidence from controlled trials that the organisms currently used in such products are those which have beneficial effects on the gut flora (Tannock, G. W. (1983) In Human Intestinal Microflora in Health and Disease 517–5399 D. J. Hentges (ed.), New York, Academic Press). The source of the microorganism is critical to its survival and therefore its function in the human intestinal tract. Lee, Y-K and Salminen, S. ((1995) Trends Food Sci. Technol. 6, 241–245) stated that as a general requirement, a probiotic strain should be of human origin as some health-promoting effects may be species dependent. It is well known that the indigenous microflora is one of the major defense mechanisms that protects the human against colonisation by allochthonous invading bacteria (Tancrede, C. (1992) Eur. J. Clin. Microbiol. Infect. Dis. 11(11), 1012–1015) and it is also the human's best ally when supporting the immune system. Bacterial populations at different levels of the gastrointestinal tract constitute complex ecosystems depending on the physiology of the host and on interactions between bacteria.
Ten Brink et al. ((1994) Journal of Applied Bacteriology 77 140–148) isolated and screened a large number (˜1000) of Lactobacillus strains for the production of antimicrobial activity. Lactobacilli were isolated from various fermented foods and feeds (sauerkraut, cheese, sausage and silage), human dental plaque and faeces derived from different laboratory animals (rat, mouse, guinea pig and quail) and human volunteers. Only eight positive strains were found and two of these were studied, namely Lactobacillus salivarius M7 and Lactobacillus acidophilus M46. The former strain produces the broad spectrum bacteriocin salivaricin B which inhibits the growth of Listeria monocytogenes, Bacillus cereus, Brochothrix thermosphacta, Enterococcus faecalis and many lactobacilli. L. acidophilus M46 produces a bacteriocin acidocin B which combines the inhibition of Clostridium sporogenes with a very narrow activity spectrum within the genus Lactobacillus. However, these strains are not indigenous to the infected host species, which is one of the criteria which is required for a successful probiotic strain for human use.
Arihara, K. et al. ((1996) Letters in Applied Microbiology 22, 420–424) have isolated Salivacin 140 a bacteriocin from Lactobacillus salivarius subsp. salicinius T140. Strain T140 was isolated from the surface of Japanese pampas grass leaves grown close to an animal barn and thus the strain was likely to have derived from animal faeces.
There is a need for probiotic strains which meet the aforementioned criteria. Bacteriocin production by lactobacilli is thought to play an important role in the competitive exclusion of pathogens and other undesirable microorganisms of the intestinal tract of humans. Bacteriocins are broadly defined as proteinaceous compounds which exhibit a bactericidal effect against a wide range of microorganisms.
Due to their diversity of species and habitats lactobacilli are the most bacteriocinogenic of the lactic acid bacteria. As many as forty bacteriocins produced by lactobacilli have now been isolated (Klaenhammer, T. R. (1993) FEMS Microbiol. Rev. 12, 39–86).
Bacteriocins have been isolated from human infant faeces. However, the bacteriocins were found to have narrow host ranges and were active only against other lactobacillus species (Toba, T. et al. (1991) Lett. Appl. Microbiol. 12, 228–231.).
There is a need for bacteriocins with a broad spectrum of activity.