Search

Given the relatively immature state of the neonatal gut and gut-associated immune system, the safety of probiotic strains for use as ingredients in infant milk formulae must be demonstrated in infant populations. As part of a double-blind placebo-controlled clinical trial of two commercially available probiotic strains in the reduction of risk for infant eczema, a number of safety outcomes were measured. Infants received daily doses of Lactobacillus rhamnosus HN001 (6 × 10 9 cfu day −1 ) or Bifidobacterium animalis subsp. lactis HN019 (9 × 10 9 cfu day −1 ), or placebo from birth to 24 months. Mothers received the same treatment from 35 weeks gestation, for up to 6 months postnatally while breastfeeding. No statistically significant differences were observed between the treatment groups for study withdrawal, incidence of adverse events, morphometric data, wheeze, and antibiotic use over the treatment period. We conclude that probiotics strains HN001 and HN019 were safe and well tolerated in infants, and did not affect normal growth.

The intestinal microflora is composed of numerous bacterial species that inhabit the distal small bowel and the large bowel. This complex microbial collection weilds marked influences on the biochemistry, physiology, immunology and disease resistance of the host. The derivation of scientifically valid probiotic products should be based on knowledge of the intestinal microflora because, by definition, consumption of the probiotic impacts on the microbial community harboured in the digestive tract. Variation in the stability and complexity of bacterial populations harboured by different human subjects may influence the outcome of probiotic administration. An understanding of the colonisation attributes, biochemical activities, and immunostimulatory properties of lactobacilli and bifidobacteria is required so that rational choices can be made in the selection of strains for incorporation into probiotic products.

An important consideration in the genetic manipulation of lactic acid bacteria is whether or not strains retain their normal industrial properties after transformation with plasmid DNA. A survey of plasmid types in various lactic acid bacteria showed that pE194-type rolling circle (RCR) plasmids were present in 24% of 70 commercial Lactococcus lactis cheese starters but not in any of 38 strains representing nine species of Lactobacillus . By contrast, theta plasmids showing homology to the pCI305 rep gene were present in most (though not all) lactococcal strains and not in any of the lactobacilli. Plasmids not belonging to either group were also present in some Lc. lactis and Lactobacillus strains. Six selected Lc. lactis subsp. cremoris strains were transformable with pFX3 (a 4.5 kb pE194-type rolling circle vector), yet four of these strains had significantly lower or zero transformation frequencies with pCI3340 (a 5.7 kb pCI305-based theta vector), possibly due to plasmid incompatibility. However, all transformants maintained full milkcoagulating activity. In addition to Lc. lactis , strains of Lc. garviae , Enterococcus faecalis and Lactobacillus reuteri were able to be transformed with pCI3340, making this a potentially useful vector for these species.

The distal small bowel and the large bowel of humans, even in health, are inhabited by a complex collection of microbes (mostly bacteria) known as the normal microflora. Gram-positive, lactic acid-producing bacteria are represented in this colection (bifidobacteria, lactobacilli, enterococci, eubacteria, peptostreptococci). The influence of the normal microflora as a whole on the host is well known from studies comparing germfree and conventional animals. More recently, using an unique experimental animal system (lactobacillus-free mice), lactobacilli have been shown to influence markedly the biochemistry of the intestinal tract (azoreductase,β-glucuronidase, bile salt hydrolase, proportions of unconjugated/conjugated bile acids). The effect of the consumption of lactic acid-producing bacteria on the normal microflora and the intestinal milieu of humans is therefore of interest. Detailed analysis of the composition, at the level of bacterial strains, of the normal microflora should be possible using DNA probes and ribotyping. These studies are necessary to provide a basis for the study of the effects of ingested lactic acid bacteria on the large bowel ecosystem, and for the derivation and use of genetically modified bacteria that will have a desirable impact on human health.