Tufts professor discusses probiotics

Concerns about antibiotic resistance have lead to an increased interest in alternative approaches for controlling common childhood infections, Christine A Wanke of Tufts University comments this week in the British Medical Journal. Probiotics are viable bacteria that colonise the intestine and modify the intestinal microflora and their metabolic activities, with a presumed beneficial effect for the host. Many of these probiotics are lactic acid bacteria, such as lactobacillus or bifidobacterium, but not all probiotics have the same characteristics and, presumably, not the same efficacy, she continued. To be effective a probiotic must be able to survive passage through the acidic environment of the stomach and grow in and colonise the intestine, even in the presence of antibiotics. To be widely used a probiotic must also be safe. The ideal probiotic bacteria would lack virulence factors, such as the ability to degrade intestinal mucus or its glycoproteins or lead to aggregation of plateletsproperties that are present in some lactobacillus strains. Probioticsare presumed to promote healing of the intestinal mucosa by reducing gut permeability and by enhancing local intestinal immune responses, particularlythe IgA response,3 as well as by reconstituting the intestinal flora. These are not universal properties among lactobacillus strains, and not all lactobacillihave shown the same beneficial effects. A study in thisweek's issue of the BMJ​ (2001;322:1327) examines the effect of a probiotic milk on diarrhoeal and respiratory infections in children attending day care centres in Finland. Carried out at the Valio Research and Development Centre and led by research nutritionist Katja Hatakka the study used Lactobacillus rhamnosus strain GG, which has been extensively studied in the treatment of childhood infections. For example, it has been shown to enhance children's recovery from rotaviral diarrhoea and to potentiate their intestinal immune response. Lactobacillus GG has been used in several randomised placebo controlled trials for treating childhood diarrhoea and has been shown to reduce theduration of acute diarrhoea, particularly that caused by rotavirus. Wanke suggest that there are far fewer data, however, on the efficacy of specific probiotics, including lactobacillus GG, in preventing diarrhoeal or respiratory diseases. Studies suggest that the lactobcacillus GG is effective in preventing antibiotic-associated and travellers diarrhoea in adults. Other prevention trialsinclude a study that examined the ability of lactobacillus GG to prevent diarrhoea in undernourished Peruvian children (aged 6-24 months)(see the Journal of Pediatrics 1999 Jan;134(1):15-20) The Peruvian study showed fewer episodes of diarrhoea in children who received lactobacillus GG (5.21 episodes v 6.02 in the placebo group,P=0.028). This benefit was particularly evident in non-breast fed children aged 18-29 months (4.69 v 5.86 episodes, P= 0.005). Hatakka et al's studysuggests that, though there was no difference in the numbers of days spent with diarrhoeal or respiratory symptoms, the group treated with lactobacillusseemed to have less severe disease, as measured by reduced numbers of days absent from day care, frequency of complications such as otitis media, andnumbers of antibiotic prescriptions. The two studies are difficult to compare as definitions, study design, and outcome variables differed. The Peruvianstudy included only undernourished children, defined an episode of diarrhoea as one day with four or more loose stools, documented rates of diarrhoeawith daily home visits, and directly administered lactobacillus as a gelatin capsule at home six days of the week. The Finnish study included olderchildren (up to 6 years); administered the probiotic in milk containers given three times a day, five days a week, with snacks; and asked parents to record adaily symptom diary for their children. The study in Peru lasted 15 months, that in Finland 7 months (in the winter, when the rates of respiratory illnessesmight be highest). Both groups looked for evidence of colonisation with stool cultures (more children in the placebo group in Finland (4% at thebeginning and 15% at the end of the study) were colonised with lactobacillus GG). Importantly, there were no adverse events in either study related to theuse of the probiotic. In short, Wanke concludes both studies offer positive results, but not overwhelmingly so. Is this related to the study design, the populations studied, or the limits of the probiotic? The results of both studies are intriguing enough to encourage additional larger, carefully controlled studies, which should incorporate lessonslearnt from these studies. Future studies should probably be done in younger children and those at highest risk of diarrhoeal or respiratory disease, withstudy personnel recording symptoms. Source: BMJ 2001;322:1318-1319​