Probiotics are defined as:
‘live microorganisms which, when administered in adequate amounts, confer a health benefit on the host’
These microorganisms are normally found in the human intestine and help stabilize and balance intestinal microflora. Although the term ‘probiotic’ was not used until the 1960s, the healthy effects of probiotic bacteria have been known for over a century.
In recent years, there has been increasing interest in the use of probiotics for the treatment of a number of diseases in both pediatric and neonatal patients. Inflammatory bowel disease, necrotizing enterocolitis (NEC) and extra-intestinal disorders including atopic dermatitis and recurrent urinary tract infections are the diseases for which a role for probiotics has been advocated, based on an ever-increasing body of data.
As more applications of probiotic therapy are considered for pediatric practice, there is increasing need to understand the underlying mechanisms, limitations and safety issues with this increasingly popular therapy.
The recent 2007 Pediatric Academic Societies’ (PAS) Annual Meeting held in Toronto, Canada, attracting 6000 pediatric and neonatology specialists from around the world, has once more brought probiotics into the spotlight.
A dedicated Topic Symposium summarized current knowledge regarding the mechanism of the beneficial effects of probiotics, current uses of different strains of probiotics in children and neonates and future trends and areas of research for disease prevention and treatment. All these areas were also extensively addressed by a number of posters that were presented during the meeting.
In the Topic Symposium, Michael Cabana (University of California San Francisco, CA, USA) and Andi L Shane (Emory University School of Medicine, GA, USA) addressed issues concerning the efficacy of probiotics in diarrheal diseases such as traveler‘s diarrhea, and antibiotic-associated diarrhoea. In both diseases, M Cabana stated that, some strains of probiotics (mainly belonging to the genus Saccharomyces boulardii, Bifodobacter and Lactobacillus) are effective. Recent methanalysis papers – including a Cochrane review – have documented a significant efficacy of some (but not all) strains in decreasing the length and severity of such illnesses.
Three pilot randomized controlled trials (RCTs), Shane added, have also demonstrated the efficacy of probiotics in preventing NEC, and NEC-associated deaths, in preterm neonates in the neonatal intensive care unit (NICU). The role of probiotics in preterm neonates is currently of great interest. Preterm neonates in NICU are, in any event, highly at risk of intestinal disturbances with proliferation of a pathogenic microflora (including fungi). In these unique patients, the methods of neonatal intensive care, such as treatment with antibiotics, total parenteral nutrition, or nursing in incubators, may delay or impair the intestinal colonization process. Preterm neonates are thus slower to acquire commensals such as bifidobacteria and more susceptible to pathogenic colonization. In addition, their feeding per os cannot always be started and maintained. It is also known that the intestine of premature infants has poor motility and is predisposed to bacterial overgrowth. The digestive tract is thus regarded as the most important reservoir and site for colonization by all kinds of pathogens and subsequent sepsis.
Probiotics could provide an innovative and less invasive approach, since they modify the bowel flora by colonizing the gastrointestinal tract.
However, Shane commented that, these three studies on the efficacy of probiotics in prevention of NEC – although of interest and of value – have some flaws. Therefore, probiotics are not yet the standard of care for the prevention of such a devastating disease. The major flaw is that none of these studies were really powered to detect adverse effects of toxicity of the probiotic supplementation and, therefore, it is still uncertain whether administration of living microorganisms for a long period of time to an immunosuppressed preterm neonate may be safe.
This area of probiotic safety has been addressed by Mark A Underwood and collaborators at the Division of Pediatrics of UC Davis (CA, USA). They presented a poster [Impact of Probiotics on Growth and Intestinal Flora of Preterm Infants, 6282.26] in which they describe a randomized, blinded, placebo-controlled prospective trial of probiotic products. A total of 90 premature infants (<35 weeks’ gestation with a birth weight of 750–2000 g) were randomly assigned to receive either a mixture of L. acidophilus, B. longum, B. bifidum, B. infantis and fructo-oligosaccharides (FOS), or L. rhamnosus GG and FOS only, or placebo twice daily for 28 days. Weekly measurements of weight, length and head circumference were recorded. Weekly stool specimens for the first 33 of these patients were obtained. A data safety monitoring committee looked for any adverse reactions related to treatment. Their results show that at 4–5 weeks of age, infants receiving the L. acidophilus, B. longum, B. bifidum, B. infantis and FOS mixture showed a tendency to greater weight gain (not significant). A total of 64% of those infants became colonized with Bifidobacteria, compared with 18% of infants receiving L. rhamnosus GG and FOS, and 27% of infants receiving placebo (p = 0.06). No adverse reactions were associated with probiotic therapy. The authors conclude that both probiotic products tested here appear safe, although they have a different impact on neonatal early growth.
EE Ziegler and colleagues from the University of Iowa (IA, USA), presented another interesting poster investigating the growth of neonates fed probiotics [Assessment of Growth of Infants Fed a Starter Infant Formula Containing Prebiotics and Probiotics, 5888.8]. They enrolled 162 nonbreast fed infants aged 14 days in a randomized, controlled, double-blind trial, and assigned them to receive either a currently marketed partially hydrolyzed whey formula with DHA and ARA (group A) or the same formula with a prebiotic (galacto and FOS; 4 g/l in a ratio of 9:1) and probiotics (Bifidobacterium longum, Lactobacillus paracasei and Lactobacillus rhamnosus) (group B). Anthropometrics were obtained every month for 4 months. Parents documented formula intake and tolerance (stool characteristics, flatulence, spitting-up/vomiting and behavior) and morbidity 2 days prior to each visit. A total of 121 infants completed the follow-up. Formula intake was similar between groups. Mean daily weight gain was 31 g for boys and 27 g for girls in the B group; 34 g for boys and 28 g for girls in the A group. The difference between B and A was not significant. There were no differences between the two treatment groups in length gain and head circumference (HC) gain. There were no differences between groups in stool frequency, consistency, color, odor or flatulence. Tolerance measures (crying, fussiness, spitting-up, vomiting and colic/cramping) were also similar between groups, and there was no difference in the incidence of diarrhea, fever, cough or doctor visits. The authors conclude that feeding of infant formula containing prebiotics and probiotics over 4 months led to similar growth as formula without prebiotics and probiotics. The study formula was well tolerated with no increased morbidity.
Similar findings were reported by a cooperative group of French researchers from Nancy, Marseille, Grenoble, Lyon and Paris (France) and led by JM Hascoet. The aim of their work was to evaluate the effect on growth, tolerance, and morbidity of three new starter formulas containing probiotics (Bifidobacterium longum [BL999], L. Rhamnosus [LPR] L. paracasei [ST11]) with or without prebiotics (short-chain FOS/galacto-oligosaccharide [GOS]) [Evaluation of Growth and Incidence of Diarrhea with a Starter Infant Formula Containing Bifidobacterium longum, Lactobacillus rhamnosus or Lactobacillus paracasei and a Mixture of Prebiotics, 7355.6].
A total of 284 healthy term newborns were enrolled and randomized 1:1:1 in a prospective double-blind study, and followed-up to 12 months of age. Equivalence in weight gain was shown for all groups. No statistically significant difference was found for length, head circumference, body mass index (BMI) or for the behavior items – flatulence, colic, spitting up and vomiting. The infants fed formulas also containing FOS/GOS had higher values for stool frequency than the controls. Infants fed formulae containing probiotics only had a significantly lower incidence of diarrhea than controls within the first year of life (OR: 0.22; 95% CI: 0.07–0.69; p = 0.027).
These researchers conclude that feeding starter formulas containing the studied probiotics with or without prebiotics (short-chain FOS/GOS) is safe, well-tolerated and results in normal growth development. The addition of probiotics alone (B. longum and L. rhamnosus) during the first months of life reduces the risk of diarrhea up to 12 months and consequently might have a long-term effect on health.
A strong background for the efficacy of probiotics in preterm neonates comes from the observation that premature infants have fewer episodes of late-onset sepsis, NEC, diarrhea and urinary tract infection, and need less antibiotic therapy when fed their own mothers’ milk compared with similar infants fed formula. Breastfeeding allows close contact between the mother and her infant, and mammary milk has biofactors that help establish Bifidobacteria and Lactobacilli (the so-called ‘bifidus flora’) as predominant intestinal bacteria. The birth of an extremely preterm infant interrupts early nutrition with maternal milk that occurs when the neonate is healthy and at term. The preterm infants cannot have close maternal contact, cannot leave the hospital shortly after birth, his/her breastfeeding is often delayed, and thus his/her intestinal flora is acquired from the NICU.
There is evidence that maternal milk nutrients, as well as probiotic bacteria and/or prebiotics (nutritional substrates that promote the growth of probiotic bacteria), through their stimulation of a normal commensal microflora may also play an important role in the regulation of IL-8 and neutrophil infiltration into the intestine development, in the enhancement of the barrier function and in the composition of the neonatal gut microbiota. As mentioned above, probiotics have been demonstrated in some pilot studies to be effective in reducing the overgrowth of pathogens in the preterm neonate‘s gut as well as the incidence of necrotizing enterocolitis and bacterial sepsis.
Kathryn Carlson and colleagues at the Department of Pediatrics, Evanston Northwestern Hospital, Evanston, IL, USA [The Two Probiotic Strains, L. acidophilus and S. thermophilus, Down-Regulate Toll-Like Receptor 4 Expression in Enterocytes, 7730.3] shed further light on the mechanisms by which enteral supplementation of probiotics may decrease the incidence of NEC. They investigated the expression of toll-like receptors (i.e., transmembrane proteins on enterocytes that are triggered through the binding of specific bacterial ligands and mediate the inflammatory response) on an animal model. In this study, rat intestinal epithelial cells (IEC-6) were pretreated with or without live L. acidophilus, S. thermophilus, or a combination of both strains with a concentration of 1 × 108/ml. Gene expression of TLR4 was then quantified through real-time RT-PCR analysis using TLR4 primers.
The researchers found that, in the absence of probiotic pretreatment, platelet-activating factor (PAF) stimulated TLR4 by 423 ± 88% (p < 0.05) of the untreated cells. Pretreatment with the two strains of probiotics significantly reduced the cPAF-induced TLR4 gene expression (148 ± 50% and 114 ± 37% of the control, p < 0.05, respectively). They conclude that this downregulation of the pro-inflammatory response of the enterocyte after pretreatment of enterocytes with probiotic agents may be one mechanism by which probiotics protect against the development of necrotizing enterocolitis.
Other authors presenting at the 2007 PAS Meeting added further contributions for a better comprehension of the mechanisms by which probiotics could be protective against the development of necrotizing enterocolitis. As AL Shane reported, NEC is possibly secondary to an inappropriate proinflammatory response and a uniquely leaky intestinal barrier associated with an immature gut. Jeanette D Hoenig and colleagues at the Neonatology of the University of Chicago, IL, USA [Probiotic Conditioned Media Improves Barrier Function in Human Intestinal Epithelial Cells, 8065.2] hypothized that the use of secreted bacterial products of L. acidophilus and B. infantis in the form of conditioned media (CM), rather than live bacteria, would inhibit the NF-κB inflammatory cascade and protect intestinal barrier function. To examine the effect of CM on inflammatory signaling, the investigators transfected human fetal H4 enterocyte monolayers with an NF-κB promoter-dependent firefly luciferase reporter construct, and then they pre-treated with the combined CM of L. acidophilus and B. infantis prior to treatment with the inflammatory mediator TNF. Luminescence was measured as an indication of NF-κB activity. To examine the effect of CM on barrier function, human Caco-2 enterocyte monolayers were pretreated with the combined CM of L. acidophilus and B. infantis. Barrier integrity through monolayers both nonstressed and stressed with the physiologic oxidant monochloramine was measured by TER and mannitol flux. Higher TER and lower mannitol flux were considered indicators of preserved barrier integrity.
The results showed that CM did not alter TNF-induced NF-κB activity in immature enterocytes; however, CM did preserve barrier function. The combined CM of L. acidophilus and B. infantis were able to protect barrier function both with and without stress, but did not inhibit the NF-κB mediated inflammatory cascade. The researchers speculate that in combination with substances from other probiotic organisms to limit the inflammatory response, secreted factors from L. acidophilus and B. infantis may confer protection against NEC without the infectious risks of live organisms.
Final comments
The 2007 PAS Meeting showed once more that the focus on probiotics, both in basic and clinical research, is high among pediatricians and neonatologists. The possibilities of clinical use of probiotics in the prevention and management of a number of diseases that affect pediatric and neonatal populations are interesting and deserve an ever increasing effort to finally achieve uncontroversial results.
The 2007 Pediatric Academic Societies’ Meeting held in Toronto last May put probiotics under the spotlight, both for basic and clinical research, with a high numbers of posters and presentations submitted.
The high interest for such ‘nutraceutics’ among pediatricians and neonatologists is a consequence of the increasing and promising body of evidence on their effectiveness in prevention and treatment of many neonatal and pediatric disorders.
This brief article summarizes the most relevant studies presented at this conference, and comments on the current possibilities and indications for clinical use of probiotics in neonatal and pediatric patients.
Financial & competing interests disclosure
The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, royalties
No writing assistance was utilized in the production of this manuscript.