Probiotic formulations and gastro-intestinal diseases in the paediatric population: a narrative review

Background/Aim: Probiotics are live microbial supplements that improve the microbial balance in the host animal when administered in adequate amounts. They play an important role in relieving symptoms of many diseases associated with gastrointestinal tract, for example, in necrotizing enterocolitis (NEC), antibiotic-associated diarrhea, relapsing Clostridium difficile colitis, Helicobacter pylori infections, and inflammatory bowel disease (IBD). In this narrative review, the authors aim to evaluate the role of different probiotic formulations in treating gastrointestinal diseases in pediatric population aged 18 years or younger and highlight the main considerations for selecting probiotic formulations for use in this population. Methodology: The authors searched PubMed and Clinicaltrials.gov from inception to 24th July 2022, without any restrictions. Using an iterative process, the authors subsequently added papers through hand-searching citations contained within retrieved articles and relevant systematic reviews and meta-analyses. Results: The effectiveness of single-organism and composite probiotics in treating gastrointestinal disorders in pediatric patients aged 18 or under were analyzed and compared in this study. A total of 39 studies were reviewed and categorized based on positive and negative outcomes, and compared with a placebo, resulting in 25 studies for single-organism and 14 studies for composite probiotics. Gastrointestinal disorders studied included NEC, acute gastroenteritis (AGE), Acute Diarrhea, Ulcerative Colitis (UC), and others. The results show that probiotics are effective in treating various gastrointestinal disorders in children under 18, with single-organism probiotics demonstrating significant positive outcomes in most studies, and composite probiotics showing positive outcomes in all studies analyzed, with a low incidence of negative outcomes for both types. Conclusion: This study concludes that single-organism and composite probiotics are effective complementary therapies for treating gastrointestinal disorders in the pediatric population. Hence, healthcare professionals should consider using probiotics in standard treatment regimens, and educating guardians can enhance the benefits of probiotic therapy. Further research is recommended to identify the optimal strains and dosages for specific conditions and demographics. The integration of probiotics in clinical practice and ongoing research can contribute to reducing the incidence and severity of gastrointestinal disorders in pediatric patients.


Introduction
Functional digestive problems have become more prevalent in recent years and can be associated with various conditions such as gastrointestinal cancers, intestinal obstruction, ulcers, and reflux diseases.Functional gastrointestinal diseases (FGIDs) are the most common type of gastrointestinal disorders, especially in infants, children, and adolescents.As of 2021, around 40% of the world's population suffers from some form of gastrointestinal disease [1] .The occurrence rates of FGIDs in pediatric populations have been documented to range from 27 to 40.5% among infants and toddlers aged 0 to 3 years, and from 9.9 to 27.5% among children and adolescents aged 4-18 years [2] .
Dysbiosis has been linked to various metabolic and chronic medical conditions including gastrointestinal disorders.However, the patterns of dysbiosis have been inconsistently observed across different countries and life stages [3] .As the human gut microbiome changes significantly over a lifetime, age-specific differences may provide insight into microbiomemediated effects on health [4] .The systematic review by Abdukhakimova et al. [5] found no clear microbiota signature associated with celiac disease in children's fecal and/or duodenal samples due to heterogeneity in study design, but suggests that certain fecal microbiota elements, particularly Bifidobacterium spp., such as Bifidobacterium longum, may be useful as diagnostic/prognostic biomarkers and for probiotic therapy and require further investigation.Similarly, study by Poddighe and Kushugulova [6] , suggested that although a clear microbiome signature for celiac disease has not been identified in humans, several studies suggest that the gut microbiota can impact disease onset and progression through various mechanisms [7] .Clinical studies on the salivary microbiome in celiac disease are less common but may provide better correlation with the duodenal bacterial environment.Further studies on the salivary microbiome in different populations are necessary to explore its usefulness in understanding celiac disease pathogenesis with potential clinical implications.
Probiotics play an important role in relieving symptoms of many other diseases associated with gastrointestinal tract for example in, necrotizing enterocolitis (NEC), antibiotic-associated diarrhea, relapsing Clostridium difficile colitis, Helicobacter pylori infections, and inflammatory bowel disease (IBD).When it pertains to extremely preterm infants between the ages of 2 weeks and 2 months, NEC is the most prevalent major gastrointestinal condition and the leading cause of mortality.The condition mostly affects babies born before 32 weeks of pregnancy, and its frequency is inversely correlated with gestational age [8] .It is linked to the use of antibiotics, acid suppression, enteral diluted hydrochloric acid, and enteral antibiotics, all of which change the microbiome of the infant's gut.These findings lend credence to the idea that dysbiosis, or aberrant gut flora, is a primary cause of NEC [8] .The hallmarks of NEC include acute inflammation, penetration of gas into the portal venous system and bowel wall, ischemic necrosis of the intestinal mucosa, and invasion by enteric gas-forming organisms.These symptoms have been linked to a higher risk of neurodevelopmental (ND) impairment (NDI) [9] .As far as antibiotic associated diarrhea is concerned, of individuals who obtain antibiotics, up to 35% suffer from diarrhea [10] .This is attributed to the gut flora's colonization resistance [11] .It is frequently mild, but it can occasionally be severe and even fatal, particularly when Clostridium difficile infection (CDI) is present [10] .In addition to frequent watery bowel movements, urgency, and dyspepsia, is linked to changes in intestinal microbiota, mucosal integrity, and vitamin/mineral metabolism.If severe, it can cause toxic megacolon, pseudomembranous colitis, electrolyte imbalances, diminution in volume, and, very rarely, death [11] .Dysbiosis is also linked to inflammatory bowel disease (IBD), which includes Crohn's disease and ulcerative colitis.Disproportionate immune responses against commensal intestinal bacteria have been observed in IBD patients, and these responses may be essential in driving intestinal inflammation [12,13] .Others, however, speculate that the main cause of inflammation in IBD is an imbalanced gut flora [14] .Commensal enteric microbes can lead to the following complications in IBD patients; superinfection with intestinal pathogens can trigger flare-ups of the illness; and opportunistic infections become more significant when immunosuppressive medication is used widely.In addition to hepatocellular abscesses, sepsis, and endocarditis, secondary bacterial invasion of mucosal ulcers also frequently results in common septic local complications such as abscesses and fistulae [14] .
According to the International Scientific Association for Probiotics and Prebiotics (ISAPP) consensus statement on the scope and appropriate use of the term probiotic and prebiotics; probiotics are live microbial feed supplements that beneficially affect the host animal by improving microbial balance when administered in adequate amounts, while prebiotics are nondigestible dietary compounds that stimulate the growth and activity of specific bacterial populations [15,16] .To ensure safety and effectiveness, a set of established criteria has been developed for selecting probiotics, as summarized in Table 1 [17] .Following this, there has been a recent increase in global consumption of nonprescription probiotics for improving overall health, as they have been found to regulate the composition of the microbiota by promoting beneficial bacteria and inhibiting harmful bacteria.However, conflicting clinical findings exist regarding the effectiveness of many probiotic strains and preparations.
Therefore, to address the variability in probiotics research in terms of disparity of studied strains this systematic review aims to assess the efficacy of different probiotic formulations, at the strain level, in treating gastrointestinal diseases in the pediatric

HIGHLIGHTS
• Probiotics are dietary supplements and foods consisting of yeast and bacteria that are commonly used, especially the Lactobacillus and Bifidobacterium species.The diseases related to the gastrointestinal tract (GIT) are often caused by an imbalance in the microbiota found in GIT.Using an iterative process, we subsequently added papers through hand-searching citations contained within retrieved articles and relevant systematic reviews and meta-analyses.Inclusion criteria: The studies needed to provide complete data related to the study topic, be randomized controlled trials, focus on evaluating the efficacy of various probiotic formulations in patients with gastrointestinal-related diseases, and be published in peer-reviewed journals in English.We specifically sought studies involving pediatric populations aged 18 years or younger diagnosed with a range of gastrointestinal diseases.Additionally, we included studies that investigated both single-organism and composite probiotic formulations, regardless of dosage or form.In determining the relevance of study outcomes, we considered only those reported in studies where the P-value was less than or equal to 0.05, indicating statistical significance.Furthermore, to facilitate analysis, we classified study outcomes as either positive, indicating health enhancement, or negative, suggesting potential harmful effects of the intervention.These classifications are detailed comprehensively in Table 3 for clarity and reference.
Exclusion criteria: All the unpublished trials, animal-based studies, study designs, that is, pilot and observational studies, reviews, editorials, commentaries, case reports, case series, and studies reporting incomplete data were excluded.

Data selection
Following the primary search and after removing duplicates, we screened 1228 articles for relevance based on title and abstract and full-text.We also manually searched for additional articles by looking through reference lists of the included full-text.In the end, a total of 39 studies were included in our review, details of the screening process are displayed in the flowchart below (Fig. 1).A list of selected examples of probiotic formulations is provided in Table 4.The studies are summarized in Table 3 based on their characteristics and findings.
Few studies reported that single-organism probiotics did not decrease the incidence of NEC [19,24,31,38] .Additionally, no improvement in stool consistency was seen, but accompanied episodes of inconsolable crying were reported [28] .A study showed that intervention was ineffective in treating rectal  Table 1 Criteria for use as a probiotic [17] .
• The organism being utilized must be recognized, that is, its genus, species, and strain must be known • The organism must be deemed viable to consume: *not infectious or harboring genes for antibiotic resistance *not converting to bile acids or degrading to the intestinal mucosa • It needs to endure intestinal transit: tolerance of bile and acid • It has to stick to the mucosa and colonize the gut (at least for a short period) • It must have known and documented impacts on health: *synthesize antimicrobials and combat harmful germs *a minimum of one phase 2 research demonstrating a benefit • During storage and processing, it must remain stable  [11] Sicily 60 Functional Abdominal Pain (FAP)

Lactobacillus reuteri
The intervention reduced perceived abdominal pain intensity N/A Serce O. et al. [18] Turkey 208 NEC Saccharomyces boulardii N/A The intervention did not decrease the incidence of NEC or sepsis Demirel G. et al. [19] Turkey 271 NEC S. boulardii Feeding intolerance and clinical sepsis were found to be significantly lower in the probiotic group The intervention was not effective at reducing the incidence of death or NEC in very low birth weight (VLBW) infants Pieścik-Lech M. et al. [20] Poland 88 AGE LGG and smectite versus LGG alone LGG plus smectite and LGG alone are equally effective for treating young children with AGE.The combined use of the two interventions is not justified N/A Francavilla R. et al. [21] Italy 74 Acute Diarrhea Lactobacillus reuteri DSM 17938 derived from L. reuteri ATCC 55730 The intervention was found beneficial in reducing the frequency, duration and recrudescence rate of the disease N/A Oliva S. et al. [22] Italy 40 Mild to Moderate Ulcerative Colitis (UC)

L. reuteri
The intervention was effective in improving mucosal inflammation and changing mucosal expression levels of some cytokines involved in the mechanisms of inflammatory bowel disease N/A Maldonado J. et al. [23] Spain 215 Incidence Of Infections The intervention was found useful for the prevention of community-acquired gastrointestinal and upper respiratory infections N/A Sari FN. et al. [24] Turkey 221 NEC Lactobacillus sporogenes Feeding intolerance was significantly lower in the probiotics group than in the control group The intervention showed no significant difference in the incidence of death or NEC between the groups Dinleyici EC. et al. [25] Turkey 68 Blastocystis Hominis Infection

Saccharomyces boulardii
Metronidazole or S. boulardii has potential beneficial effects on B. hominis infection N/A Indrio F. et al. [26] Italy 42 Regurgitation Lactobacillus reuteri Intervention reduces gastric distension and accelerates gastric emptying.In addition, this probiotic strain seems to diminish the frequency of regurgitation N/A Francavilla R. et al. [12] Italy 141 Irritable Bowel Syndrome (IBS) or (FAP) LGG The intervention seemed to significantly reduce the frequency and severity of abdominal pain in children with IBS; this effect is sustained and may be secondary to the improvement of the gut barrier N/A Martens U. et al. [13] Iran 52 IBS LGG The key IBS symptoms (abdominal pain, stool frequency), as well as the other symptoms (bloating, mucous and blood in stool, need for straining at stools, urge to defecate), improved significantly during treatment.Global assessment of therapy by parents and doctors was altogether positive No adverse effects were shown Coccorullo P. et al. [14] Naples 44 Functional Chronic Constipation Lactobacillus reuteri (DSM 17938) The intervention caused a higher frequency of bowel movements The intervention showed no improvement in stool consistency and episodes of inconsolable crying episodes Hojsak I. et al. [15] Croatia 742 Nosocomial Gastrointestinal Tract Infections LGG The intervention caused the risk for gastrointestinal infections, vomiting episodes and diarrheal episodes, episodes of gastrointestinal infections, episodes of respiratory tract infections that lasted 3 days to significantly decrease N/A Hojsak I. et al. [16] Daycare centers are located in 4 separate locations in the Zagreb area 281

Gastrointestinal Tract Infections
LGG Intervention reduced the risk of gastrointestinal infections, vomiting episodes, and diarrheal episodes.However, intervention caused no reduction in the number of days with gastrointestinal symptoms N/A Baldassarre ME. et al. [17] Bari hospital 30 Hematochezia and Fecal Calprotectin LGG LGG resulted in significant improvement of hematochezia and fecal calprotectin compared with the extensively hydrolyzed casein formula (EHCF) alone Sentongo TA. et al. [27] Chicago, IL 21 Short Bowel Syndrome (SBS) LGG N/A Findings do not support empiric LGG therapy to enhance IP in children with SBS Szajewska H. et al. [28] Poland 29 Rectal Bleeding LGG N/A The intervention was ineffective in treating rectal bleeding in breastfed infants.No adverse effects were reported Bauserman M. et al. [29] Children's medical center pediatric gastroenterology 50

IBS
LGG The intervention showed improvement in abdominal distention Lactobacillus GG was not superior to placebo in the treatment of abdominal pain in children with IBS Sýkora J. et al. [30] Czech republic 86 Helicobacter Pylori Lactobacillus casei (L.casei) DN-114 001 Eradication success was higher due to intervention Side effects were infrequent Dani C. et al. [31] Italy 585 Urinary Tract Infection, Bacterial Sepsis and NEC LGG It was found that infants who received Lactobacillus GG were less affected by NEC after 1 week of treatment The intervention was not effective in reducing the incidence of UTIs, NEC and sepsis in preterm infants Saran S. et al. [32] India 100 Diarrhea Lactobacillus acidophilus There were significantly fewer cases of diarrhea and fever due to the intervention N/A Rosenfeldt V. et al. [33] Denmark 43 Acute Diarrhea L. reuteri DSM 17938 The intervention was effective in reducing the duration of diarrhea N/A Guandalini S. et al. [34] Eleven centers in 10 countries 287 Acute Diarrhea LGG The intervention was deemed safe and results were obtained in a shorter duration of diarrhea.There was less chance of a protracted course, and patients were discharged earlier from the hospital No adverse effects (rash, drug-related fever or nausea, etc.) related to the synbiotic use were noted Composite Probiotic vs. Placebo Muhammed Majeed.et al. [35] Three clinical sites i) Mysore Medical College and K R Hospital, Mysore, India ii) Sapthagiri Institute of Medical Sciences and Research Center, Bangalore, India and iii) Kempegowda Institute of Medical Sciences, Bangalore, India 36 Diarrhea Predominant IBS

Bifidobacterium breve, Lactobacillus casei and Galactooligosaccharides
The intervention caused a significant change/decrease in clinical symptoms like bloating, vomiting, diarrhea, and abdominal pain.
Stool frequency disease severity also decreased and the quality of life increased in the patient due to the intervention No serious adverse effects were shown Evette Van Niekerk.et al. [36] Neonatal high care unit of Tygerberg Children's Hospital (TBCH), Cape Town, South Africa 184 NEC Probiotic Mixture (Bifidobacteria infantis, Streptococcus thermophilus, and Bifidobacteria bifidus; Solgar, Israel) reduced the incidence of NEC reduction in the severity of disease was found in the HIV-exposed study group The intervention failed to show that probiotics lowered the incidence of NEC in HIV-exposed premature infants Ali İşlek.et al. [37] Pediatric Emergency and Pediatric Gastroenterology Departments of the Akdeniz University Hospital 156 Acute Infectious Diarrhea

Infloran
The duration of diarrhea was significantly shorter in the synbiotic group than in the placebo The duration of diarrhea was shorter for patients who started the synbiotic therapy within the first 24 h than for those who started their treatment later No adverse effects were shown Xiaolin Wang.et al. [38] Three The incidence of HAEC (three out of 30, 10.0%) in the probiotictreated group was significantly reduced the severity of HAEC in the probiotic-treated group was significantly reduced Probiotics-balanced T lymphocyte, IFN-γ, and IL-6 were significantly decreased inflammatory cytokine IL-10 was remarkably increased N/A Marta Olivares.et al. [39] Hospital Universitari Sant Joan (Reus, Tarragona) and Hospital Universitario Sant Joan de Deu (Barcelona)

33
Colic Disease a capsule containing either B. longum CECT 7347 (109 colony forming units) The intervention caused a significant increase in the height percentile, decreased levels of peripheral CD3+ T lymphocytes and slightly reduced TNF-a concentration, The B. longum CECT 7347 group also had reduced numbers of the Bacteroides fragilis group and lower sIgA content in stools compared to the placebo group No adverse events were reported during the intervention Fernández-Carrocera LA. et al. [40] Mexico 150 NEC Bifidobacterium infantis, Streptococcus thermophilus, and Bifidobacterium lactis containing 1 × 10(9) Total Organisms) The intervention caused a reduction of NEC frequency, significantly lowered risk for the combined risk of NEC or death No adverse effects were shown during hospitalization Braga TD. et al. [41] Northeast brazil 231 NEC VSL#3 The intervention reduced the occurrence of NEC (Bell's stage ≥ 2).It was considered that an improvement in intestinal motility might have contributed to this result N/A Cazzola M. et al. [42] France 135 Prevention of common winter diseases in children Lactobacillus acidophilus, Lactobacillus rhamnosus, Bifidobacterium bifidum, Bifidobacterium longum, Enterococcus faecium, Intervention decreased the risk of occurrence of common infectious diseases in children and limited the risk of school day loss N/A Guandalini S. et al. [43] Italy (4) and in India (1) Chicago, IL (1) 59 IBS

Bifidobacterium breve and Lactobacillus casei
The intervention caused improvement in IBS symptoms No adverse event was recorded Lin HC. et al. [44] Taiwan 217 NEC Mixture of Bifidobacterium longum (BB536) and Lactobacillus johnsonii (La1 ) The incidence of death or NEC (stage 2) was significantly lower No adverse effect, such as sepsis, flatulence, or diarrhea, was noted Bin-Nun A. et al. [45] Shaare zedek medical center 145 NEC Probiotic Mixture (Bifidobacteria infantis, Bifidobacteria bifidum, Bifidobacteria longum and Lactobacillus acidophilus reduced both the incidence and severity of NEC No adverse effects were shown Kliegman RM. et al. [46] Houston, texas 155 NEC Bifidobacterium bifidum and

Lactobacillus acidophilus
The incidence of death or NEC (stage 2) was significantly lower N/A Vandenplas Y. et al. [47] Belgium 111 Acute Diarrhea Synbiotic food supplement Probiotical (Streptoccoccus thermophilus, Lactobacillus rhamnosus, Lactobacillus acidophilus, Bifidobacterium lactis, Bifidobacterium infantis, fructooligosaccharides) The median duration of diarrhea was significantly 1 day shorter in the synbiotic than in the placebo group, associated with decreased prescription of additional medications N/A Miele E. et al. [48] Italy 29 UC VSL#3 Endoscopic and histological scores were significantly lower in the VSL#3 group Remission was achieved in 13 patients No adverse effects were shown bleeding in breastfed infants [40] .Lactobacillus rhamnosus therapy in children with short bowel syndrome did not improve intestinal permeability and was associated with conversion to positive hydrogen breath test results [46] .
Similarly, one study reported that the median duration of diarrhea was 1 day shorter in synbiotic food supplement Probiotical (Streptoccoccus thermophilus, Lactobacillus rhamnosus, Lactobacillus acidophilus, Bifidobacterium lactis, Bifidobacterium infantis, fructo-oligosaccharides) than the placebo group and hence, was associated with a decreased prescription of additional medications [48] .Another study reported that remission was achieved in active UC patients and endoscopic and histological scores were significantly lower in the VSL #3 group (Table 4) compared to the placebo group [22] .

Discussion: a way forward
In this study, the effectiveness of single-organism and composite probiotics in treating gastrointestinal disorders in the pediatric population aged 18 or under were analyzed and compared.A total of 39 studies were reviewed and categorized based on their outcomes, which included positive and negative effects of the probiotics.The studies were compared with a placebo, both individually and as a group, resulting in 25 studies for singleorganism probiotics and 14 studies for composite probiotics.Gastrointestinal disorders studied included NEC, AGE, Acute Diarrhea, UC, and others.The findings of the study emphasize the effectiveness of probiotics in treating various gastrointestinal disorders in pediatric aged 18 or younger, with single-organism probiotics showing significant positive outcomes in most studies and composite probiotics showing positive outcomes in all studies analyzed, with low incidence of negative outcomes for both types of probiotics.
The possible mechanism of activity of some probiotic characteristics may be present in a uniform manner across different species or even genera [58] .As such, efficacy may vary across different strains.For instance, both Bifidobacterium spp.and Lactobacillus spp.can generate the enzyme β-galactosidase, which can help address lactase insufficiency [59] .In contrast, other traits may be specific to certain species [60] or even strains [61] , or may require interactions between different probiotic strains [62] .Some probiotic preparations, particularly those containing specific strains such as S. boulardii and LGG, have been shown in several meta-analyses and systematic reviews to help alleviate acute diarrhea in children and reduce its duration of diarrhea [63][64][65] .However, one recent updated meta-analysis based on large-scale randomized placebo-controlled trials [66,67] involving over nine-tenth children in their total sample size with AGE concluded that large trials with low risk of bias suggest that probiotics are unlikely to have a significant impact on the incidence of diarrhea lasting 48 h or longer, and there is uncertainty regarding their effectiveness in reducing the duration of diarrhea [63] .Earlier guidelines that supported the use of probiotics in the management of AGE, based on lower-quality evidence, are now contradicting with these new findings.
There is evidence to suggest that probiotics may be effective in averting neonatal late-onset sepsis and NEC, a digestive illness that frequently impacts premature infants [68] .Research conducted on animals and human cell cultures proposes that specific types of probiotics, including LGG, could safeguard against NEC by strengthening the body's defense mechanisms against harmful microorganisms, encouraging the growth of the immune system and cells lining the intestine, and reducing inflammation [69] .However, other trials involving very preterm infants in England using Bifidobacterium breve BBG-001 showed no significant effect on NEC or sepsis prevention [70] .Previous systematic reviews and meta-analyses have produced conflicting outcomes on the effectiveness of enteral probiotics in preterm infants.A 2014 Cochrane review involving more than 5000 infants concluded that the administration of enteral probiotics containing either Lactobacillus alone or in combination with Bifidobacterium can decrease the occurrence of NEC and mortality in preterm infants, but not nosocomial sepsis [71] .Similarly, different systematic review and meta-analysis showed that probiotics are useful in reducing the occurrence of late-onset sepsis in preterm infants when given as mixtures and exclusively to those fed with human milk [72] .However, other meta-analyses did not find any significant effect of probiotics in preventing NEC or sepsis in infants with extremely low birth weights [73,74] .Depending on the disease and the particular probiotic being used, there may also be variations among the ideal dosage and period of probiotic treatment.Any probiotic strain has to reach its ideal mass or dosage for it to thrive and colonize the gut.Present literature shows that probiotics must be living and at high enough dosages (usually 106-107 colony-forming units (cfu)/g of product) in order to be effective [75] .However, Stool colonization rates indicate large studies often employ doses of 1 × 108 or 1 × 109 [76] , and greater doses (1 × 1010) do not appear to enhance colonization rates [77] .
Prebiotics, on the other hand, which comprise different combinations of acidity, fructo-oligosaccharides, and galactooligosaccharides from nonhuman milk, have been researched in preterm children for a long time.These prebiotic mixes promote gastric peristalsis, minimize eating intolerance, raise stool sIgA, modify the fecal microbiota, and lower stool pH levels [78] .In contrast to probiotics which have some evidence of reducing incidence of NEC and sepsis in preterm infants, a meta-analysis of seven prebiotics placebo-controlled randomized clinical studies reveals that they play no role in the reduction in NEC, sepsis, or death in preterm infants [79] .
To the best of our knowledge, the present study is the first one to examine the efficacy of probiotics on multiple gastrointestinal diseases among pediatric population younger or 18 years of age, highlighting all positive and negative outcomes for each probiotic to enable a more detailed comparison of the specific strains of each probiotic when used individually or in a composite.This approach provides valuable insights into the response of gastrointestinal disorders to probiotics, with a focus on strain-specific efficacy.By excluding animal studies, our synthesis solely focused on the effects of the intervention on human participants, which enhance the validity and reliability of our article.However, despite its well-designed methodology, further research is required to gain a more comprehensive understanding of the topic.

Clinical implications
The findings of this study suggest that both single-organism and composite probiotic formulations are effective complementary therapies for treating various gastrointestinal disorders in pediatric patients aged 18 years and under.As such, healthcare professionals should consider incorporating probiotics into standard treatment regimens.Gastrointestinal disorders among children are a significant cause of mortality, and probiotics have proven to be a safe and effective intervention.Fortunately, The National Institute of Health (NIH) has progressed with multiple ongoing clinical trials that aim to cater to various gastrointestinal disorders.A list of ongoing clinical trials listed in Table 5 provide valuable resources for clinicians and researchers interested in studying the effectiveness of strain-specific probiotic formulations for various gastrointestinal disorders in different age groups.However, there are many challenges to there are some challenges in clinical implications.The American Academy of Pediatrics 2021 guidelines highlight several warnings against recommending probiotics for preterm infants, particularly in infants with extremely low birth weight, including the absence of positive outcomes in a large RCT from the UK, the shortages of pharmaceutical-grade probiotics in the USA, the diversity of probiotic strains, demographic baselines of participants, and setting, and insufficient safety data [80] .Probiotic usage in healthy individuals may be safe, but in early newborns, it has been linked to an increased likelihood of infection and/or morbidity [81] and underweight newborns [82] .This is most likely attributed to the transmigration of the administered strain or strains over the intestinal wall is most likely involved in the pathophysiology of probiotic sepsis [83] .It may further be challenging to detect because of difficulty forming colonies of obligate anaerobes using conventional culture techniques [84] .
Probiotics can also lead to harmful metabolic activities.Increased D-lactate, which may result in D-lactate acidosis, is one example.Not only do the majority of preterm babies already likely to be acidotic, but blood gases cannot regularly quantify D-lactate, which makes it extremely challenging to catch [84] Probiotics also possess the potential to sometimes cause allergic responses, especially when Saccharomyces boulardii is employed in those who have a history of yeast allergies.In the early stages of treatment, abdominal pain and bloating are possible side effects.Antibiotic resistance genes, like those of enterococci, can also be transferred on by some probiotics.Some probiotic strains like Bacillus cereus may also release emetic and enterotoxin [85] .As such, a personalized plan is essential, and medical professionals should evaluate the unique condition and treatment response of every child.Selecting reliable brands and products is crucial since there may be variations in the quality and purity of probiotics.Since probiotics are typically sold as nutritional supplements rather than pharmaceuticals, the market for them is unregulated, allowing producers to alter the composition of their products or the method of manufacturing without appropriately addressing these concerns [86] .For instance, it was reported that contamination of a composite prebiotic was linked to a deadly case of gastrointestinal mucomycosis [87] .To relay trial results to clinical practise, it is crucial to ensure accurate product identity at the strain level both during research and throughout real clinical application [88] .

Future insights and recommendations
It is recommended that guardians of pediatric age groups must be educated on the management of symptoms of gastrointestinal disorders.Oral rehydration for diarrhea, laxatives for constipation, and anti-emetics for vomiting are baseline treatments, this information can be provided to guardians through their doctor visits, health-care helpline and even educational health campaigns.The guardians must also ensure to keenly observe their children's dietary and hygiene habits as that immensely affects gut health, routine checkup on bowel habits is recommended.
While the present study is a valuable addition to current knowledge on probiotics and their efficacy in treating gastrointestinal disorders, further research into identifying the optimal type, dose, and duration of probiotic therapy for specific conditions and strains that are most effective is needed to gain a more comprehensive understanding of their effectiveness.Specifically, future studies should focus on directly comparing single-organism and composite probiotic formulations, as well as examining the specific strains used as interventions.This would provide Table 5 List of ongoing trials analyzing single-organism and composite probiotic formulations against gastrointestinal diseases.

Single-organism probiotic vs. placebo
Trial ID Age Intervention NCT04160767 [69] up to 14 years Drug: Probiotic Vivomixx Behavioral: Gluten-free diet Other: Placebo NCT03562221 [70] 4 months to 4 months Other: Gluten-free diet Dietary Supplement: Probiotics Dietary Supplement: Placebo NCT04103216 [71] 12 months to 36 months Nitazoxanide with Lactobacillus Reuteri DSM 17938 Nitazoxanide Composite Probiotics vs. Placebo NCT04922476 [72] 8 years to 18 years Dietary Supplement: Alflorex NCT04021303 [73] 4 to 12 months old Dietary Supplement: Experimental cereal Dietary Supplement: Conventional cereal NCT04541771 [74] 28 weeks to 34  weeks Drug: Lactobacillus Reuteri DSM 17938 Drug: Placebo NCT04014660 [75] 10 years to 18 years Probiotic L.plantarum Heal 9 and L. paracasei 8700:2 more precise guidelines for selecting effective probiotic formulations.Preclinical studies on mice have shown clinical benefits in alleviating symptoms following gastrointestinal diseases [69,89] .However, the effects observed in animal models do not necessarily translate to humans [90] , and further research is necessary to identify the molecular players involved including the gut-brain axis.Furthermore, despite the promising results, caution is necessary when using probiotics in the treatment of NEC.The treatment's effectiveness depends on factors such as the specific strains used, the dosage, the mode of administration, and the inclusion of prebiotics.The patient's characteristics, such as their baseline risk concerning birth weight, environmental exposure to microorganisms, and diet, should also be taken into account [58] .The long-term effects of using probiotics on the natural gut microbiome and their impact on gut health need more research.Furthermore, large-scale studies analyzing microbiota signatures related to various disorders, like celiac disease, can help clinicians choose the most effective probiotic formulations for functional gastrointestinal disorders in children.

Limitations
One limitation of this study is the relatively small sample size and demographic scope, which may not be representative of a broader population or geographical area.Unfortunately, for the majority of the aforementioned clinical indications, there are also studies of similarly high methodological quality featuring opposing and negative results which cause disparity in overall inferences.In addition, the techniques employed in these experiments vary greatly, and encompass estimations from cell cultures, in vitro studies animal models, and human research.The diversity of strains investigated in probiotics research is another factor contributing to its unpredictability.Even now, Lactobacillus and Bifidobacterium genera, Lactococcus species, Streptococcus thermophilus, E. coli, and Saccharomyces boulardii are the predominant microorganisms employed in the probiotics sector.Certain health-related mechanisms of action-like the synthesis of bile salt hydrolases-are shared by several probiotic genera and species, while other characteristics may be unique to a particular strain or they might need to interact with one another to have an outcome.In addition, human responses to the same intervention may vary due to their great degree of heterogeneity in terms of nutrition, age range, genetic makeup, and gut microbiome composition, which sets them apart from animal models.It is also important to consider that individual responses to probiotics for gastrointestinal disorders can vary based on metabolites, genetics, and environmental factors.Therefore, the results obtained in this study may not be generalizable to all populations Lastly, a large number of probiotic research are financed by probiotic industry commercial entities or by professional advocacy groups closely affiliated and supported by the same industry.Additionally, biased results may occur due to the lack of randomization in the sample selection process.There is a need for independent verification of effectiveness claims through nonbiased research.Future human-based trials should also aim to overcome these limitations by conducting larger and more diverse studies, and implementing rigorous randomization protocols to reduce potential sources of bias scientific and medical organizations.

Conclusion
In conclusion, this study highlights the potential of both singleorganism and composite probiotic formulations as effective complementary therapies for gastrointestinal disorders in pediatric patients.However, due to inconsistency and limitation of our paper we cannot conclude which type of formulation, single or composite, is superior over the other.Hence, this paper warrants large-scale trials to validate the efficacy of either type.Overall, healthcare professionals should consider incorporating probiotics into standard treatment regimens and educate guardians on symptom management and gut health.Addressing colonization resistance is crucial for optimizing probiotic therapy, and the development of predictive algorithms based on host and microbiome features can aid in personalized treatment strategies.Further research into various gut microbes and microbiomes with specific demographics is recommended to enhance our understanding and application of probiotic interventions.

Table 2
Detailed search strategy.

Table 3
List of randomized controlled trials analyzing different types of that is, single-organism and composite probiotic formulations.