Does a glucose-based hydrogen and methane breath test detect bacterial overgrowth in the jejunum?

Critical appraisal of the SIBO hypothesis and breath testing: A clinical practice update endorsed by the European society of neurogastroenterology and motility (ESNM) and the American neurogastroenterology and motility society (ANMS)

BACKGROUND

There is compelling evidence that microbe-host interactions in the intestinal tract underlie many human disorders, including disorders of gut-brain interactions (previously termed functional bowel disorders), such as irritable bowel syndrome (IBS). Small intestinal bacterial overgrowth (SIBO) has been recognized for over a century in patients with predisposing conditions causing intestinal stasis, such as surgical alteration of the small bowel or chronic diseases, including scleroderma and is associated with diarrhea and signs of malabsorption. Over 20 years ago, it was hypothesized that increased numbers of small intestine bacteria might also account for symptoms in the absence of malabsorption in IBS and related disorders. This SIBO-IBS hypothesis stimulated significant research and helped focus the profession's attention on the importance of microbe-host interactions as a potential pathophysiological mechanism in IBS.

PURPOSE

However, after two decades, this hypothesis remains unproven. Moreover, it has led to serious unintended consequences, namely the widespread use of unreliable and unvalidated breath tests as a diagnostic test for SIBO and a resultant injudicious use of antibiotics. In this review, we examine why the SIBO hypothesis remains unproven and, given the unintended consequences, discuss why it is time to reject this hypothesis and its reliance on breath testing. We also examine recent IBS studies of bacterial communities in the GI tract, their composition and functions, and their interactions with the host. While these studies provide important insights to guide future research, they highlight the need for further mechanistic studies of microbe-host interactions in IBS patients before we can understand their possible role in diagnosis and treatment of patient with IBS and related disorders.

Small Intestinal Bacterial Overgrowth-Pathophysiology and Its Implications for Definition and Management

The concept of small intestinal bacterial overgrowth (SIBO) arose in the context of maldigestion and malabsorption among patients with obvious risk factors that permitted the small bowel to be colonized by potentially injurious colonic microbiota. Such colonization resulted in clinical signs, symptoms, and laboratory abnormalities that were explicable within a coherent pathophysiological framework. Coincident with advances in medical science, diagnostic testing evolved from small bowel culture to breath tests and on to next-generation, culture-independent microbial analytics. The advent and ready availability of breath tests generated a dramatic expansion in both the rate of diagnosis of SIBO and the range of associated gastrointestinal and nongastrointestinal clinical scenarios. However, issues with the specificity of these same breath tests have clouded their interpretation and aroused some skepticism regarding the role of SIBO in this expanded clinical repertoire. Furthermore, the pathophysiological plausibility that underpins SIBO as a cause of maldigestion/malabsorption is lacking in regard to its purported role in irritable bowel syndrome, for example. One hopes that the application of an ever-expanding armamentarium of modern molecular microbiology to the human small intestinal microbiome in both health and disease will ultimately resolve this impasse and provide an objective basis for the diagnosis of SIBO.

Small Intestine Bacterial Overgrowth Can Form an Indigenous Proinflammatory Environment in the Duodenum: A Prospective Study

Small intestinal bacterial overgrowth (SIBO) contributes to the formation of an inflammatory environment in various intestinal and extraintestinal diseases. Cytokines that participate in these mechanisms are yet to be examined. Upper gastrointestinal endoscopy with duodenal aspiration was performed in 224 patients. Quantitative cultures of aerobic species were performed, concentrations of interleukin 1β (IL-1β), interleukin 6 (IL-6), and tumor necrosis factor alpha (TNF-α) were measured, and loads of Escherichia coli, Klebsiella pneumoniae, Methanobevibacter smithii, and Aeromonas spp. were detected via real-time PCR in the duodenal fluid. Analysis showed that the odds ratio (OR) for elevated IL-1β levels was 2.61 (1.06-6.43, p = 0.037) among patients with SIBO compared to patients without SIBO, while there was no significant difference at elevated IL-6 and TNF-α levels between patients with and without SIBO, using ≥10³ cfu/mL as a cut-off. The presence of all three elevated cytokine levels has OR 3.47 (1.06-11.34, p = 0.030) among patients with SIBO. Klebsiella pneumoniae detection was positively related with IL-6 and TNF-α levels, when Methanobevibacter smithii was positively related with IL-1β levels. The presence of SIBO is associated with elevated IL-1β levels in the duodenal fluid. There is a high prevalence of all three proinflammatory cytokine levels elevated (IL-1β, IL-6, and TNF-α) in the duodenal fluid among patients with SIBO.

Immune responses in the irritable bowel syndromes: time to consider the small intestine

BACKGROUND

Irritable bowel syndrome (IBS) is considered a disorder of gut-brain interaction (DGBI), presenting as chronic abdominal pain and altered defaecation. Symptoms are often food related. Much work in the field has focused on identifying physiological, immune and microbial abnormalities in the colon of patients; however, evidence of small intestinal immune activation and microbial imbalance has been reported in small studies. The significance of such findings has been largely underappreciated despite a growing body of work implicating small intestinal homeostatic imbalance in the pathogenesis of DGBIs.

MAIN TEXT

Small intestinal mechanosensation is a characteristic feature of IBS. Furthermore, altered small intestinal barrier functions have been demonstrated in IBS patients with the diarrhoea-predominant subtype. Small intestinal bacterial overgrowth and increased populations of small intestinal mast cells are frequently associated with IBS, implicating microbial imbalance and low-grade inflammation in the pathogenesis of IBS. Furthermore, reports of localised food hypersensitivity responses in IBS patients implicate the small intestine as the site of immune-microbial-food interactions.

CONCLUSIONS

Given the association of IBS symptoms with food intake in a large proportion of patients and the emerging evidence of immune activation in these patients, the current literature suggests the pathogenesis of IBS is not limited to the colon but rather may involve dysfunction of the entire intestinal tract. It remains unclear if regional variation in IBS pathology explains the various symptom phenotypes and further work should consider the intestinal tract as a whole to answer this question.

Small Intestinal Bacterial Overgrowth

The term "small intestinal bacterial overgrowth" (SIBO) has been used to refer to a disorder resulting from the colonization of the small bowel by an increased number of microorganisms or by the presence of bacteria that are not usual constituents of this part of the gastrointestinal tract. Clinical presentations, often in patients with certain risk factors, can range from a full-blown malabsorption syndrome to such "functional" complaints as bloating and flatulence. SIBO is diagnosed by either culture of a small bowel aspirate or one of several breath tests. Treatment of SIBO entails risk factor modification, correction of nutritional deficiencies, and oral antibiotics.

Early hydrogen excretion peaks during breath tests. Small intestinal bacterial overgrowth or accelerated transit?

BACKGROUND

Small intestinal bacterial overgrowth (SIBO) has been reported with varying prevalence, depending upon the criteria used for diagnosis. Lactulose and glucose breath tests are the most used in clinical settings. Early rises of hydrogen excretion during a lactose breath test suggest SIBO, but the finding could result from accelerated mouth-to-caecum transit time.

AIMS

Defining the prevalence of early hydrogen peaks during lactose breath tests and assessing the proportion of patients affected by SIBO.

METHODS

An early (≤ 60') hydrogen excretion peak was observed in 120/663 patients with positive lactose hydrogen breath test. Eighty-one of them underwent a 50 g-9sample-glucose hydrogen breath test to diagnose SIBO.

RESULTS

The glucose breath test proved positive in 11/81 (13.6%) patients. The positivity rate was 18.2% (2/11) in those with the first peak detected at 30' and 12.8% (9/70) in those with the peak occurring at 60'.

CONCLUSIONS

Early hydrogen excretion peaks are rarely associated with SIBO. The low positive predictive value indicates that the finding does not help identifying patients at high risk for this condition. Indirectly, the present data support the opinion that the prevalence of SIBO diagnosed by standard lactulose breath tests is much lower than reported, and the reliability of the test is low.

Induced volatolomics of pathologies

Volatolomics allows us to elucidate cell metabolic processes in real time. In particular, a volatile organic compound (VOC) excreted from our bodies may be specific for a certain disease, such that measuring this VOC may afford a simple, fast, accessible and safe diagnostic approach. Yet, finding the optimal endogenous volatile marker specific to a pathology is non-trivial because of interlaboratory disparities in sample preparation and analysis, as well as high interindividual variability. These limit the sensitivity and specificity of volatolomics and its applications in biological and clinical fields but have motivated the development of induced volatolomics. This approach aims to overcome issues by measuring VOCs that result not from an endogenous metabolite but, rather, from the pathogen-specific or metabolic-specific enzymatic metabolism of an exogenous biological or chemical probe. In this Review, we introduce volatile-compound-based probes and discuss how they can be exploited to detect and discriminate pathogenic infections, to assess organ function and to diagnose and monitor cancers in real time. We focus on cases in which labelled probes have informed us about metabolic processes and consider the potential and drawbacks of the probes for clinical trials. Beyond diagnostics, VOC-based probes may also be effective tools to explore biological processes more generally.

Delayed Gastric Emptying Is Not Associated with a Microbiological Diagnosis of Small Intestinal Bacterial Overgrowth

BACKGROUND

Clinical symptoms of patients with small intestinal bacterial overgrowth (SIBO) may overlap with symptoms of gastroparesis. Prior studies suggest delayed small intestinal transit is associated with SIBO, but have not shown an association between delayed gastric emptying and SIBO. However, these studies have generally relied on the indirect method of breath testing to diagnose SIBO.

AIMS

The aim of this study was to examine the association between a microbiological diagnosis of SIBO and delayed gastric emptying by scintigraphy.

METHODS

In a single-center retrospective study of previous research participants who presented for small bowel enteroscopy for diagnostic evaluation of SIBO, we identified 73 participants who underwent gastric emptying study by scintigraphy. A microbiological diagnosis of SIBO was made in patients based on culture results of jejunal aspirates. Clinical symptoms were assessed using the total gastroparesis cardinal symptom index (GCSI) score. We compared delayed gastric emptying, 2- and 4-h gastric retention, and gastroparesis symptoms between patients with and without a microbiological diagnosis of SIBO.

KEY RESULTS

Among 29 participants with SIBO and 44 without SIBO, 33 (45%) had evidence of delayed gastric emptying. There was no significant association between a microbiological diagnosis of SIBO and delayed gastric emptying by scintigraphy. Percent retained at 2 and 4 h, and total GCSI scores did not differ significantly between those with and without SIBO.

CONCLUSIONS

Although delayed gastric emptying is common in patients with suspected SIBO, gastric emptying is not associated with a microbiological diagnosis of SIBO.

Factors That Affect Prevalence of Small Intestinal Bacterial Overgrowth in Chronic Pancreatitis: A Systematic Review, Meta-Analysis, and Meta-Regression

OBJECTIVES

Small intestinal bacterial overgrowth (SIBO) can complicate chronic pancreatitis (CP) and interfere with management. Its predisposing factors in CP and treatment response are unknown. In this review, we evaluated factors affecting disease burden.

METHODS

A computerized search of PubMed and EMBASE databases from inception through May 2019 was done for studies correlating SIBO with CP. Studies were screened, and relevant data were extracted and analyzed. Pooled prevalence, odds ratio (OR), and meta-regression were performed using the random effects model as classically described by Borenstein et al. (2009). SIBO's relation to diabetes mellitus (DM), pancreatic exocrine insufficiency (PEI), narcotic use, and proton-pump inhibitor use was investigated. Treatment response was pooled across studies. P value < 0.05 was considered significant.

RESULTS

In 13 studies containing 518 patients with CP, SIBO prevalence was 38.6% (95% confidence interval [CI] 25.5-53.5). OR for SIBO in CP vs controls was 5.58 (95% CI 2.26-13.75). Meta-regression showed that PEI and the diagnostic test used were able to explain 54% and 43% of the variance in SIBO prevalence across studies, respectively. DM and PEI were associated with increased SIBO in CP with OR (2.1, 95% CI 1.2-3.5) and OR (2.5, 95% CI 1.3-4.8), respectively. Symptomatic improvement was reported in 76% of patients after SIBO treatment.

DISCUSSION

SIBO complicates 38% of CP with OR of 5.58 indicating a predisposition for this condition. PEI correlates with SIBO in CP and might play a role in pathophysiology. DM and PEI are associated with increased SIBO in CP. Treatment of SIBO may lead to symptomatic improvement.

Small Intestinal Bacterial Overgrowth Diagnosed by a Breath Test and Improved by Rifaximin in a Patient with Hepatic Encephalopathy and Alcoholic Liver Cirrhosis

A 66-year-old Japanese man was admitted to our hospital with grade 2 hepatic encephalopathy (HE). Abdominal computed tomography and laboratory examinations revealed decompensated liver cirrhosis. Intravenous administration of branched-chain amino acids immediately ameliorated the HE, and lactulose was initiated. However, a breath test revealed small intestinal bacterial overgrowth (SIBO); therefore, rifaximin was additionally initiated. The breath test was repeated after discharge, when no evidence of SIBO or overt HE was identified. This case suggested that a breath test is effective for the identification of SIBO and that the administration of a poorly absorbed antibiotic should be considered in SIBO-positive HE patients taking lactulose.

A comparison of small bowel and fecal microbiota in children with short bowel syndrome

BACKGROUND

Babies with short bowel syndrome (SBS) have small intestinal microbial disturbances that impact gut function. Characterizing the small bowel microbiota is challenging, and the utility of sampling stool is unclear. This study compares the microbiota from fecal samples and the small bowel.

METHODS

Stool samples were collected (2016-2017) from infants with SBS and colon in continuity (COLON) or SBS with small bowel ostomy (sbSTOMA). The abundance and quantity of major bacterial genera was compared between groups and to healthy controls using 16S rRNA sequencing and qPCR. Kruskall-Wallis test was used for analysis with P values <0.05 considered significant.

RESULTS

Samples (n = 41) were collected from 15 SBS infants (<2 years) (9 sbSTOMA, 6 COLON) and 3 healthy infants. Demographics and small intestinal length did not differ between sbSTOMA and COLON infants. The microbiota of SBS groups differed significantly from healthy controls. Fecal samples contained higher quantities of bacteria, but there were no significant differences between sbSTOMA and COLON groups in the abundance of facultative or obligate anaerobes, anti-inflammatory Clostridia, Enterobacteriaceae, or Bifidobacterium.

CONCLUSION

Infants with SBS have disturbances to their intestinal microbiota. Sampling small intestinal effluent is challenging. Stool samples may provide a window into the more proximal microbial community.

TYPE OF STUDY

Diagnostic.

LEVEL OF EVIDENCE

Level II.

Factors Related to the Development of Small-Bowel Bacterial Overgrowth in Pediatric Intestinal Failure: A Retrospective Cohort Study

BACKGROUND

Small bowel bacterial overgrowth (SBBO) is a challenge in the management of pediatric intestinal failure (PIF). Our goal was to determine the proportion of patients treated for SBBO and factors related to its development.

METHODS

We completed a retrospective analysis of PIF patients referred between 2008 and 2014. Data were collected on factors related to intestinal failure (IF) and SBBO. The cohort was stratified on the diagnosis of SBBO and refractory SBBO. Statistical testing completed using t-test, χ² test, and logistic regression.

RESULTS

Thirty-five of 102 patients developed SBBO (34%), and 16 (16%) had refractory SBBO. SBBO was more likely in gastroschisis (40.0% vs 19.4%, P = .025), a shorter residual small bowel (SB) (45.4% vs 66.5%, P = .004), and patients were less likely to wean from parenteral nutrition (PN) (51.4% vs 85.1%, P < .0001). Refractory SBBO patients were likely to have gastroschisis (50.0% vs 22.1%, P = .020) and a shorter residual SB and large bowel remaining (23.2% vs 65.9%, P < .0001 and 60.6% vs 79.4%, P = .03, respectively) and less likely to wean from PN (37.5% vs 80.2%, P = .001). Logistic regression demonstrated that longer SB residual was protective (P = .001; odds ratio [OR], 0.95; 95% CI, 0.93-0.99), and short bowel syndrome (SBS) as a cause of IF was a risk factor (P = .001; OR, 0.04; 95% CI, 0.01-0.27).

CONCLUSION

A longer SB remnant was protective against SBBO. Patients with SBBO were more likely to have PIF caused by SBS.

ACG Clinical Guideline: Small Intestinal Bacterial Overgrowth

Small intestinal bacterial overgrowth is defined as the presence of excessive numbers of bacteria in the small bowel, causing gastrointestinal symptoms. This guideline statement evaluates criteria for diagnosis, defines the optimal methods for diagnostic testing, and summarizes treatment options for small intestinal bacterial overgrowth. This guideline provides an evidence-based evaluation of the literature through the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) process. In instances where the available evidence was not appropriate for a formal GRADE recommendation, key concepts were developed using expert consensus.

Breath Tests for the Non-invasive Diagnosis of Small Intestinal Bacterial Overgrowth: A Systematic Review With Meta-analysis

BACKGROUND/AIMS

Small intestinal bacterial overgrowth (SIBO) diagnosis is usually based on non-invasive breath tests (BTs), namely lactulose BT (LBT) and glucose BT (GBT). However, divergent opinions and problems of parameter standardization are still controversial aspects. We aim to perform a meta-analysis to analyze diagnostic performance of LBT/GBT for SIBO diagnosis.

METHODS

We searched in main literature databases articles in which SIBO diagnosis was achieved by LBT/GBT in comparison to jejunal aspirate culture (reference gold standard). We calculated pooled sensitivity, specificity, positive, and negative likelihood ratios and diagnostic odd ratios. Summary receiver operating characteristic curves were drawn and pooled areas under the curve were calculated.

RESULTS

We selected 14 studies. Pooled sensitivity of LBT and GBT was 42.0% and 54.5%, respectively. Pooled specificity of LBT and GBT was 70.6% and 83.2%, respectively. When delta over baseline cut-off > 20 H2 parts per million (ppm) was used, GBT sensitivity and specificity were 47.3% and 80.9%; when the cutoff was other than and lower than > 20 ppm, sensitivity and specificity were 61.7% and 86.0%. In patients with abdominal surgery history, pooled GBT sensitivity and specificity gave the impression of having a better performance (81.7% and 78.8%) compared to subjects without any SIBO predisposing condition (sensitivity = 40.6% and specificity = 84.0%).

CONCLUSIONS

GBT seems to work better than LBT. A cut-off of delta H2 expired other than and lower than > 20 ppm shows a slightly better result than > 20 ppm. BTs demonstrate the best effectiveness in patients with surgical reconstructions of gastrointestinal tract.

Enhancing our understanding of small bowel function using modern imaging techniques

Small intestinal function is critical to digestive health and patients believe an abnormal reaction to food is responsible for many of their symptoms. Despite this, our ability to assess disturbed function in clinical practice has been limited, particularly after ingestion of the complex nutrients which make up normal food. Recent advances in both wireless capsules and magnetic resonance imaging have provided new insights. This review will briefly describe the limitations of past techniques and focus on how these newer techniques are changing our understanding, particularly of how patients' gastrointestinal tracts respond to food.

Small Intestinal Bacterial Overgrowth in Children: A State-Of-The-Art Review

Small intestinal bacterial overgrowth (SIBO) is a heterogenous and poorly understood entity characterised by an excessive growth of select microorganisms within the small intestine. This excessive bacterial biomass, in turn, disrupts host physiology in a myriad of ways, leading to gastrointestinal and non-gastrointestinal symptoms and complications. SIBO is a common cause of non-specific gastrointestinal symptoms in children, such as chronic abdominal pain, abdominal distention, diarrhoea, and flatulence, amongst others. In addition, it has recently been implicated in the pathophysiology of stunting, a disease that affects millions of children worldwide. Risk factors such as acid-suppressive therapies, alterations in gastrointestinal motility and anatomy, as well as impoverished conditions, have been shown to predispose children to SIBO. SIBO can be diagnosed via culture-dependant or culture-independent approaches. SIBO's epidemiology is limited due to the lack of uniformity and consensus of its diagnostic criteria, as well as the paucity of literature available. Antibiotics remain the first-line treatment option for SIBO, although emerging modalities such as probiotics and diet manipulation could also have a role. Herein, we present a state-of-the-art-review which aims to comprehensively outline the most current information on SIBO in children, with particular emphasis on the gut microbiota.

The Spectrum of Small Intestinal Bacterial Overgrowth (SIBO)

PURPOSE OF REVIEW

To critically review recent (past 3 years) literature on the definition, diagnosis, and management of small intestinal bacterial overgrowth (SIBO).

RECENT FINDINGS

While various series continue to illustrate the occurrence of SIBO in disease states where well-known risk factors for its occurrence are present (hypochlorhydria, disorders of intestinal structure or motor function, pancreatic insufficiency, and chronic liver disease, for example), the current challenge is in defining the limits of SIBO. Is SIBO truly common among those with "functional" gastrointestinal symptoms where there is no evidence of maldigestion or malabsorption; the original hallmarks of SIBO? Our attempts to address this question continue to be hampered by the limitations of our diagnostic tool kit. There is hope-the application of modern molecular techniques to the study of the small intestinal microbiome, together with some innovative sampling techniques, such as real-time intestinal gas sampling, may soon allow us to truly define the spectrum of SIBO. SIBO, once removed from its original confines as a cause of malabsorption syndrome, has proven to be an elusive and moving target. Only the most rigorous studies employing validated methodologies will finally corral this mysterious entity.

The diagnosis of small intestinal bacterial overgrowth: Two steps forward, one step backwards?

Small intestinal bacterial overgrowth (SIBO) was originally described decades ago as a cause of malabsorption among individuals with abnormal intestinal anatomy and/or impaired gastric acid secretion and intestinal motor functions. More recently, the concept of SIBO has been expanded to explain symptoms among a much broader patient population-a move that brings the definition of SIBO into much sharper focus. For largely logistical reasons, breath tests and, especially, those based on the excretion of hydrogen consequent on the fermentation of unabsorbed carbohydrate substrates, have almost entirely replaced jejunal aspirates in the diagnosis of SIBO. Ever bedeviled by concerns regarding their reliability, hydrogen breath tests have now come under even more critical scrutiny with the study from Sundin and colleagues in this issue suggesting that their sole function is to detect carbohydrate malabsorption and that they are incapable of defining SIBO.