Gastrointestinal surgery and the gut microbiome: a systematic literature review

Preventive effect of probiotics on infections following colorectal cancer surgery: An umbrella meta-analysis

BACKGROUND

Postoperative infections remain a significant source of morbidity among patients undergoing colorectal cancer (CRC) surgery. While probiotics have been proposed as a potential strategy to mitigate the risk of these infections, contemporary meta-analyses have produced conflicting findings.

AIM

To synthesize the available evidence regarding the prophylactic efficacy of probiotics in preventing infections following CRC surgery.

METHODS

A comprehensive search of PubMed and Scopus was conducted to identify relevant meta-analyses published up to February 2024. To assess the efficacy of probiotics on outcomes, relative risks (RR) and their corresponding 95%CI were pooled using a random effects model.

RESULTS

This comprehensive umbrella meta-analysis integrated eleven meta-analyses encompassing 11518 participants who fulfilled the inclusion criteria. Probiotics administration resulted in a statistically significant reduction in the incidence of total infections (RR: 0.40, 95%CI: 0.31-0.51; moderate certainty), surgical site infections (RR: 0.56, 95%CI: 0.49-0.63; high certainty), pneumonia (RR: 0.38, 95%CI: 0.30-0.48; high certainty), urinary tract infections (RR: 0.44, 95%CI: 0.31-0.61; moderate certainty), bacteremia (RR: 0.41, 95%CI: 0.30-0.56; high certainty), and sepsis (RR: 0.35, 95%CI: 0.25-0.44; high certainty). However, probiotics did not significantly affect intra-abdominal, central line, or peritoneal infections.

CONCLUSION

Probiotics have demonstrated potential in mitigating postoperative infectious complications among patients undergoing CRC surgery.

Assessing the causal relationship between gut microbiota and prostate cancer: A two-sample Mendelian randomization study

BACKGROUND

Numerous studies indicate that the gut microbiome is closely associated with prostate cancer (PCa), however, owing to various confounding factors, the causal relationship between gut microbiota and PCa remains unclear.

METHODS

A 2-sample Mendelian randomization (MR) analysis utilized genome-wide association study (GWAS) data on the gut microbiota of 18,340 participants and GWAS summary statistics on PCa involving 46,3010 participants. Inverse variance weighted (IVW) served as the primary method, complemented by the MR-Egger method, weighted median method (WME), simple mode method (SM), and weighted mode method (WM). Finally, to confirm the robustness of the results, heterogeneity test, pleiotropy test, and leave-one-out sensitivity test were conducted.

RESULTS

IVW analysis revealed that 12 specific gut microbial taxa were potentially causally associated with PCa; the genera Victivallis, Akkermansia, Odoribacter, Butyrivibrio, and the families Enterobacteriaceae, Verrucomicrobiaceae, as well as the orders Verrucomicrobiales, Enterobacteriales and the class Verrucomicrobiae, were found to be positively associated with PCa risk. Conversely, the genera Eubacterium ruminantium group, Candidatus Soleaferrea, and RuminococcaceaeUCG003 were negatively associated with PCa risk.

CONCLUSIONS

Our MR study's results support a genetically predicted causal relationship between the gut microbiota and PCa, and we identified 12 specific gut microbial taxa. These findings could offer new targets for PCa screening and treatment.

The Combined Effect of Western Diet Consumption and Diclofenac Administration Alters the Gut Microbiota and Promotes Anastomotic Leakage in the Distal Colon

BACKGROUND

Obesity, Western diet (WD) consumption, and the use of non-steroidal anti-inflammatory drugs (NSAIDs) are co-occurring and modifiable factors associated with microbiome dysbiosis and anastomotic leakage. We studied the combined effect of a Western-type diet (WD) and diclofenac, a standard NSAID used in surgical patients, on anastomotic healing and gut microbiota composition following distal colon resection.

METHODS

Forty-two rats were fed a WD for 6 weeks, after which they were randomized to either parenteral diclofenac 3 mg/kg/day or saline started on the day of surgery and continued for three days. The surgical procedure involved distal colon resection with anastomosis. Animals were sacrificed on postoperative day (POD)-3 or POD-5. Anastomotic healing was assessed and correlated with diclofenac treatment and gut microbiota composition, analyzed by 16S rRNA marker gene amplicon sequencing. Mucosal integrity of the anastomosis was evaluated by histological analysis.

RESULTS

Anastomotic leakage rate was 100 percent (8/8) in diclofenac-treated rats and 10 percent (1/10) in saline-treated controls on POD-5. Diclofenac administration in WD-fed animals induced a shift in microbiota composition, characterized by an increase in microbiota diversity on POD-5 and a significant 15-fold, 4-fold, and 16-fold increase of Proteobacteria, Bacteroidetes, and Verrucomicrobia, respectively. Diclofenac use in WD-fed animals caused mucosal erosion on POD-5, a phenomenon not observed in control animals.

CONCLUSIONS

Consumption of a Western diet combined with diclofenac administration shifts the microbiota composition, associated with clinically relevant AL in the distal colon of rats.

Postoperative delayed gastric emptying: may gut microbiota play a role?

Postoperative delayed gastric emptying is a prevalent complication following surgical procedures, imposing heavy physical and financial burdens on patients. However, current treatment options remain suboptimal. In recent years, an increasing number of studies have highlighted that the gut microbiota and its metabolites are closely associated with postoperative complications. Various factors can disrupt the gut microbiome after surgery. This review discusses the potential mechanisms by which the gut microbiota and their metabolites may contribute to the pathogenesis of postoperative delayed gastric emptying. However, the current knowledge base is limited in terms of fully understanding the exact mechanisms involved. It is therefore evident that further research is required to fully elucidate the role of the gut microbiome in postoperative delayed gastric emptying, with the aim of uncovering new possibilities for preventive measures and therapeutic treatments.

The Impact of Surgical Bowel Preparation on the Microbiome in Colon and Rectal Surgery

Preoperative bowel preparation, through iterations over time, has evolved with the goal of optimizing surgical outcomes after colon and rectal surgery. Although bowel preparation is commonplace in current practice, its precise mechanism of action, particularly its effect on the human gut microbiome, has yet to be fully elucidated. Absent intervention, the gut microbiota is largely stable, yet reacts to dietary influences, tissue injury, and microbiota-specific byproducts of metabolism. The routine use of oral antibiotics and mechanical bowel preparation prior to intestinal surgical procedures may have detrimental effects previously thought to be negligible. Recent evidence highlights the sensitivity of gut microbiota to antibiotics, bowel preparation, and surgery; however, there is a lack of knowledge regarding specific causal pathways that could lead to therapeutic interventions. As our understanding of the complex interactions between the human host and gut microbiota grows, we can explore the role of bowel preparation in specific microbiome alterations to refine perioperative care and improve outcomes. In this review, we outline the current fund of information regarding the impact of surgical bowel preparation and its components on the adult gut microbiome. We also emphasize key questions pertinent to future microbiome research and their implications for patients undergoing colorectal surgery.

The impact of faecal diversion on the gut microbiome: a systematic review

Diversion of the faecal stream is associated with diversion colitis (DC). Preliminary studies indicate that microbiome dysbiosis contributes to its development and potentially treatment. This review aims to characterise these changes in the context of faecal diversion and identify their clinical impact. A systematic search was conducted using MEDLINE, EMBASE and CENTRAL databases using a predefined search strategy identifying studies investigating changes in microbiome following diversion. Findings reported according to PRISMA guidelines. Of 743 results, 6 met inclusion criteria. Five reported significantly decreased microbiome diversity in the diverted colon. At phylum level, decreases in Bacillota with a concomitant increase in Pseudomonadota were observed, consistent with dysbiosis. At genus level, studies reported decreases in beneficial lactic acid bacteria which produce short-chain fatty acid (SCFA), which inversely correlated with disease severity. Significant losses in commensals were also noted. These changes were seen to be partially reversible with restoration of bowel continuity. Changes within the microbiome were reflected by histopathological findings suggestive of intestinal dysfunction. Faecal diversion is associated with dysbiosis in the diverted colon which may have clinical implications. This is reflected in loss of microbiome diversity, increases in potentially pathogenic-associated phyla and reduction in SCFA-producing and commensal bacteria.

Influence of the bile acid/microbiota axis in ileal surgery: a systematic review

AIM

The gastrointestinal bile acid (BA)/microbiota axis has emerged as a potential mediator of health and disease, particularly in relation to pathologies such as inflammatory bowel disease (IBD) and colorectal cancer. Whilst it presents an exciting new avenue for therapies, it has not yet been characterized in surgical resection of the ileum, where BA reabsorption occurs. The identification of BA/microbiota signatures may provide future therapies with perioperative personalized medicine. In this work we conduct a systematic review with the aim of investigating the microbiome and BA changes that are associated with resection of the ileum.

METHOD

The databases included were MEDLINE, EMBASE, Web of Science and Cochrane libraries. The outcomes of interest were faecal microbiome and BA signatures after ileal resection.

RESULTS

Of the initial 3106 articles, three studies met the inclusion/exclusion criteria for data extraction. A total of 257 patients (46% surgery, 54% nonsurgery controls) were included in the three studies. Two studies included patients with short bowel syndrome and the other included patients with IBD. Large-scale microbiota changes were reported. In general, alpha diversity had decreased amongst patients with ileal surgery. Phylum-level changes included decreased Bacteroidetes and increased Proteobacteria and Fusobacteria in patients with an intestinal resection. Surgery was associated with increased total faecal BAs, cholic acid and chenodeoxycholic acid. There were decreases in deoxycholic acid and glycine and taurine conjugated bile salts. Integrated BA and microbiota data identified correlations with several bacterial families and BA.

CONCLUSION

The BA/microbiota axis is still a novel area with minimal observational data in surgery. Further mechanistic research is necessary to further explore this and identify its role in improving perioperative outcomes.

Gut dysbiosis-related thrombosis in inflammatory bowel disease: Potential disease mechanisms and emerging therapeutic strategies

Patients with inflammatory bowel disease (IBD) have an increased risk of developing venous thromboembolic events, which have a considerable impact on morbidity and mortality. Chronic inflammation plays a crucial role in the pathogenesis of thrombotic events in patients with IBD. However, many unresolved questions remain, particularly regarding the mechanisms that determine the persistent inflammatory state independent of disease activity. This review explored the role of gut microbiota dysbiosis and intestinal barrier dysfunction, which are considered distinctive features of IBD, in determining pro-thrombotic tendencies. Gut-derived endotoxemia due to the translocation of bacterial lipopolysaccharides (LPS) from the intestine to the bloodstream and the bacterial metabolite trimethylamine-N-oxide (TMAO) are the most important molecules involved in gut dysbiosis-related thrombosis. The pathogenic prothrombotic pathways linked to LPS and TMAO have been discussed. Finally, we present emerging therapeutic approaches that can help reduce LPS-mediated endotoxemia and TMAO, such as restoring intestinal eubiosis, normalizing intestinal barrier function, and counterbalancing the effects of LPS and TMAO.

The gut microbiome and cardiac surgery an unusual symphony

The relationship between the gut microbiome and various organ systems has gained interest throughout the scientific community in recent times. The understanding of these complex relationships has greatly improved with clinical benefits now being seen. Cardiopulmonary bypass (CPB) is a form of extracorporeal circulation that provides circulatory and respiratory support during cardiac surgery. This physiological support facilitates a still and bloodless field facilitating operations on the heart to be performed. Through various mechanisms CPB results in a systemic inflammatory response syndrome (SIRS). This response can vary from mild hypotension to multiple organ failure. It remains difficult to predict the degree to which a patient will experience SIRS post-operatively. The relationship between the composition of the gut microbiome and inflammatory processes associated with disease has been seen across several fields including gastroenterology, neurology, psychiatry and cardiology. To date, minimal research has been undertaken to examine the impact the gut microbiome has on outcomes following cardiac surgery. This review paper explores the pathophysiology behind the SIRS response associated with CPB for cardiac surgery and the hypothesis that a correlation exists between a patients gut microbiome composition and the degree of inflammatory response experienced following cardiac surgery.

Alterations of gut microbiome following gastrointestinal surgical procedures and their potential complications

Intestinal microorganisms play a crucial role in shaping the host immunity and maintaining homeostasis. Nevertheless, alterations in gut bacterial composition may occur and these alterations have been linked with the pathogenesis of several diseases. In surgical practice, studies revealed that the microbiome of patients undergoing surgery changes and several post-operative complications seem to be associated with the gut microbiota composition. In this review, we aim to provide an overview of gut microbiota (GM) in surgical disease. We refer to several studies which describe alterations of GM in patients undergoing different types of surgery, we focus on the impacts of peri-operative interventions on GM and the role of GM in development of post-operative complications, such as anastomotic leak. The review aims to enhance comprehension regarding the correlation between GM and surgical procedures based in the current knowledge. However, preoperative and postoperative synthesis of GM needs to be further examined in future studies, so that GM-targeted measures could be assessed and the different surgery complications could be reduced.

Role of the Microbiome in Malignancy

The conceptual underpinning of carcinogenesis has been strongly influenced by an expanded understanding of the human microbiome. Malignancy risks in diverse organs have been uniquely tied to aspects of the resident microbiota in different organs and systems including the colon, lungs, pancreas, ovaries, uterine cervix, and stomach; other organs are increasingly linked to maladaptive aspects of the microbiome as well. In this way, the maladaptive microbiome may be termed an oncobiome. Microbe-driven inflammation, anti-inflammation, and mucosal protection failure, as well as diet-induced microbiome derangement are all mechanisms that influence malignancy risk. Therefore, they also offer potential avenues of diagnostic and therapeutic intervention to modify malignancy risk, and to perhaps interrupt progression toward cancer in different sites. Each of these mechanisms will be explored using colorectal malignancy as a prototype condition to demonstrate the microbiome's role in carcinogenesis.

Microbiota Phenotype Promotes Anastomotic Leakage in a Model of Rats with Ischemic Colon Resection

Anastomotic leakage (AL) is a major cause of morbidity and mortality after colorectal surgery, but the mechanism behind this complication is still not fully understood. Despite the advances in surgical techniques and perioperative care, the complication rates have remained steady. Recently, it has been suggested that colon microbiota may be involved in the development of complications after colorectal surgery. The aim of this study was to evaluate the association of gut microbiota in the development of colorectal AL and their possible virulence strategies to better understand the phenomenon. Using 16S rRNA sequencing of samples collected on the day of surgery and the sixth day following surgery, we analyzed the changes in tissue-associated microbiota at anastomotic sites created in a model of rats with ischemic colon resection. We discovered a trend for lower microbial diversity in the AL group compared to non-leak anastomosis (NLA). There were no differences in relative abundance in the different types of microbial respiration between these groups and the high abundance of the facultative anaerobic Gemella palaticanis is a marker species that stands out as a distinctive feature.

What Is the Microbiome? A Description of a Social Network

The gut microbiome has coevolved with its hosts over the years, forming a complex and symbiotic relationship. It is formed by what we do, what we eat, where we live, and with whom we live. The microbiome is known to influence our health by training our immune system and providing nutrients for the human body. However, when the microbiome becomes out of balance and dysbiosis occurs, the microorganisms within can cause or contribute to diseases. This major influencer on our health is studied intensively, but it is unfortunately often overlooked by the surgeon and in surgical practice. Because of that, there is not much literature about the microbiome and its influence on surgical patients or procedures. However, there is evidence that it plays a major role, showing that it needs to be a topic of interest for the surgeon. This review is written to show the surgeon the importance of the microbiome and why it should be taken into consideration when preparing or treating patients.

Selective Decontamination of the Digestive Tract in Pancreatic Head Resections-A Propensity Score-Matched Analysis

(1) Background: The postoperative morbidity rate after pancreatic head resection remains high, partly due to infectious complications. The primary aim of this study was to analyze the influence of selective decontamination of the digestive tract (SDD) on the postoperative infection rate after pancreatic surgery. (2) Methods: From January 2019, the standard of care for patients undergoing pancreatic head resections at the Department for Visceral, Thoracic, and Vascular Surgery, University Hospital Dresden was the preoperative oral administration of SDD. The influence of SDD was evaluated for patients operated on between January 2019 and June 2020 in comparison to a propensity score-matched cohort, extracted from an existing database including all pancreatic resections from 2012 to 2018. The primary endpoint of the study was the shift of the bacterial load on the intraoperative bile swab test. The secondary endpoint was the association of SDD with postoperative complications. (3) Results: In total, 200 patients either with SDD (n = 100; 50%) or without SDD (non-SDD, n = 100; 50%) were analyzed. In the patient group without a preoperative biliary stent, 44% (n = 11) of the non-SDD group displayed positive bacterial results, whereas that was the case for only 21.7% (n = 10) in the SDD group (p = 0.05). Particularly, Enterobacter species (spp.) were reduced from 41.2% (n = 14) (non-SDD group) to 23.5% (n = 12) (SDD group) (p = 0.08), and Citrobacter spp. were reduced by 13.7% (p = 0.09) from the non-SDD to the SDD cohort. In patients with a preoperative biliary stent, the Gram-negative Enterobacter spp. were significantly reduced from 52.2% (n = 12) in the non-SDD group to 26.8% (n = 11) in the SDD group (p = 0.04). Similarly, Citrobacter spp. decreased by 20.6% from 30.4% (n = 7) to 9.8% (n = 4) in the non-SDD compared to the SDD group (p = 0.04). In general, deep fluid collection and abscesses occurred more frequently in the non-SDD group (36%; n = 36 vs. 27%; n = 27; p = 0.17). (4) Conclusions: Adoption of SDD before pancreatic head surgery may reduce the bacterial load in bile fluid. SDD administration does not significantly affect the postoperative infectious complication rate after pancreatic head resections.

Dysbiosis and Gastrointestinal Surgery: Current Insights and Future Research

Surgery of the gastrointestinal tract can result in deep changes among the gut commensals in terms of abundance, function and health consequences. Elective colorectal surgery can occur for neoplastic or inflammatory bowel disease; in these settings, microbiota imbalance is described as a preoperative condition, and it is linked to post-operative complications, as well. The study of bariatric patients led to several insights into the role of gut microbiota in obesity and after major surgical injuries. Preoperative dysbiosis and post-surgical microbiota reassessment are still poorly understood, and they could become a key part of preventing post-surgical complications. In the current review, we outline the most recent literature regarding agents and molecular pathways involved in pre- and post-operative dysbiosis in patients undergoing gastrointestinal surgery. Defining the standard method for microbiota assessment in these patients could set up the future approach and clinical practice.

Ruminiclostridium 5, Parabacteroides distasonis, and bile acid profile are modulated by prebiotic diet and associate with facilitated sleep/clock realignment after chronic disruption of rhythms

Chronic disruption of rhythms (CDR) impacts sleep and can result in circadian misalignment of physiological systems which, in turn, is associated with increased disease risk. Exposure to repeated or severe stressors also disturbs sleep and diurnal rhythms. Prebiotic nutrients produce favorable changes in gut microbial ecology, the gut metabolome, and reduce several negative impacts of acute severe stressor exposure, including disturbed sleep, core body temperature rhythmicity, and gut microbial dysbiosis. In light of previous compelling evidence that prebiotic diet broadly reduces negative impacts of acute, severe stressors, we hypothesize that prebiotic diet will also effectively mitigate the negative impacts of chronic disruption of circadian rhythms on physiology and sleep/wake behavior. Male, Sprague Dawley rats were fed diets enriched in prebiotic substrates or calorically matched control chow. After 5 weeks on diet, rats were exposed to CDR (12 h light/dark reversal, weekly for 8 weeks) or remained on undisturbed normal light/dark cycles (NLD). Sleep EEG, core body temperature, and locomotor activity were recorded via biotelemetry in freely moving rats. Fecal samples were collected on experimental days -33, 0 (day of onset of CDR), and 42. Taxonomic identification and relative abundances of gut microbes were measured in fecal samples using 16S rRNA gene sequencing and shotgun metagenomics. Fecal primary, bacterially modified secondary, and conjugated bile acids were measured using liquid chromatography with tandem mass spectrometry (LC-MS/MS). Prebiotic diet produced rapid and stable increases in the relative abundances of Parabacteroides distasonis and Ruminiclostridium 5. Shotgun metagenomics analyses confirmed reliable increases in relative abundances of Parabacteroides distasonis and Clostridium leptum, a member of the Ruminiclostridium genus. Prebiotic diet also modified fecal bile acid profiles; and based on correlational and step-wise regression analyses, Parabacteroides distasonis and Ruminiclostridium 5 were positively associated with each other and negatively associated with secondary and conjugated bile acids. Prebiotic diet, but not CDR, impacted beta diversity. Measures of alpha diversity evenness were decreased by CDR and prebiotic diet prevented that effect. Rats exposed to CDR while eating prebiotic, compared to control diet, more quickly realigned NREM sleep and core body temperature (ClockLab) diurnal rhythms to the altered light/dark cycle. Finally, both cholic acid and Ruminiclostridium 5 prior to CDR were associated with time to realign CBT rhythms to the new light/dark cycle after CDR; whereas both Ruminiclostridium 5 and taurocholic acid prior to CDR were associated with NREM sleep recovery after CDR. These results support our hypothesis and suggest that ingestion of prebiotic substrates is an effective strategy to increase the relative abundance of health promoting microbes, alter the fecal bile acid profile, and facilitate the recovery and realignment of sleep and diurnal rhythms after circadian disruption.