By using Web of Science Core Collection (WoSCC), we performed a data search related to gut microbiota and trauma, retrieving SCI documents with no language limitation. The research strategy we designed was [(TS = trauma) OR (TS = traumatic)] AND [(TS = gut) OR (TS = intestin*) OR (TS= gastrointestin*) OR (TS = gastro-intestin*)] AND [(TS = microbiot*) OR (TS = microbiome*) OR (TS = flora) OR (TS = microflora) OR (TS = bacteria) OR (TS = prebiotic) OR (TS = probiotic)]. We conducted the retrieval on May 15, 2022. After excluding reviews and books and restricting the scope to “article”, the information of all the remaining 625 relevant articles, which we analyzed subsequently, was downloaded as TXT files (Peng et al., 2022). All the retrieval works and data collection were accomplished on May 15, 2022.

The TXT files were imported into Biblioshiny, a web application for a bibliometric tool developed in R version 4.2.0 (Institute for Statistics and Mathematics, Vienna, Austria; www.r-project.org) (Aria and Cuccurullo, 2017). The application was mainly employed to visualize sources, authors, and documents' analysis and present the conceptual, intellectual, and social structure, with the bibliometrix package. Besides, we utilized CiteSpace software version 6.1.2R, a computational tool based on JAVA for data visualization (Chen, 2004), and VOSviewer version 1.6.18, a bibliometric program for constructing visualized networks (van Eck and Waltman, 2010), to repeat the process and validate the results.

Annual scientific production and average citations were acquired to analyze the overall trend in this field. The impactive countries, institutions, journals and authors were mostly estimated by their production and citations. The algorithms like Bradford's law (Brookes, 1969), Lotka's law (Pao, 1985) and h-index (Hirsch, 2005) were applied to find the core journals and authors. We also visualized the collaboration of countries to assess the global relationship between countries. In order to detect the hotspots, after capturing high-frequency keywords and important documents and building networks of co-word and direct citations, we accessed the concrete content of some relevant articles in this field. The trend topic in this field was obtained from the trend topics map and direct citation network.

Based on the retrieval process shown in Figure 1, 625 relevant articles were collected from WoSCC. The first SCI publication with complete citation information in gut microbiota and trauma research, was found to published in 1976. Figure 2A presents the number of published documents per year. The quantity of production showed no obvious change until the first small peak in 1987. In 1991, the number of documents published per year increased to 14. It's noteworthy that the manifestly explosive growth started from 2016 and didn't reach the peak, pointing out that scholars made scientific breakthroughs or more research directions were detected. The growing trend indicated the role of gut microbiota in trauma were gaining increasing traction and had great development potential in both clinical and basic experiments.

The statistics of annual article citations per year were revealed in Figure 2B. The two peaks, respectively, occurred in 1988 and 2016, implicating that important research outcomes were gained. More information of documents analysis is included in point 3.4.3.

Forty-nine countries took part in the field of gut microbiota and trauma, spanning from 1976 to 2022. The map developed by Biblioshiny depicted the distribution and quantity of countries of publication (Figure 3A). The frequency of publication in these countries was based on the nationality statistics of the corresponding authors. China was the most prolific country (n = 215), followed by the USA (n = 176) and German (n = 22) (Table 1), illustrating the absolutely leading position of China and the USA in terms of publication volume. However, with high quantity of production, the number of the citation of China was nearly half of the USA (Figure 3B), emphasizing the powerful influence of the USA in this field. In the collaboration analysis, we set the minimum edge to two and labeled the numbers of collaborations on the map (Figure 3C). According to the country collaboration map, the USA had the most ties with other major publishing countries. There were 130 collaborations between countries worldwide, 51 of which were between the USA and other countries. The line between the USA and China was widest, highlighting the association between the two countries for gut microbiota and trauma research. As a whole, the link lines between countries were sparse and scattered, which corresponds with the information that the single country publications were much more than the multiple country publications (Table 1). These results suggested that cooperation among countries should be promoted.

According to our retrieved data, 878 institutions participated in the research of gut microbiota and trauma. We listed the top 20 prolific institutions (Figure 4). It's not surprising that three of the top three institutions, including the University of Colorado (n = 37), the University of Pittsburgh (n = 30), and the University of Louisville (n = 22), were located in the USA. Another institution tied for third was Wenzhou Medical University, which was from China. Except for Chulalongkorn University (Thailand, n = 15), University of Patras (Greece, n = 14) and Maastricht University (Holland, n = 12), other institutions were from either the USA or China, proving remarkable achievement of the two countries in this field again.

There are rare documents published between 1976 and 1986 in this field. However, in 1987, Deitch et al. demonstrated the phenomenon that trauma enhances bacterial translocation from guts to MLN (mesenteric lymph nodes) or other systematic organs in rats, especially when combined with residual necrotic tissue, which connects gut microbiota and trauma directly (Deitch et al., 1987). In Baker's animal model of hemorrhagic shock, bacterial translocation was found, and Escherichia coli was the most commonly translocated bacteria isolated from solid viscera (Baker et al., 1988), corresponding with Agalar's model (Agalar et al., 1998). In Koziol's study, bacterial translocation was also discovered in hemorrhagic shock, while Pseudomonas and Enterococcus dominated in the early stages and cultures became polymicrobial with time (Koziol et al., 1988). Subsequently, some scholars proposed that bacterial infiltration, possibly from the gut, contributes to sepsis in patients who have experienced hemorrhagic shock, based on animal experiments (Sori et al., 1988; Sorell et al., 1993). Rush et al. (1988) found that the seriously injured patients with lower blood pressure had a higher rate of positive blood cultures, and the mortality of these patients was also higher, which suggested that straight absorption of germs and endotoxin into the circulation of the traumatic and hypotensive patient plays an important role in the beginning of the syndrome that follows hemorrhagic shock. What's more, there was evidence that the occurrence of bacterial/endotoxin translocation in hemorrhagic shock might be accompanied by TNF generation, and endogenous endotoxemia may be involved in the development of multiple organ failure following shock and trauma (Yao et al., 1995). Accordingly, gut bacterial translocation appears to play an important role in some severe complications of trauma. Afterwards, more scholars flung themselves into the research of the gut bacterial translocation in trauma (Moore et al., 1991, 1992; Peitzman et al., 1991; Brathwaite et al., 1993; Sedman et al., 1994), resulting in the growth of output since 1991. Additionally, it has been reported that bacterial translocation increases the risk of postoperative infection in patients with abdominal trauma (Nieves et al., 2011; Schietroma et al., 2018). MacFie et al. (2006) reported that postoperative sepsis was more common in patients with bacterial translocation than those without (42.3 vs. 19.9%, p < 0.001), and Escherichia coli was the most common enteric organism isolated. In other perspective, a healthy gut microenvironment is also an instinctively biological barrier to resist the colonization of pathogenic bacteria. Disruption of the biological barrier probably generates infection. Earley et al. (2015) verified that burn injury altered gut microbiota and promoted the growth of γ-Proteobacteria, especially those belonging to the family Enterobacteriaceae, which contained many sepsis-related pathogens. Meanwhile, with greater α-diversity of the gut microbiome, the survival of mice with sepsis can be improved, which is possibly due to an enhanced T cell response (Cabrera-Perez et al., 2016; Fay et al., 2019). Therefore, gut bacteria may be a potential therapeutic target to improve the outcomes of patients with trauma by reducing infection. As for the mechanism of bacterial translocation in trauma, it involved the increased intestinal permeability in trauma patients, which might be related to the inflammatory response, such as the raised IL-6 level in serum (Spindler-Vesel et al., 2006; Hanscom et al., 2021). There was also a conjecture that the use of glucocorticoid might promote bacterial translocation via damnification of mucosal IgA synthesis (Alverdy and Aoys, 1991). However, the concretely regulatory mechanism of bacterial translocation in trauma is largely unclear and need more exploration.

From 2016, documents on gut microbiota and nervous system injury began to increase, which may be attributed to the establishment of the consensus that gut microbiota interacts with the nervous system and modulates the function of CNS (Cryan and Dinan, 2012; Forsythe and Kunze, 2013; Borre et al., 2014). Of the top 20 local cited documents, six refer to the gut microbiota in patients with nervous system injuries, and they were all published in 2016 and beyond. Coincidentally, the annual publications in this field have also rocketed up since 2016, with an increase in the frequency of “inflammation” and “expression.” Thus, we deduced that scholars focus more on the gut microbiota's impact on inflammation following nervous system injury than on other forms of trauma.

In 2016, Gungor et al. (2016) reported that spine core injured (SCI) patients may have a lower level of butyrate production compared with healthy subjects. Butyrate, a kind of short chain fatty acids (SCFAs), is an important metabolite created by some gut bacteria, possessing powerful anti-inflammatory action (Chen et al., 2007; Furusawa et al., 2013; Dalile et al., 2019). Moreover, gut bacterial dysbiosis caused by SCI has been found to trigger inflammation in GALT (Kigerl et al., 2016) and influence systemic and intraspinal inflammation by inducing the activation of mucosal immune cells in GALT (Dinan et al., 2013). Hence gut bacterial dysbiosis caused by SCI may in turn be related to the inflammation in SCI and affect recovery of patients. Besides SCI, bacterial dysbiosis is also found in traumatic brain injury (TBI) (Houlden et al., 2016; Treangen et al., 2018; Nicholson et al., 2019; Urban et al., 2020; Opeyemi et al., 2021). Houlden et al. observed the increased noradrenaline (NE) release in the caecum of brain-injured mice models, as well as the positive correlation between the abundance of Peptococcaceae and RANTES (CCR5) level, a type of proinflammatory cytokine, in the gut tissue (Houlden et al., 2016). The responses of proinflammatory Th1 and Th17 elicited by bacterial dysbiosis and the link between bacterial dysbiosis and degenerative outcome in mice with massive brain infarction were also observed (Singh et al., 2016). It has also been reported that LPS, a kind of toxic bacterial component, can induce the activation of microglia, which then aggravates neuroinflammation in TBI (Wen et al., 2018). What's more, You et al. (2022) discovered the decreased level of bile acid, especially the secondary bile acid, in feces and plasma after TBI, which might be related to the gut bacteria such as Staphylococcus and Lachnospiraceae. Then the deficiency in secondary bile acids might boost intestinal inflammation in patients (Sinha et al., 2020). These findings demonstrated the presence of bacterial dysbiosis in neurotrauma as well as the critical role of gut microbiota in inflammation. As the study of this theme hasn't been carried out for a long time, the specific pathways by which gut microbiota affect the pathogenesis of neurotrauma are still not entirely clear and need more exploration.

Not only the mechanisms of the impact of gut bacteria on trauma but also the methods that can alter gut microbiota have attracted people's attention. Two of the most local cited documents documented the functions of probiotic supplements in treatment of alcohol-induced liver injury, including suppressing inflammation (Kirpich et al., 2008; Wang et al., 2013). Meanwhile, the supplementation of probiotic Lactobacillus rhamnosus GG (LGG) might improve intestinal integrity by inhibiting miR122a, which resulted in occludin restoration, and increasing mRNA expression of tight junction (TJ) proteins in mice with alcohol-induced liver injury (Zhao et al., 2015; Chen et al., 2016). The positive effect of probiotic treatment has been documented in SCI as well, including locomotor recovery and regulating T lymphocyte activation (Kigerl et al., 2016). In serious TBI, with probiotic treatment, the deviated Th1/Th2 response might be mitigated, which then could lower the risk of nosocomial infections (Tan et al., 2011). Moreover, fecal microbiota transplantation (FMT), another method to alter gut microbiota, was found to increase the production of SCFAs and suppress the IL-1/NF-κB signaling in the spinal cord and NF-κB signaling in the intestine after SCI (Jing et al., 2021). FMT was also reported to relieve neurological deficits after TBI through TMA-TMAO-MsrA signaling pathway (Du et al., 2021). Some specific bacteria had also been shown to have neuroprotective effects through different mechanisms in mice with TBI (Li et al., 2018; Ma et al., 2019). What's more, there are experiments verifying that dietary structures such as high protein and supplements of specific foods like rice bran phenolic extract, oolong tea and so on can lead to changes in the gut microbiota and aggravation or relief of inflammation in injuries (Zhang et al., 2014; Power et al., 2016; Feng et al., 2020; Xiao et al., 2020; Ge et al., 2021; Li et al., 2021; Snelson et al., 2021). Most of these experiments were conducted in animal models, which means that we need more clinical evidence to support the therapeutic functions of these methods.

With the development of high-throughput sequencing technology, researchers are able to directly explore the changes and functions of the microorganisms in trauma, which may partly contribute to the result that topics concerning gut microorganisms in trauma may attract more attention than the topics regarding to intestinal barrier, in factorial analysis. Moreover, here we extrapolate that with the continual update of research techniques, such as single-cell RNA sequencing, spatial transcriptome sequencing and multi-omics analysis, scholars can further disclose the concrete regulatory networks and pathways induced by microbiota in the mechanism of trauma development, which may be a direction for future research in this field. The studies on the therapies will also continue and more clinical trials will be carried out.

To our knowledge, this study is the first biliometric analysis involving the influence of gut microbiota in trauma patients. Nevertheless, there are still some limitations. Firstly, bibliometrics can't appraise the quality, rationality, and limitations of the articles that we analyzed. Thus, the study can't replace some other review types, such as systematic review and meta-analysis. Secondly, we retrieved articles that were recorded in the Web of Science Core Collection (WoSCC) by May 15, 2022. Due to the restriction of retrieval and analysis technology, WoSCC was the only database we utilized to download publication information. Therefore, the related articles, which were not in the database, and some recently published researches, were not included in the study. Thirdly, due to the limitation of the retrieval method, we didn't distinguish basic and clinical researches and we paid more attention to conclusions of the articles. Last but not least, as we tended to analyze the articles with high citations, some cutting-edge articles with low citations might be ignored, resulting in the hysteresis quality of the study to some extent.