A Global Bibliometric and Visualized Analysis in The State of Pseudomonas Aeruginosa E ux Pump Research

Ruiqin Zhang Second Hospital of Shanxi Medical University Siyang Wang Second Hospital of Shanxi Medical University Jian Ren Second Hospital of Shanxi Medical University Jinxin feng Shanxi Medical University Zhen Li Shanxi Medical University Hongxia Wang Second Hospital of Shanxi Medical University Tingting Zhi Second Hospital of Shanxi Medical University Yuanyuan Zhu Second Hospital of Shanxi Medical University Yanhui wang Shanxi Medical University Zhiqing Yao Shanxi Medical University jinju duan (  1403997832@qq.com ) Second Hospital of Shanxi Medical University


Introduction
Pseudomonas aeruginosa is an opportunistic pathogen responsible for high rates of nosocomial infections and mortality. P. aeruginosa strains commonly exhibit high rates of antibiotic resistance that are primarily attributable to the activity of the bacterial e ux pump system. Indeed, P. aeruginosa e ux pump research has become an area of active research interest in recent years [1][2][3] . E ux pump systems are commonly expressed by Gram-negative bacteria, and enable these microbes to expel drugs 4 . High levels of e ux pump expression can lead to robust drug resistance. E ux pump systems are separated into ve families based upon sequence homology and structural characteristics including the resistance nodulation cell division (RND), major facilitator super (MFS), multidrug and toxic compound extrusion (MATE), small multidrug resistance (SMR), and ATB-binding cassette (ABC) families. RND family e ux pump overexpression is the most common cause of multi-drug resistance in clinical P. aeruginosa isolates 1,5 . Studies of P. aeruginosa e ux mechanisms offer valuable insights into the antibiotic resistance properties of these bacteria, highlighting novel approaches to developing new drugs to treat these dangerous bacterial infections.
Herein, we studied trends in the eld of P. aeruginosa e ux pump research, using online databases to conduct bibliometric analyses in an effort to quantitatively evaluate the relative contributions of different researchers, countries, and institutions 6 . Such analyses have previously been utilized to guide the design of clinical policies and guidelines 7 , and provide the added bene t of making research areas more transparent and approachable 8,9 . To the best of our knowledge, no such bibliometric analyses of the P. aeruginosa e ux pump research eld have been performed to date. As such, this study was designed to speci cally evaluate trends in this eld of research.

Data sources
These bibliometric analyses were conducted using the Science Citation Index-Expanded (SCI-E) database from the Web of Science (WoS) 10 .

Search strategy
Relevant studies published in the Web of Science as of December 31, 2019 were identi ed using the following search strategy: theme = Pseudomonas aeruginosa e ux pump * AND publishing year = (1994-2019) AND Language = (English) AND Document type = (ARTICLE OR REVIEW). Data regarding particular countries and regions was established through WoS indexing. In total, 2583 records were retrieved for analysis.

Data collection
For each publication, records pertaining to the year of publication, title, authors, nationality, a liation, keywords, abstract, and journal were downloaded from the Web of Science in the form of a .txt document which was imported into Microsoft Excel 2016. These data were independently extracted by the authors of this study, and any inconsistencies were resolved through discussion or consultation of experts. GraphPad Prism 5 was used to analyze all data.

Bibliometric analysis
Basic characteristics of included studies were described using the functions of Web of Science. H-index values were used to measure the impact of these studies, and were calculated based upon h having published h studies that have been cited at least h times 11 , providing a combined summary of publications and citations per publication. This index is thus a better indicator of scienti c achievement relative to total numbers of papers or citations.

2.5.Visualized analysis
VOSviewer is a free bibliometric analytical program designed by Nees Jan van Eck and Ludo Waltman of the University of Leiden (The Netherlands) that allows for bibliometric map construction based upon cocitation principles in a range of research elds. These analyses facilitate overviews of research progress in different countries, institutions, and research teams while highlighting key journals and publications in a given research context. These analyses also allowed us to identify key trends and future directions in this eld, displaying these results in a readily-interpretable visual format 12 .

P. aeruginosa e ux pump systems
Gram-negative bacteria possess e ux pump systems composed of an inner membrane transporter, an outer membrane channel, and membrane fusion proteins. E ux activity does not require a given substrate to accumulate within the periplasmic space, indicating that these compounds are e ciently expelled through the inner and outer membranes ( Fig. 1) 13 . RND e ux pumps are able to effectively remove antimicrobial compounds from the cytoplasm through this mechanism (Poole 2004  The overall frequency of research pertaining to P. aeruginosa e ux pumps was 112,062, the total number of citations removed from the citation is 87,308 the index of the cited article is 52,656, and the citation index for the self-introduction is 50,484, the average citation is The number of times is 46.81 and the hindex is 159. This underscores the rapid developments in the eld of P. aeruginosa e ux pump research, and suggests that this is an active and collaborative research eld. Publications from the USA exhibited the greatest number of total citations (39,290), followed by Japan (9,569), the UK (9,342), Canada (9,163), France (8,951), Spain (6,504), Germany (4,970), Switzerland (3,462), Denmark (3,383), and Belgium (2,381) (Fig. 3a).

Bibliographic coupling analysis
We next performed bibliographic coupling analyses to evaluate the similarity relationships between different articles. Bibliographic coupling occurs when a given pair of articles cite a common third article, and serves as an indicator that these studies are focused on related topics.

Journal
A total of 134 journals were identi ed in this study and were analyzed using VOSviewer (

Institutions
We assessed studies from 173 different research institutions in the present analysis, focusing on institutions with more than ve publications (Fig. 4b)

Countries
We analyzed articles from 74 different countries in this analysis using VOSviewer, focusing speci cally on countries with more than ve publications (Fig. 4c). The countries with the greatest total link strength values in this analysis were, in order, the USA, France, Japan, Canada, and the UK (with total link strength values of 694,743, 306,153, 299,809, 272,971, and 228,589 times, respectively.

Authors
A co-authorship analysis was used to evaluate the linkage strength based upon numbers of co-authored papers. In total, we identi ed 206 authors with over 5 documents (Fig. 5a). The authors with the greatest total linkage strength values were, as follows, Lee VJ, Lomovskaya O, Nakae T, Nishino Kunihiko, and Nakayama K (with total linkage strength values of 77, 64, 64, 64, and 50, respectively).

Institutions
We identi ed institutions with over 5 publications (Fig. 5b)

Countries
We identi ed 51 total countries with over 5 publications in this study (Fig. 5c). The countries with the greatest total link strength were the USA, France, the UK, Germany, and Japan (link strength scores of 200, 97, 81, 70, and 64, respectively).
3.6.Co-citation analysis 3.6.1. Authors A co-citation analysis was conducted based upon the number of times articles were cited together. We identi ed 867 references with over 20 citations (Fig. 6a). The authors with the greatest total linkage strength values in this analysis were, in order, Poole

Journal
Next, a co-citation analysis of 475 identi ed journals with over 20 citations was conducted (Fig. 6b). The journals with the highest total link strength values were, in order, Antimicrob Agents Chemother, J Bacteriol, J Antimicrob, Mol Microbiol, and P Nat Acad Sci USA (with total link strength scores of 1,489,446, 873,877, 593,826, 379,217, and 329,069 times, respectively.

Co-occurrence analysis
A co-occurrence analysis was additionally performed with the goal of identifying research directions within this eld based upon speci c keywords that were used at high frequencies in published studies 29 .
We speci cally focused on keywords that were used ve or more times in titles and abstracts, leading to the identi cation of 651 keywords that we were able to classify into three primary clusters: "E ux pump resistance mechanism research", "Multidrug e ux transporter mechanism research", and "E ux pump inhibitor research" (Fig. 7a). This suggests that these are primary areas of research interest in the P. aeruginosa e ux pump research eld.
We additionally separated these keywords by color based on the frequencies with which they appeared in included publications in a time-dependent fashion, with blue and red keywords corresponding to terms that appeared less recently and more recently, respectively (Fig. 7b). This approach suggested that most research before 2019 was primarily focused on "resistance molecular mechanism research" and "transfer mechanism research", whereas "inhibitor research" represents a growing area of future research interest.

Trends in Pseudomonas aeruginosa e ux pump research
Bibliometrics and visual analyses provide a high-level overview of a given research eld, offering key insights regarding the top researchers, institutions, and countries active in a given area of research. By analyzing these trends and assessing core research topics in a given eld, it is possible to gauge and guide future research directions 30,31 . The P. aeruginosa e ux pump system enables these clinically relevant pathogens to resist antibiotic treatment 32 , and it is thus a topic of signi cant research interest. We therefore surveyed the eld of P. aeruginosa e ux pump research with respect to contributing countries, institutions, and research topics, revealing clear increases in the volume of research in this eld in recent years. Overall, we found that 74 countries had published articles in this research eld, including 759 articles (29.38%) from the USA, which was also home to 6 of the top 10 most productive journals in this research eld. The prominence of the USA in this eld may be associated with social and economic trends, or with the overall strength of research in this nation.

Global publication quality and status
The H-index was rst proposed by J. E. Jirsch in 2005 as a superior metric for individual scienti c research performance 33 , yielding an effective balance between quality and quantity. Researchers that focus speci cally on quantity are less likely to explore important research topics in detail, making it vital that quantity not be the sole focus of research output. Total numbers of citations and H-index values for a given country thus correspond to the quality and impact of its publications. We found that the USA had made the greatest contributions to the eld of P. aeruginosa e ux plump research, followed by Japan, France, Canada, and the UK with respect to both H-index value and numbers of publications. Denmark had the highest average number of citations, whereas China exhibited the seventh-highest total number of publications but had H-index values and total numbers of citations which did not rank in the top 10 of analyzed nations. This discrepancy between the number of citations and the number of publications from China may be attributable to the fact that the Chinese academic system primarily focuses on publication quantity rather than quality 34 . This has led the Chinese government to call for the reorientation of academic evaluation processes, and as the quality of these publications improves, Chinese publication trends may become more consistent with those of global publications in this eld. Fig. 4a  We additionally performed a bibliographic coupling, co-authorship, and co-citation analyses to better understand the collaborative nature of research in the P. aeruginosa e ux pump eld. These analyses revealed that Antimicrobial Agents and Chemotherapy is the most frequently cited journal in this eld, that the USA is the leading nation in this eld with respect to research output, and that articles published by Poole K are the most commonly cited with a total link strength of 66,431 times. In 1995, this author positive in Antimicrobial Agents and Chemotherapy that "some proteins contribute to the intrinsic resistance of P. Aeruginosa through the multi-drug active e ux process." 35 . Many other prominent researchers likely to shape this research eld are also listed in this study, and their research output should be closely monitored to clearly identify the latest developments in this eld.

Trends in Pseudomonas aeruginosa e ux pump research
Co-occurrence analyses can be used to de ne popular areas of research in a given eld and to predict future research trends associated with a given discipline. As such, we performed a co-occurrence analysis of keywords appearing more than 5 times in the titles and abstracts of articles included in this study, enabling us to classify these 651 keywords into three primary clusters: "E ux pump resistance mechanism research", "E ux pump transfer mechanism research", and "E ux pump inhibitor research". This suggests that these are the three main P. aeruginosa e ux pump research topics at present. When we assessed time-dependent trends in the frequencies with which these keywords were used, we found that most studies before 2019 had focused upon "resistance mechanism research", and "transfer mechanism research", whereas "inhibitor research" is likely to be a primary focus of future research.

Strengths and limitations
This study utilizes a bibliometric and visualized analysis approach to analyze the current status and trend of development of Pseudomonas aeruginosa e ux pump research.This gives a Large amounts of information that reveals important trends through many different dimensions.Nevertheless, the analyses are hardly without certain limitations.First, it surveyed just the publications in the WoS database. Although WoS is the most frequently used and trusted search engine, a few outlier publications might not have been included.Second, only English language studies from the WoS database were included in the analysis. leading to language bias. Third,the standardization of terms were completed based on ndings on the VOSviewer©,and may not be accurate in certain cases, which causes another sort of bias.For example,some authors might have different spelling of names, This might generate inaccurate research output for these authors.

Conclusion
Rates of P. aeruginosa multidrug resistance are steadily rising, posing a signi cant threat to human health. Active e ux pump systems mediate P. aeruginosa resistance to antibiotics, thereby improving the pathogenicity and stress resistance of these bacteria. Our results indicate that the USA remains a global leader in P. aeruginosa e ux pump research, with most studies of this topic having been published in the Antimicrobial Agents and Chemotherapy journal. Poole K is the most cited researcher in this eld, and future studies of new antibiotics that are not e ux pump substrates or of the use of EPIs to inhibit e ux pump activity hold great promise.     that the linked articles were cited in a given paper, with shorter lines corresponding to closer links between papers. Points of a given color share a research direction. (b) An overview of co-cited journals in this research eld, with 475 points corresponding to 475 identi ed journals. Point sizes correspond to citation frequencies, while lines between points indicate that co-citation in a given journal. Shorter lines correspond to closer links between journals, while points of a given color share a research direction.

Figure 7
Co-occurrence analyses of global trends in the P. aeruginosa e ux pump research eld. (a) An overview of keywords in this research area. Point sizes correspond to appearance frequencies, with keywords being separated into three primary clusters: blue (e ux pump resistance mechanisms), green (e ux pump transfer mechanisms), and red (e ux pump inhibitors). (b) Keyword distributions over time, with the most recent keywords being shown in red, followed by those in yellow and those in blue. (c) Keyword distributions based upon mean appearance frequency. Red keywords appeared most frequently, followed by those in yellow, green, and cyan.