Malaysian Journal of Microbiology, Vol 17(3) 2021, pp. 333-337 DOI: http://dx.doi.org/10.21161/mjm.201034 Malaysian Journal of Microbiology Published by Malaysian Society for Microbiology (In since 2011) 333 ISSN (print): 1823-8262, ISSN (online): 2231-7538 *Corresponding author Short Communication The effect of tryptamine on Serratia marcescens, Pseudomonas aeruginosa and Escherichia coli Arif Luqman 1,2 *, Ruben Amian Ruiz 2 , Friedrich Götz 2 , Maya Shovitri 1 , Enny Zulaika 1 , Dewi Hidayati 1 and Triono Bagus Saputro 1 1 Biology Department, Institut Teknologi Sepuluh Nopember, 60111 Surabaya, Indonesia. 2 Microbial Genetics, University of Tuebingen, 72076 Tuebingen, Germany. Email: arif.luqman@its.ac.id Received 29 October 2020; Received in revised form 28 December 2020; Accepted 17 February 2021 ABSTRACT Aims: Tryptamine is an amine compound derived from tryptophan by decarboxylation process. This compound can be found in fermented food and beverages, and in human gut and skin as well. This study aims to investigate the effect of tryptamine, on Gram-negative bacteria, namely Escherichia coli, Serratia marcescens and Pseudomonas aeruginosa. Methodology and results: In this study, we used E. coli, S. marcescens and P. aeruginosa due to their relatively observable quorum sensing-regulated phenotype, such as motility, prodigiosin and pyocyanin sequentially. Our results showed that tryptamine started to inhibit the growth and prodigiosin production of S. marcescens at concentration 250 μg/mL, while it inhibits the growth and pyocyanin production of P. aeruginosa at concentration 250 μg/mL and 500 μg/mL, respectively. Tryptamine inhibits both the growth and motility of E. coli at concentration 100 μg/mL. Conclusion, significance and impact of study: These results suggest that tryptamine is able to inhibit the growth of E. coli, S. marcescens and P. aeruginosa at relatively high concentration, thus decreases the quorum sensing-regulated phenotypes. It implies that the growth and quorum sensing of Gram-negative bacteria most likely will not be affected by the low concentration of tryptamine that present in the gut. Keywords: Tryptamine, Gram-negative bacteria, growth, quorum sensing-regulated phenotype INTRODUCTION Tryptamine is an amine compound produced from a decarboxylation process of an aromatic amino acid, tryptophan. Tryptamine can be produced by many organisms such as mammals, human, plants, bacteria and fungi (Halász et al., 1994; Mercolini, 2019). Tryptamine has a broad potential due to its capability to interact with various receptors found in mammals, such as α1- , α2- and β-adrenergic receptor, serotonin 1A and 2A receptor (5HT1A and 5HT2A), and trace amines-associated receptor 1 (TAAR1) (Greene, 2013; Berry et al., 2017; Luqman et al., 2018, 2019, 2020a, 2020b) . In human, tryptamine can be found in brain, gut and the bacteria which inhabited in the gut as well (Berry, 2004; Luqman et al., 2019). It was reported that this particular compound able to induce the intestine motility (Williams et al., 2014) and increase bacterial adherence and internalization into intestine (Luqman et al., 2018). However, the presence of high concentration tryptamine might lead to gastrointestinal disorder due to the over expression of TAAR1 in the gut (Gwilt et al., 2020). Human intestine is an organ where microorganisms inhabit with the most number compared to the other organs. As tryptamine can be found in intestine, it is possible that tryptamine might also affect the microorganisms there. Although it is reported that tryptamine showed no significant effect on bacterial adrenergic receptor QseC, a Gram-negative quorum sensing which can detect adrenaline (Luqman et al., 2020a), we wonder whether other quorum sensing systems in Gram-negative bacteria can be affected. Here, we showed that tryptamine interferes with the growth of Gram-negative bacteria, namely Serratia marcescens, Pseudomonas aeruginosa and Escherichia coli at relatively high concentration (≥ 100 μg/mL).