Journal of Applied Microbiology, 2023, 134, 1–12 https://doi.org/10.1093/jambio/lxad031 Advance access publication date: 21 February 2023 Review Article Occurrence of potential virulence determinants in Aeromonas spp. isolated from different aquatic environments Sana Majeed, Liyana Arachchilage Dinithi Sandunika De Silva, Prasanga Madhushani Kumarage, Gang-Joon Heo * Veterinary Medical Center and College of Veterinary Medicine, Chungbuk National University, Cheongju 28644, South Korea ∗ Corresponding aurhor. Laboratory of Aquatic Animal Medicine, Veterinary Medical Center and College of Veterinary Medicine, Chungbuk National University, Chungdae-to 1, Seowon-gu, Cheongju, Chungbuk 28644, South Korea. E-mail: gjheo@cbu.ac.kr Abstract Aeromonas species are bacterial pathogens that cause signifcant economic losses in the aquaculture industry worldwide. They are widely distributed in aquatic environments and cause several diseases in both humans and aquatic animals. The presence of various virulent Aeromonas spp. in aquatic environments predisposes infections in aquatic animals and humans. Concern about the transfer of pathogens from fsh to humans also increased with the substantial increase in seafood consumption. Aeromonas spp. are also primary human pathogens that cause local and systemic infections, both in immunologically compromised and immunologically competent hosts. The most common Aeromonas spp. causing infections in aquatic animals and humans are A. hydrophila, A. salmonicida, A. caviae, and A. veronii biotype sobria. The ability of Aeromonas spp. to produce a variety of virulence factors enhances their pathogenic ability. Literature has supplied evidence for the presence of various virulence factors, including proteases, enterotoxins, hemolysin, and toxin genes of Aeromonas spp. in aquatic environments. The high prevalence of Aeromonas spp. in the aquatic environment is also a threat to public health. Because the Aeromonas spp. infections in humans are generally the result of ingestion or exposure to contaminated food and water. This review summarizes the recently published information on various virulence factors and virulence genes of Aeromonas spp. isolated from various aquatic environments, including seawater, freshwater, wastewater, and drinking water. It is also intended to highlight the risks associated with Aeromonas species’ virulence properties for both aquaculture and public health. Keywords: Aeromonas spp., aquatic environments, virulence genes, aquaculture, public health Introduction The ubiquitous nature of the genus Aeromonas allows them to distribute in all kinds of environments. They can be found in food, animals, and humans (Kim et al. 2015, Liu et al. 2022). As autochthonous inhabitants of the aquatic environments, Aeromonas spp. are present in marine water, brackish water, freshwater lakes, ponds, rivers, municipal drinking water, and bottled mineral water (Khor et al. 2015, Harnisz and Korze- niewska 2018). They have also been found in wastewater ef- fuents and raw and treated sewage (Skwor et al. 2020). The genus Aeromonas belongs to family Aeromonadaceae, order Aeromonadales, and class Gammaproteobacterias. Af- ter the continuous change in the taxonomy of the genus Aeromonas since 1992, 36 Aeromonas spp. have been re- ported so far. They are Gram-negative bacilli-shaped bacteria, positive for catalase and oxidase tests. Also, they are capable of glucose fermentation and nitrate degradation (Fernández- Bravo and Figueras 2020). The genus Aeromonas can be di- vided into two major groups, including psychrophiles and mesophiles. Mesophilic Aeromonas spp. are motile organisms that can cause human diarrheal disease, and wound infections that are mostly followed by bacteremia. Immunocompro- mised patients are more susceptible to mesophilic Aeromonas spp. infections. Mesophilic Aeromonas spp. show optimal growth at 35 ◦ C–37 ◦ C (Teunis and Figueras 2016). In con- trast, psychrophilic Aeromonas spp. are common inhabitants that cause diseases in fsh and shellfsh and grow at a temper- ature range of 22 ◦ C–25 ◦ C (De Silva et al. 2021). The detec- tion of virulence factors is a key component of determining the pathogenic potential of bacteria. These virulence factors allow them to attach, colonize, invade, multiply, and damage the host’s cells, with the potential to kill the host (Sreedha- ran et al. 2013). The virulence of Aeromonas spp. is multi- functional and multifactorial because they cause disease by producing different virulence factors, such as hemolysins, li- pases, proteases, bioflm formation, and mediating the expres- sion of virulence factors through quorum sensing (Rasmussen- Ivey et al. 2016). Several putative virulence factors have been described in several species of the genus Aeromonas. Virulence factors of Aeromonas spp. are involved in a complex network of pathogenic mechanisms and contribute to Aeromonas spp. effciency in the development of a wide variety of infec- tions in both aquatic animals and humans (Sen and Rodgers 2004). Aeromonas spp. can tolerate a wide range of environ- mental conditions, such as nutrient-limited conditions, wide temperature ranges, and different salinity levels. Differ- ences in physio-chemical parameters of water may alter the Aeromonas spp. population and seasonality of their disease occurrence in both aquatic animals and humans (Sadique et al. 2021). Aeromonas spp. caused huge economic losses since 1989 in the Chinese aquaculture system, which is a major Received: June 14, 2022. Revised: September 8, 2022. Accepted: February 20, 2023 C  The Author(s) 2023. Published by Oxford University Press on behalf of Applied Microbiology International. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com Downloaded from https://academic.oup.com/jambio/article/134/3/lxad031/7049966 by guest on 13 March 2023