BIODIVERSITAS ISSN: 1412-033X Volume 22, Number 11, November 2021 E-ISSN: 2085-4722 Pages: 4839-4846 DOI: 10.13057/biodiv/d221117 Antibiotic resistance of Aeromonas spp. isolated from diseased walking catfish (Clarias sp.) DINI SISWANI MULIA 1 , ALIM ISNANSETYO 2,♥ , RARASTOETI PRATIWI 3 , WIDYA ASMARA 4 1 Department of Biology Education, Faculty of Teacher Training and Education, Universitas Muhammadiyah Purwokerto. Jl. KH. Ahmad Dahlan, Purwokerto Utara, Banyumas 53182, Central Java, Indonesia. 2 Department of Fisheries, Faculty of Agriculture, Universitas Gadjah Mada. Jl. Flora, Bulaksumur, Sleman 55281, Yogyakarta, Indonesia. Tel.: +62-274-551218, ♥ email: isnansetyo@ugm.ac.id 3 Faculty of Biology, Universitas Gadjah Mada. Jl. Teknika Selatan, Senolowo, Sleman 55281, Yogyakarta, Indonesia 4 Faculty of Veterinary Medicine, Universitas Gadjah Mada. Jl. Fauna, Caturtunggal, Sleman 55281, Yogyakarta, Indonesia Manuscript received: 29 August 2021. Revision accepted: 17 October 2021. Abstract. Mulia DS, Isnansetyo A, Pratiwi R, Asmara W. 2021. Antibiotic resistance of Aeromonas spp. isolated from diseased walking catfish (Clarias sp.). Biodiversitas 22: 4839-4846. Aeromonas spp. is known to be pathogenic to freshwater fish, including catfish. Antibiotics are often used to overcome bacterial attacks. However, the indiscriminate use of antibiotics, especially at incorrect doses and frequencies, could result in the emergence of resistant bacteria. The presence of resistance genes is also suspected to trigger the resistance potential of Aeromonas sp. against antibiotics. The objective of this study is to characterize the resistance genes of Aeromonas spp. isolated from diseased walking catfish (Clarias sp.). Ten Aeromonas spp. were isolated from infected walking catfish cultivated in Java. The resistance genes assessed included tetA, strA-strB, and qnrA. The antibiotics tested consisted of ampicillin (AMP), erythromycin (ERY), oxytetracycline (OXT), kanamycin (KAN), enrofloxacin (ENRO), and chloramphenicol (CHL). Results showed that some Aeromonas spp. had at least one out of the three genes assessed (i.e., tetA and strA-strB) but none had the qnrA gene. Aeromonas spp. were sensitive to KAN, ENRO, and CHL but resistant to AMP, ERY, and OXT. Thus, KAN, ENRO, and CHL are effective antibiotics for treating fish infected with Aeromonas spp. Keywords: Aeromonas, antibiotics, walking catfish, gene, resistance INTRODUCTION Several obstacles, especially disease, must be addressed for successful freshwater fish cultivation. The diseases cause high mortality rates in fish, which can result in crop failure and massive financial losses. This problem is prevalent even in walking catfish (Clarias sp.) cultivation. Motile Aeromonas septicemia disease or aeromoniasis is caused by Aeromonas spp. These pathogens are opportunistic, gram negative, rod-shaped, facultative anaerobic bacteria, oxidase-positive, motile or non-motile, and non-spore-forming (Erdem et al. 2011; Parker and Shaw 2011; Aravena-Román et al. 2013; Percival and Williams 2014; Martínez-Murcia et al. 2016; Stratev and Odeyemi 2016). Aeromonas spp. can attack nearly all types of fish and aquatic biota. Previous studies reported that Aeromonas spp. attacks catfish (Clarias gariepinus), Nile tilapia (Oreochromis niloticus), Arapaima gigas, eel (Anguilla japonica), rainbow trout (Onchorynchus mykiss), shrimp (Litopenaeus vannamei, Penaeus monodon), Chinese giant salamander (Andrias davidianus), and turtle (Ocadia sinensis, Pseudemys peninsularis) (Wang et al. 2012; Vega-Sanchez et al. 2014; Yano et al. 2015; Dias et al. 2016; Guo et al. 2016; Hassan et al. 2017; Wimalasena et al. 2017; Sellegounder et al. 2018; Eid et al. 2019). In Indonesia, the first Aeromonas spp. outbreak was recorded in West Java in 1980. Aeromonas spp. attack caused the death of 82.2 tons of fish within 1 month. Another attack was recorded in Central Java in 1984, in which approximately 1.6 tons of catfish died (Angka 2001). Since then, Aeromonas spp. infection in fish has become increasingly common. Besides its virulence potential, the ability of Aeromonas spp. to cause disease in fish may be attributed to its resistance to antibiotics; this resistance enables the bacteria to survive, become immune to antibiotics, and continue infecting fish and other aquatic biotas. Aeromonas spp. are well known for their resistance genes and natural defense system. Despite the potential dangers of Aeromonas spp. infection, there is a lack of research concerning this important pathogen in Indonesia . Research abroad has successfully detected various resistance genes in Aeromonas spp., including tetE, tetO, tetA, blaTEM, strA-strB, qnrS2, and qnrA (Nawaz et al. 2012; Deng et al. 2014; Varela et al. 2016; Harnisz and Korzeniewska 2018; De Silva et al. 2020). Knowledge of the resistance genes of this bacterium is essential to determine the most suitable antibiotics for controlling Aeromonas spp. infection. Several antibiotics, including chlortetracycline, oxytetracycline (OXT), tetracycline, erythromycin (ERY), and enrofloxacin (ENRO) (Kepmen-KP 2014), as well as ampicillin (AMP), kanamycin (KAN), and chloramphenicol (CHL), are often used to control virulent bacteria. However, the inappropriate use of antibiotics, especially in terms of time, dose, and target, is common.