INTRODUCTION

Aquaculture has become a cornerstone of global food production, with freshwater prawn farming representing a rapidly growing sector in Southeast Asia. The giant freshwater prawn (Macrobrachium rosenbergii) is one of the most commercially important aquaculture species because of its rapid growth, high market value, and adaptability to diverse farming systems [1, 2]. In Northeastern Thailand, particularly in Kalasin Province, freshwater prawn farming contributes substantially to rural livelihoods and local food security. However, the intensification of aquaculture production has led to increasing challenges associated with disease outbreaks and environmental health. Opportunistic bacterial pathogens, particularly Aeromonas spp., are frequently associated with motile aeromonad septicemia and other infectious diseases in cultured prawns [3, 4]. Consequently, antibiotics are commonly used for disease prevention and treatment in aquaculture systems, often without strict veterinary oversight, raising growing concerns about antimicrobial resistance (AMR), antibiotic-resistant bacteria (ARB), and antibiotic resistance genes (ARGs) in aquatic environments [5, 6]. Environmental dissemination of clinically important resistance genes, including blaSHV, blaOXA, and blaKPC-2, has increasingly been reported in aquatic bacterial species such as Aeromonas spp., Klebsiella spp., and Enterobacter spp., highlighting the potential public health risks associated with aquaculture-associated AMR [7–10]. In response to these concerns, the World Health Organization has emphasized the importance of integrated AMR surveillance under a One Health framework [11].

Despite growing global concern about AMR in aquaculture, most investigations in Thailand have focused primarily on marine shrimp farming systems or cage-cultured fish, including studies associated with Lam Pao Dam and coastal aquaculture regions. In contrast, earthen pond systems used for culturing _M. _rosenbergii in Northeastern Thailand remain poorly characterized with respect to profiles and the occurrence of clinically relevant ARGs. This knowledge gap is particularly important because small-scale freshwater prawn farming represents a major source of income and food security for rural communities in Kalasin Province and surrounding regions. Furthermore, previous studies have generally investigated bacterial diversity or antimicrobial susceptibility independently, whereas only a limited number have integrated culture-based bacterial isolation, molecular identification using 16S rRNA gene sequencing, antimicrobial susceptibility profiling, and targeted detection of clinically important β-lactamase genes in freshwater prawn aquaculture systems. Information regarding carbapenemase-associated genes, particularly blaKPC-2, in environmental isolates from freshwater prawn ponds remains scarce in Thailand. In addition, the occurrence and distribution of clinically important β-lactamase genes among ARB associated with freshwater prawn farming systems have not been comprehensively characterized. This lack of information limits ecological risk assessment and hinders the development of effective surveillance and antimicrobial stewardship strategies under a One Health framework.

Therefore, this study aimed to isolate and identify ARB from _M. _rosenbergii aquaculture ponds in Kalasin Province, Thailand, and to characterize their antimicrobial susceptibility patterns and associated β-lactamase resistance genes, including blaSHV and blaKPC-2. By integrating culture-based bacterial isolation, molecular identification using 16S rRNA gene sequencing, antimicrobial susceptibility testing, and targeted polymerase chain reaction (PCR)-based detection of resistance genes, this study provides important baseline information regarding multidrug-resistant (MDR) bacteria and clinically relevant ARGs in freshwater aquaculture environments. The findings are expected to improve the understanding of AMR dissemination in small-scale freshwater aquaculture systems and support future surveillance and antimicrobial stewardship strategies in Thailand under a One Health perspective.