Antimicrobial susceptibility of common foodborne bacteria isolated from freshwater fish

Abstract

Freshwater fish are widely consumed as an important source of protein for humans, especially in Malaysia. However, improper handling and distribution may expose consumers to foodborne pathogens or species that pose public health risks. This study focuses on identifying and profiling the antibiotic resistance of selected foodborne bacteria, Vibrio spp. and Escherichia coli. The bacteria were isolated from freshwater fish purchased at supermarkets and wet markets in Kuala Pilah, Negeri Sembilan. Primary isolation was performed using selective and differential media, including thiosulfate citrate bile salts sucrose (TCBS) agar and MacConkey agar, followed by a series of biochemical tests for species confirmation, and enumeration was conducted using the total viable count (TVC) method, expressed as colony-forming units per gram (CFU/g). Antimicrobial susceptibility was assessed by the Kirby–Bauer disc diffusion method with selected antibiotics, and resistance profiles were further evaluated by calculating the multiple antibiotic resistance (MAR) index. The results revealed differences in bacterial prevalence and resistance patterns between sample sources and market types, with E. coli isolates generally showing higher resistance than Vibrio spp. This indicates that E. coli species poses a higher risk to humans. Both the aquatic and market environments offer conditions that support bacterial survival, colonization, and transmission, especially where hygiene control is lacking. Cross-contamination may also occur in the sales area. MAR index values above 0.2 suggest exposure to antibiotics and possible high-risk contamination sources. In conclusion, this study offers important insights into the microbiological safety of freshwater fish and highlights the necessity of monitoring bacterial contamination and antibiotic resistance in food supply chains to protect public health.