Efflux Pump and Biofilm Forming Capabilities of Antibiotic Resistant, Serratia marcescens from Freshwater Fish Farms in Andhra Pradesh, India

Abstract

Serratia marcescens gains much attention due to its ubiquitous distribution in soil, water and plant, on the surface of animals, as well as in the intestinal tract of animals, posing problems for both public and animal health. There is a scarcity of information on its distribution in aquaculture settings. Hence, the present study was taken to identify S. marcescens, its antibiotic-resistant pattern, and underlying mechanisms in freshwater fish farms in Andhra Pradesh, India. Sampling was done in 54 freshwater fish farms from August 2021 to April 2022, and 31 isolates were confirmed as S. marcescens by standard morphological and biochemical methods. The majority of strains were isolated from water (n=13) followed by gill swabs (n=9), skin swabs (n=5) and sediment (n=4). Antibiotic susceptibility testing revealed that 71 %, 48 %, 48 % and 9.7 % of isolates were resistant to furazolidone, oxytetracycline, doxycycline hydrochloride and co-trimoxazole, respectively, whereas 100 % of isolates were sensitive to ciprofloxacin and enrofloxacin. The minimum inhibitory concentrations for furazolidone, oxytetracycline, and doxycycline were found to be 256 μg/ml, 192 μg/ml and 64 μg/ml, respectively. Only three isolates were found to be multi-drug resistant, having resistance to furazolidone, oxytetracycline, and co-trimoxazole. All the isolates had the ability to form biofilms, and 48.4 %, 32.2 % and 19.4 % of the strains were strong, moderate, and weak biofilm formers, respectively. Spearman rank correlation revealed a strong correlation between biofilm formation and antibiotic resistance. Twenty-five resistant isolates possessed efflux pump activity, as evident in 0.5 to 2.5 mg/L concentrations of ethidium bromide containing agar plates. Biofilm formation and efflux pump activities of S. marcescens contribute to enhanced antimicrobial resistance to different antibiotics in the environment and could cause serious public health implications. To the best of our knowledge, this is the first report of S. marcescens isolated from freshwater finfish farms in India.