Antibiotic resistance of bacteria associated with larval stages of giant freshwater prawn (Macrobrachium rosenbergii)

Abstract

The evolved antibiotic resistance of pathogenic bacteria associated with various life stages of Macrobrachium rosenbergii may lead to disease outbreaks, resulting in reduced yield. The present study determines the antibiotic sensitivity of all larvae (11 larval stages) and post-larvae of M. rosenbergii qualitatively against commonly used antibiotics. All samples were collected from the Freshwater Prawn Breeding Centre, Kahandamodara, Sri Lanka. Individuals of each sample (n=150) were homogenised and inoculated onto nutrient agar plates using the spread plate technique. After overnight incubation at ambient temperature, individual colonies were selected and transferred into nutrient broth cultures. Kirby-Bauer antibiotic sensitivity test (ABST) was then carried out to investigate the antibiotic resistance of bacteria against ten antibiotics; Amikacin-30µg (AK30), Cefixime-5µg (CFM5), Cephalothin-30µg (KF30), Chloramphenico-30µg (C30), Erythromycin-15µg (E15), Kanamycin-30µg (K30), Metronidazole-25µg (MTZ5), Streptomycin-10µg (S10), Sulfamethoxazole-25µg (RL25), and Tetracycline-30µg (TE30). Bacteria from all samples were 100% resistant to MTZ5. Except for three larval stages, the other eight larval and post-larval (75%) stages were sensitive to TE30, making it the most efficient antibiotic. Other tested antibiotics exhibited varying degrees of efficacy, with TE30 leading the group, followed by C30, AK30, and S10. Of the bacteria from all larvae and post-larvae samples, 83.3%, 75%, 66.7%, 50%, and 33.3% were resistant to CFM5, KF30, RL25, E15, and K30 respectively, whilst bacteria from the rest of the samples showed intermediate resistance. The present study concludes that administering MTZ5, CFM5, KF30, RL25, E15, and K30 as treatments for diseases is ineffective, as none of the bacteria in any larval stage or post-larvae were sensitive. Four of the ten tested antibiotics, (TE30, C30, AK30, and S10) were efficient against the bacteria associated with different larval stages and post-larvae.