Optimizing culture medium to facilitate rapid Renibacterium salmoninarum growth

Abstract

This study presents significant improvements in the culturing of Renibacterium salmoninarum, the causative agent of bacterial kidney disease (BKD) in salmonids. Our goal was to improve R. salmoninarum cultivation and its detection in salmon farming by adjusting to 1.5%wv−1 NaCl into kidney disease medium-2 (KDM2), which significantly expedited growth without further effects from varying NaCl concentrations. The reductions in incubation periods of cultivation, this approach enhances early and accurate bacterial and disease surveillance, enabling prompt intervention. The modified medium significantly accelerated R. salmoninarum growth, achieving an optical density at 600 nm of 0.5 within 5–6 days post-incubation, marking a notable improvement over traditional KDM2. Exploring a range of NaCl concentrations in solid and liquid media revealed distinct growth patterns of R. salmoninarum across various strains. Among these, 1.5%wv−1 NaCl proved highly effective in promoting rapid pathogen proliferation while preserving essential components roles in the medium, with an average of 75% of reduction in incubation times in plate agar culture media. Strains isolated from salmon organs in the Los Lagos and Magallanes region exhibited high pathogenicity, leading to 80–100% mortality within 30 days, underscoring the wide-ranging efficacy of NaCl in enhancing growth, irrespective of geographic origins. Moreover, the modified media, enriched with NaCl, demonstrated no compromise in the pathogenicity of R. salmoninarum strains. These results highlight the potential of NaCl supplementation, supporting its addition in the media of R. salmoninarum. This inclusion could expedite biomass growth within shortened timeframes, stimulate microbial aggregates, and enhance bacterial multiplication within the medium. These findings affirm the utility of KDM2-NaCl in enhancing R. salmoninarum effective cultivation and detection, offering cost-effective strategies for managing infections and supporting targeted interventions in the salmon industry.