Identification of bacterial pathogens in cultured fish using Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS)
Abstract Background Majority of infectious diseases of cultured fish is caused by bacteria. Rapid identification of bacterial pathogen is necessary for immediate management. The present study developed Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) for a fast identification of fish bacterial pathogens. Streptococcus agalactiae, S. iniae, Aeromonas hydrophila, A. veronii, and Edwardsiella tarda obtained from diseased fish were used as representative bacterial pathogens in this study. Bacterial peptides were extracted to create the Main Spectra Profile (MSP), and the MSP of each bacterial species was added into the MALDI Biotyper database. Ten additional field isolates of each bacterial species were tested to validate the technique.Results The MSP of all field isolates were clearly distinguishable, and the MSPs of the same species were clustered together. However, the species identification when matching with the public MALDI Biotyper library (Bruker MALDI Biotyper) showed unreliable result at the species level. The accurate identification only obtained when the custom-made database was used, giving a 100% matching result.Conclusion This study demonstrates a newly developed technique for the effective identification of fish bacterial pathogens. Further applications require a broad, well-established database to accommodate the prudent identification of many fish bacterial pathogens by MALDI-TOF MS.