Characterisation of histamine-producing bacteria from farmed blackspot seabream (Pagellus bogaraveo) and turbot (Psetta maxima)

Turbot (Psetta maxima) and blackspot seabream (Pagellus bogaraveo) represent two of the most important emerging farmed fish species in European countries. However, no information of the presence and development of histamine-producing bacteria on them has been reported so far. Accordingly, the aim of this study was to isolate and identify the main histamine-producing bacteria in farmed turbot and blackspot seabream. For this study, 24 isolates (12 from turbot and 12 from blackspot seabream) were preliminarily selected on Niven medium. Two of these isolates were confirmed as prolific histamine producers by HPLC. Thus, Pseudomonas fragi (isolated from turbot) and Pseudomonas syringae (isolated from blackspot seabream) were able to produce 272 ± 69 ppm and 173 ± 45 ppm of histamine in vitro, respectively, after incubation at 30 °C/24 h. While turbot fillets proved to be quite resistant to histamine formation at temperatures below 10 °C, blackspot seabream fillets inoculated with P. syringae and the prolific histamine former Morganella morganii accumulated 696 ± 84 and 760 ± 59 ppm histamine, respectively, under such conditions. Genetic identification based on 16S rRNA sequencing was performed in parallel with the investigation of characteristic mass spectral profiles of the isolates by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF MS). The MALDI-TOF MS analyses provided species-specific fingerprints, which allow rapid identification and classification of the isolates. Six genus-specific mass peaks in the range of 2218–4434 m/z were shared by both strains. Bacterial identification was achieved by the identification of six species-specific mass peaks in the ranges of 2534–7183 m/z and 2536–9113 m/z for P. fragi and P. syringae, respectively.

► Pseudomonas fragi, isolated from turbot, produced 272 ppm histamine in vitro.
► Pseudomonas syringae, isolated from seabream, produced 173 ppm histamine in vitro.
► Refrigerated seabream inoculated with P. syringae accumulated 696 ppm histamine.
► MALDI-TOF provided species-specific fingerprints of both histamine-forming strains.