Source and identification of histamine-producing bacteria from fresh and temperature-abused albacore.

Histamine-producing bacteria were isolated from fresh and temperature-abused albacore using two different isolation procedures. Typically, the bacterial isolates on Niven's or modified Niven's medium produced negligible or low levels of histamine (<300 ppm) in histamine enumeration broth. The most frequently found species using this approach was Hafnia alvei. By prescreening on selective media (eosin methylene blue [EMB] agar for enteric bacteria; deMan Rogosa Sharpe agar for lactic acid bacteria: KF streptococcus agar for streptococci; pseudomonas isolation [PI] agar for pseudomonads; and staphylococcus medium 110 agar for staphylococci) prior to plating on histidine decarboxylase differential media, detection rate of true histamine formers increased. Prolific histamine producers capable of forming >1,000 ppm histamine in culture broth were isolated when PI and EMB agars were used for prescreening. Among the selective media tested, EMB agar was most effective in selecting high histamine producers, as demonstrated by the highest rate of true positives based on histamine analysis. Histamine-producing isolates were mostly enteric bacteria, including Morganella morganii, H. alvei, Klebsiella spp., Citrobacter freundii, Enterobacter spp., and Serratia spp. M. morganii isolated on PI agar from temperature-abused albacore muscle was found to be the highest histamine former. This species was not isolated from fresh albacore. while other enteric bacteria were frequently detected on the gills. However, only a few species isolated from both fresh and temperature-abused muscles were identified as high histamine formers.