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

Histamine-producing bacteria were isolated from fresh and temperature-abuse d albacore using two different isolation procedures. Typically, the bacteri al isolates on Niven's or modified Niven's medium produced negligible or lo w levels of histamine (< 300 ppm) in histamine enumeration broth. The most frequently found species using this approach was Hafnia alvei. By prescreen ing on selective media (eosin methylene blue [EMB] agar for enteric bacteri a; deMan Rogosa Sharpe agar For lactic acid bacteria; KF streptococcus agar for streptococci; pseudomonas isolation [PI] agar for pseudomonads; and st aphylococcus medium 110 agar for staphylococci) prior to plating on histidi ne decarboxylase differential media, detection rate of true histamine forme rs increased. Prolific histamine producers capable of forming >1,000 ppm hi stamine 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 isolate s were mostly enteric bacteria, including Morganella morganii H. alvei. Kle bsiella spp., Citrobacter freundii. Enterobacter spp., and Serratio spp. M. morganii isolated on PI agar from temperature-abused albacore muscle was f ound to be the highest histamine former. This species was not isolated from fresh albacore, while other enteric bacteria were frequently detected on t he gills. However, only a few species isolated from both fresh and temperat ure-abused muscles were identified as high histamine formers.