To isolate histamine-forming bacteria, a 0.1 ml aliquot of the sample dilute was spread on histamine-forming bacterium isolation agar (HBI agar) fortified with L-histidine.Following incubation of the differential agar plates for 4 d at 35c, colonies with blue or purple color on plates were picked and further streaked on trypticase soy agar (TSA) to obtain pure cultures.