The E. aerogenes isolate that produced the
highest histamine content of 500 ppm in the culture broth was
used in this study to inoculate into the tuna dumpling stuffing.
One loop of the bacterial culture was inoculated into TSB and incubated
at 37 C for 18 h. One ml of the culture was serially diluted in
0.1% peptone water and 0.1 ml aliquots of the dilutes were spread
plated on aerobic plate count (APC) agar (Difco) containing 0.5%
NaCl. Bacterial colonies were counted after the plates were incubated
at 35 C for 24 h. Based on the bacterial concentration so
determined, the bacterial culture stored at refrigerator for 24 h
was then serially diluted with 0.1% peptone water to obtain the
suspension with the desired bacterial concentration.