Thesis (M.Sc.) - Cairo University - Faculty of Veterinary Medicine - Department of Zoonoses

Histamine fish poisoning becomes highly concern not only in public health but also economic aspect. Therefore, this study was attempted to detect histamine producing bacteria (HPB) in fish and fish handlers, as well as in canned tuna. Screening of 207 fish samples using Modified Niven{u2019}s medium (MNM), evidenced 108 isolated colonies were HPB, and significantly higher proportion wasin fresh sardine (95.7%), followed by frozen mackerel (53 %), frozen sardine (36.4 %) and canned tuna (14 %). Among those, only 88 isolates showed HPB based on plating on Violet Red Bile Glucose Agar (VRBG) agar, were 83 isolates identified as Enterobacteriacae, while only 5 isolates were identified as non-Enterobacteriacae. The most common isolates were K. pneumonia, E. aerogenes, Enterobacter cloacae and C. freundii following the biochemical identification using API20E. Out of 83 HP Enterobacteriacea strains from fish muscles 22 isolates (26.5%) were positive for hdc gene using conventional PCR, likewise, Citrobacter braakii evidenced hdc gene. While out of 5 non- Enterobacteriacea strains only one isolate was positive for hdc gene. The measuring of histamine level in some selected positive fish muscles using High-Performance Liquid Chromatography (HPLC) showed that the level of histamine in sardine muscles is significantly higher than that in mackerel muscles. On the other side, out of 20 hand swabs from fish handlers, 19 isolates of HPB were identified as Enterobacteriacea, and classified as K. pneumonia,C. freundii, E. cloacae and K. oxytoca, surprisingly, only one isolate was positive for hdc gene. A strong correlation was noticed between the occurrence of certain species of HP-Enterobacteriaceae in both fish and fish handlers at same localities. Phylogenetic analysis of hdc gene of different bacterial species,highlight the probability that the gram negative hdc gene might get transferred within the same and between the different genus of bacteria, this is alarming as they can be potential hazard to humans

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