In this study, samples were investigated from frozen fish, meat and sausage for contamination by histamine producing bacteria and the results revealed that 72.5% of the examined frozen fish, 27 % of the examined frozen meat and 41.6 % of the examined frozen sausage were positive for isolation of histamine producing bacteria. The most isolated species from the examined fish samples were Morganella morganii followed by Klebsiella pneumoniae and Serratia marscense .While, isolated species from frozen meat were Klebsiella pneumoniae followed by Morganella morganii and Pseudomonas aeroguinosa . Lastly, isolated species from frozen sausage were Escherichia coli followed by Klebsiella pneumoniae and Morganella morganii . Molecular examination for histamine producing bacteria species from the last mentioned samples using convential PCR technique targeting HDC gene from chromosomal DNA revealed that most strong histamine formers like Morganella morganii gave positive PCR results while most weak histamine formers like Citrobacter brakii gave negative PCR results. HPLC measured all levels of histamine produced by the different isolates and Morganella morganii was the most histamine producer isolate which produce (5931 ppm).Otherwise, Elisa technique failed to detect histamine level in examined samples. Sensitivity of random isolates of histamine producing bacteria to the different types of antibiotics showed that most isolates were sensitive to Enrofloxacin, Ceftriaxone while most isolates were resistant to Erythromycin and Ampicillin. Histopathological study on the effect of histamine on the gastrointestinal tract of albino rats resulting from the ingestion of foods containing excessive amount of histamine showed acute and chronic inflammation according to the level of histamine in food.
Key words: Histamine, microorganisms, food