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Abstract
Summary
A total of 520 samples collected from food processing units of Assiut university restaurants including hospital’s restaurants (103), central restaurants (200), girl’s restaurants (100), and student’s restaurants (117). These samples were examined for the presence of Listeria species. The percentage of Listeria species. Were detected out of 103 (1.98%), 200 (0.5%), 100 (1%) and 117 (0%) respectively.
Listeria monocytogenes was isolated (10%) from 10 samples from the central restaurants in the refrigerators. Listeria innocua was isolated (16%) from 12 samples obtained from hospital’s restaurant, (10 samples from the refrigerators for thawing, 2 from tables for mincing meat related to mincer). L. Seeligeri was isolated (10%) from 10 samples from the girl’s restaurants in the refrigerators .On the other hand , Listeria failed to be detected in the examined food processing units in the students restaurants.
Investigation of the attachment of L. monocytogenes isolates to the glass surfaces and to find decontamination procedures to remove these bacteria in biofilms was the main aim of this study. Biofilm was prepared by growing L. monocytogenes isolates from food plant environments on glass surfaces. Seven decontamination treatments at different pH, temperatures and time of exposure were tested against
L. monocytogenes biofilms. They were citric acid pH 2, acetic acid pH 3, phosphoric acid pH 2, Combination between acetic acid and citric acid, citric acid and phosphoric acid, acetic acid and phosphoric acid and the combination of all antimicrobial treatment.
It was found that the most efficient antimicrobial solution is acetic acid at pH 3 when used alone where the treatment efficacy was less than one log CFU/cm2 and the treatment more than five log CFU/cm2 at temperature 70 °C after 60 minutes.
As well as the synergistic effect of the combination of citric acid with phosphoric acid and acetic acid was observed. They had the same results as regard the efficacy and treatment.
from this study, it was also observed that the effect of the pH of antimicrobial treatment is an important factor affecting the L. monocytogenes growth and survival, especially by using the organic acids like acetic acid.
The effect of temperature was studied. It was found that increasing the temperature up to 70°C played a significant role in increasing the treatment by increasing the time of exposure (60 minutes).
The public health importance of the organism and the steps which should be taken to control this organism in food processing units as well as the recommended sanitary measures, were also discussed.