الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
number of features make L. monocytogenes a potential hazard to the dairy industry not least of which is its ability to grow at the low temperatures commonly used for the storage of milk on both the farm and the processing site. Although the risk of contamination with Listeria in dairy products appears to be low, the lack of information about the infective dose in humans and the high mortality rate in people suffering from listeriosis mean that the dairy industry can not afford to be complacent. Thus, the research and publicity centered on L. monocytogenes worldwide, far from being ”Listeria hysteria”, is necessary to allow the food industry to maintain the high standards of safety which are expected of it. The findings of this study, together with data cited from the
literatures, may lead to the following conclusions:
•The results obtained from this study have indicated that L. monocytogenes is wide] distributed in dairy products. The psychrotrophic nature of this organism makes its growth on dairy products as a ready-to-eat foods during refrigerated storage possibility and increases the risk of large numbers of Listeria surviving in finishix
products at the food service level.
•Although Listeria can grow at low temperatures, it is still important to keep foods refrigerated so those microorganisms can not multiply as fast as they wotilc
unrefrigerated.
•Incrimination of dairy products in the outbreaks of listeriosis has emphasized the necc. for systemic control of L. monocytogenes in raw milk. The occurrence of 1
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monocytogenes in the samples screened in this study underline the fact that the control of Listeria should begin at the farm level by giving more attention to the hygiene measures in animal rearing, feeding, milking procedures, processing, storage, and distribution of milk.
•The most likely sources of the organism in raw bulk-tank milk at the farm level are environmental in nature, with silage and milking cups playing a major role.
•Since pasteurization eliminates the organism, proper pasteurization and careful handling is recommended to avoid risk of milk borne infection.
•Foods linked previously by epidemiological studies to listeriosis are required to be free of L. monocytogenes. When these foods are found to be contaminated, they should subject to recall action with consideration of public alert.
•The groups of people likely to be vulnerable to infection by L. monocytogenes like pregnant women, those with underlying malignancy, people with renal diseases, diabetics and Liver diseases are advised to avoid eating certain types of soft cheeses (brie, camembert, and blue-veined types). They are also advised to reheat cooked and chilled meals.
•Cheese contamination with L. monocytogenes is of utmost importance for public health authorities as well as industry. Because of the characteristics of the bacteria, which is able to grow at 4°C and in the presence of the high concentration of NaCl and which is widespread in the environment, its total elimination from the dairy chain, and generally from the food chain, seems to be an impossible task. In order to limit or best prevent Listeria contamination, it is therefore important to adhere to
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good hygienic practices and to insure that the policy is implemented by making regular checks of foodstuffs, processing equipment and the plant environment.
•Guidelines for good hygienic practice in the production of soft and fresh cheeses should be prepared and distributed to all those who are working in the dairy industry.
•The results obtained in this research emphasize the fact that the manufacturing of cheese using raw milk presents a public health risk. Adequate heat treatment of milk and restricted rules should be undertaken to prohibit the use of raw milk for cheese manufacture. Moreover, good hygiene in the dairies so as to prevent post-processing contamination, is recommended to prevent cheese-borne listeriosis.
•In order to eliminate Listeria from dairy products, attention must be also focused on the environment within the dairy plant. The primary sources of Listeria spp. in processing plants are probably floors and floor drains especially areas in and around coolers or places subject to outside contamination. All the effective measures for control of Listeria on the farm and in the plant should concentrate on the reducing the contamination of raw milk by Listeria, minimizing environmental contamination of milk products and ensuring good sanitation practices designed to eliminate Listeria from food.
•Control of the food production environment is an essential factor in preventing contamination of the finished product. Listreria monocytogenes is not particularly resistant to chlorine and the common sanitizing agents, and its control in the food industry by a good program of cleaning and sanitizing should be implemented in the dairy plants.
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•Attention should be paid to controlling insects and vermin around the dairy plants as it has been suggested that ants can act as a vector for the spread of Listeria within dairy plants.
•Intensive food monitoring programs like The Hazard Analysis of Critical Control points (HACCP) should be designed to establish environmental monitoring programs to minimize the potential for contamination of finished products and to identify contaminated foods before distribution. Beside HACCP, certain control measures should be enforced in manufacturing and processing plants. Such measures are: knowing the source of the food materials, maintaining clean transportation vehicles and practicing general sanitation of the entire food-processing environment.
•At least two enrichment methods must be used in combination to recover Listeria spp. from naturally contaminated foods. Regarding the comparison of methods used for detection of Listeria, the M. USDA was the method of choice for detetion of Listeria in milk samples, while the USDA was the method of choice in screening the farm and dairy environment for presence of Listeria.
•The acting of the VIDASTM and BAXTM PCR Listeria assays as a rapid methods for detection of Listeria was satisfying comparing to the individual cultural methods used in this investigation.
•The use of the PCR technology as a rapid method for detection of Listeria, in dairy plant environment proved that there is no difference between the results obtained using the BAXTM PCR assay after 24 and 48 h of the sample enrichment.
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•Ribotyping analysis confirmed that raw milk and farm environment harbor differe strains of L. monocytogenes which can not be easily differentiated without us strain-specific typing technique.
•Standard typing methods, such as serotyping and phage typing as well as molecul typing methods like ribotyping used for characterization of isolated strains, should added as tools for L. monocytogenes food investigations