THE EFFECT OF TEMPERATURE AND LOW PH ON SURVIVAL OF SHIGELLA DYSENTERIAE (IN VITRO)MOJTABA ANVARINEJAD, MEHDI AZAMI, MARYAM JAMSHIDIAN GHALESEFIDI AND NARGHES ABDALIAbstract Shigellosis still remains an important cause of mortality and morbidity in developing countries. Incidences of food-borne shigellosis are associated with consumption of fresh produce and vegetables. The safety of fruit and fruit products relies mainly on their low pH and storage under refrigeration which are considered as barriers for growth and survival of microbes. However, a few closely related species of Shigella showed extraordinary tolerance to low pH. The aim of this study is use of intrinsic and extrinsic factors such as reduced pH and temperature can indeed inhibit the outgrowth but may induce prolonged survival of highly virulent of Shigella. With this objective, the growth and survival efficiency of shigellae in acidified media was monitored at different time intervals and viable counts were determined. At 37ºC shigellae die rapidly at pH 4.0 or lower, but these pathogens could survive for an extended period under similar adverse pH conditions when kept at refrigeration temperatures. A die-off of the shigellae was observed at pH 3.5 -4.0 and pH 3.0-3.5, respectively after 10 days at 4ºC and 6 days at 20ºC. Thus the recovery of shigellae was affected by exposure to reduced pH but increases with refrigeration. So it can be concluded that acid foods usually kept at refrigeration temperatures, may support survival of Shigella and cause food poisoning. Once contaminated during cutting, juicing or in transit, these pathogens can survive for an extended period even under adverse pH conditions and these foods may serve as a vehicle for Shigella infections.
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