Cryptosporidium parvum studies with dairy products

Cryptosporidium parvum is a protozoan parasite capable of causing massive w aterborne outbreaks. This study was conducted to model the transfer of C. p arvum oocysts from contaminated water via food contact surfaces into yogurt and ice-cream, as well as to examine oocyst survival. Propidium iodide sta ining, combined with a direct immunofluorescence assay, was used for oocyst viability determination. Oocysts were recovered from milk products by a su crose flotation-based procedure, with average recoveries of 82.3, 60.7, and 62.5% from low (1%) fat milk, 9% fat ice-cream, and 98% fat-free yogurt, r espectively. Oocysts were also recovered, by rinsing with tap water, from s tainless steel surfaces inoculated with oocyst suspension, with average rec overies of 93.1% when the surface was still wet and 69.0% after the surface had air-dried at room temperature. Viability of oocysts on the surface was significantly affected by desiccation; 5% of the oocysts remained viable a fter 4 h of air-drying at room temperature, while the proportion of viable oocysts was 81, 69, and 45% after air-drying for 10 min, 1 h, and 2 h, resp ectively. In contrast, oocyst viability only dropped from 82 to 75% after 3 0 min contact at room temperature with 5% bleach solution (equivalent to 0. 26% NaOCl). Transfer of oocysts from milk and stainless steel surfaces into yogurt, and oocyst survival during the process were analyzed. Yogurt was m ade from pasteurized low fat milk and live yogurt starter by incubating at 37 degrees C for 48 h and then stored at 4 degrees C. Oocyst viability decr eased from 83% (80%) to approximately 60% after 48 h at 37 degrees C and to approximately 58% following 8 days of storage, similar to oocyst survival in the controls using pasteurized milk without the addition of live yogurt. Oocyst survival in ice-cream was investigated by inoculating oocysts into ice-cream mix, and mixing and freezing in an ice-cream freezer, and hardeni ng at - 20 degrees C. Although approximately 20% (25 and 18%) of oocysts we re viable before hardening, none were viable after 24 h at - 20 degrees C. Control samples of oocysts suspended in distilled water and stored at - 20 degrees C were taken at the same time intervals and 8% of the oocysts were still viable after 24 h. (C) 1999 Elsevier Science B.V. All rights reserved .