No abstract

Two serotypes of Yersinia enterocolitica (0:3 and 0:8) were added to a 1% (w/v) whole egg suspension and their survival was followed during exposure to conditions which reflected those used during commercial egg washing. Trials were conducted over a range of pH (7,9.5,10 and 10.5) at 38 and 42°C. The potential for Yersinia growth during transport of samples from grading stations to the laboratory at a number of storage temperatures (6,10,12 and 15°C) was also examined. Y. entercolitica strain 125 (serotype 0:3) was able to grow in synthetic egg washwater at pH 10 and 38°C (conditions frequently found at egg grading stations). Both Yersinia strains were able to grow at refrigerator temperatures when the pH was ⩽10. Recommendations concerning the conditions of egg washing were made in view of the potential for Yersinia growth in washwater during the period of its transportation to the laboratory for analysis and in view of Yersinia survival in the recycled washwater.

Long-term phenotypic and genotypic stability is a fundamental prerequisite for the successful biotechnological exploitation of any micro-organism, as without stable starter cultures productivity can not be guaranteed. In this study two biotechnological algal production strains; Porphyridium cruentum A-408, which produces zeaxanthin, and Planktothrix A-404, which produces a potent cytotoxin, were successfully cryopreserved using a two step protocol (cooling to −40 • C prior to plunging into liquid nitrogen). Post-thaw viability levels of 114 ± 27% were obtained for P. cruentum A-408 and 67 ± 18% for Planktothrix A-404. Unchanged productivity levels of Zeaxanthin and beta-carotene (77% and 12% of total carotenoids respectively) were obtained in batches of P. cruentum A-408 produced from standard (serial transfer) and utilizing post-thaw (ex-cryopreserved) inocula. In addition, cytotoxin production by Planktothrix A-404 was not influenced by the origin of the inoculum, with standard (serial transfer) and post-thaw (ex-cryopreserved) inocula giving high levels of activity.

An evaluation of methods for monitoring the quality of water used to wash eggs at grading stations was undertaken to improve maintenance of bacterial viability during overnight sample transport. Bacterial content of samples at analysis would then better reflect conditions at the time eggs were washed. The interactive effects of temperature and the highly alkaline water conditions upon viability were the subjects of this study. Nine transport methods were examined for their efficacy in recovering total and coliform bacteria from recycled water used to wash eggs, and these were compared with samples analyzed at two commercial egg grading stations. Samples were shipped under test to the laboratory for analysis the following day. The survival of Staphylococcus aureus and Escherichia coli was also examined, but in a synthetic washwater matrix under various combinations of temperature (6 to 32°C) and pH (9.5 to 10.5) to determine whether there was likely to be a different response to variations in transport treatment among gram-positive and-negative bacteria. S. aureus was much more resistant to the lethal effects of high pH and moderate temperature than E. coli. These results indicated that samples of high pH should be held (transported) at l13°C to optimize bacterial survival. Considering cost, ease of manipulation, and the ability to protect both coliforms and the bacterial population as a whole, the method of choice for transport of industrial samples was the direct addition of washwater to containers in which powdered KH2PO4 and Na2S203 had been placed to yield final concentrations, when dissolved, of 0.2 and 0.05% (wt/vol), respectively.