Coliform Depuration Of Chesapeake Bay Oysters

Oysters contaminated in nature depurated fecal coliforms to levels below 50/100 g in 48 hr over a wide range of environmental conditions typical of the lower Chesapeake Bay region. Temperature was found to be the most crilical environmental factor with conditions below 10-12°C having the potential of inhibiting depuration. Coliform clearance did not appear to be correlated with pumping rate or biodeposition activity of oysters. Oysters infected with the pathogens Dermocystidium marinum and Minchinia nelsoni (MSX) depurated as rapidly as uninfected ones. Meat quality and size of oysters likewise did not affect depuration. Four commercial-size tanks of different designs were found to yield satisfactory results in 48 hr. Water flow rates over the ranges studied and location of trays within the tanks did not influence depuration. Biodeposits contained high levels of total and fecal coliforms, but their accumulation in the tanks did not have a detrimental effect under the conditions studied. Pooling oysters during monitoring of\u27 depuration samples was necessary due lo the variation of coliform levels in individual oysters. Samples of 6-8 pooled oysters appeared to be adequate for estimating coliform levels. The Medium A-1 test was superior to the elevated temperature coliform plate_ (ETCP) procedure of Cabelli and Heffernan for determination of fecal coliforms in oysters.https://scholarworks.wm.edu/vimsbooks/1020/thumbnail.jp