Validity of Members of the Total Coliform and Fecal Coliform Groups for Indicating the Presence of Salmonella in the Quahaug, Mercenaria mercenaria

Abstract

To determine the relationship of most probable number (MPN) of the total and fecal coliform groups in shellfish and shellfish-growing waters to the presence of Salmonella in quahaugs (Mercenaria mercenaria), a microbiological survey of 214 samples of the quahaug, or hard-shell clam, was done over 24 months. For purposes of this study, waters were classified as safe for shellfish harvesting by one of two criteria: (a) a total coliform MPN of ≤ 70/100 ml of water or (b) a fecal coliform MPN value of ⩽ 14/100 ml of water. None of the quahaug samples harvested from waters meeting these standards contained Salmonella. Additionally, Salmonella was not detected in any of the quahaug samples meeting the wholesale market quality standard of 230 fecal coliforms per 100 g of shellfish as specified by the National Shellfish Sanitation Program. An increase in the total coliform and fecal coliform MPN of the waters more closely paralleled an increase in the fecal coliform MPN, as compared to the total coliform MPN of the quahaug meats. Five Salmonella serotypes, including Salmonella parathyphi B, were found singly and in combination in five (2.3%) of the quahaug samples in this survey.