Microbiological quality and safety of quahog clams, Mercenaria mercenaria,during refrigeration and at elevated storage temperatures

The effects of storage temperatures and times on the microbiological qualit y and safety of hard-shelled quahog clams (Mercenaria mercenaria) were exam ined. Samples were stored at four different incubation temperatures (3.3, 7 .2, 10.0, and 12.8 degreesC) for a period of 3 weeks, following their harve st from summer growing waters (greater than or equal to 27 degreesC) and wi nter waters (less than or equal to4 degreesC). Clams were analyzed for two naturally occurring pathogens, Vibrio parahaemolyticus and Vibrio vulnificu s. During the summer, V. parahaemolyticus was isolated from 56% of the stor ed samples, with the highest concentration, 6,100/g, occurring on day 12 at 12.8 degreesC, Also, during the summer, V vulnificus was isolated from 11% of the stored samples, with the highest concentration of 1,500/g occurring on day 15 at 7.2 degreesC. No Vibrio spp. were detected during the winter. During summer storage, aerobic mesophilic counts on plate count agar (PCA) containing 2% NaCl ranged from 10(4) to 10(8) CFU/g, and during storage of the winter samples, aerobic mesophilic PCA (with added NaCl) counts ranged from <100 to 10(4) CFU/g. Comparatively, summer storage mesophilic counts on PCA containing no added NaCl ranged from <100 to 10(5) CFU/g, and for th e winter samples the range was <100 to 10(2) CFU/g. Coliform and fecal coli form counts ranged from <0.3 to 61.1/g and <0.3 to 24.4/g, respectively. Th ere was no statistical correlation between the length of storage or the tem perature of incubation and the presence of V. parahaemolyticus, V. vulnific us, coliforms, or fecal coliforms. However, storage time and incubation tem perature affected the PCA counts (P <less than or equal to> 0.05) in quahog clams.