SURVIVAL OF VIBRIO SPP. INCLUDING INOCULATED VIBRIO-CHOLERAE O139 DURING HEAT-TREATMENT OF COCKLES (ANADARA-GRANOSA)

The effect of heat-treatment on the internal temperature of raw cockle s (Anadara granosa) and survival of their intrinsic flora of Vibrio sp p. as well as of inoculated V. cholerae 0139 was examined. The cockles were purchased from markets in Malaysia and had an average weight inc luding shells of 8.90+/-2.45 g. In one experiment heatpenetration of i ndividual cockles was examined. Cockles weighing < 8 g (including shel l) exhibited maximum internal temperatures of between 50 and 75 degree s C when heated in water at 99 degrees C for 10 s and 71-93 degrees C when heated for 30 s. Cockles weighing > 12 g exhibited maximum intern al temperatures between 42 and 58 degrees C when heated in water at 99 degrees C for 10 s and 56-69 degrees C when heated for 30 s. In anoth er experiment, heat-treatment of 10 cockles treated as a group at 99 d egrees C for 10 or 30 s resulted in reduction of levels of intrinsic V ibrio spp. (enumerated directly on thiosulphate-citrate-bile salt sucr ose agar; TCBS) from 5.73 to 3.15 log cfu g(-1) or below 1 log cfu g(- 1), respectively. The levels of Vibrio spp. after heat-treatment decre ased with an increase in numbers of cockles grouped together during tr eatment. In a third experiment V. cholerae 0139 was inoculated into co ckles and subjected to heat-treatment at 99 degrees C for 0, 10, 15, 2 0, 25 or 30 s. The levels of Vibrio spp. in uninoculated, non-heat-tre ated cockles was 4.89 log cfu g(-1) on TCBS, and the predominant speci es were V. parahaemolyticus and V. alginolyticus. V. cholerae 0139 ino culated into cockles with an average weight of 13.5 +/- 1.90 g (includ ing shell) decreased for samples examined immediately after heat-treat ment from 6 log cfu g(-1) initially to 3.5 log cfu g(-1) after 25 s an d < 1 log cfu g(-1) (TCBS) after 30 s of heat-treatment. The most prob able number method by enrichment in alkaline peptone water gave in gen eral within 1 log unit higher counts than TCBS direct enumeration. TCB S direct enumeration and MPN counts were up to 2.38 or 1.30 log units higher, respectively, for samples heat-treated for 20 s or longer and stored for 6 h at 30 degrees C before examination, than for samples he at-treated for same periods of time and examined immediately. This stu dy shows that a mild heat-treatment of cockles for up to 25 s is inade quate to ensure a large reduction in numbers of Vibrio spp., including V. cholerae 0139. (C) 1998 Elsevier Science B.V.