The occurrence and initial numbers of Listeria in Irish meat and fish products and the recovery of injured cells from frozen products

Abstract

A total of 549 samples of meat, fish and poultry products purchased from retail outlets in the Dublin area were examined for the presence of Listeria spp., using a standard recovery method and a new resuscitation method. Listeria spp. were most frequently isolated from frozen beef burgers (97%) and fish fingers (95%). Cooked meats which were prepackaged by the manufacturer were negative for Listeria spp. The pathogen was isolated from 21% of cooked meats which were sold retail unpackaged indicating post-process contamination. Standard recovery methods gave Listeria counts of between 0.7 and log10 5.0 cfu/g on frozen products. Using a resuscitation method, counts were up to log10 2.5 cfu/g higher, indicating the presence of large numbers of injured Listeria cells. The significance of the numbers of Listeria found in the various foods as well as the recovery of injured cells with the new resuscitation method is discussed.