Use of Salmonella enterica serovar Typhimurium DT104 expressing lux genes to assess, in real time and in situ, heat inactivation and recovery on a range of contaminated food surfaces

A self-bioluminescent construct of Salmonella enterica serovar Typhimurium DT104 was used to evaluate dry and wet surface pasteurisation of a wide range of meat and vegetable surfaces in a test rig. Bioluminescence was shown to be a sensitive measure of metabolic activity in real time and spatial position. Recovery of bioluminescence showed that limited dry heating with holding times of 3 min at both 60 °C and 90 °C, was relatively poor at reducing bacterial contamination. The type of food influenced the rates of bacterial recovery, with skinless chicken allowing the most rapid recovery. Whilst wet heat was shown to be very effective at reducing survivors to below detection levels, in some instances bioluminescence was detected after a 24 h recovery period, not in the area of initial inoculation, but in protected areas between the edge of the sample and the sample holder. This finding may explain anomalous results reported by other workers using sample destructive viable counts and also shows that steaming can dislodge and redistribute surface contaminants without killing.