Control and monitoring of Listeria monocytogenes with the use of natural antimicrobial techniques including the bacteriocin nisin

According to the Department of Agriculture, Food and the Marine (DAFM) the agri-food industry contributes €24 billion to the Irish economy. One of DAFM’s chief concerns is the maintenance of Ireland’s reputation for high food quality and food safety. Listeria monocytogenes is of a particular risk to this reputation especially for food businesses within the ready to eat (RTE) food sector as L. monocytogenes is extraordinarily well adapted to the harsh conditions employed for food preservation. This thesis, through the literature review discusses the risk factors associated with the bacteria, the preventative measures taken to reduce occurrence and their effectiveness, outbreaks and potential solutions to the problem of L. monocytogenes within the ready-to-eat food industry specifically the fresh-cut fruit and vegetable produce sector. Experimentally, three individual experiments were conducted with the aims of: a) to establish if the effects of inoculation density induces any experimental biases on studies of growth of L. monocytogenes b) to test the effect of nisin A and L. lactis as potential viable antilisterial agents without the negative organoleptic effects of other antimicrobials currently used on fresh-cut lettuce such as essential oils c) to partake in a national sampling program for L. monocytogenes occurrence and persistence rates in Irish food businesses. Results from these experiments it was shown that a) low initial cell densities can lead to higher growth rates when compared to higher inoculation densities potentially leading to a need to reclassify high inoculation based L. monocytogenes growth experiments. b) demonstrated that the introduction of low amounts of purified commercial nisin A can reduce L. monocytogenes counts by a significant amount without a substantial negative effect of other antilisterial compounds on the sensory quality of the lettuce. c) Provided prevalence data from dairy, meat and vegetable producing industries as part of a 3-year national L. monocytogenes sampling program and displayed that vigilance and awareness of a potential pathogen can lead to a reduction in its occurrence.