This chapter reviews issues related to the occurrence and growth of Listeria monocytogenes in food processing and food service environments. L. monocytogenes is a food-borne pathogen with the capacity to contaminate raw or minimally processed foods such as chilled ready-to-eat [RTE] foods. The consumption of food contaminated with L. monocytogenes can result in a disease known as listeriosis among vulnerable groups of people such as pregnant women and fetuses, newborns, adults between the ages of 65 and 75, and people with weakened immune systems. L. monocytogenes is ubiquitous and has been isolated from soil, vegetation, sewage, water, animal feed, fresh and frozen meat including poultry, slaughterhouse wastes and the feces of healthy animals and humans. The bacterium is both acid tolerant and salt tolerant. It is able to grow at refrigerator temperature, and is therefore often associated with the consumption of raw or minimally processed and often chilled RTE foods. L. monocytogenes is able to form biofilms on food processing and preparation surfaces, which protects it from antimicrobial action. Continuous education of vulnerable groups regarding food safety will increase their awareness of the importance of practicing safer food handling practices such as hand washing and safe storage of RTE foods as a means to prevent listeriosis.
- Listeria monocytogenes
- ready to eat food
- listeriosis
- food safety
Listeria monocytogenesis a bacterium which is ubiquitous in nature, and occurs frequently in food processing and handling environments [1]. The consumption of food contaminated with L. monocytogenescan result in a disease known as listeriosis, to which pregnant women and their newborns, adults aged 65 or older, and people with weakened immune systems are particularly vulnerable [2]. In healthy adults, listeriosis is most likely to manifest as mild gastroenteritis. However, in some instances it can result in more severe symptoms, which can lead to life-threatening illnesses such as endocarditis, encephalitis or meningitis, and severe sepsis [3].
Inadequate food hygiene practices during food preparation are primarily responsible for the propagation of the bacterium and contamination of ready-to-eat [RTE] foods [Table 1] during processing, distribution and handling [4]. Small to medium-sized enterprises [SMEs] are more likely to experience L. monocytogenesoutbreaks than renowned large-scale food processing enterprises owing to differences in the implementation of food safety measures [5].
| 2017 | Creamy, soft, raw-milk cheeses [2] | USA |
| 2016 | Frozen vegetables [62] | USA |
| 2016 | Raw milk chocolate milk products [63] | USA |
| 2016 | Packaged salad [64] | USA |
| 2015 | Soft cheese [65] | USA |
| 2015 | Ice cream [66] | |
| 2014 | Commercially produced, pre-packaged caramel apples [67] | USA |
| 2014 | Mung bean sprouts [68] | USA |
| 2014 | Soft cheese [69] | USA |
| 2014 | Cheese products [70] | USA |
| 2017–2017 | Various food products [71] | South Africa |
| 2017 | Not determined [72] | Australia |
| 2014 | Various food products [73] | 28 EU/EEA countries |
Some records of global Listeriaoutbreaks between 2014 and 2017.
CDC: Centre for Disease Control, NICD: National Institute for Communicable Diseases, ECDC: European Centre for Disease Prevention and Control, USA: United States of America, EU: European Union, EEA: European Economic Area.
RTE foods, which are often stored at low temperatures, are the type most susceptible to contamination with L. monocytogenessince the bacterium is psychrotrophic and possesses the ability to survive and grow in the presence of many food preservation systems, such as low pH and high salt concentrations [6]. The contamination of minimally processed fruit and vegetable products with L. monocytogenesis often a concern, considering that these foods, which are attractive to consumers, are often not subjected to lethal treatments during processing to inactivate potential pathogens [7]. Moreover, the manner in which RTE vegetables are sliced can affect the survival of Listeriaand the effectiveness of decontamination procedures in the finished products. Hand tearing or manual slicing with a razor blade reduced the survival and growth of E. coliand L. innocua, probably because of less damage to the vegetable tissues and minimal leakage of nutrients from damaged plant tissues [8].
L. monocytogeneshas the ability to attach itself to food preparation contact surfaces and grow to form protective biofilms, which generally protect the bacterial cells from antimicrobial action during cleaning and sterilisation processes [9]. However, low concentrations [