1. Introduction
During the last years, the consumption of fresh vegetables has been increasing as consumers strive to eat healthy diets
and the availability of these produce, up till recently considered as seasonal, has been extended over the whole year
[1,2]. In addition, the consumption of “four range” vegetables, a term that refers to packaged, cleaned, possibly
chopped and mixed vegetables ready to be seasoned and eaten, have gained popularity among consumers. Fresh
vegetables normally carry natural non-pathogenic epiphytic microorganisms, but during growth, harvest, transportation
and further handling the produce can be contaminated with pathogens from animal and human sources. As most of these
produce are eating without further processing, their microbial content may represent a risk factor for the consumer’s
health and therefore a food safety problem [3-5]. Contamination can arise as a consequence of treating soil with organic
fertilisers, such as sewage sludge and manure, and from the irrigation water, as well as from the ability of pathogens to
persist and proliferate in vegetables [4,6]. The epidemiology of foodborne disease has changed rapidly over the last
decades as, shortly after some major human pathogens were recognized to be spread from animal reservoirs, fresh
vegetables have emerged as new vehicles for the transmission of these infectious diseases. Since the early 1990s,
awareness of the potential of fresh produce to cause foodborne disease has increased, and reported outbreaks associated
with consumption of fresh vegetables have grown steadily. Most of the reported outbreaks of gastrointestinal disease
linked to the fresh produce have been associated with bacterial contamination, particularly with members of the
Enterobacteriaceae family [4,5,7-9] .