**Water activity (Aw)**

Minimum water activity is 0,940, below which multiplication does not cease, but the bacterial charge decreases, without disappearing though. *Salmonella* can survive for long periods in conditions of dehydration. This was detected several times in sweets, including chocolate, which led to outbreaks of food infection (Werber *et al*., 2005). In fact, the high fat and sugar content of sweet, may lead to a protective effect against it. Of course, in chocolate,

Food as Cause of Human Salmonellosis 55

Gadi Frankel (2008) of the Imperial College, London, UK, have revealed how salmonellae use their flagella to stick to salad and basil leaves. The results were presented at the 21st ICFMH International Symposium "Food Micro 2008" held in Aberdeen. This ability to attach itself to vegetables is described for a certain strain, *S. enterica* ser. Senftenberg, but not for *S.* Typhimurium (Frankel, 2009). Increased understanding of the mechanism that pathogens such as *Salmonella* use to adhere to vegetables is important if scientists are to develop new methods to prevent this type of contamination and the disease it causes (Berger *et al*., 2010). Schikora *et al*. (2008) have shown that *S.* Typhimurium, until now considered dangerous only for animals, can be a real danger for the vegetable kingdom too. Like any other plant pathogen, *S.* Typhimurium triggers the plant's immune defences and does not just cover the root surface, but enters physically into the plant's cells. The researchers attached a fluorescent probe to the bacterium and injected it, following its route: in just 17 hours the root cells were infected. Moreover, the infection later occurred simply by placing the plant (*Arabidopsis*) and the bacterium in the same liquid. *Salmonella* strains were detected in: aubergines, green salads, fennel, lettuce, onions, mustard, orange juice, pepper, parsley, spinach, strawberries, tomatoes, watermelons, coconuts, cereals, barley, chocolate and soy sauce (Cantoni & Bersani, 2010; Cantoni & Ripamonti, 1998). Today more and more ready-to-eat (RTE) vegetables are available in supermarket fridges because they are offered to the consumer as a convenience food, every part can be used, and, being already washed, peeled and chopped, they are quick and easy to prepare (Catellani *et al*., 2005). For their packing, various techniques are used, such as modified atmosphere packaging (MAP) – the gaseous composition of which varies according to the vegetable –, vacuum packaging, and ordinary atmosphere packaging. For the first two methods, the product should be packaged at refrigeration temperature, while with ordinary atmosphere it just needs to be kept cool. CO2 has the function to slow the breathing and the appearance of rotting, to inhibit pectinolytic enzymes and the development of *Pseudomonas* and other Gram-negative bacteria (Galli & Franzetti, 1998). Manvell & Ackland (1986) show that RTE vegetables can host various saprophytic microbial forms: 80-90% are Gram negative spoiling bacteria (including *Pseudomonas* spp, *Enterobacter* spp, *Erwinia* spp) and the rest are yeasts and moulds. If Good Manufacture Practices are respected, pathogens (*Salmonella* spp., *L. monocytogenes*, *E. coli* O157, enterovirus) or protozoa (*Giardia*, *Entamoeba, Cryptosporidium*) are detected only occasionally (Catellani *et al*., 2005). The study of *Salmonella* has dramatically contributed to the knowledge of the epidemiology of these infections. Large-scale distribution, particularly of fruit and vegetables, sets the conditions for events that touch a very wide area, involve the exposure of a big number of individuals, and that are difficult to recognize for lack of sophisticated surveillance systems that should involve international

collaboration networks.

**5.** *Salmonella* **in eggs and egg products** 

Eggs laid by healthy animals are generally safe to eat because if they kept in sound hygiene conditions they can be considered almost sterile inside, especially as regards bacterial agents of food diseases (Bozzo, 2008; Galli & Neviani, 2005). Nevertheless, *Salmonella* spp. is the most important pathogen transmitted by eggs (ICMSF, 1998). The natural defence factors


that may affect the egg's infection by microbiological contaminations are:

there cannot be any growth, but rather a sublethal stress which leads to an adaptation of the pathogen (Jasson *et al*., 2011). In the presence of NaCl concentrations between 3 and 4%, the development of *Salmonella* is usually inhibited. However, it appears that the inhibitory action of salt increases with increasing storage temperature. Variations depending on the serotype can be noticed (ICSFM, 1996).
