**2. Animals as** *Salmonella* **reservoir**

The transmission cycle of *Salmonella* to humans through food presents many complexities because it involves animal reservoirs, vector food and the environment (Graziani *et al*., 2005). Mammals, birds, rodents, reptiles, amphibians and insects act as environmental reservoirs of *Salmonella* and can transfer the pathogen to man (D'Aoust, 2007). On intensive farming facilities the role of the "healthy carriers" is important: even if they do not show any symptoms of the disease, they contaminate the environment and contribute to spreading salmonellae on the farm, sometimes creating endemic situations. The absence of symptoms in most of the infected animals and the technical difficulties in detecting the carriers during the inspection of the meat cause a continuous contamination of foods of animal origin.

Graziani *et al*. (2005) argue that various *Salmonella* serotypes may prefer various animal species: some are considered specific to one animal species (S. Gallinarum in chickens), others are defined as "host-adapted" because they prefer one host over another (S. Dublin for cattle, S. Enteritidis in egg-laying hens, S. Hadar in birds); on the other hand, other serotypes, such as S. Typhimurium, are ubiquitous. The role as reservoir is played by many animal species, but poultry and pigs are the predominant reservoirs for *Salmonella* (Cantoni & Bersani, 2010). In birds, species-specific serotypes are present, such as S. Pullorum and S. Gallinarum (Cantoni & Ripamonti, 1998), as well as host-adapted serotypes, such as S. Hadar and S. Enteritidis in chickens in Italy, while S. Blockley is found more predominantly in turkeys (Graziani *et al*., 2005). The importance of broilers and other farm birds as *Salmonella* reservoirs should not be underestimated (D'Aoust, 2007). Although *S*. Pullorum and *S*. Gallinarum have been eradicated from industrial production thanks to *in loco* monitoring and eradication programs in reproducers, it is known that infections by S. Enteritidis and S. Typhimurium have been quite common in farm birds recently, therefore strict hygiene rules must be followed to prevent the contamination of finished products.

For pigs, the pathogenic salmonellae are *S*. Choleraesuis and S. Typhi suis (Cantoni & Ripamonti, 1998). Over the past ten years a marked increase in the prevalence of *S. enterica*

to ascertain and report to the EFSA the proportion of "national" cases of salmonellosis and those "acquired" from abroad. We would like to recall that in 2005 the EU issued the 2073/2005 (EC) Regulation which identified the *food safety criteria* for some of the major food groups most at risk of transmitting diseases to man. *Salmonella* was adopted as a parameter for the safety of fresh meat and products derived from it, raw milk and dairy products made with it, edible bivalve molluscs, as well as for pre-cut fruits and vegetables. In accordance with the EU provisions, *Salmonella* must be absent from 25 or 10 grams of examined sample of these foods in order for them to be destined for human consumption. In the EU which foodstuffs did not comply with this criterion and exceeded it? In 2009, as in 2008, the highest percentage of non-compliance was found in food derived from fresh meat, and particularly from minced meat and meat preparations containing chicken or turkey (8.7% of the total non-complying foods). Secondly, in order of prevalence, are bivalve molluscs and echinoderms, which are often traditionally consumed raw or hardly cooked (3.4% of all samples). Much less at risk are currently liquid eggs which go through a pasteurization process before entering the food manufacturing industry. Some concern arises from the fact that there are rather large percentages of non-compliance even among meat preparations for raw human consumption (the samples tested positive for *Salmonella* during official tests

The transmission cycle of *Salmonella* to humans through food presents many complexities because it involves animal reservoirs, vector food and the environment (Graziani *et al*., 2005). Mammals, birds, rodents, reptiles, amphibians and insects act as environmental reservoirs of *Salmonella* and can transfer the pathogen to man (D'Aoust, 2007). On intensive farming facilities the role of the "healthy carriers" is important: even if they do not show any symptoms of the disease, they contaminate the environment and contribute to spreading salmonellae on the farm, sometimes creating endemic situations. The absence of symptoms in most of the infected animals and the technical difficulties in detecting the carriers during the inspection of the meat cause a continuous contamination of foods of animal origin. Graziani *et al*. (2005) argue that various *Salmonella* serotypes may prefer various animal species: some are considered specific to one animal species (S. Gallinarum in chickens), others are defined as "host-adapted" because they prefer one host over another (S. Dublin for cattle, S. Enteritidis in egg-laying hens, S. Hadar in birds); on the other hand, other serotypes, such as S. Typhimurium, are ubiquitous. The role as reservoir is played by many animal species, but poultry and pigs are the predominant reservoirs for *Salmonella* (Cantoni & Bersani, 2010). In birds, species-specific serotypes are present, such as S. Pullorum and S. Gallinarum (Cantoni & Ripamonti, 1998), as well as host-adapted serotypes, such as S. Hadar and S. Enteritidis in chickens in Italy, while S. Blockley is found more predominantly in turkeys (Graziani *et al*., 2005). The importance of broilers and other farm birds as *Salmonella* reservoirs should not be underestimated (D'Aoust, 2007). Although *S*. Pullorum and *S*. Gallinarum have been eradicated from industrial production thanks to *in loco* monitoring and eradication programs in reproducers, it is known that infections by S. Enteritidis and S. Typhimurium have been quite common in farm birds recently, therefore strict hygiene rules must be followed to prevent the contamination of finished products. For pigs, the pathogenic salmonellae are *S*. Choleraesuis and S. Typhi suis (Cantoni & Ripamonti, 1998). Over the past ten years a marked increase in the prevalence of *S. enterica*

ranged from 1,2% to 1,7 % of the total tested samples).

**2. Animals as** *Salmonella* **reservoir** 

serovar 4, [5], 12:i- has been observed in many European countries (Hopkins *et al*., 2010). It is resistant to ampicillin, streptomycin, sulphonamides and tetracycline in food-borne infections, in pigs and pork. The results indicate that genetically related strains of serovar 4, [5], 12:i:- of the DT193 and DT120 phage types with resistance to ampicillin, streptomycin, sulphonamides and tetracycline have emerged in many European countries and that pigs are the likely reservoir of the infection. A survey by the European Food Safety Authority has established the prevalence of *Salmonella* in pigs for slaughter in the EU-25 plus Norway (EFSA, 2008). This survey, as well as discovering that one pig every ten is affected, also identified the prevalent serotypes in infected pigs (*S*. Typhimurium and *S*. Derby), the same ones as in the cases of human infection.

Cattle are often colonized by S. Dublin and S. Typhimurium, with infections that vary in duration and clinical manifestation (Graziani *et al*., 2005). Cattle are particularly susceptible to infection by *Salmonella* in the first weeks of life (Cantoni & Ripamonti, 1998). S. Dublin can stay in the host for a long time, in some cases all its life and often causes serious bouts of illness (Graziani *et al*., 2005). As healthy carriers, they can pass S. Dublin and S. Typhimurium in their faeces, and those can remain viable in the outside for at least six months (Cantoni & Ripamonti, 1998).

In the meat-processing industry, eggs and poultry meat are the main groups of raw materials which usually carry *Salmonella* (D'Aoust & Maurer, 2007) and in many States they overshadow other sources such as pork, beef and mutton as a means of infection (WHO, 1988). To conclude, we can say that the biological cycle of *Salmonella* spp. is complex (see Table 1) and involves animals, environment and food (D'Aoust & Maurer, 2007), and that animals act as the most important reservoirs for its conservation (Graziani et al., 2005).

Table 1. *Salmonella* life cycle and transmission to humans (adapted from WHO, 1988).

Food as Cause of Human Salmonellosis 53

**Conditions Minimum Optimum Maximum** 

In particular, we can say that the minimum temperature for the growth of *Salmonella* is 7 °C (at 8 °C generation time is 22-35 hours); under 15 °C its development is still low. The storage of food at temperatures below 5 °C therefore prevents the multiplication of all serotypes; the only one able to develop up to 5.3 °C is *S*. Heidelberg (Matches & Liston, 1968). The highest mortality occurs during the slow freezing phase (0 to -10 °C), while in the deep-freezing one, for reaching temperatures below -17 °C rapidly, its survival is more likely, as damage to the cell membrane is minor. However, freezing does not guarantee the destruction of *Salmonella*: they have been found in frozen foods stored for years (ICMSF, 1996; Farkas, 1997), due to the changes and the production of cold shock and cold acclimation proteins (Scherer & Neuhaus, 2002). Maximum development temperature is 49.3 °C, beyond which *Salmonella* begin to die due to the denaturation of cell wall components and to the inactivation of heat-sensible enzymes. Although a temperature of 55 °C is sufficient to kill them, the legal limit for the storage of cooked foods meant to be eaten hot is normally 63 °C. *Salmonella* is not particularly resistant, so a pasteurization process is more than enough to destroy it. Several authors agree that the most heat-resistant serotype is *S*. Senftenberg 775W which registers D65= 0.29-2.0 and D60=1.0-9.0 when the substrate is in normal conditions, but the D value decreases if you move away from the optimal range for growth. Finally, its z value is 5,6-6,4 (°C). Resistance to heat is influenced

 water activity: the lower it is, the greater the pathogen's heat resistance, since the presence of water favours the thermal break of the peptide bonds and in their absence

the composition of the food, and its fat content, which enhance its resistance, as well as

pH levels, which, if maintained at around neutrality, allow for greater heat resistance of

the age of the microbial cells, since the young ones are more sensitive to heat in

adaptation to high incubation temperatures, for a genetic selection that favours the

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,

the pathogen, whereas sensitivity increases if it is lowered or raised;

development of strains which are more resistant to heat (Jay, 1996).

more energy is needed for achieving the same result;

Table 2. Limits and optimum growth in relation to intrinsic and extrinsic factors for

Salmonella spp. Notes. \*: Some serotypes. (Source: ICMSF, 1996; amended).

35-43 7.00-7.50 -- --

46.2 (49.3 \*) 9.50 -- 4

7.0 (5.2 \*) 4.00 (3.80 \*) 0.940 (0.900 \*) --

T °C pH Aw Tolerance to salt (%)

by other factors, such as:

**Water activity (Aw)** 

the glycerol or sucrose contents;

logarithmic growth phase;

**Temperature** 
