Foodborne Bacterial Infections ◾ 341
selective pressure. Multidrug resistance in DT104 is a result of chromosomal integration of a
43 kb Salmonella genomic island 1 (SGI1) carrying antibiotic resistant genes.
During the last 10 years, foodborne salmonellosis from Sal. enterica ser. Enteritidis has
increased greatly, and at present, the frequency of incidences from it is as high as that caused by
Sal. enterica ser. Typhimurium. Among the strains, serotype Enteritidis PT4 and several other
types are involved in salmonellosis in high frequency. The reasons for this could be the way the
poultry is raised and also increased consumption of poultry.
Characteristics
The Salmonella cells are Gram-negative, nonsporulating, facultative anaerobic motile rods. They
form gas while growing in media containing glucose. Generally, they ferment dulcitol, but not
lactose; utilize citrate as carbon source; produce hydrogen sulfide, decarboxylate lysine, and ornithine; do not produce indole; and are negative for urease. They are mesophilic with an optimum
growth temperature between 35°C and 37°C but generally have a growth range of 5°C–46°C.
They are killed by pasteurization temperatures and sensitive to low pH (4.5 or below) and do
not multiply at A W 0.94, especially in combination with a pH at 5.5 and below. The cells survive
under frozen and dried states for a long time. They are capable of multiplying in many foods
without affecting the acceptance qualities. In recent years, Salmonella outbreaks associated with
low- moisture foods, including peanuts, almonds, peanut butter, spices, and wheat flours indicate
that they can survive at A W of as low as 0.2 for an extended period of time (over 1000 days). 4
Habitat
Salmonellae are natural inhabitants of the gastrointestinal tracts of domesticated and wild animals, birds, pets (including turtles and frogs), and insects. In animals and birds, they can cause
salmonellosis and then persist in a carrier state. Humans can also be carriers following an infection and shed the pathogens through feces for a long time. They have also been isolated from soil,
water, and sewage contaminated with fecal matters.
Disease and Symptoms 5,6
Human salmonellosis is different from typhoid and paratyphoid fever caused by Sal. enterica ser.
Typhi and Sal. enterica ser. Paratyphi, respectively. Although there are some Salmonella serovars
specific against different animals and birds, all are considered to be potential human pathogens
capable of causing salmonellosis. Foodborne salmonellosis is characterized by gastrointestinal disorders manifested predominantly by diarrhea and abdominal cramp. A dose of >10 2–3 cells is
needed to be consumed to initiate infection; however, there are some virulent strains of which
ingestion of fewer cells can cause the disease. Strains that are sensitive to gastric acidity generally need more cells to establish in the intestine and cause the disease; conversely, acid-resistant
strains may require fewer cells to cause the disease. The infectious dose decreases if the pathogen
is consumed with food that neutralizes the stomach acidity, such as milk, cheese, and so forth.
Progression of disease also depends on the physiological state of the host. Elderly persons with
high gastric pH are vulnerable to salmonellosis.
Following ingestion, the pathogen colonizes in the small and large intestines, and most of
the pathological lesions are reported to be found in the large intestine rather than in the small
intestine. The organism adheres to the mucosal cells using fimbriae or other adhesion factors and
selective pressure. Multidrug resistance in DT104 is a result of chromosomal integration of a
43 kb Salmonella genomic island 1 (SGI1) carrying antibiotic resistant genes.
During the last 10 years, foodborne salmonellosis from Sal. enterica ser. Enteritidis has
increased greatly, and at present, the frequency of incidences from it is as high as that caused by
Sal. enterica ser. Typhimurium. Among the strains, serotype Enteritidis PT4 and several other
types are involved in salmonellosis in high frequency. The reasons for this could be the way the
poultry is raised and also increased consumption of poultry.
Characteristics
The Salmonella cells are Gram-negative, nonsporulating, facultative anaerobic motile rods. They
form gas while growing in media containing glucose. Generally, they ferment dulcitol, but not
lactose; utilize citrate as carbon source; produce hydrogen sulfide, decarboxylate lysine, and ornithine; do not produce indole; and are negative for urease. They are mesophilic with an optimum
growth temperature between 35°C and 37°C but generally have a growth range of 5°C–46°C.
They are killed by pasteurization temperatures and sensitive to low pH (4.5 or below) and do
not multiply at A W 0.94, especially in combination with a pH at 5.5 and below. The cells survive
under frozen and dried states for a long time. They are capable of multiplying in many foods
without affecting the acceptance qualities. In recent years, Salmonella outbreaks associated with
low- moisture foods, including peanuts, almonds, peanut butter, spices, and wheat flours indicate
that they can survive at A W of as low as 0.2 for an extended period of time (over 1000 days). 4
Habitat
Salmonellae are natural inhabitants of the gastrointestinal tracts of domesticated and wild animals, birds, pets (including turtles and frogs), and insects. In animals and birds, they can cause
salmonellosis and then persist in a carrier state. Humans can also be carriers following an infection and shed the pathogens through feces for a long time. They have also been isolated from soil,
water, and sewage contaminated with fecal matters.
Disease and Symptoms 5,6
Human salmonellosis is different from typhoid and paratyphoid fever caused by Sal. enterica ser.
Typhi and Sal. enterica ser. Paratyphi, respectively. Although there are some Salmonella serovars
specific against different animals and birds, all are considered to be potential human pathogens
capable of causing salmonellosis. Foodborne salmonellosis is characterized by gastrointestinal disorders manifested predominantly by diarrhea and abdominal cramp. A dose of >10 2–3 cells is
needed to be consumed to initiate infection; however, there are some virulent strains of which
ingestion of fewer cells can cause the disease. Strains that are sensitive to gastric acidity generally need more cells to establish in the intestine and cause the disease; conversely, acid-resistant
strains may require fewer cells to cause the disease. The infectious dose decreases if the pathogen
is consumed with food that neutralizes the stomach acidity, such as milk, cheese, and so forth.
Progression of disease also depends on the physiological state of the host. Elderly persons with
high gastric pH are vulnerable to salmonellosis.
Following ingestion, the pathogen colonizes in the small and large intestines, and most of
the pathological lesions are reported to be found in the large intestine rather than in the small
intestine. The organism adheres to the mucosal cells using fimbriae or other adhesion factors and