Fundamental Food Microbiology, Third Edition - Fuad Fathir

364 FUNDAMENTAL FOOD MICROBIOLOGY
harbor serotype Typhimurium in a carrier state, whereas serotype Enteritidis can
infect the ovaries of poultry, especially chicken, and can be transmitted through eggs.
Because of the increase in antibiotic use in feed of food animals and birds,
there is an increase in multidrug-resistant (MDR) strains among Sal. enterica
serotypes. One that has created concern is the MDR Salmonella Typhimurium
definitive phage type (DT) 104. The strains are resistant to several antibiotics,
including ampicillin, chloramphenicol, streptomycin, sulfonamides, and tetracycline.
It is suspected that they are transferred among strains or serovars by
different methods of genetic recombinations, especially under antibiotic selective
pressure. 5
During the last 10 years, foodborne salmonellosis from Salmonella Enteritidis
has increased greatly, and, at present, the frequency of incidence from it is as high
as that caused by Salmonella Typhimurium. Among the strains, serotype Enteritidis
phage type (DT) 4 and several other types are involved in salmonellosis in high
frequency. One of the reasons for this could be the way the poultry is raised.
B. Characteristics
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 a carbon source; produce hydrogen
sulfide, decarboxylate lysine, and ornithine; do not produce indole; and are negative
for urease. They are mesophilic, with optimum growth temperature between 35 and
37�C, but generally have a growth range of 5 to 46�C. They are killed by pasteurization
temperature and time, sensitive to low pH (4.5 or below), and do not multiply
at an A w of 0.94, especially in combination with a pH of 5.5 and below. The cells
survive in frozen and dried states for a long time. They can multiply in many foods
without affecting the acceptance qualities. 6,7
C. Habitat
Salmonellae are natural inhabitants of the gastrointestinal tracts of domesticated and
wild animals, birds, and 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. 6,7
D. Toxins
Following ingestion of Salmonella cells, the pathogens invade mucosa of the small
intestine, proliferate in the epithelial cells, and produce a toxin, resulting in an
inflammatory reaction and fluid accumulation in the intestine. The ability of the
pathogens to invade and damage the cells is attributed to the production of a
thermostable cytotoxic factor. Once inside the epithelial cells, the pathogens multiply
and produce a thermolabile enterotoxin that is directly related to the secretion of