Chapter 26
Foodborne Gastroenteritis Caused
by Salmonella and Shigella
Among the Gram-negative rods that cause foodborne gastroenteritis, the most important are the
members of the genus Salmonella. This syndrome and that caused by Shigella spp. are discussed in
this chapter. The general prevalence of these organisms in a variety of foods can be found in Chapters
4, 5, 6, 7, and 9.
SALMONELLOSIS
The salmonellae are small, Gram-negative, non-sporing rods that are indistinguishable from E. coli
under the microscope or on ordinary nutrient media. They are widely distributed in nature, with humans
and animals being their primary reservoirs. Salmonella food poisoning results from the ingestion of
foods containing appropriate strains of this genus in significant numbers.
Some significant changes have been adopted for the taxonomy of Salmonella. Although food microbiologists, scientists, and epidemiologists treat the 2,400 or so Salmonella serovars as though each
was a species, all salmonellae have been placed in two species, S. enterica and S. bongori, with the
2,000 or so serovars being divided into five subspecies or groups, most of which are classified under
S. enterica, the type species.
33 The major groups correspond to the following subspecies: group II
(S. enterica subsp. salamae); group IIIa (S. enterica subsp. arizonae); group IIIb (S. enterica subsp.
diarizonae); group IV (S. enterica subsp. houtenae); and group VI (S. enterica subsp. indica). The
former group V organisms have been elevated to species status as S. bongori.
46 These changes are
based on DNA-DNA hybridization and multilocus enzyme electrophoretic characterizations of the
salmonellae (see Chapter 11). Thus, the long-standing practice of treating salmonellae serovars as
species is no longer valid. For example, S. Typhimurium should be S. enterica serovar Typhimurium,
or Salmonella Typhimurium (note that “typhimurium” is capitalized but not italicized).
For epidemiological purposes, the salmonellae can be placed into three groups:
1. Those that infect humans only: These include S. Typhi, S. Paratyphi A, S. Paratyphi C. This
group includes the agents of typhoid and the paratyphoid fevers, which are the most severe of
all diseases caused by salmonellae. Typhoid fever has the longest incubation time, produces the
619
Foodborne Gastroenteritis Caused
by Salmonella and Shigella
Among the Gram-negative rods that cause foodborne gastroenteritis, the most important are the
members of the genus Salmonella. This syndrome and that caused by Shigella spp. are discussed in
this chapter. The general prevalence of these organisms in a variety of foods can be found in Chapters
4, 5, 6, 7, and 9.
SALMONELLOSIS
The salmonellae are small, Gram-negative, non-sporing rods that are indistinguishable from E. coli
under the microscope or on ordinary nutrient media. They are widely distributed in nature, with humans
and animals being their primary reservoirs. Salmonella food poisoning results from the ingestion of
foods containing appropriate strains of this genus in significant numbers.
Some significant changes have been adopted for the taxonomy of Salmonella. Although food microbiologists, scientists, and epidemiologists treat the 2,400 or so Salmonella serovars as though each
was a species, all salmonellae have been placed in two species, S. enterica and S. bongori, with the
2,000 or so serovars being divided into five subspecies or groups, most of which are classified under
S. enterica, the type species.
33 The major groups correspond to the following subspecies: group II
(S. enterica subsp. salamae); group IIIa (S. enterica subsp. arizonae); group IIIb (S. enterica subsp.
diarizonae); group IV (S. enterica subsp. houtenae); and group VI (S. enterica subsp. indica). The
former group V organisms have been elevated to species status as S. bongori.
46 These changes are
based on DNA-DNA hybridization and multilocus enzyme electrophoretic characterizations of the
salmonellae (see Chapter 11). Thus, the long-standing practice of treating salmonellae serovars as
species is no longer valid. For example, S. Typhimurium should be S. enterica serovar Typhimurium,
or Salmonella Typhimurium (note that “typhimurium” is capitalized but not italicized).
For epidemiological purposes, the salmonellae can be placed into three groups:
1. Those that infect humans only: These include S. Typhi, S. Paratyphi A, S. Paratyphi C. This
group includes the agents of typhoid and the paratyphoid fevers, which are the most severe of
all diseases caused by salmonellae. Typhoid fever has the longest incubation time, produces the
619