490 Chapter 28
nineteenth century and early twentieth
century. The organism is under control in
many industrialized countries; however, it is
still a very important waterborne disease in
places with poor sanitary conditions. The
classical work of John Snow in 1854 showed
the transmission of V. cholerae through
poorly designed water - delivery systems in
London. His work led to the development of
much improved water - delivery systems and
water - treatment systems by public health
offi cial and environmental engineers in
developed countries around the world. In the
United States in 2002, there was one out-
break, two cases, and no deaths reported. The
appearance of V. cholerae in industrialized
countries often causes panic, since this organ-
ism has the potential to start a pandemic
infection.
It is a Gram - negative, curved rod that
looks like a comma under the microscope;
thus, the original name of V. comma. No
spore is formed. V. cholerae grows well in
alkaline medium and is actively motile with
a single polar fl agellum.
The organism is endemic in India and
Southeast Asia, and is spread by person - to -
person contact, water, milk, food, and insects.
The organism produces enterotoxins and
endotoxins in the intestines and causes severe
irritation to the mucous membranes, with
resultant outfl ow of fl uid and salts, and
impairs the sodium pump of mammalian
cells, thus causing severe diarrhea, dehydra-
tion, acidosis, shock, and even death. The
mortality rate may be as high as 25% to 50%.
The most effective therapy is replacement of
water and electrolytes to correct severe dehy-
dration and salt depletion.
Vibrio cholerae remains a dreaded com-
municable disease in many parts of the
world, and much education and public health
work needs to be done to reduce human suf-
fering from this organism. Besides conv-
entional biochemical tests, currently there
are immunologic and DNA probes and
PCR methods for rapid detection of this
organism.others are fi nding their ways into food micro-
biology laboratories.
Because Salmonella is heat sensitive,
proper cooking will destroy the organism.
Also, proper chilling, refrigeration, and good
sanitation will minimize the problem.
Salmonella remains one of the most impor-
tant food pathogens in our food supply.
Shigella
Shigella is a Gram - negative, facultative
anaerobic non - spore - forming rod quite often
confused with Salmonella in the bacterio-
logic diagnostic process. It is nonmotile and
hydrogen sulfi de negative. The colonies are
smaller than Salmonella. In terms of food -
borne infection, Shigella is not as prevalent
as Salmonella but this organism is very
important in waterborne diseases, especially
in tropical and subtropical countries where
sanitation conditions are poor. In 2002, there
were 43 outbreaks, 1,555 cases, and no deaths
reported to the CDC. The organism is trans-
mitted by water, food, humans, and animals.
The four F ’ s involved in the transmission of
Shigella are food, fi ngers, feces, and fl ies.
One to four days after ingestion of the organ-
isms, there will be an infl ammation of the
walls of the large intestines and ileum.
Invasion of the blood is rare. Bloody stool
will occur, owing to superfi cial ulceration.
The cell wall of Shigella , when lysed, will
release endotoxins. In addition, S. dysente-
riae produces an exotoxin that is a highly
toxic neurotoxin. This toxin can be neutral-
ized by a specifi c antibody. The mortality
rate of shigellosis is higher than that of
salmonellosis. Prevention of shigellosis can
be achieved by sanitation, good hygiene,
water treatment, prevention of contamina-
tion, detection of carriers, and isolation of
patients from the general public.
Vibrio cholerae
Vibrio cholerae was worldwide a very impor-
tant disease - causing organism in the late