Enterobacterial infections WORLD OF MICROBIOLOGY AND IMMUNOLOGY188•
atric diarrheal cases in the United States. However, they are a
leading cause of infant mortality in developing countries. Only
a few organisms are need to cause this fecal-orally transmitted
infection. Prevention of the disease is achieved by proper
sewage disposal and water chlorination, as well as personal
hygienesuch as handwashing. Antibiotics are only used in
more severe cases.
Salmonellainfections are classified as nontyphoidal or
typhoidal. Nontyphoidal infections can cause gastroenteritis,
and are usually due to contaminated food or water and can be
transmitted by animals or humans. These infections cause one
of the largest communicable bacterial diseases in the United
States. They are found in contaminated animal products such
as beef, pork, poultry, and raw chicken eggs. As a result, any
food product that uses raw eggs, such as mayonnaise, home-
made ice cream, or Caesar salad, could carry these bacteria.
The best prevention when serving these dishes is to adhere
strictly to refrigeration guidelines.
Typhoid Salmonellainfections are also found in con-
taminated food and water. Typhoid Mary was a cook in New
York from 1868 to 1914. She was typhoid carrier who con-
taminated much of the food she handled and was responsible
for hundreds of typhoid cases. Typhoid feveris characterized
by septicemia (blood poisoning), accompanied by a very high
fever and intestinal lesions. Typhoid fever is treated with the
drugs Ampicillin and Chloramphenicol.
Certain Yersiniabacteria cause one of the most notori-
ous and fatal infections known to man. Yersinia pestisis the
agent of bubonic plagueand is highly fatal without treatment.
The bubonic plague is carried by a rat flea and is thought to
have killed at least 100 million people in the sixth century as
well as 25% of the fourteenth century European population.
This plague was also known as the “black death,” because it
caused darkened hemorrhagic skin patches. The last wide-
spread epidemic of Y. pestisbegan in Hong Kong in 1892 and
spread to India and eventually San Francisco in 1900. The
bacteria can reside in squirrels, prairie dogs, mice, and other
rodents, and are mainly found (in the U.S.) in the Southwest.
Since 1960, fewer than 400 cases have resulted in only a few
deaths, due to rapid antibiotic treatment.
Two less severe Yersiniastrains are Y. pseudotuberculo-
sisand Y. enterocolotica. Y. pseudotuberculosisis transmitted
to humans by wild or domestic animals and causes a non-fatal
disease which resembles appendicitis. Y. enterocoloticacan be
transmitted from animals or humans via a fecal-oral route and
causes severe diarrhea.See alsoColony and colony formation; Enterobacterial infec-
tions; Infection and resistance; Microbial flora of the stomach
and gastrointestinal tractEEnterobacterial infectionsNTEROBACTERIAL INFECTIONS
Enterobacterial infections are caused by a group of bacteria
that dwell in the intestinal tract of humans and other warm-
blooded animals. The bacteria are all Gram-negative and rod-
shaped. As a group they are termed Enterobacteriaceae. Aprominent member of this group is Escherichia coli. Other
members are the various species in the genera Salmonella,
Shigella, Klebsiella, Enterobacter, Serratia, Proteus, and
Yersinia.
The various enterobacteria cause intestinal maladies. As
well, if they infect regions of the body other than their normal
intestinal habitat, infections can arise. Often, the bacterial
infectionarises during the course of a hospital stay. Such infec-
tions are described as being nosocomial, or hospital acquired,
infections. For example, both Klebsiella and Proteusare capa-
ble of establishing infections in the lung, ear, sinuses, and the
urinary tract if they gain entry to these niches. As another
example, both Enterobacterand Serratiacan cause an infec-
tion of the blood, particularly in people whose immune systems
are compromised as a result of therapy or other illness.
A common aspect of enterobacterial infections is the
presence of diarrhea. Indeed, the diarrhea caused by enter-
obacteria is a common problem even in countries like the
United States, which has an excellent medical infrastructure.
In the United States is has been estimated that each person in
the country experiences 1.5 episodes of diarrhea each year.
While for most of those afflicted the diarrhea is a temporary
inconvenience, those who are young, old, or whose immune
systems are malfunctioning can be killed by the infection.
Moreover, in other countries where the medical facilities are
less advanced, enterobacterial infections remain a serious
health problem.
Even in the intestinal tract, where they normally reside,
enterobacteria can cause problems. Typically, intestinal mal-
adies arise from types of the enterobacteria that are not part of
the normal flora. An example is E. coliO157:H7. While this
bacterial strain is a normal resident in the intestinal tract of
cattle, its presence in the human intestinal tract is abnormal
and problematic.
The O157:H7 strain establishes an infection by invading
host tissue. Other bacteria, including other strains of
Escherichia coli, do not invade host cells. Rather, they adhere
to the intestinal surface of the cells and can exert their destruc-
tive effect by means of toxins they elaborate. Both types of
infections can produce diarrhea. Bloody diarrhea (which is
also known as dysentery) can result when host cells are dam-
aged. Some types of Escherichia coli, Salmonella, and
Shigellaproduce dysentery.
Escherichia coliO157:H7 can also become dissemi-
nated in the blood and cause destruction of red blood cells and
impaired or complete loss of function of the kidneys. This
debilitating and even life-threatening infection is known as
hemolytic-uremic syndrome.
Another intestinal upset that occurs in prematurely born
infants is called necrotizing enterocolitis. Likely the result of
a bacterial (or perhaps a viral) infection, the cells lining the
bowel is killed. In any person such an infection is serious. But
in a prematurely borne infant, whose immune systemis not
able to deal with an infection, necrotizing enterocolitis can be
lethal. The enterobacteria that have been associated with the
disease are Salmonella, Escherichia coli, Klebsiella, and
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