What are Escherichia?

Definition

Escherichia are gram-negative, facultative anaerobic
bacteria that ferment lactose and other sugars.
Escherichia is found in humans and animals, and some
Escherichia species can cause mild to serious infections.

Natural Habitat and Features

Escherichia is found in the intestines of warm-blooded animals, particularly cattle and humans. They are also found in soil, sand, and water.
E. coli
has been found in some marine animals. Different species are identified by their similarities to
Shigella
,
Salmonella
, and
Klebsiella
(O), motility by flagella (H), capsular antigens (K), and enterotoxin strains (CFAII, CRAIII). They are also differentiated by the sugars they do or do not ferment, by whether or not they produce toxins, and by how their disease mechanisms work to cause illness. Deoxyribonucleic acid (DNA) sequencing of E. coli has been extensive, and several subtypes of the species have been identified.

Microscopically, Escherichia appear as straight rods either nonmotile or motile with flagella. E. coli can be grown in a nutrient-rich Luria or Lennox broth at a temperature of 37° Fahrenheit (2.8° Celsius) or higher for twenty-four hours. A cloudy, fecal-smelling mix will result, which can be plated on clear agar; this will produce visible white colonies. Clinically, tests for Escherichia infections are cultured on a sorbital-MacConkey medium with a typing antiserum to check for the appearance of gram-negative rods. DNA analysis using the polymerase chain reaction method is also used to differentiate Escherichia species.

Pathogenicity and Clinical Significance

There are six main strains of E. coli, for example, that
attack the human gut, each strain with distinct qualities. Enterohemorrhagic
E. coli (EHEC) includes the most lethal strain of E.
coli (that is, strain 0157:17), which produces a Shiga-toxin. EHEC is
extremely virulent and can cause hemolytic-uremic syndrome in children and
postdiarrheal thrombotic purpura in the elderly. Infantile diarrhea in developing
countries can be caused by, primarily, three main species of E.
coli: enteropathogenic E. coli (EPEC), enterotogenic
E. coli (ETAC), and enteroaggregative E. coli
(EAEC). ETEC is a major cause of travelers’ diarrhea. Enteroinvasive
E. coli (EIEC), also seen in developing countries, causes a
type of mucus-filled diarrhea called bacillary dysentery.

Uropathogenic E. coli (UPEC) causes 90 percent of all
urinary tract
infections. Women are fourteen times more likely than men to
get a UPEC infection. Gram-negative neonatal sepsis or meningitis caused by
cross-contamination of maternal genital E. coli during birth can
develop in neonates.

E. albertii has five strains and has been identified as a cause
of diarrhea in Bangladeshi children. E. albertii is believed to
act like the attaching and effacing gene that is typical of enterpathogenic
E. coli.
E. fergusonii is an emerging pathogen and little is known about
its natural habitat. It has been found in wound infections, urinary tract
infections, diarrhea, and pleural infections. Naturally found in water and soil,
E. hermanii acts as an infectious agent in wounds, sputum, and
stool. E. hermanii is never the primary cause of an infection;
for example, in an infected wound, a culture may show five bacteria present, two
of which might be E. hermanii and C. botulinum.
Treatment will focus on the virulent C. botulinum because the
rest of the bacteria are secondary. Another species of
Escherichia, E. vulneris
(vulneris is Latin for “to wound”) is also found in wounds,
often with other bacteria present.

In 1988, Richard Lenski began long-term evolution experiments using E. coli by directly observing a major evolutionary shift of the organism in the laboratory. He observed one population of E. coli unexpectedly evolve the ability to aerobically metabolize citrate, a capacity that is extremely rare in E. coli. The inability to grow aerobically is normally used as a diagnostic criterion to differentiate E. coli from other, closely related bacteria such as Salmonella.

E. coli has continued to have significant clinical relevance in
the laboratory for biochemists and geneticists and is frequently used as a model
organism in microbiology studies. The ability to use plasmids and restriction
enzymes to create recombinant DNA was instrumental in creating the field of
biotechnology. E. coli is considered to be
one of the most versatile organisms, enabling researchers to facilitate these
procedures. Researchers manipulate the genes of E. coli to change
its nature, leading to the creation of biotech products such as human insulin and
vaccines. Cultivated strains of E. coli such as E.
coli K12, which is used in the laboratory, are no longer pathogenic.

Drug Susceptibility

Antibiotic
resistance is a major issue for all species of
Escherichia; however some infections are still susceptible to
certain kinds of antibiotics. EIEC and ETAC are usually treated with
trimethoprim-sultramethoxazole or flouroquinolones. Urinary tract infections are
treated with a three-day course of trimethoprim-sulfamethoxazole or a
fluoroquinoline. Treatment for neonatal meningitis and sepsis is antibiotic
therapy with ampicillin and an aminoglycoside, or with an expanded-spectrum
cephalosporin.

E. fergusononii is a multi-drug-resistant pathogen. Both E. hermanii and E. vulneris are more resistant to antibiotics than the majority of community acquired E. coli infections.

Bibliography

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Ash, Caroline. "The Benefits of Escherichia coli." Science 350.6260 (2015): 524–26. Print.

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Donnenberg, Michael S., ed. Escherichia coli: Pathotypes and Principles of Pathogenesis. 2nd ed. Boston: Academic, 2013. Print.

Pien, F. D., et al. “Colonization of Human Wounds by Escherichia vulneris and Escherichia hermannii.” Journal of Clinical Microbiology 22 (1985): 283–85. Print.

Savini, V., et al. “Multi-drug Resistant Escherichia fergusonii: A Case of Acute Cystitis.” Journal of Clinical Microbiology 46 (2008): 1551-1552.

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