Escherichia
Escherichia refers to a genus of gram-negative, facultative anaerobic bacteria, primarily known for the species Escherichia coli (E. coli). These bacteria are naturally found in the intestines of warm-blooded animals, such as humans and cattle, as well as in various environmental settings including soil and water. While many strains of E. coli are harmless and play a role in gut health, some can cause significant infections ranging from mild gastrointestinal issues to severe conditions like hemolytic-uremic syndrome, particularly in vulnerable populations such as children.
There are several pathogenic strains of E. coli, each linked to specific illnesses; for example, enterotoxigenic E. coli (ETEC) is a common cause of traveler's diarrhea, while uropathogenic E. coli (UPEC) is a major contributor to urinary tract infections. The genus also includes emerging pathogens like E. fergusonii, which has been associated with various infections. Due to their importance in clinical microbiology, Escherichia species are widely studied in laboratory settings, contributing to advancements in biotechnology, such as recombinant DNA technology.
However, antibiotic resistance poses a challenge for treating infections caused by Escherichia, necessitating ongoing research and adaptation of treatment protocols. Overall, Escherichia represents a complex group of bacteria that are significant in both health and disease, highlighting the need for awareness regarding their potential impact.
Escherichia
- TRANSMISSION ROUTE: Direct contact, ingestion
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 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 sorbitol-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 (strain 0157:17), which produces a Shiga-toxin. EHEC is extremely virulent and can cause hemolytic-uremic syndrome in children and post-diarrheal thrombotic purpura in older patients. Infantile diarrhea in developing countries can be caused by primarily three main species of E. coli: enteropathogenic E. coli (EPEC), enterotoxigenic E. coli (ETEC), 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 a large percent of all urinary tract infections. Women are 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 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. hermannii acts as an infectious agent in wounds, sputum, and stool. E. hermannii 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. hermannii 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 it 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 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 ETEC are usually treated with trimethoprim-sulfamethoxazole or fluoroquinolones. Urinary tract infections are treated with a three-day course of trimethoprim-sulfamethoxazole or a fluoroquinolone. Due to the rise in antibiotic resistance, nitrofurantoin, fosfomycin, or pivmecillinam have emerged as first-line options. 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. hermannii and E. vulneris are more resistant to antibiotics than the majority of community acquired E. coli infections.
Bibliography
Abbott, S. L., et al. "Biochemical Properties of Newly Described Escherichia Species Escherichia albertii." Journal of Clinical Microbiology, vol. 41, 2003, pp. 4852–854.
Ash, Caroline. "The Benefits of Escherichia coli." Science, vol. 350, no. 6260, 2015, pp. 524–26.
Donnenberg, Michael S., editor. Escherichia coli: Pathotypes and Principles of Pathogenesis. 2nd ed., Academic, 2013.
"E. Coli." World Health Organization (WHO), 7 Feb. 2018, www.who.int/news-room/fact-sheets/detail/e-coli. Accessed 10 Nov. 2024.
"E. Coli Infection." Cleveland Clinic, 22 Nov. 2022, my.clevelandclinic.org/health/diseases/16638-e-coli-infection. Accessed 10 Nov. 2024.
Gardiner, Bradley J., et al. "Nitrofurantoin and Fosfomycin for Resistant Urinary Tract Infections: Old Drugs for Emerging Problems." Australian Prescriber, vol. 42, no. 1, 2019, p. 14, doi.org/10.18773/austprescr.2019.002. Accessed 10 Nov. 2024.
Pien, F. D., et al. "Colonization of Human Wounds by Escherichia vulneris and Escherichia hermannii." Journal of Clinical Microbiology, vol. 22, 1985, pp. 283–85.
Savini, V., et al. "Multi-drug Resistant Escherichia fergusonii: A Case of Acute Cystitis." Journal of Clinical Microbiology, vol. 46, 2008, pp. 1551-1552.
Snyder, Larry, and Wendy Champness. Molecular Genetics of Bacteria. 4th ed., ASM, 2013.
Meuller, Matthew, and Christopher R. Tainter. "Escherichia Coli Infection - StatPearls." NCBI, 13 July 2023, www.ncbi.nlm.nih.gov/books/NBK564298. Accessed 10 Nov. 2024.
Thielman, N. M., et al. "Acute Infectious Diarrhea." New England Journal of Medicine, vol. 350, 2004, pp. 38–47.
Zimmer, C. Microcosm: "E. coli" and the New Science of Life. Pantheon, 2008.