Escherichia coli

Escherichia coli (E. coli) are enteric bacteria classified in the family Enterobacteriaceae, more recently named Enterobacterales. It is a commensal normally found in the vertebrate gut and is involved in various intestinal and extra-intestinal infections as an opportunistic pathogen. E. coli infections cause approximately 265,000 illnesses and about 100 deaths in the United States each year. Approximately 40% of these infections are caused by the strain E. coli O157:H7, a strain that is part of the shiga toxin-producing group of E. coli bacteria (STEC). The other 60% of E. coli cases are caused by non-0157:H7 shiga toxin-producing E. coli (STEC). Normally, a harmless commensal, but it can acquire a mixture of comprehensive mobile genetic elements encoding virulence factors, ultimately becoming a human pathogen capable of causing a broad spectrum of diseases. Salmonella, Shigella, Klebsiella and Yersinia are a few other examples of pathogenic forms who belong to the same family. E. coli are motile facultative anaerobic Gram-negative rods. In addition, they are flagellated and capable of fermenting lactose and glucose. Within hours to days after birth, these bacteria colonize the gastrointestinal tract of most warm-blooded animals. Under normal conditions, a symbiotic relationship occurs because the enteric flora provides a source of vitamin K (menaquinones) and B-complex vitamins. However, factors like infection or chemotherapy may tilt the habitat's balance and favor growth of more virulent species or make the commensal dysfunctional (Robbens et al., 2014). Most E. coli strains are avirulent. However, some may cause urinary tract infections (UTIs), meningitis in neonates, and intestinal diseases known as gastroenteritis. Probiotic strains of E. coli exist as well, including the strain Nissle 1917 from fecal origin used for disease prophylaxis. Different genetic determinants differentiate between avirulent and virulent strains, but some serotypes cause more diseases than others (Robbens et al., 2014). Conversely, E. coli is used constructively in environmental monitoring and applications in toxicology. Genetic studies of E. coli since the 1950s has led to a broadened array of information, contributing to applications in molecular biology, molecular genetics, and genomics in general. Toxicological response profiles (TRPs) of E. coli have been used to assess the risks of chemical compounds. Also, E. coli have been used as bioreporters in ecotoxicology, as an early warning system. E. coli have several virulence factors and toxins which contribute to their pathogenicity. These include organ toxicities: mainly nephrotoxicity, gastrointestinal toxicity, and hepatotoxicity (Robbens et al., 2014). Multidrug resistance in E. coli has become a serious issue that is increasingly observed in human veterinary medicine Worldwide. Over the last few decades, E. coli has a shown great capacity to gather resistance genes via horizontal gene transfer although it is susceptible to most clinically relevant antimicrobial drugs. Currently, this type of situations are combated by combination drug regimens.