Introduciton
Bacterial infections are the most frequent human diseases throughout life. In particular, E. coli is a type of gram-negative rod-shaped bacteria that is widespread in the lower intestines of warm-blooded animals. Escherichia coli represents the most abundant aerobic commensals in the colon. Most strains of E. coli are harmless, but serotype O157: H7 can cause severe food poisoning in humans and animals.
Description of E. coli
E. coli is a gram-negative bacterium, facultative anaerobic; it does not form endospores. The cells are rod-shaped, with slightly rounded ends, 0.4-0.8 × 1-3 μm in size, and the cell volume is about 0.6-0.7 μm3 (Frankel & Ron, 2018). E. coli can live on different substrates; under anaerobic conditions, it forms lactate, succinate, ethanol, acetate, and carbon dioxide as a waste product. This often produces molecular hydrogen, which interferes with the formation of the above metabolites; therefore, E. coli often coexists with microorganisms that consume hydrogen, such as methanogens or bacteria that reduce sulfate (Sperandio & Bonach, 2015). E. coli cells have pili (fimbria) and are motile due to the peritrichial flagella.
Escherichia coli is a classical object of molecular genetics; 87.8% of the genome is occupied by real and probable protein-coding genes, or cistrons (Sperandio & Bonach, 2015). This type of bacteria can be examined using a light microscope or atomic force microscopy. According to the Gram method, Escherichias are colored pink (gram-negative); the smears under the microscope are randomly arranged.
Virulence Factors
ExPEC E. coli are characterized by a wide range of virulence-associated factors, in particular, toxins, adhesins, iron acquisition factors, polysaccharide capsules, lipopolysaccharides, and invasins, plasmids, as well as other genetic elements of mobile nature. Diseases caused by E. coli are called coli infections, or Escherichiosis (Rojas-Lopez et al., 2017). Intestinal infections, occupying a leading position in the structure of Escherichiosis, are associated with four different groups: E. coli-enterotoxigenic (ETCP), enteroinvasive (EICP), enteropathogenic (EPEC), and enterohemorrhagic (EHEC).
Immunity
The key factor in the mechanism of innate immunity of the mucous membranes is TLR4, which recognizes pathogens, promotes the induction of the production of cytokines, interferons, antimicrobial peptides. The microbiocidal molecules of the mucous membrane – antimicrobial peptides, defensins, cathelicidins, lactoferrin – are also mediators of the innate immune response. Uropathogenic Escherichia coli triggers an inflammatory response via virulence factors that mediate adhesion to the urothelium.
Primary ligand-binding receptors, represented by chemokine receptors, are involved in the recognition of pathogen-associated molecular patterns (PAMP). The second receptors, represented by TLR-4, provide a transmembrane signal (Rojas-Lopez et al., 2017). This is followed by the release of mediators of inflammation, immunity, differentiation of cytokine cells, recruitment of neutrophils from the vessels into the blood, and their penetration into the bladder cavity (Rojas-Lopez et al., 2017). As a result, bacteria are cleared and urine cleansed; this is the scheme of an acute inflammatory process in the bladder mucosa. According to the researchers, the impaired immune response is possible at any level and may be associated with insufficient expression of defensins, TLRs, as well as with an imbalance in the cytokine profile (Torres, 2016). Usually, the disease begins with abdominal pain, diarrhea, vomiting, and fever, flowing in the form of enteritis.
Infectious disease information
Escherichiosis refers to acute intestinal diseases with a fecal-oral transmission mechanism. Each of the classes of pathogenic E. coli is characterized by certain differences in the disease course, which in its symptoms may resemble cholera or dysentery. The incubation period lasts 3-6 days (usually 4-5 days). Most commonly, E. coli causes urinary tract infection, which is often an ascending infection (for example, from the perineum through the urethra). E. coli can also lead to prostatitis and pelvic inflammatory disease. As a whole, E. Coli diseases can be listed as follows (Frankel & Ron, 2018):
- Urinary tract infections (most common);
- Intestinal infection (some strains);
- Invasive infection (rare, except in newborns);
- Infections of other organs and tissues.
Epidemiology
The reservoir and source of infection is a sick person or a carrier. The most dangerous are patients with Escherichiosis caused by EPEC and EIKP, less – patients with Escherichiosis caused by ETCP, EHEC, and EACP (Frankel & Ron, 2018). The period of contagiousness of the source depends on the properties of the pathogen. With escherichiosis caused by ETCP and EHEC, the patient is contagious only in the first days of the disease, with diseases caused by EICP and EHEC, 1-2 weeks (sometimes up to 3 weeks) (Frankel & Ron, 2018). The mechanism of transmission of the pathogen is fecal-oral; transmission routes can be food, water, home (through contaminated hands, toys, etc.). The main sources of STEC outbreaks are raw or undercooked minced meat products, raw milk, and fecal-contaminated vegetables; below, the transmission mechanism is presented schematically.
Prevention
Preventive measures are reduced to the observance of the sanitary-hygienic regime and the rules of personal hygiene; no specific prophylaxis is performed. A childhood vaccine is not applied to the general population; however, the vaccine was created. The efficacy of the E. coli Escherichia coli (ETEC) vaccine developed by Swedish researchers has been confirmed in clinical trials, and now it is in the process of further trials (Erjavec, 2019). For now, to prevent infection, control measures must be followed at all stages of the food chain – from agricultural production on farms to processing and preparation of food, both in commercial enterprises and at home. On the household level, it is recommended to use chlorine-based disinfectant cleaners when cleaning plumbing fixtures and all surfaces.
Treatment
Treatment should be started empirically based on the location and severity of the infection and then modified based on antibiotic susceptibility testing. The agents cause violation of cell wall synthesis or damage to the cytoplasmic membrane. Many strains are resistant to ampicillin and tetracyclines, so other drugs must be used; these include ticarcillin, piperacillin, cephalosporins, carbapenems, fosfomycin, nitrofurantoin, aminoglycosides, trimethoprim/sulfamethoxazole (TMP/SMX), and fluoroquinolones (Frankel & Ron, 2018). Surgery may be required to debride the source of infection (to drain pus, debride necrotic lesions, or remove foreign bodies). EHEC infections of the gastrointestinal tract are not treated with antibiotics.
Critical Relevance
In addition to resistance to ampicillin and tetracycline, E. coli is becoming increasingly resistant to TMP/SMC and fluoroquinolones. Moreover, multidrug-resistant strains that produce extended-spectrum beta-lactamases (ESBLs) are often a major important cause of community-acquired (domestic) urinary tract infections and sepsis. ESBLs can hydrolyze most beta-lactams, including penicillins and broad-spectrum cephalosporins, and monobactams, but not carbapenems (imipenem, meropenem, doripenem, ertapenem); they should be used to treat E. coli infections that produce ESBLs (Frankel & Ron, 2018). Fosfomycin is active against multidrug-resistant strains and is an alternative oral drug for lower urinary tract infections.
Conclusion
Urinary tract infections are among the most common infectious diseases that occur widely in both outpatient and inpatient practice. This is one of the most pressing problems in most countries of the world. Uropathogenic strains of E. coli are able to form biofilms (microcolonies) on the mucous membrane of the bladder and inside epithelial cells. Due to the widespread prevalence of diseases caused by E. coli, the study of the characteristics of this microorganism and the dissemination of knowledge about methods of treatment and prevention are of particular importance.
References
Erjavec, M. (2019). The Universe of Escherichia coli. IntechOpen.
Frankel, G., & Ron, E. (Eds.). (2018). Escherichia coli, a versatile pathogen. Springer.
Rojas-Lopez, M., Monterio, R., Pizza, M., Desvaux, M., Rosin, R. (2017). Intestinal pathogenic Escherichia coli: Insights for vaccine development. Frontiers of Microbiology, 9, 1–14. Web.
Sperandio, V., & Bonach, C. H. (2015). Enterohemorrhagic Eecherichia coli and other shiga toxin-producing E. coli (1st ed.). ASM Press.
Torres, A. G. (Ed.). (2016). Escherichia coli in the Americas. Springer.