Escherichia coli

E. Coli notes by Joseph(2nd year) med student

1. Escherichia Coli J.JOSEPH SAMRAJ U21MB345 (89)

2. Objectives Introduction Etiology Virulence factors Properties of enterotoxins of E. coli Clinical manifestation Laboratory diagnosis Treatment

3. Introduction Escherichia coli (E. coli) is a Gram-negative, facultative anaerobic, rod-shaped bacterium that is commonly found in the lower intestine of warm-blooded organisms. However, some strains of E. coli can cause disease, when it enters other system. These pathogenic strains can be found in contaminated food, water, or soil.

4. Etiology Escherichia coli is the most important species encountered as a human pathogen. It is also the most common aerobe to be harbored in the gut of humans and animals. After being excreted in feces, E. coli remains viable only for some days in the environment. This means that detection of E. coli, especially a variant called thermotolerant E. coli (which survives at 44°C), can be used as an indicator of recent contamination of drinking water with h uman or animal feces. Other species of E. coli are less important as human pathogens. These include E. fergusonii E. hermannii E. vulneris…. which are rarely isolated from clinical specimens.

5. Virulence factors Virulence factors of E. coli is grouped into surface antigens & toxins SURFACE ANTIGENS Somatic or O Antigen: Present on lipo-polysaccharide (LPS) antigen. Major surface antigen inducing antibody formation. Flagellar or H Antigen: Responsible for bacterial motility and virulence. Capsular or K Antigen: Polysaccharide capsular antigen on the envelope. Expressed by strains causing neonatal meningitis, pyelonephritis, and septicemia. Fimbrial Antigen (Pilus): Organ of adhesion, aiding in attachment and colonization. Various types include CFA, Mannose resistant fimbriae, and P fimbriae.

6. Toxins Enterotoxins : Produced by diarrheagenic E. coli strains. Three types: heat-labile toxin, heat-stable toxin, and verocytotoxin. Cytotoxic Necrotizing Factor 1 (CNF1) and Secreted Autotransporter Toxin (SAT): Cytotoxic to bladder and kidney cells. Act as virulence factors for urinary tract infections (UTIs).

7. Properties of enterotoxins of E. Coli Type : There are three main types of enterotoxins produced by E. coli: heat-labile (LT), heat-stable (ST) and verocytotoxin (shiga toxin) Mode of action: Heat-labile enterotoxin (LT): LT is a large protein that is encoded by a bacteriophage. LT is a potent toxin, and can cause diarrhea within hours of ingestion. Heat-stable enterotoxin (ST): ST is a smaller protein that is encoded by the bacterium's chromosome. ST toxins are less potent than LT, and can take several days to cause diarrhea. Verocytotoxin works by inhibiting protein synthesis in cells. This prevents the cell from making new proteins, which eventually leads to cell death.

8. Clinical manifestation Urinary tract infection (UTI): E. coli is the most common cause of UTI, accounting for 70-75% of all cases. Diarrhea: E. coli can cause six different types of diarrhea, including: Enteropathogenic E. coli (EPEC) Enterotoxigenic E. coli (ETEC) Enteroinvasive E. coli (EIEC) Enterohemorrhagic E. coli (EHEC) Enteroaggregative E. coli (EAEC) Diffusely adherent E. coli (DAEC) Other infections: E. coli can also cause a variety of other infections, including: Abdominal infections, such as primary bacterial peritonitis and secondary bacterial peritonitis Pneumonia Meningitis Wound and soft tissue infections Bacterial prostatitis

9. Laboratory diagnosis Sample collection: The sample to be collected depends on the site of infection. For example, urine, stool, pus, wound swab, blood, or cerebrospinal fluid (CSF) may be collected. Direct smear: A Gram stain of the sample is performed to visualize the bacteria. E. coli is a gram-negative rod. Pus cells may also be seen in the smear. Culture: The sample is cultured on blood agar and MacConkey agar. On blood agar, E. coli colonies appear gray and moist. On MacConkey agar, E. coli colonies appear flat and pink. Culture smear and motility: A Gram stain of the culture is performed to confirm the identification of E. coli. E. coli is a motile gram-negative rod. Antimicrobial susceptibility testing: Antimicrobial susceptibility testing is performed to determine which antibiotics are effective against E. coli.

10. Treatment Treatment for hospital-acquired multidrug-resistant E. coli (MDR E. coli) infections is based on the antimicrobial susceptibility test report. If the E. coli is susceptible to aminocillins, third-generation cephalosporins, quinolones, or cotrimoxazole, then these agents may be preferred. Carbapenems, amikacin, or β-lactam/β-lactamase inhibitor combinations (BL/BLIS) are usually the agent of choice for hospital-acquired MDR E. coli infections. Polymyxins, fosfomycin, or tigecycline are the next line antimicrobials for carbapenem-resistant isolates. In healthcare facilities with high prevalence of MDR E. coli, empirical treatment should be started with higher spectrum antimicrobial such as carbapenem . Reference: Apurba S Sastry, Sandhya Bhat Essential of Medical Microbiology. 4th ed

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12. Enteropathogenic E. coli (EPEC) Causes intestinal infections and is known for attaching to the intestinal lining, leading to diarrhea, especially in infants and young children. Enterotoxigenic E. coli (ETEC) Produces toxins that cause traveler's diarrhea and other gastrointestinal illnesses, often associated with contaminated food and water. Enteroinvasive E. coli (EIEC) Invades the intestinal lining, causing inflammation and symptoms similar to those of Shigella, including dysentery and fever. Enterohemorrhagic E. coli (EHEC) Produces toxins that can lead to severe foodborne illnesses, including bloody diarrhea and, in some cases, kidney failure (hemolytic uremic syndrome). Enteroaggregative E. coli (EAEC) Forms clumps on the intestinal lining, leading to persistent diarrhea, especially in young children and immunocompromised individuals. Diffusely adherent E. coli (DAEC) Causes diarrhea and adheres to the intestinal lining diffusely, without forming clumps.