Escherichia coli (E. coli)

 

1. What is E. coli?


Cultural Characteristics of E. coli

Escherichia coli (E. coli) is a Gram-negative, rod-shaped bacterium commonly found in the intestines of humans and warm-blooded animals. Most strains are harmless and part of the normal gut flora, but some can cause serious food poisoning and infections12.

2. Transmission of E. coli

E. coli is typically transmitted through the fecal-oral route. This can occur by consuming contaminated food or water, contact with infected animals or their environment, and person-to-person contact, especially in settings with poor hygiene34.

3. Epidemiology of E. coli

E. coli infections are common worldwide. In high-income countries, Shiga toxin-producing E. coli (STEC) is a significant cause of foodborne illness. In low-income countries, other types like enterotoxigenic E. coli (ETEC) are more prevalent, often causing traveler’s diarrhea56.

4. Pathology, Disease, and Infection Caused by E. coli

E. coli can cause a variety of infections, including:

  • Gastroenteritis: Diarrhea, abdominal cramps, and vomiting.
  • Urinary Tract Infections (UTIs): Frequent urination, pain during urination.
  • Neonatal Meningitis: Inflammation of the membranes covering the brain and spinal cord in newborns.
  • Sepsis: A life-threatening response to infection.
  • Pneumonia: Lung infection, though rare789.

5. Laboratory Tests for E. coli

6. Specimen Types for E. coli

Specimens for E. coli testing can include: urine, feces, blood, pus, cerebrospinal fluid (especially in infants), and other body fluids depending on the site of infection1415.

7. Site of Sample Collection for E. coli

Samples are typically collected from areas such as the urinary tract (urine), gastrointestinal tract (stool), blood, and other infected sites. Proper aseptic techniques are crucial to avoid contamination1617.

8. Colony Morphology of E. coli




The World Health Organization (WHO) recommends certain antibiotics as first-line treatments for E. coli infections, though treatment depends on the specific strain and infection type (e.g., urinary tract infection, bloodstream infection). Here are the general guidelines:

  1. Uncomplicated Urinary Tract Infections (UTIs): Nitrofurantoin, fosfomycin, and trimethoprim-sulfamethoxazole are preferred as first-line treatments for UTIs caused by E. coli.
  2. Complicated UTIs and Pyelonephritis: Ciprofloxacin or levofloxacin may be used, but local resistance patterns must be checked, as resistance to fluoroquinolones is rising.
  3. Bloodstream Infections and Sepsis: Carbapenems, such as meropenem or imipenem, are recommended for severe or resistant infections, especially for extended-spectrum beta-lactamase (ESBL) producing E. coli.

However, local resistance patterns and antimicrobial susceptibility tests (AST) are critical in guiding appropriate therapy​(

World Health Organization (WHO)
World Health Organization (WHO)

For more severe infections or those caused by antibiotic-resistant strains, other antibiotics such as carbapenems or cephalosporins may be used12.

It’s important to consult a healthcare provider for an accurate diagnosis and appropriate treatment plan tailored to the specific type of E. coli infection. Do you have any specific symptoms or concerns you’d like to discuss?

Learn more

1idsociety.org2sso.uptodate.com3publications.aap.org4link.springer.com

10. Antimicrobial Susceptibility Testing (AST) of E. coli


Antimicrobial Susceptibility Testing (AST) of Escherichia coli (E. coli) is an essential laboratory procedure used to determine the sensitivity or resistance of the bacterium to various antibiotics. This helps guide appropriate treatment options, particularly in infections such as urinary tract infections (UTIs), sepsis, and gastrointestinal infections caused by E. coli. Here's an overview of the AST process:

Methods of AST for E. coli:

  1. Disk Diffusion Method (Kirby-Bauer Test):

    • A widely used, simple, and cost-effective method.
    • Involves placing antibiotic-impregnated paper disks onto an agar plate inoculated with E. coli.
    • After incubation, the zones of inhibition around the disks are measured to determine susceptibility.
    • Results are interpreted according to the Clinical and Laboratory Standards Institute (CLSI) or the European Committee on Antimicrobial Susceptibility Testing (EUCAST) guidelines.
    • Common antibiotics tested for E. coli include:
      • Ampicillin
      • Ciprofloxacin
      • Ceftriaxone
      • Gentamicin
      • Meropenem (for carbapenemase-producing E. coli)

  2. Broth Dilution Method:

    • Can be performed as microdilution or macrodilution.
    • Serial dilutions of antibiotics are prepared in broth, and a standardized number of E. coli bacteria are added.
    • The minimum inhibitory concentration (MIC) is the lowest concentration of an antibiotic that prevents visible growth.
    • MIC values guide treatment decisions, with lower MIC values indicating susceptibility and higher values suggesting resistance.

  3. E-test (Epsilometer Test):

    • A strip containing a gradient of antibiotic concentrations is placed on an agar plate inoculated with E. coli.
    • The MIC is read where the bacterial growth intersects with the strip, making it a hybrid between disk diffusion and broth dilution methods.
    • It's commonly used for difficult-to-treat pathogens and critical antibiotics, such as carbapenems and colistin.

  4. Automated Systems:

    • Laboratories often use automated systems such as VITEK 2, MicroScan, or Phoenix for rapid AST results.
    • These systems measure growth and resistance patterns of bacteria like E. coli in the presence of multiple antibiotics simultaneously.
    • Automated systems reduce human error and increase throughput, though they may be more expensive.

  5. Genotypic Testing:

    • Polymerase Chain Reaction (PCR) and whole-genome sequencing are used to detect specific resistance genes, such as:
      • blaTEM, blaSHV, blaCTX-M (for extended-spectrum beta-lactamases, or ESBLs)
      • mcr-1 (for colistin resistance)
    • These molecular techniques are particularly important in epidemiological studies and outbreak investigations.

Common Resistance Mechanisms in E. coli:

  • Beta-lactamase production: Enzymes like ESBLs and carbapenemases (e.g., NDM-1, KPC) that hydrolyze beta-lactam antibiotics.
  • Fluoroquinolone resistance: Mutations in the gyrA and parC genes, leading to reduced susceptibility to quinolones like ciprofloxacin.
  • Aminoglycoside resistance: Enzymatic modification or efflux of drugs like gentamicin.
  • Colistin resistance: Primarily plasmid-mediated by the mcr-1 gene.

Clinical Interpretation:

  • Results are typically reported as Susceptible (S), Intermediate (I), or Resistant (R) based on breakpoints provided by CLSI or EUCAST.
  • Treatment decisions should consider the local antibiotic resistance patterns and pharmacokinetics/pharmacodynamics of the chosen drug.

For more information on interpreting AST results and guidelines, you can refer to resources like CLSI and EUCAST.

1link.springer.com2mayocliniclabs.com3

clsi.org4clsi.org

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