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Interpretation table
© Wellcome Genome Campus Advanced Courses and Scientific Conferences

Interpretation of the disc diffusion test.

The bacteria that have been tested are two strains of Escherichia coli. Compare your measurements against the table below to determine if the bacteria are resistant or susceptible to the antimicrobials tested.

Note: if you measured the radius, multiply it by 2

Table 1 Excerpt of EUCAST clinical breakpoint table v_10.0

  Zone diameter breakpoint (mm) Zone diameter breakpoint (mm) Zone diameter breakpoint (mm)
Disc S>= R< ATU
cip 5 25 22 22-24
cpd 10 21 21  
cn 10 17 17  

cip 5 – Ciprofloxacin 5ug

cpd 10 – Cefpodoxime 10ug

cn 10 – Gentamicin 10ug

S – Susceptible

R – Resistant

ATU Area of technical uncertainty – an area where natural variation can occur for some bacteria and antimicrobials. EUCAST recommends performing an alternative test, such as an MIC test, or to report the result as uncertain.

Gentamicin An aminoglycoside used for systemic infections in combination with another antimicrobial, or for urinary tract infections

Cefpodoxime A cephalosporin used for urinary tract infections. Resistance to cephalosporins is an indication that the bacteria is an extended-spectrum beta-lactamase (ESBL) producer, and further testing should be done to confirm. ESBLs are an important class of resistant bacteria

Ciprofloxacin A fluoroquinolone broad-spectrum antibiotic effective against many bacteria and types of infections

What were your results for the two isolates tested?

© Wellcome Genome Campus Advanced Courses and Scientific Conferences
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Bacterial Genomes: Antimicrobial Resistance in Bacterial Pathogens

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