Module 9: Urine Culture and Sensitivity

Module 9.6: Let’s Practice!

Practice example

You have isolated E. coli from the urine of a dog that has had multiple UTIs and been refractory to treatment. You decide to run antibiotic susceptibility testing on the animal.

The following is an image of the ZOI from your Kirby Bauer Disc Diffusion and the interpretation table for the various drugs.


TMS drug has a ZOI of 0 mm (no clear zone around disk). Amox/Clav drug has ZOI of 20 mm. Ampicillin drug has ZOI of 12 mm.
Zones of inhibition from Kirby Bauer Disc Diffusion
Table 9.1: Reference intervals for several drugs and bacteria

Size of Zone of Inhibition (ZOI in mm)


Resistant (R)
Intermediate (I)
Sensitive (S)
     Staphylococcus spp. ≤10 11-15 ≥16
     Enterobacteriaceae* ≤10 11-15 ≥16
     Haemophilus influenzae ≤10 11-15 ≥16
     Streptococcus pneumoniae ≤15 16-19 ≥19
Amoxicillin/Clavulanic  acid
     Staphylococcus spp. ≤19 ≥20
     Other organisms ≤13   14-17 ≥18
≤15 16-20 ≥21
≤14 15-16 ≥17
     Staphylococcus sp. ≤28 ≥29
     Enterobacteriaceae ≤13 14-16 ≥17
     Streptococcus (not S. pneumoniae) ≤18 19-25 ≥26
≤13 14-20 ≥21

*Remember E. coli is in the Family Enterobacteriaceae*

Knowledge check

Key Takeaways

  • Cystocentesis is the preferred collection method for culture when indicated
  • The urinary bladder is not sterile and has its own and unique microbiome
  • Antibiotic resistance and sensitivity profiles may change over time with continued antibiotic use
  • The ISCAID guidelines are the gold stand for UTI management and treatment recommendations in veterinary medicine
You have now reached the end of Module 9. If you are enrolled in CVM 6925, please go to the Canvas page and take the quiz: “Module 9: Urine C&S quiz.” There is an assignment that accompanies the in-person laboratory for this module.


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