Ear Swab: Pseudomonas aeruginosa  – Shipped 15 February 2016


A simulated ear swab sample collected from a 58 year old male diabetic patient with a sore ear was sent to category A and B laboratories.

Participants were expected to isolate and identify Pseudomonas aeruginosa and perform susceptibility testing.


  1. Pseudomonas aeruginosa is the most frequent etiologic agent of acute diffuse otitis externa (swimmer’s ear) and malignant (invasive) otitis externa. Acute diffuse otitis externa normally responds to topical antimicrobials in the form of otic drops, which may be delivered in combination with corticosteroid drops, while invasive otitis externa generally requires a prolonged course of systemic antimicrobials and therapy should be directed by antimicrobial susceptibility testing.
  2. The Clinical and Laboratory Standards Institute (CLSI) M100-S26 (2016) Performance Standard for Antimicrobial Susceptibility Testing currently recommends routine testing and reporting of ceftazidime, piperacillin-tazobactam, gentamicin, and tobramycin for all clinically significant isolates of Pseudomonas aeruginosa as well as primary testing and selective reporting of a fluoroquinolone (ciprofloxacin, levofloxacin), a carbapenem (doripenem, imipenem, meropenem), amikacin, cefepime, aztreonam, and ceftolozane-tazobactam.
  3. Manufacturers of automated susceptibility testing platforms are not able to adapt CLSI breakpoints changes immediately, therefore, the onus is on laboratories to keep their antimicrobial susceptibility testing interpretative criteria up to date with current standards and adjust their reporting accordingly. A new CLSI Performance Standard for Antimicrobial Susceptibility Testing is published every year and needs to be acquired and reviewed by laboratories.

Full critique (PDF)

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