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Colistin susceptibility test evaluation of multiple-resistance-level Pseudomonas aeruginosa isolates generated in a

Mumina Javed1,2, Viola Ueltzhoeffer1, Maximilian Heinrich1,2

  • 1Interfaculty Institute of Microbiology and Infection Medicine Tübingen, Institute of Medical Microbiology and Hygiene, Tübingen, Germany.

The Journal of Antimicrobial Chemotherapy
|August 24, 2018
PubMed
Abstract

Insights

Generating colistin-resistant Pseudomonas aeruginosa strains in a morbidostat is effective for evaluating antimicrobial susceptibility testing (AST) methods. However, commercial AST methods showed high discrepancy rates, especially for low-level resistance, failing to meet clinical guidelines.

Area of Science:

  • Microbiology
  • Clinical Science
  • Infectious Diseases

Background:

  • Colistin is a critical last-resort antibiotic for treating Pseudomonas aeruginosa infections.
  • Accurate susceptibility testing for colistin in P. aeruginosa is challenging due to a lack of well-characterized resistant isolates.
  • Evaluating antimicrobial susceptibility testing (AST) methods requires a diverse panel of resistant strains, including those near the susceptibility breakpoint.

Purpose of the Study:

  • To generate colistin-resistant Pseudomonas aeruginosa strains using a morbidostat device for AST method evaluation.
  • To compare the performance of five commercial AST methods against the gold standard broth microdilution (BMD) method for colistin susceptibility testing.

Main Methods:

  • A morbidostat device was employed to cultivate susceptible P. aeruginosa strains, inducing a range of colistin minimum inhibitory concentrations (MICs).
  • Five commercial AST methods (MICRONAUT-S, SensiTest, Sensititre, Rapid Polymyxin Pseudomonas, Etest) were evaluated.
  • Broth microdilution (BMD) served as the gold standard for comparison.

Main Results:

  • A total of 131 P. aeruginosa isolates were tested (100 susceptible, 31 resistant).
  • The morbidostat successfully generated 31 resistant isolates with MICs ranging from 4-512 mg/L, demonstrating 100% resistance generation efficacy.
  • Sensititre achieved the highest categorical agreement (CA) at 96.9%, while Etest had the lowest at 84%. Very major discrepancy (VMD) rates exceeded the CLSI limit for all tested methods.

Conclusions:

  • The morbidostat is an efficient tool for generating colistin-resistant P. aeruginosa strains crucial for AST method validation.
  • While commercial AST methods showed high CA rates (except Etest), none met the stringent CLSI VMD rate limit of ≤1.5%.
  • The performance of AST methods was notably inferior when assessing isolates with low-level colistin resistance.

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