[Discrepancy in the disk diffusion susceptibility test of Pseudomonas aeruginosa strains isolated from cystic fibrosis patients after anaerobic preincubation and its potential clinical relevance].

Introduction: In cystic fibrosis, the Pseudomonas aeruginosa cells grow inside the thick mucus layer. In spite of being an obligate aerobe, P. aeruginosa is able to grow in a limited oxygen environment. Bacterial cells could be suddenly exposed to high oxygen levels due to the movements of the mucus mass. The aim of study was to determine the impact of a previous anaerobic incubation on the antimicrobial susceptibility of P. aeruginosa strains isolated from patients with cystic fibrosis.

Materials And Methods: Four P. aeruginosa strains were used in this study (ATCC 23389 and 3 clinical isolates). The disk diffusion method was used to determine the antimicrobial susceptibility.

Results: The anaerobic pre-incubation produced changes on the susceptibility in all studied strains. All susceptible strains after an aerobic incubation remained susceptible after an anaerobic incubation except one clinical strain, which became resistant to betalactams. The response was strain-dependent and the most significant increase in susceptibility was observed in two of the three clinical isolates when ciprofloxacin was used.

Conclusions: The antimicrobial susceptibility of P. aeruginosa strains varies after their exposure to anaerobic conditions. Treatments promoting mucus fluidization could contribute to increase the antimicrobial efficacy.