RESUMO
BACKGROUND: Long-term persistence of Pseudomonas aeruginosa in the lung of individuals with cystic fibrosis (CF) is associated with progressive selection of diverse genotypes and phenotypes. This bacterial adaptation leads to chronic infection and increased morbidity and mortality. The aim of this study was to establish the prevalence, clonal relatedness, antimicrobial susceptibility and virulence-associated phenotypes of P. aeruginosa isolates in a cohort of 50 Mexican children with CF-associated chronic lung infection. METHODS: Clonal relatedness of P. aeruginosa isolates was verified by pulsed-field gel electrophoresis. The antimicrobial susceptibility was determined by an automated system that performs bacterial identificación and antibiotic susceptibility testing (VITEK 2) and/or broth microdilution method. Biofilm formation was quantified with the crystal violet method; swarming motility was measured on soft agar, and susceptibility to normal human serum determined by reduction of colony formed units (CFUs). RESULTS: High prevalence of P. aeruginosa colonization among Mexican children with CF was confirmed; 20% (10/49) of clones identified showed a multidrug-resistant phenotype and 8.2% (4/49) an extensive drug resistance phenotype; 26.5% (13/49) of the isolates were resistant to colistin, 42.9% (21/49) presented a phenotype of adaptation associated with chronic infection and 79.6% (39/49) showed increased ability to survive in normal human serum. CONCLUSIONS: This cohort of children with CF reveals that colonizing P. aeruginosa strains predominantly display resistance to several first-line antibiotics, although most isolates were susceptible to meropenem and tobramycin; 42.9% of isolates showed a phenotype consistent with adaptation to chronic lung infection.