Resumo

Background: Pseudomonas aeruginosa (Pa) is associated with a range of nosocomial infections and is noted for its intrinsic and acquired antibiotic resistance. The aim of this study was to characterize isolates of carbapenem- non-susceptible Pa co-infecting the liquor of a pediatric patient with acute lymphoblastic leukemia (ALL). Methods: Homogeneus Pa colonies were isolated from liquor of a child with ALL. Surprisingly, a serial dilution colony counts method, from homogeneous Pa, revealed the presence of heterogeneous colonies, which were characterized by antibiogram, MBL production [Etest® strips (AB Biodisk), imipenem/EDTA combined disc (CD) assay], and PCR screening to blaSMP-1, blaIMP-like, blaVIM-like MBL, and blaOXA-like ESBL genes. Colonies were genotyped by ERIC-PCR. Results: Two morfologically distinct bacterial colonies (i.e., small and big colony) were isolated. These two genotipically distinct colonies, showed different ERIC-PCR band patterns, and different antibiotic resistance profile. Big colonies exhibited resistance to ceftazidime (CAZ) and imipenem (IPM, MIC = 256 µg/ml) and susceptibility to aztreonam (ATM), while small colonies exhibited an intermediate resistance profile to IPM (MIC = 8 µg/ml) and resistance to CAZ and ATM. MBL production by big colonies was confirmed by both CD and Etest MBL strip, which was due to the prescence of the blaSMP-1 gene. Otherwise, no MBL encoding genes were observed in small colonies, whereas resistance to ATM was due to the presence of the blaOXA-2-like gene, which was not found in the big Pa colony. Conclusions: Two different strains were isolated from de same patient and presented distinct antibiotic resistance profile and beta-lactamase genotypes. Both strains contributed to therapeutic failure and patient death. Acknowledgments: We would like to thank to Cefar Diagnóstica Ltda. for kindly supplying antibiotic disks