In169, A New Class 1 Integron that Encoded bla_IMP-18 in a Multidrug-Resistant Pseudomonas aeruginosa Isolate from Mexico

Background and Aims

Carbapenem resistance in Pseudomonas aeruginosa may be due to the presence of metallo-β-lactamases (MβL). The genes that encode these enzymes can be located in association with aminoglycoside-modifying enzymes on class 1 integrons. This study describes the bla_IMP-18 class 1 integron array (In169) from a carbapenem-resistant P. aeruginosa clinical isolate obtained at the Centro Medico Nacional La Raza (CMNR) in Mexico City and compares it to other bla_IMP-type producers.

Methods

Twenty six multiresistant P. aeruginosa clinical isolates were recovered between June and December 2004 and tested by MicroScan and CLSI agar dilution methods. The MβL production was screened by a disk approximation test and MβL Etest strips, whereas MβL genes and integrons were detected using PCR primers. DNA sequence analysis was carried out by BLAST, and epidemiological typing was performed by pulsed-field gel electrophoresis (PFGE). A Southern hybridization analysis was performed with a bla_IMP specific DNA probe.

Results

Nine of 26 P. aeruginosa isolates were imipenem-resistant with unique PFGE patterns (no clonal relation), and only one strain (5106) was positive for MβL production, corresponding to the IMP-type. The class 1 integron encoding the MβL was characterized: it contained the IMP-18, two copies of aadA2 and OXA-2 genes, corresponding to a new class 1 integron array, denoted In169. P. aeruginosa isolate 5106 is genetically related to bla_IMP-18 positive P. aeruginosa isolate from a distant hospital (Hospital Infantil de Morelia).

Conclusion

This report is the first to describe the bla_IMP-18 in two genetically related isolates from two different institutions.

Key Words: P. aeruginosa, Carbapenem resistance, Classs 1 integron, Metallo-β-lactamase, IMP-18