PURPOSE

infections in hospitals constitute an important problem due to the increasing multidrug resistance (MDR) and carbapenems resistance. The knowledge of resistance mechanisms in strains is an important issue for an adequate antimicrobial treatment. Therefore, the objective was to investigate other antimicrobial resistance mechanisms in MDR strains carrying , make a partial plasmids characterization, and determine if modifications in gene affect the expression of the OprD protein.

METHODOLOGY

Susceptibility testing was performed by Kirby Baüer and by Minimum Inhibitory Concentration (presence/absence of efflux pump inhibitor); molecular typing by Pulsed-field gel electrophoresis (PFGE), resistance genotyping and integrons by PCR and sequencing; OprD expression by Western blot; plasmid characterization by MOB Typing Technique, molecular size by PFGE-S1; and location by Southern blot.

RESULTS

Among the 59 studied isolates, 41 multidrug resistance and carbapenems resistance isolates were detected and classified in 38 different PFGE patterns. Thirteen strains carried 16 and four carried both genes. This study centered on the 17 strains har-boring . New variants of β-lactamases were identified ( , , ) inside of new arrangements of class 1 integrons. The presence of gene was detected in two plasmids in the same strain. The participation of the OprD protein and efflux pumps in the resistance to carbapenems and quinolones is shown. No expression of the porin OprD due to stop codon or IS in the gene was found.

CONCLUSIONS

This study shows the participation of different resistance mechanisms, which are reflected in the levels of MIC to carbapenems. This is the first report of the presence of three new variants of β-lactamases inside of new arrangements of class 1 integrons, as well as the presence of two plasmids carrying in the same strain isolated in a Mexican hospital.