Abstract

Objectives

To study the distribution, diversity and activity of Acinetobacter-derived cephalosporinase (ADC)-, carbapenem-hydrolysing oxacillinase (CHO)- and metallo-β-lactamase (MBL)-encoding genes, and of the most common insertion sequences (ISs), in the genome of nosocomial, epidemic, multidrug-resistant Acinetobacter baumannii (MDRAB) clones from Spain.

Methods

The studied population included 59 MDRAB strains previously genotyped by PFGE and multilocus sequence typing. The search for the ADC (blaADC), CHO (blaOXA-51-like, blaOXA-23-like, blaOXA-40-like and blaOXA-58-like) and MBL (blaIMP, blaVIM, blaSIM-1, blaGIM-1, blaSPM-1 and blaNDM-1) genes, and for the ISs (ISAba1, ISAba2, ISAba3, ISAba4 and IS18) was done by PCR assays. The phenotypic presence of MBL enzymes was examined using imipenem/imipenem + EDTA strips.

Results

The most prevalent IS, ISAba1 (93.2%), was detected upstream of blaADC and blaOXA-51-like. These genes showed ample diversity (10 and 8 alleles, respectively). Four ADC sequences (ADC-1-likeP240S, ADC-2-likeN260H/T264N, ADC-11-likeQ163K and ADC-11-likeG342R) are described here for the first time. blaOXA-58-like was carried by 20.3% of strains, in association with ISAba2, ISAba3 or IS18. blaOXA-40-like was the most prevalent acquired CHO gene (57.6%), and was associated with none of the studied ISs. Neither blaOXA-23-like nor ISAba4 was detected in any strain. Some 67.8% of strains with MBL activity showed no corresponding gene in PCR; these results were more common in strains with a highly active CHO, such as OXA-40.

Conclusions

All the studied genes and their related ISs showed a clonal distribution. Imipenem resistance was probably provided by OXA-40 for the most part, while MBL- and OXA-23-encoding genes were absent in the studied population.

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