The OXA-51-like enzymes of Acinetobacter baumannii: markers of success?

Abstract number: O296

Evans B., Hamouda A., Towner K., Amyes S.

Objectives:Acinetobacter baumannii has become a prevalent nosocomial pathogen due to the spread of major epidemic lineages. The diversity of the intrinsic blaOXA-51-like genes may provide insights into the evolution of this species. This study aimed to examine the relationship between the sequences of the OXA-51-like enzyme family and the properties of a collection of A. baumannii isolates.

Methods: Sixty A. baumannii isolates had their blaOXA-51-like gene amplified by PCR using external primers, and the products sequenced and identified using BLAST and MultAlin software. The external primers allowed the simultaneous identification of ISAba1 upstream of the blaOXA-51-like genes. MICs for imipenem and meropenem were determined according to British Society for Antimicrobial Chemotherapy (BSAC) guidelines. Isolates were assigned to sequence groups (SGs) based on PCR amplification of fragments of their blaOXA-51-like, ompA and csuE genes. All publicly available OXA-51-like amino-acid sequences were retrieved and used to construct a linkage map showing the relationships of the enzymes to one another.

Results: The linkage map revealed that some of the enzymes form closely related clusters while others are less closely related. The largest number of isolates, including European clone II, contained enzymes in the OXA-66 cluster, and were assigned to SG1. The second largest group of isolates, including European clone I, contained enzymes in the OXA-69 cluster, and were assigned to SG2. The third largest isolate group, including European clone III, were assigned to SG3 and contained an OXA-71 enzyme. Eight isolates contained enzymes not found in a major cluster, or could not be assigned to a SG. ISAba1 was found upstream of the blaOXA-51-like gene in ten isolates, but was only associated with enzymes on branch tips in the OXA-66 and OXA-69 clusters. MICs for imipenem and meropenem ranged from 0.06 and 0.12 mg/L respectively up to >128 mg/L for both antibiotics. Isolates with ISAba1 upstream of the blaOXA-51-like gene tended to have MICs towards the higher end of this range, from 0.5 and 2 mg/L up to 8 and 32 mg/L.

Conclusion: SG1 and SG2 represent the most prevalent epidemic lineages of A. baumannii and encode specific sub-sets of OXA-51-like enzymes. SG3 is not as prevalent, but is also associated with a specific OXA-51-like enzyme. A minority of isolates cannot be grouped using this typing scheme. Evolution of the OXA-51-like enzymes appears to be occurring in real time.

Session Details

Date: 19/04/2008
Time: 00:00-00:00
Session name: 18th European Congress of Clinical Microbiology and Infectious Diseases
Location: Barcelona, Spain
Presentation type:
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