Molecular characterization of carbapenem-resistant Acinetobacter species in an Irish university hospital: predominance of Acinetobacter genomic species 3

1 Department of Clinical Microbiology, Trinity College, University of Dublin, James's Street, Dublin 8, Ireland 2 Central Pathology Laboratory, Department of Microbiology, St James's Hospital, James's Street, Dublin 8, Ireland Correspondence B. Crowley bcrowley{at}stjames.ie Received July 10, 2008 Accepted October 9, 2008 A 30 month prospective study of Acinetobacter species encountered in the Central Pathology Laboratory of St James's Hospital, Dublin, Ireland, was conducted to investigate the prevalence and molecular epidemiology of carbapenem resistance in such isolates. Acinetobacter genomic species 3 (AG3) was found to be the predominant Acinetobacter species (45/114, 39 %) in our institution. A total of 11 % of all Acinetobacter species (12/114) and 22 % of AG3 isolates (10/45) were carbapenem resistant. Carbapenem resistance was mediated by Ambler class D β -lactamase OXA-23 in all 12 isolates, with insertion sequence IS Aba1 found upstream of bla OXA-23 . IS Aba1 was also found upstream of bla ADC-25 , which encodes the enzyme AmpC, in an Acinetobacter baumannii isolate, and upstream of the aminoglycoside-acetyltransferase-encoding gene aacC2 in three AG3 isolates. Inter-species plasmidic transfer was most likely involved in the emergence and spread of bla OXA-23 among the Acinetobacter isolates within our institution. The emergence of carbapenem resistance was associated not only with prior carbapenem use but also with the use of other antimicrobial agents, most notably β -lactam/ β -lactamase-inhibitor combinations. The study demonstrated the emerging trend of carbapenem resistance in the wider context of the Acinetobacter genus, and reiterated the paramount importance of the prudent use of antimicrobial agents, stringent infection control measures and resistance surveillance of pathogens. Abbreviations: AG3, Acinetobacter genomic species 3; CLSI, Clinical and Laboratory Standards Institute; ICU, intensive care unit; MBL, metallo β -lactamase. The GenBank/EMBL/DDBJ accession numbers for the Acinetobacter sequences reported in this paper are as follows: EU827524 ( Acinetobacter genomic species 3 IS Aba1 / bla OXA-23 /ATPase), EU827525 ( Acinetobacter johnsonii IS Aba1 / bla OXA-23 /ATPase), EU827526 ( Acinetobacter baumannii IS Aba1 / bla OXA-23 /ATPase), EU835512 ( Acinetobacter baumannii IS Aba1 / bla ADC-25 ), EU839488 ( Acinetobacter genomic species 3 IS Aba1 / aacC2 ), EU872057 ( Acinetobacter johnsonnii aacC2 ). A table of primer sequences i