3rd meeting of young researchers at UP 1 - IJUP - Universidade do ...

Clonal diversity of Acinetobacter baumannii population carrying
carbapenem-hydrolyzing oxacillinases in Portuguese hospitals
Ana Ramos 1 , F. Grosso 1 , S. Quinteira 1,2 , L. Peixe 1
1 Department of Microbiology, Faculdade de Farmácia, Universidade do Porto, Portugal.
2 CITS/IPSN-CESPU, Famalicão, Portugal
Acinetobacter baumannii is a gram-negative organism that is increasingly recognized as a
major pathogen causing nosocomial infections. Increasing resistance to carbapenems has been
observed worldwide in the past decade, frequently mediated by production of class D βlactamases
with carbapenemase activity: OXA-23, OXA-40, and OXA-58 groups. They were
all detected in Portugal, but their prevalence in Portuguese hospitals changed over time: since
1998 to 2001 blaOXA-40 pulsotype prevailed, between 2001 and 2004 the blaOXA-58
pulsotype was the dominant, being replaced until 2006 by the OXA-40 producer clone. After
2006 we observed an increase in the appearance of OXA-23-producers. Together they greatly
contributed to the high rate of imipenem-resistance in this species in Portuguese hospitals. The
aim of this work was to investigate the clonal relationship between blaOXA-23, blaOXA-58
and blaOXA-40-carrying isolates by an MLST scheme, a new epidemiology tool were the
internal portions of 7 housekeeping genes (gltA, gyrB, gdhB, recA, cpn60, gpi, and rpoD) are
amplified, sequenced and analized using the Acinetobacter baumannii MLST database website
(http://pubmlst.org/abaumannii/).
We analysed the population structure of ten isolates representative of blaOXA-23 (n=4),
blaOXA-40 (n=3) and blaOXA-58 (n=2) carrying strains, disseminated and persisting over
years, that were selected among well characterized 324 AB isolates recovered from 5
Portuguese hospitals. A carbapenem-susceptible isolate (CSAB) was also included. Isolates
were identified by API32GN and by 16S rRNA sequencing. Susceptibility testing was
performed according to CLSI standard procedures. blaOXA-23, blaOXA-40, and blaOXA-58
genes were identified by sequencing of respective amplicons. MLST scheme was performed
according to Bartual et al (2005).
MLST typing revelead that both blaOXA-23-carrying AB and CSAB belonged to the
disseminated ST22. The OXA-40-producing AB isolates corresponded to a new ST-ST33,
which is a double locus variant of ST22. The blaOXA-58 carrying isolates clustered in the
ST38, already detected in Argentina but not related with the STs 22 and 33.
In our country, carbapenem-resistant AB are mainly related to the dissemination of three
different STs, and curiously each one is associated to a different acquired OXA-type. The rapid
increase in the recently described OXA-23 producers is associated with the spread of the
worldwide disseminated ST22 AB clone. Remarkably, MLST data indicates a common origin
between ST22 and the ST 33 OXA-40-producing clone.
302 3 rd meeting of young researchers at UP