Widespread carbapenem resistant Acinetobacter baumannii clones in Italian hospitals revealed by a multicenter study
Introduction
Acinetobacter baumannii and the genetically related Acinetobacter genomic species (gen. sp.) 3 and 13TU (recently named, respectively, as “Acinetobacter pittii” and “Acinetobacter nosocomialis”) (Nemec et al., 2011) are the Acinetobacter species most commonly involved in human infections and hospitals outbreaks. A. pittii and A. nosocomialis will be validly published by citation on Validation List 140 (publication in the July 2011 issue of the IJSEM, J. Euzeby, personal comunication). A. baumannii in particular is notorious for its resistance to antibiotics and ability to spread (Dijkshoorn et al., 2007, Peleg et al., 2008, Towner, 2009). Many outbreaks have been associated with three major international clones, European (EU) clones I–III (Dijkshoorn et al., 1996, van Dessel et al., 2004). Until recently, carbapenems were among the last options for treatment but resistance to carbapenem in A. baumannii is now frequent (Higgins et al., 2010, Poirel and Nordmann, 2006). Resistance to other potentially useful drugs (i.e. colistin and tigecyclin) has also been described (Al-Sweih et al., 2011, Navon-Venezia et al., 2007).
Few reports have focused on A. baumannii in Italy, mainly descriptions of local outbreaks (D’Arezzo et al., 2009, Giannouli et al., 2010). In 2006, a study group of the Association for Prevention and Study of Infections (APSI) evaluated the usefulness of the semi-automated repetitive-sequence-based PCR (rep-PCR) (Healy et al., 2005) for typing A. baumannii isolated over a 4-week period in 13 Italian hospitals (Carretto et al., 2008). That study also provided a diverse picture of incidence, clinical significance and antibiotic susceptibility of A. baumannii in Italy. To obtain a more detailed view of the epidemiology and antibiotic resistance of A. baumannii, a new prospective study was proposed by the APSI “Acinetobacter Study Group” (AASG). The aim was to assess the population diversity and antibiotic susceptibility of A. baumannii in 17 Italian hospitals over a 6-months’ period in 2007. Semi-automated rep-PCR method was used for initial typing, while AFLP™ analysis and multi-locus sequence typing MLST (Diancourt et al., 2010) were used for definitive characterization of isolates at species, strain and clonal level. Furthermore, antibiotic susceptibilities and presence of carbapenem resistance-related genes were determined.
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Hospitals and bacteria
The AASG, representing 17 hospitals scattered over Italy (Fig. 1) of different size and classification, collected A. baumannii isolates from 1 February till 31 July 2007. The number of beds of these hospitals ranged from 300 to 3500 (median 1000), with a total study population of 18,000 beds. Only the first isolate from each patient was included in the study. Strains were sent to the reference laboratory (Pavia) and stored at –80 °C until testing. For each strain, a report containing presumptive
Bacterial strains
A total of 320 putative A. baumannii isolates were recovered by 16 out of the 17 Centers. Of these, 311 isolates were received by the reference laboratory for phenotypic characterization (Gerner-Smidt et al., 1991). Two hundred and eighty isolates from 15 hospitals grew in a static BHI broth culture at 44 °C which identified them to A. baumannii or Acinetobacter nosocomialis (Gerner-Smidt et al., 1991). The number of A. baumannii isolates from the 15 hospitals ranged from 1 to 54 (median 14).
Molecular analysis
Discussion and conclusions
The aim of the present study was to assess, further to a previous study, the prevalence, type diversity, and antimicrobial resistance of A. baumannii in a representative group of Italian hospitals. Multidrug resistance was noticed in most but not all hospitals. Carbapenem resistance was nearly exclusively associated with OXA-58, while OXA-23 or OXA-24 was not detected, although OXA-23 has been reported for other parts of the country and, recently, in some hospitals that took part in this study (
Transparency declaration
BioMérieux Italia kindly provided to APSI the materials used for the rep-PCR experiments.
Acknowledgments
This work was supported by grants to Piero Marone (Ricerca Corrente 2007–2011: “Sorveglianza delle infezioni associate all’assistenza nei pazienti immunodepressi: tipizzazione epidemiologica e studio delle resistenze dei patogeni ospedalieri”).
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Associazione Prevenzione Studio Infezioni, Italy (see Appendix A).