We have investigated the molecular epidemiology and distribution of carbapenemase genes in 492 imipenem-non-susceptible Acinetobacter baumannii worldwide isolates (North and Latin America, Europe, Asia, South Africa and Australia). MICs were determined by broth microdilution and Etest. The presence of carbapenemase-encoding genes was investigated by PCR. Molecular epidemiology was performed by repetitive sequence-based PCR (rep-PCR; DiversiLab), sequence-type multiplex PCR and PFGE. Imipenem non-susceptibility was associated with ISAba1 upstream of the intrinsic bla_OXA-51-like or the acquired carbapenemase bla_OXA-23-like, bla_OXA-40-like or bla_OXA-58-like. Isolates were grouped into eight distinct clusters including European clones I, II and III. European clone II was the largest (246 isolates) and most widespread group (USA, pan-Europe, Israel, Asia, Australia and South Africa). The global dissemination of eight carbapenem-resistant lineages illustrates the success this organism has had in epidemic spread. The acquired OXA enzymes are widely distributed but are not the sole carbapenem resistance determinant in A. baumannii.

To give an update on the molecular epidemiology and global distribution of carbapenemase encoding genes, we subjected 313 carbapenem-resistant Acinetobacter baumannii isolated from 114 study centers in 47 countries in five world regions, Africa, Asia, Europe, Latin America, and North America, to whole genome sequencing. Numbers of isolates investigated were proportional to the population size of the contributing countries. Molecular epidemiology was investigated using seven-loci and core genome multilocus sequence typing, whole-genome single nucleotide polymorphism phylogenies, and the intrinsic bla _OXA-51-like variant. Carbapenemase encoding genes were identified by multiplex PCR and ResFinder. Among the total of 313 isolates, 289 (92.3%) were assigned to A. baumannii international clones (IC) IC1–IC8. IC2 predominated with 196 isolates (62.6%) and was spread worldwide, followed by IC5 with 44 isolates (14.1%) mainly confined to Latin America. Six isolates (1.9%) originating from Belgium, Egypt, Italy, and Pakistan represent the novel IC9. Acquired OXA-type carbapenemase genes were found in 300 (96%) isolates with bla _OXA-23-like and bla _OXA-40-like predominating, which constitutes a significant increase compared to our findings from 2010. Metallo-beta-lactamases were rare with seven isolates (2.2%). The distribution of ICs and carbapenemase determinants can vary widely among different geographical regions. IMPORTANCE: Carbapenem-resistant Acinetobacter baumannii are of increasing public health importance, as they are resistant to last-line antibiotics. International clones with well-characterized resistance genes dominate globally; however, locally, other lineages with different properties may be of importance to consider. This study investigated isolates from a broad geographic origin from 114 hospitals in 47 countries and from five world regions ensuring the greatest possible diversity in an organism known for its propensity for clonal epidemic spread and reflecting the current global epidemiology of carbapenem-resistant A. baumannii . In Latin America, a lineage different from other geographic regions circulates, with a different resistance gene profile. This knowledge is important to adjust local infection prevention measures. In a global world with migration and increasing use of antimicrobials, multidrug-resistant bacteria will continue to adapt and challenge our healthcare systems worldwide.

A carbapenem-resistant Acinetobacter baumannii strain was isolated in Brazil in 2004 in which no known carbapenemase gene was detected by PCR. Cloning experiments, followed by expression in Escherichia coli , gave an E. coli recombinant strain expressing a novel carbapenem-hydrolyzing class D β-lactamase (CHDL). OXA-143 showed 88% amino acid sequence identity with OXA-40, 63% identity with OXA-23, and 52% identity with OXA-58. It hydrolyzed penicillins, oxacillin, meropenem, and imipenem but not expanded-spectrum cephalosporins. The bla _OXA-143 gene was located on a ca. 30-kb plasmid. After transformation into reference strain A. baumannii ATCC 19606, it conferred resistance to carbapenems. Analysis of the genetic environment of bla _OXA-143 revealed that it was associated with neither insertion sequences nor integron structures. However, it was bracketed by similar replicase-encoding genes at both ends, suggesting acquisition through a homologous recombination process. This study identified a novel class D β-lactamase involved in carbapenem resistance in A. baumannii . This enzyme is the first member of a novel subgroup of CHDLs whose prevalence remains to be determined.

To investigate the molecular epidemiology, antimicrobial susceptibility and carbapenem resistance determinants of Acinetobacter baumannii isolates from respiratory tract samples of patients diagnosed with ventilator-associated pneumonia (VAP) who were enrolled in the MagicBullet clinical trial. A. baumannii isolates were prospectively cultured from respiratory tract samples from 65 patients from 15 hospitals in Greece, Italy and Spain. Susceptibility testing was performed by broth microdilution. Carbapenem resistance determinants were identified by PCR and sequencing. Molecular epidemiology was investigated using rep-PCR (DiversiLab) and international clones (IC) were identified using our in-house database. Of 65 isolates, all but two isolates (97%) were resistant to imipenem and these were always associated with an acquired carbapenemase, OXA-23 (80%), OXA-40 (4.6%), OXA-58 (1.5%) or OXA-23/58 (1.5%). Resistance to colistin was 47.7%. Twenty-two isolates were XDR, and 20 isolates were pandrug-resistant (PDR). The majority of isolates clustered with IC2 (n = 54) with one major subtype comprising isolates from 12 hospitals in the three countries, which included 19 XDR and 16 PDR isolates. Carbapenem resistance rates were very high in A. baumannii recovered from patients with VAP. Almost half of the isolates were colistin resistant, and 42 (64.6%) isolates were XDR or PDR. Rep-PCR confirmed IC2 is the predominant clonal lineage in Europe and suggests the presence of an epidemic XDR/PDR A. baumannii clone that has spread in Greece, Italy and Spain. These data highlight the difficulty in empirical treatment of patients with A. baumannii VAP in centres with a high prevalence of carbapenem-resistant A. baumannii.

We investigated the mechanism of carbapenem resistance in 10 Acinetobacter baumannii strains isolated from the United States and Mexico between 2005 and 2009. The detection of known metallo-β-lactamase or carbapenem-hydrolyzing oxacillinase (OXA) genes by PCR was negative. The presence of plasmid-encoded carbapenem resistance genes was investigated by transformation of A. baumannii ATCC 17978. Shotgun cloning experiments and sequencing were performed, followed by the expression of a novel β-lactamase in A. baumannii . Three novel OXA enzymes were identified, OXA-235 in 8 isolates and the amino acid variants OXA-236 (Glu173-Val) and OXA-237 (Asp208-Gly) in 1 isolate each. The deduced amino acid sequences shared 85% identity with OXA-134, 54% to 57% identities with the acquired OXA-23, OXA-24, OXA-58, and OXA-143, and 56% identity with the intrinsic OXA-51 and, thus, represent a novel subclass of OXA. The expression of OXA-235 in A. baumannii led to reduced carbapenem susceptibility, while cephalosporin MICs were unaffected. Genetic analysis revealed that bla _OXA-235 , bla _OXA-236 , and bla _OXA-237 were bracketed between two IS Aba1 insertion sequences. In addition, the presence of these acquired β-lactamase genes might result from a transposition-mediated mechanism. This highlights the propensity of A. baumannii to acquire multiple carbapenem resistance determinants.