Methods: The species identity of 56 clinical Acinetobacter spp. isolates were determined using the Siemens MicroScan System, bioMérieux Vitek MS Plus MALDI-TOF, Bruker MALDI Biotyper, the BAC-BSI assay in development on the PCR/ESI-MS platform (Ibis Biosciences), and targeted PCR assays: gyrB multiplex PCR (species specific amplicons) and presence of Acinetobacter species-specific oxacillinases. Rep-PCR (DiversiLab Acinetobacter Fingerprinting kit) was used to determine if the isolates grouped by species.
Results: Both MicroScan and MALDI-TOF platforms identified all 56 isolates as A. baumannii (Ab). When tested using the BAC-BSI assay on the PCR/ESI-MS platform, 16 were identified as Ab and the remaining 40 as A. calcoaceticus (Ac). This discrepency prompted further investigation with targeted PCRs. The gyrB multiplex PCR confirmed the previous species identification of Ab in the 16 isolates (75% CR, 12/16); however, among the 40 designated as Ac, gyrB multiplex PCR identified 35 as A. pittii (Ap, 100% CS), 3 as A. nosocomialis (An, 100% CS), and 2 as Ab (100% CS). The blaOXA-51-like PCR confirmed the gyrB Ab species identification in all 18 Ab isolates. All 35 Ap identified by gyrB multiplex PCR were positive for the Ap intrinsic blaOXA-270-like gene; all others were negative. The intrinsic OXA multiplex PCR also revealed that 1 Ap isolate harbored both the intrinsic Ac and Ap specific blaOXA genes. As expected, all An were negative for intrinsic blaOXAs (this species has none). Rep-PCR was consistent with gyrB multiplex PCR groupings.
Conclusion: In the analysis of 56 Acinetobacter isolates, current standard post culture ID systems identified all isolates as Ab. Only the BAC-BSI assay alerted us to the presence of multiple species, upon which further targeted PCR revealed An or Ap. High-quality research and clinical studies require platforms to correctly identify Acinetobacter to the species level.
T. N. Domitrovic,
P. Higgins, None
H. Seifert, None
K. M. Hujer, None
M. R. Jacobs, None
T. Hall, Ibis Biosciences, an Abbott Company: Employee , Salary
C. Marzan, Ibis Biosciences, an Abbott Company: Employee , Salary
B. N. Kreiswirth, None
R. A. Bonomo, AstraZeneca: Grant Investigator , Research grant
Merck: Grant Investigator , Research grant
Melinta: Grant Investigator , Research grant
VA Merit Review Board: Grant Investigator , Research grant
NIH: Grant Investigator , Research grant