Species identification within Acinetobacter calcoaceticus–baumannii complex using MALDI-TOF MS

Abstract

Acinetobacter baumannii, one of the more clinically relevant species in the Acinetobacter genus is well known to be multi-drug resistant and associated with bacteremia, urinary tract infection, pneumonia, wound infection and meningitis. However, it cannot be differentiated from closely related species such as A. calcoaceticus, A. pittii and A. nosocomialis by most phenotypic tests and can only be differentiated by specific, time consuming genotypic tests with very limited use in clinical microbiological laboratories. As a result, these species are grouped into the A.calcoaceticus -A. baumannii (Acb) complex. Herein we investigated the mass spectra of 73 Acinetobacter spp., representing ten different species, using an AB SCIEX 5800 MALDI -TOF MS to differentiate members of the Acinetobacter genus, including the species of the Acb complex. RpoB gene sequencing, 16S rRNA sequencing, and gyrB multiplex PCR were also evaluated as orthogonal methods to identify the organisms used in this study. We found that whilst 16S rRNA and rpoB gene sequencing could not differentiate A. pittii or A. calcoaceticus, they can be differentiated using gyrB multiplex PCR and MALDI -TOF MS. All ten Acinetobacter species investigated could be differentiated by their MALDI -TOF mass spectra.

Head-to-head comparison of Microflex LT and Vitek MS systems for routine identification of microorganisms by MALDI-TOF mass spectrometry in Chile

“…bronchioseptica and among Aeromonas species. It is worth noting that 16S rRNA sequencing was also inconclusive in many of these difficult-to-identify species groups, as previously described [12,56]. Further investigations are needed to determine which of these limitations are inherent to the technique and which can be overcome with broader spectra databases.…”

A Prospective Study of Acinetobacter baumannii Complex Isolates and Colistin Susceptibility Monitoring by Mass Spectrometry of Microbial Membrane Glycolipids

“…Species-level identification based on genetic methods (e.g., rpoB sequencing, rRNA intergenic spacer sequencing) has enabled differentiation of the A. baumannii complex species for research purposes. It has been demonstrated that MALDI-TOF MS can be utilized as an alternative method to reliably identify A. baumannii complex species (13,22,29,30). Using these methods, the prevalence of A. baumannii, A. nosocomialis, and A. pittii within the A. baumannii complex has been shown to be highly variable among clinical isolates depending on the epidemiological settings (31)(32)(33)(34)(35).…”

“…A log score of Ն1.7 denotes a probable species identification according to the manufacturer's recommendations, with a score of Ն2.0 denoting a positive identification; however, multiple publications have shown that lowering the threshold to 1.7 does not affect or minimally affects specificity (20,21). The MALDI Biotyper system can reliably determine the species of the A. baumannii complex organisms (13,22).…”

Accurate and Rapid Differentiation of Acinetobacter baumannii Strains by Raman Spectroscopy: a Comparative Study

“…Therefore, many studies have explored alternative methods of microbial identification that are accurate, rapid, and cost-effective, such as MS and Raman spectroscopy (4, 10, 12–18, 33, 34). Other methods, such as DNA sequencing and AST, have also been used to differentiate among strains of microorganisms, including A.…”

“…baumannii isolates at the species level (5–7, 33, 34), difficulties seem to arise with MS when it is applied for strain-level identification of A. baumannii isolates (4, 8–11).…”