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

Abstract

In recent years, matrix-assisted laser desorption ionization–time of flight mass spectrometry (MALDI-TOF MS) has become the standard for routine bacterial species identification due to its rapidity and low costs for consumables compared to those of traditional DNA-based methods. However, it has been observed that strains of some bacterial species, such as Acinetobacter baumannii strains, cannot be reliably identified using mass spectrometry (MS). Raman spectroscopy is a rapid technique, as fast as MALDI-TOF, and has been shown to accurately identify bacterial strains and species. In this study, we compared hierarchical clustering results for MS, genomic, and antimicrobial susceptibility test data to hierarchical clustering results from Raman spectroscopic data for 31 A. baumannii clinical isolates labeled according to their pulsed-field gel electrophoresis data for strain differentiation. In addition to performing hierarchical cluster analysis (HCA), multiple chemometric methods of analysis, including principal-component analysis (PCA) and partial least-squares discriminant analysis (PLSDA), were performed on the MS and Raman spectral data, along with a variety of spectral preprocessing techniques for best discriminative results. Finally, simple HCA algorithms were performed on all of the data sets to explore the relationships between, and natural groupings of, the strains and to compare results for the four data sets. To obtain numerical comparison values of the clustering results, the external cluster evaluation criteria of the Rand index of the HCA dendrograms were calculated. With a Rand index value of 0.88, Raman spectroscopy outperformed the other techniques, including MS (with a Rand index value of 0.58).

<p>Evaluation of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry for identifying VIM- and SPM-type metallo-β-lactamase-producing <em>Pseudomonas aeruginosa</em> clinical isolates</p>

“…The VITEK MS plus is currently available worldwide and is currently used in our laboratory. Manual calibration is an important step before using the RUO application for bacterial identification 16,20,21. If the calibration is not congruent, the spectra obtained by the MALDI-TOF MS can be of lower quality, resulting in a wrong interpretation 22,23.…”

Classification of cancer cell lines using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and statistical analysis

“…The major difference from MALDI-TOF MS is that Raman microscopy does not use a laser to ablate the proteins from the target. Although Raman spectroscopy has proven to be a valuable technique, MALDI-TOF MS is a more widely established as a routine technique in many laboratories ( 27 ). It does not require complex sample preparation and requires minimal training, particularly after the technique was standardized and validated ( 5 ).…”

Characteristics of Quinolone Resistance in Multidrug-Resistant Acinetobacter baumannii Strains Isolated from General Hospitals

“…the most rapid method for distinguishing and identifying A. baumannii and four other A. baumannii complexes (5,6). Matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometry (MS) analysis identifies the measurable molecular weight (100 Da to 100 kDa) and the bacterial cell count corresponding to one or two colonies (105 to 106) by examining the protein peaks (7).…”