CHARACTERIZATION OF BLUE PSEUDOMONAS FLUORESCENS THROUGH NEAR-INFRARED SPECTROSCOPY

Abstract Content: Near infrared spectroscopy (NIRs) has been widely suggested as a rapid technique to characterize foodborne bacteria through the analysis of spectra of whole cells or microbial suspensions. The use of spectra collected from broth cultures could be used as a fingerprint for strains classification in a combined polyphasic approach. The aim of this study was to evaluate the feasibility of the NIRs technique in the characterization of strains belonging to the Pseudomonas fluorescens group. The bacteria were isolated from different food matrices and during some cases of spoilage (e.g Blue discoloration). A total of 81 strains (field and Type strains) previously identified at species level through a Multilocus Sequence Typing approach were grown in Minimal Bacterial Medium broth in standardized condition at 22 °C. This medium was composed by salts with trisodium citrate and glucose as carbon sources and exalts the production of blue pigment. Two biological replicates were centrifuged in order to separate the bacterial cells from the extracellular products. Six aliquots per strain were analyzed on small ring cup in transflectance mode (680-2500 nm, gap 2 nm) at room temperature. Several chemometrics approaches were tested to assess the NIRs performances. Principal component analysis and Principal coordinate analysis showed a clear distinction among the blue producing strains and all the others strains according to the raw spectral data. Soft Independent Modelling of Class Analogy approach was applied to build several models using PLS Discriminant Analysis (PLS-DA). According to the variable importance criterion (VIP) the 1892-2020 nm spectral region showed the highest level of discrimination between blue strains and others (93.43% accuracy). Other additional information were provided by 680-886 region and 1454-1768 nm region (aromatic CH) and 2036-2134 nm (fatty acid). This approach suggests the use of NIRs as instrument for the extracellular products characterization and the strains classification.