• Cristino, Sandra
• Marino, Federica
• Pascale, Maria Rosaria
• Mazzotta, Marta
• Girolamini, Luna
• Cordovana, Miriam
• Monte, Paola Dal
• Scaturro, Maria
• Ricci, Maria Luisa
• Bisognin, Francesco

Abstract

<jats:p><jats:italic>Legionella</jats:italic> spp. are Gram-negative bacteria that inhabit freshwater environments representing a serious risk for human health. <jats:italic>Legionella pneumophila</jats:italic> (<jats:italic>Lp</jats:italic>) is the species most frequently responsible for a severe pneumonia known as Legionnaires' disease. <jats:italic>Lp</jats:italic> consists of 15 serogroups (Sgs), usually identified by monoclonal or polyclonal antibodies. With regard to <jats:italic>Lp</jats:italic> serogrouping, it is well known that phenotyping methods do not have a sufficiently high discriminating power, while genotypic methods although very effective, are expensive and laborious. Recently, mass spectrometry and infrared spectroscopy have proved to be rapid and successful approaches for the microbial identification and typing. Different biomolecules (e.g., lipopolysaccharides) adsorb infrared radiation originating from a specific microbial fingerprint. The development of a classification system based on the intra-species identification features allows a rapid and reliable typing of strains for diagnostic and epidemiological purposes. The aim of the study was the evaluation of Fourier Transform Infrared Spectroscopy using the IR Biotyper® system (Bruker Daltonik, Germany) for the identification of <jats:italic>Lp</jats:italic> at the serogroup (Sg) level for diagnostic purposes as well as in outbreak events. A large dataset of <jats:italic>Lp</jats:italic> isolates (<jats:italic>n</jats:italic> = 133) and ATCC reference strains representing the 15 <jats:italic>Lp</jats:italic> serogroups were included. The discriminatory power of the instrument's classifier, was tested by Principal Component Analysis (PCA) and Linear Discriminant Analysis (LDA). All isolates were classified as follows: 12/133 (9.0%) as <jats:italic>Lp</jats:italic> Sg1 and 115/133 (86.5%) as <jats:italic>Lp</jats:italic> Sg 2–15 (including both ATCC and environmental <jats:italic>Lp</jats:italic> serogroup). Moreover, a mis-classification for 2/133 (1.5%) isolates of <jats:italic>Lp</jats:italic> Sg 2–15 that returned as <jats:italic>Lp</jats:italic> Sg1 was observed, and 4/133 (3.0%) isolates were not classified. An accuracy of 95.49% and an error rate of 4.51% were calculated. IR Biotyper® is able provide a quick and cost-effective reliable <jats:italic>Lp</jats:italic> classification with advantages compared with agglutination tests that show ambiguous and unspecific results. Further studies including a larger number of isolates could be useful to implement the classifier obtaining a robust and reliable tool for the routine <jats:italic>Lp</jats:italic> serogrouping. IR Biotyper® could be a powerful and easy-to-use tool to identify <jats:italic>Lp</jats:italic> Sgs, especially during cluster/outbreak investigations, to trace the source of the infection and promptly adopt preventive and control strategies.</jats:p>

Topics

• impedance spectroscopy
• cluster
• mass spectrometry
• Fourier transform infrared spectroscopy
• spectrometry