title: Identification of the 'Streptococcus anginosus group' by matrix-assisted laser desorption ionization--time-of-flight mass spectrometry.
abstract: Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) provides rapid, accurate and cost-effective identification of a range of bacteria and is rapidly changing the face of routine diagnostic microbiology. However, certain groups of bacteria, for example streptococci (in particular viridans or non-haemolytic streptococci), are less reliably identified by this method. We studied the performance of MALDI-TOF MS for identification of the 'Streptococcus anginosus group' (SAG) to species level. In total, 116 stored bacteraemia isolates identified by conventional methods as belonging to the SAG were analysed by MALDI-TOF MS. Partial 16S rRNA gene sequencing, supplemented with sialidase activity testing, was performed on all isolates to provide 'gold standard' identification against which to compare MALDI-TOF MS performance. Overall, 100 % of isolates were correctly identified to the genus level and 93.1 % to the species level by MALDI-TOF MS. However, only 77.6 % were correctly identified to the genus level and 59.5 % to the species level by a MALDI-TOF MS direct transfer method alone. Use of a rapid in situ extraction method significantly improved identification rates when compared with the direct transfer method (P<0.001). We recommend routine use of this method to reduce the number of time-consuming full extractions required for identification of this group of bacteria by MALDI-TOF MS in the routine diagnostic laboratory. Only 22 % (1/9) of Streptococcus intermedius isolates were reliably identified by MALDI-TOF MS to the species level, even after full extraction. MALDI-TOF MS reliably identifies S. anginosus and Streptococcus constellatus to the species level but does not reliably identify S. intermedius.
authors.affiliation: Directorate of Infection, Guys & St Thomas Hospitals NHS Foundation Trust, 5th Floor North Wing, St Thomas' Hospital, Westminster Bridge Road, London SE1 7EH, UK.
authors.forename: Katherine
authors.initials: K
authors.lastname: Woods
authors.affiliation: Department of Oral Biology, Leeds Dental Institute, University of Leeds, Clarendon Way, Leeds LS2 9LU, UK.|Department of Microbiology, KCL Dental Institute, Floor 17, Guys Tower, London SE1 9RT, UK.
authors.forename: David
authors.initials: D
authors.lastname: Beighton
authors.affiliation: Directorate of Infection, Guys & St Thomas Hospitals NHS Foundation Trust, 5th Floor North Wing, St Thomas' Hospital, Westminster Bridge Road, London SE1 7EH, UK.
authors.forename: John L
authors.initials: JL
authors.lastname: Klein
mesh_terms: D016470:Bacteremia / Q000382:microbiology; D001431:Bacteriological Techniques / Q000379:methods*; D006801:Humans; D013048:Specimen Handling / Q000379:methods*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods*; D013290:Streptococcal Infections / Q000175:diagnosis / Q000382:microbiology; D034366:Streptococcus anginosus / Q000737:chemistry / Q000145:classification / Q000302:isolation & purification*; D034365:Streptococcus constellatus / Q000737:chemistry / Q000145:classification / Q000302:isolation & purification*; D034367:Streptococcus intermedius / Q000737:chemistry / Q000145:classification / Q000302:isolation & purification*