title: Comparison of growth on mannitol salt agar, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, VITEK®2 with partial sequencing of 16S rRNA gene for identification of coagulase-negative staphylococci.
abstract: Mannitol salt agar (MSA) is often used in resources' limited laboratories for identification of S. aureus however, coagulase-negative staphylococci (CoNS) grows and ferments mannitol on MSA. 171 strains of CoNS which have been previously misidentified as S. aureus due to growth on MSA were collected from different locations in Nigeria and two methods for identification of CoNS were compared i.e. ViTEK 2 and MALDI-TOF MS with partial 16S rRNA gene sequencing as gold standard. Partial tuf gene sequencing was used for contradicting identification. All 171 strains (13 species) grew on MSA and ferments mannitol. All tested strains of S. epidermidis, S. haemolyticus, S. nepalensis, S. pasteuri, S. sciuri,, S. warneri, S. xylosus, S. capitis were correctly identified by MALDI-TOF while variable identification were observed in S. saprophyticus and S. cohnii (90%, 81%). There was low identification of S. arlettae (14%) while all strains of S. kloosii and S. gallinarum were misidentified. There is absence of S. gallinarum in the MALDI-TOF database at the period of this study. All tested strains of S. epidermidis, S. gallinarum, S. haemolyticus, S. sciuri,, S. warneri, S. xylosus and S. capitis were correctly identified by ViTEK while variable identification were observed in S. saprophyticus, S. arlettae, S. cohnii, S. kloosii, (84%, 86%, 75%, 60%) and misidentification of S. nepalensis, S. pasteuri. Partial sequencing of 16S rRNA gene was used as gold standard for most strains except S. capitis and S. xylosus where the two species were misidentified by partial sequencing of 16S rRNA contrary to MALDI-TOF and ViTEK identification. Tuf gene sequencing was used for correct identification. Characteristic growth on MSA for CoNS is also identical to S. aureus growth on the media and therefore, MSA could not differentiate between S. aureus and CoNS. The percentage accuracy of ViTEK was better than MALDI-TOF in identification of CoNS. Although partial sequencing of 16S rRNA gene was used as gold standard in this study, it could not correctly identify S. capitis and S. xylosus.
authors.affiliation: Department of Pharmaceutical Microbiology, Faculty of Pharmacy, University of Ibadan, Ibadan, Nigeria; Department of Clinical Microbiology, Aarhus University Hospital, Aarhus, Denmark.
authors.forename: Funmilola A
authors.initials: FA
authors.lastname: Ayeni
authors.affiliation: Department of Clinical Microbiology, Aarhus University Hospital, Aarhus, Denmark.
authors.forename: Camilla
authors.initials: C
authors.lastname: Andersen
authors.affiliation: Department of Clinical Microbiology, Aarhus University Hospital, Aarhus, Denmark. Electronic address: nielnoer@rm.dk.
authors.forename: Niels
authors.initials: N
authors.lastname: Nørskov-Lauritsen
mesh_terms: D000362:Agar; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D015373:Bacterial Typing Techniques / Q000295:instrumentation / Q000379:methods*; D003030:Coagulase / Q000235:genetics / Q000378:metabolism; D003470:Culture Media; D016208:Databases, Factual; D008353:Mannitol; D010802:Phylogeny; D012336:RNA, Ribosomal, 16S / Q000235:genetics*; D015203:Reproducibility of Results; D017422:Sequence Analysis, DNA; D012965:Sodium Chloride; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000295:instrumentation / Q000379:methods; D013210:Staphylococcus / Q000235:genetics / Q000254:growth & development* / Q000302:isolation & purification / Q000378:metabolism*; D013211:Staphylococcus aureus / Q000235:genetics / Q000254:growth & development / Q000302:isolation & purification / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D003030:Coagulase; D003470:Culture Media; D012336:RNA, Ribosomal, 16S; D008353:Mannitol; D012965:Sodium Chloride; D000362:Agar
keywords: Coagulase negative staphylococci; Identification; MALDI-TOF; Mannitol salt agar; VITEK