Genotypic and phenotypic characterisation of
Staphylococcus epidermidis isolated from prosthetic
joint infections
av
Bengt Hellmark
Akademisk avhandling
Avhandling för medicine doktorsexamen i Medicinsk vetenskap med inriktning biomedicin,
som enligt beslut av rektor kommer att försvaras offentligt fredagen den 13 maj 2011 kl. 09.00,
Wilandersalen, Universitetssjukhuset Örebro Opponent: Docent Tor Monsen Institutionen för klinisk mikrobiologi,
Umeå universitet
Örebro universitet Hälsoakademin
© Bengt Hellmark, 2011
Title: Genotypic and phenotypic characterisation of Staphylococcus epidermidis isolated from prosthetic joint infections.
Publisher: Örebro University 2011 www.publications.oru.se
trycksaker@oru.se
Print: Intellecta Infolog, Kållered 04/2011 ISSN 1652-4063
ISBN 978-91-7668-793-2
Abstract
Bengt Hellmark (2011): Genotypic and phenotypic characterisation of Staphylococcus epidermidis isolated from prosthetic joint infections. Örebro Studies in Medicine 53, 117 pp.
Staphylococcus epidermidis has emerged in recent years as an important nosoco-mial pathogen, especially in infections associated with implanted foreign body materials (e.g., prosthetic joints and heart valves) and in individuals with a com-promised immune system (e.g., cancer patients and neonates). Although rare, im-plant infections are long lasting and cause severe suffering for the patient that in-cludes pain and disability and even increased mortality.
One aim of the present thesis was to develop and evaluate a genetic method for species identification and simultaneous detection of rifampicin resistance in staphy-lococci. A second aim was to examine S. epidermidis isolated from prosthetic joint infections (PJIs) and from wrists and nares of healthy individuals regarding their antibiotic susceptibility, biofilm production, virulence factors, and epidemiology.
Comparison with phenotypic diagnostics revealed that 8 (16%) of 49 isolates differed in their species identification in favour of the genetic method. In addition, mutations associated with rifampicin resistance, including two not previously re-ported, were possible to detect in all isolates resistant to rifampicin. Antibiotic susceptibility testing of 61 PJI isolates showed multi-drug resistance in 91%. Fur-thermore, the results of the synergy testing revealed that no antibiotic combination was significantly better than the others. Hence, the effects that were possible to detect were isolate dependent.
To find a method for discriminating between invasive (n=61) and commensal (n=24) isolates of S. epidermidis genotypic and phenotypic characterisations of biofilm production (including the ica and aap genes), antibiotic susceptibility, viru-lence-related genes (such as agr and ACME) and epidemiology were performed (using multilocus sequence typing [MLST], typing of the staphylococcal chromo-some cassette mec [SCCmec] and PhenePlate). Significant differences were found in antibiotic susceptibility, i.e. there was more resistance among invasive isolates. MLST sequence types (ST) ST2 and ST215 dominated the invasive isolates.
Keywords: Staphylococcus epidermidis, prosthetic joint infections, antibiotic sus-ceptibility, virulence factors, epidemiology, MLST, agr, SCCmec.
Bengt Hellmark, Department of Laboratory Medicine, Clinical Microbiology, Örebro University Hospital, SE-701 85 Örebro, Sweden. E-mail:
