Genotypic and phenotypic characterisation of Staphylococcus epidermidis isolated from prosthetic joint infections

B

eng

t H

el

lm

ar

k G

en

ot

ypi

c a

nd

p

he

no

ty

pi

c c

ha

rac

ter

isa

tio

n o

f St

ap

hy

lo

co

cc

us

e

pid

er

m

id

is is

ola

ted

f

ro

m

P

JIs

Bengt Hellmark was born in Mjölby in 1971. He gra-duated as medical technologist in 1995 and received his BSc degree in biomedical science in 2007, both at Öre-bro University. His interest in research was first sparked during the degree project in 2007 at the Department of Laboratory Medicine, Clinical Microbiology, Örebro University Hospital, and subsequently continued with his doctoral studies.

Staphylococcus epidermidis is the most common bacteria on the human skin and mucosal membranes and has previously been considered to be apatho-genic. However, in recent years it has emerged as an important pathogen in hospital-associated infections, especially in infections related to implanted foreign body materials (e.g., prosthetic joints and heart valves) and in im-munocompromised patients (e.g., cancer patients and neonates). In Sweden in 2009 almost 30 000 patients received an artificial hip or knee prosthetic joint. Although rare (<1%), infections related to foreign body materials are long lasting and cause severe suffering for the patient that includes pain and disability and even increased mortality. Prosthetic joint infections caused by S. epidermidis are often difficult to treat, which is mainly due to two abilities of S. epidermidis: acquired resistance to antibiotics and production of biofilm (e.g., extracellular matrix of polysaccharides). A challenge for the clinical microbiology laboratories is to determine whether a finding of S. epidermidis is clinically relevant or if it is a contamination, when analysing samples from a suspected prosthetic joint infection.

On the basis of this, two main aims for the present thesis were formed. The first aim was to develop and evaluate a genetic method for species identifica-tion and simultaneous detecidentifica-tion of rifampicin resistance in staphylococci. The second aim was to compare invasive S. epidermidis isolated from prosthetic joint infections and commensal S. epidermidis from healthy individuals re-garding their antibiotic susceptibility pattern, biofilm production, virulence factors, and epidemiology.

In conclusion, significant differences could be seen with respect to antibiotic susceptibility (a majority of the invasive isolates were multi-resistant), presence of ACME (more frequently detected in commensal isolates), and molecular epi-demiology (two sequence types, ST2 and ST215, were dominant among the in-vasive isolates whereas the commensal isolates were diverse and heterogeneous).

Örebro Studies in Medicine 53

örebro 2011 Doctoral Dissertation

Genotypic and phenotypic characterisation of

Staphylococcus epidermidis isolated from prosthetic

joint infections

Bengt Hellmark

Medical Science with focus on Biomedicine

B

eng

t H

el

lm

a

r

k

_{Genotypic and phenotypic characterisation}

of

Staph

ylococcus epidermidis