Implant Related Infections - Biomedical Technology - page 161

from the skin flora and the detection of Propionibacterium acnes seemed to support
this view. However, the frequency of P. acnes in the biofilm communities was too
low to identify the skin as main origin of the bacteria.
The lack of pathogens in these biofilms explains the asymptomatic nature of
these biofilm communities. One obvious question is: what is the role of these non-
virulent biofilm communities in implant infections? Are these biofilms the entry port
for pathogens, do they not contribute at all to implant infections or do they even
prevent the colonization of the implants by pathogens? These questions concern
the functional roles individual members of these biofilm communities have in their
interactions with other bacteria and the host. Answers to these questions are not easy
to find but a comparison between biofilm communities from asymptomatic implants
with those showing clinical signs of infections may provide some clues.
2.2 Biofilm Communities of Infected Implants
From 71 infected rhythm management devices DNA could be extracted from 95.8%
and the biofilm communities analyzed. As for the asymptomatic devices only biofilm
communities were found and no mono-specific biofilms. Compared to the asymp-
tomatic devices generally a higher biodiversity of the biofilm communities could be
observed which were, contrary to the findings with the asymptomatic devices, domi-
nated by Staphylococcus species. All devices with clinical signs of infection showed
without exception the presence of Staphylococcus species. Due to the shortness of
the 16rRNA gene sequences the underlying Staphylococcus species could not been
identified. The sequence analyses identified Staphylococcus aureus or the closely
related S. capitis or S. epidermidis as the main bacteria in all pathogenic biofilm
communities [ 15 ]. This finding agreed perfectly with the microbiological analysis
based on cultivation. Staphylococcus aureus, S. epidermidis and S. capitis are long
known as the main pathogens in cardiovascular implant infections [ 16 ] but are these
single- or a multi-pathogen infections and what is the role of the accompanying
bacterial species?
To shed some light on this problem a phylogenetic analysis of the detected bacte-
rial species were undertaken. Again a huge diversity of very different bacteria could
be identified and is shown in a phylogenetic tree together with closest known species
in Fig. 1 . Remarkable is the large diversity of Pseudomonas species detected in the
pathogenic biofilm communities but none of the identified Pseudomonas species
has yet been connected with infections in humans. Again several rare bacterial
species could be identified, among them Labrenzia , Leptotrichia [ 17 ], or Sphin-
gobium species [ 18 ]. At this point it became interesting to compare the asymp-
tomatic biofilm communities with the infectious ones. It turned out that in both
groups Pseudomonas species were detected but any given Pseudomonas species
occurred either in the asymptomatic or the infectious biofilm communities but never
in both. A comparison of the occurrence of bacterial species in the biofilm commu-
nities led to the identification of species preferable present in asymptomatic biofilms