**3.4.1 Native material**

The simplest way of tissue sample processing is mincing by a scalpel. This allows efficient investigation of multiple samples from each patient (see 3.2.3). If carried out under a laminar air flow workbench it is not highly prone to contamination (Atkins et al., 1998; Schäfer et al., 2008; Trampuz et al., 2006, 2007).

Some authors favor scraping the surface of the explanted material. This has been reported to be more sensitive than tissue culture but also liable to contamination (Bjerkan et al., 2009; Neut et al., 2003).

Infections in Hip and Knee Arthroplasty:

(Achermann et al., 2010).

**3.6 Culture conditions 3.6.1 Culture media** 

**3.6.2 Culture duration** 

patients (Schäfer et al., 2008).

spectrum of causative ("late") species (Table 1).

coagulase-negative staphylococci

future.

Challenges to and Chances for the Microbiological Laboratory 445

Although important antibiotic resistance mechanisms like methicillin resistance can be identified genotypically with PCR (Kobayashi et al., 2009; Tarkin et al., 2003), for most substance classes phenotypic susceptibility testing will be necessary in the foreseeable

There is no straightforward method to determine whether microbial DNA as detected by PCR reflects living organisms. On the other hand, it cannot be ruled out that previous therapy with antibiotics hampers the sensitivity not only of culture, but also of PCR

A combination of solid (usually blood agar, chocolate agar, and Schaedler agar) and liquid media (e. g. brain-heart infusion broth and Schaedler broth) is used by standard for aerobic and anaerobic cultivation. Solid media alone lack sensitivity to detect low-grade infections because because the medium eventually dries out. On the other hand, infections involving more than one agent can be overlooked if only broth media are utilized because slower-

"Standard" cultivation periods (mostly ≤ 7 days in the literature) are generally questionable in infections where biofilms are involved, due to low cell counts of planktonic bacteria and impaired growth rates of sessile organisms in the biofilm. However, the issue was not addressed for a long time. Prolonged cultivation for 14 days was described sporadically (Ince et al., 2004) and even included as a standard recommendation into German practice guidelines, but not assessed under controlled conditions. Thus, our group systematically evaluated a 14-day culture period with periprosthetic tissue samples from hip and knee

Using the algorithm described under 3.1.1 to distinguish infecting agents from contaminating strains, only 74% of the infections (caused by "early" agents) were found within the first week of cultivation (Schäfer et al., 2008). In the second week we not only identified a significant amount of additional infections, but also a completely different

**(%)**

*Enterococcus* species 3.8 2 *Streptococcus* species 3.8 1.5 Enterobacteriaceae 1.9 5

*Propionibacterium* species 13.4 11 *Finegoldia* species 3.2 8 others 1.9 9.5

55.4 4

**median time to detection (days)** 

growing organisms may be inhibited in the presence of fast-growing bacteria.

**isolated organisms frequency** 

**early species** *Staphylococcus aureus* 8.9 2

**late species** coryneform bacteria 7.6 10

Table 1. Spectrum of bacteria detected over a 14-day cultivation period.
