In addition to standard microbiological culture, we examined explanted suture and tissue specimens using CM to determine whether bacterial selleck compound biofilms were present. Specimens were prepared as described previously (Kathju et al., 2009a, b). Briefly, suture

and tissue recovered at surgery were placed in Hanks balanced salt solution (HBSS) and placed on wet ice, directly after removal. After rinsing in the HBSS (to remove unattached bacteria) and blotting on sterile paper, specimens were mounted on the bottom of a 35-mm Petri plate on partially solidified agar (Kathju et al., 2009a, b). Specimens were stained for viability assessment using Molecular Probes BacLight Live/Dead kit (Molecular Probes, Eugene, OR). The BacLight kit consists of two nucleic acid stains, Syto9 (green), which enters all bacteria, and propidium iodide (red), which can only enter bacteria with porous cell walls. Once inside the bacteria, the propidium iodide suppresses the Syto9 fluorescence so that live bacteria appear green, whereas dead or damaged cells appear red. In some cases, bacteria stain with both dyes

and appear yellow – these have been interpreted as live, but nonculturable. The nuclei of human cells also take up these nucleic acid stains, but rapidly turn red. They are readily distinguished from bacteria on the basis of size and morphology. In addition, these stains have been used to stain extracellular bacterial DNA Phospholipase D1 (eDNA), which is commonly found in the EPS and appears as a diffuse staining MLN0128 nmr surrounding the bacterial cells (Böckelmann et al., 2006; Thomas et al.,

2008). Fully hydrated specimens were then imaged by CM using a Leica DM RXE upright microscope attached to a TCS SP2 AOBS confocal system (Leica Microsystems, Exton, PA) using either a × 20 air objective or a × 63 long working distance water immersion objective. Live (green) and ‘dead’ (red) bacteria were imaged using 488 and 594 nm lasers; the suture and xenograft were imaged using reflected CM (blue) and bright-field microscopy (gray). Examination of one of the pieces of explanted Surgisis xenograft by CM showed heterogeneously distributed patches of live and dead bacteria and evidence of associated eDNA attached to the xenograft material (Fig. 2a). These organisms had a primarily coccal appearance, consistent with the solitary finding by culture of staphylococci. Interestingly, only one of the four specimens yielded a positive culture result, illustrating the inherent difficulty in detecting biofilm infections and making the case for multiple specimens to be sent for clinical culture, as well as the utility of using independent culture-free methods. Biofilms are commonly patchy on surfaces and this heterogeneity might partly explain the inconsistency in culture data. Examination of explanted suture material also showed evidence of attached and viable biofilm bacteria (Fig. 2c and d).