Chronic Osteomyelitis with Staphylococcus aureus Deformation in Submicron Canaliculi of Osteocytes: A Case Report

Abstract

Case: A patient presenting with an infected diabetic foot ulcer and Staphylococcus aureus chronic osteomyelitis was studied to validate the clinical importance of bacterial colonization of osteocytic-canalicular networks, as we recently reported in a mouse model. We utilized transmission electron microscopy to describe the deformation of S. aureus, from round cocci to rod-shaped bacteria, in the submicron osteocytic-canalicular networks of amputated bone tissue.

Conclusion: To our knowledge, this is the first evidence of S. aureus deformation and invasion of the osteocytic-canalicular system in human bone, which supports a new mechanism of persistence in the pathogenesis of chronic osteomyelitis.

Fig. 1

Preoperative radiographs. Fig. 1-A Anteroposterior view of the right foot and the infected fourth toe tip (arrow) with clawing. Fig. 1-B Lateral view of the right foot and the infected fourth toe. Note the osteolysis at the distal phalanx of the fourth toe (arrow).

Fig. 2

Figs. 2-A through 2-H TEM evidence of bacterial deformation and invasion of the submicron osteocytic-canalicular system. MC = marrow cavity, OC = osteocyte, and N = nucleus. Fig. 2-A Light microscopy image demonstrating positive Gram- stained bacteria in a section from the paraffin-embedded bone tissue of the fourth toe (×60). Fig. 2-B From the TEM epoxy-embedded portion of bone, a 1-μm epoxy section stained with toluidine blue reveals dark-blue bacteria scalloping the live bone tissue (red arrow) (note the OCs and black arrows adjacent to the MC) (×60). Fig. 2-C TEM image of a dead OC and its canaliculus (red arrow), colonized by deformed rod-shaped bacteria (×6,000). Fig. 2-D Higher magnification of the area adjacent to the red arrow in Figure 2-C reveals the septal plane of the dividing bacteria within the submicron space of the canaliculus (×30,000). Note the asymmetric plane of the 2 daughter cells. Fig. 2-E High magnification of the osteocyte in Figure 2-C displaying condensed nuclear debris and round bacteria occupying its lacunar space (×15,000). Fig. 2-F Another dead osteocyte’s lacuna containing remnants of condensed chromatin bodies and round bacteria (×8,000). Fig. 2-G A TEM image from thin sections deeper into the bone tissue reveals rod-shaped bacteria within a canaliculus (×6,000). Fig. 2-H Higher-magnification TEM image of the boxed area in Figure 2-G measuring submicron-sized deformed and elongated bacteria (×15,000).