A surgical procedure allowed the placement of a silicone rubber catheter in the marrow cavity of the tibia of a rabbit and also allowed the introduction of a sclerosing agent (sodium morrhuate) and cells of Staphylococcus aureus. Osteomyelitis developed in 60% of the animals so treated, and the infecting microorganism was recovered from the infected tibias of the animals that developed this disease. All blood cultures taken 24 h after the infection were negative for S. aureus. Radiological findings consisted of osteolytic changes, the occurrence of sequestration and periosteal reactions, and sclerosis in the infected bones. Sections of bone prepared for histological examination confirmed the diagnosis of osteomyelitis. Transmission and scanning electron microscopy of samples of bone marrow, bone chips, and the catheters taken from the infected tibiae revealed gram-positive cocci embedded in a very extensive matrix of ruthenium red-staining glycocalyx adhering to the bone and the implanted catheter. It is proposed that this extensive glycocalyx served a protective function for the bacteria and was important in bacterial adherence and thus played an important role in bacterial persistence and the development of osteomyelitis in these rabbits.

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When cells of both Staphylococcus aureus and Staphylococcus epidermidis are grown in batch culture in nutrient-rich media, their cell walls are regular in thickness, their cell size is within the normal range for each species, and their septation patterns are orderly. When cells of each of these species are examined directly in infected tissue in the rabbit tibia model infection, their cell wall thickness is often much increased and very irregular around the circumference of the cell, their cell size is often increased, and their septation patterns are often severely deranged. All of these alterations in cell wall structure occur in the absence of antibiotics, and we suggest that they may be an expression of phenotypic plasticity in response to altered environmental conditions such as specific nutrient limitations, the presence of antibacterial factors, and growth of the cells on hard surfaces such as rabbit bone or plastic catheters. Some of these specific cell wall alterations are also seen when staphylococcal cells are exposed, in vitro or in vivo, to antibiotics such as clindamycin, but we emphasize that growth in tissue alone is sufficient for their induction.