Contemporary Clinical Isolates of Staphylococcus aureus from Pediatric Osteomyelitis Patients Display Unique Characteristics in a Mouse Model of Hematogenous Osteomyelitis

Abstract

Osteomyelitis can result from the direct inoculation of pathogens into bone during injury or surgery, or from spread via the bloodstream, a condition called hematogenous osteomyelitis (HOM). HOM disproportionally affects children, and more than half of cases are caused by Staphylococcus (S.) aureus . Laboratory models of osteomyelitis mostly utilize direct injection of bacteria into the bone or the implantation of foreign material, and therefore do not directly interrogate the pathogenesis of pediatric hematogenous osteomyelitis. In this study, we inoculated mice intravenously and characterized resultant musculoskeletal infections using two strains isolated from adults (USA300-LAC and NRS384) and five new methicillin-resistant S. aureus isolates from pediatric osteomyelitis patients. All strains were capable of creating stable infections over five weeks, although the incidence varied. Micro-computed tomography (microCT) analysis demonstrated decreases in trabecular bone volume fraction but little effect on bone cortices. Histologic assessment revealed differences in the precise focus of musculoskeletal infection, with varying mixtures of bone-centered osteomyelitis and joint-centered septic arthritis. Whole genome sequencing of three new isolates demonstrated distinct strains, two within the USA300 lineage and one USA100 isolate. Interestingly, this USA100 isolate showed a distinct predilection for septic arthritis, compared to the other isolates tested, including NRS384 and LAC, which more frequently led to osteomyelitis or mixed bone and joint infections. Collectively, these data outline the feasibility of using pediatric osteomyelitis clinical isolates to study the pathogenesis of HOM in murine models and lay the groundwork for future studies investigating strain-dependent differences in musculoskeletal infection.

Staphylococcus aureus From an Acute Fracture-related Infection Displays Important Bacteriological and Histopathologic Differences From a Chronic Equivalent in a Murine Bone Infection Model

“…This approach could be particularly useful in cases where traditional antibiotics are not effective because of antibiotic resistance or toxicity [5]. Conversely, reduced pathogenicity and toxicity may result in slower progression of infection but provide better survival and persistence in the host, which may require prolonged antibiotic treatment or a more radical surgical approach because of increased biofilm formation and sessile pathogens in a quasidormant state [3,21,29]. Trouillet-Assant et al [27] yielded results similar to those presented here.…”

“…These exoproteins are believed to substantially contribute to increased cell death and bone destruction, systemic spread of infection, and maintenance of a proinflammatory environment while evading host immune defenses [3,11,19,29]. Conversely, attenuation of the Agr system in osteomyelitis models decreases infection severity, including the number of abscesses, tissue and bone destruction, and histologic inflammation [2,4,21,27]. Consistent with the results presented here, studies comparing recurrent Agr-deficient strains with initial isolates with intact Agr systems in chronic osteomyelitis also found decreased cytokine release [3,27].…”

Choosing the right animal model for osteomyelitis research: Considerations and challenges

“…It has a worldwide incidence of 1:1000–2000 [ 226 ] and is most frequently seen in prepubertal children and elderly patients. This monomicrobial disease manifests age-related distinctions in pathogenesis and epidemiology, with 85 % of patients being under 17 years old, and more than half of all patients being under 5 years old, bearing the risk of recurrence extending into adulthood, which may occur in up to 9 % of cases [ 3 , 228 ]. In general, S. aureus is the most commonly isolated organism, accounting for over half of all cases, while Group B Streptococcus and enteric Gram-negative bacteria such as E. coli are also isolated in neonatal infections.…”

“…Strep pneumoniae is reported to cause osteomyelitis in children under 2 years old, while Kingella kingae causes indolent osteoarticular infections most frequently in children under 4 years old [ 172 , 229 ], excluding the neonatal period. The infection predominantly involves the metaphysis of long bones, especially the proximal tibia and distal femur [ 228 ], due to their abundant vascular architecture and relatively lower fluid flow [ 1 , 3 , 4 ]. Although rare in adults, HO is frequently identified in vertebral bodies, generally in the lower dorsal or lumbar spine, with the infecting microorganisms being Entercoccus spp., S.…”

“…Age-related differences in the clinical presentation, pathology, pathophysiology and pathogenesis of HO have attracted multiple researchers. Roper et al explored the unique characteristics of S. aureus isolated from pediatric and adult patients [ 228 ]. The study involved injecting two USA300 strains isolated from adults, NRS384 and LAC, into 6-week-old C57BL/6-albino mice with a mutation in the tyrosinase gene at a period of rapid growth, which is a preferred age-related model for HO.…”