A porcine model of acute, haematogenous, localized osteomyelitis due to Staphylococcus aureus: a pathomorphological study

Abstract

A porcine model of acute, haematogenous, localized osteomyelitis was established. Serial dilutions of Staphylococcus aureus [5-50-500-5000-50 000 CFU/kg body weight (BW) suspended in saline or saline alone] were inoculated into the right brachial artery of pigs (BW 15 kg) separated into six groups of two animals. During the infection, blood was collected for cultivation, and after the animals were killed from day 5 to 15, they were necropsied and tissues were sampled for histopathology. Animals receiving ≤500 CFU/kg BW were free of lesions. Pigs inoculated with 5000 and 50 000 CFU/kg BW only developed microabscesses in bones of the infected legs. In the centre of microabscesses, S. aureus was regularly demonstrated together with necrotic neutrophils. Often, bone lesions resulted in trabecular osteonecrosis. The present localized model of acute haematogenous osteomyelitis revealed a pattern of development and presence of lesions similar to the situation in children. Therefore, this model should be reliably applied in studies of this disease with respect to e.g. pathophysiology and pathomorphology. Moreover, because of the regional containment of the infection to a defined number of bones, the model should be applicable also for screening of new therapy strategies.

Fig. 1

The inoculation procedure. (A) Anaesthetized pig in right lateral recumbency with the right medial ante-brachium prepared for surgery. (B) Schematic drawing, the skin incision is indicated by the punctured line and the asterisk (*) shows the location of the bone protuberance epicondylus medialis humeri. (C) Inoculation through a catheter equipped with a three-way stopcock inserted into the right brachial artery fixated with a ligature ().

Fig. 2

Histopathology in pigs inoculated intra-arterially (a. brachialis dextra) with 50 000 CFU/kg BW. (A) Radius: a microabscess located deep in the metaphyseal area, H&E. (B) Metacarpale III: colonies of bacteria (→) are present at the junction between the growth plate (GP) and the metaphysis (MP) and the epiphysis (EP), H&E. (C) Epiphysis of phalanx proximalis III: multiple Staphylococcus aureus bacteria are seen centrally in the microabscess. Surrounding cells are arranged in a pattern of palisades. Immunostaining for S. aureus. (D) The centre of the microabscesses was made up by accumulation of neutrophils, H&E. (E) Within the blood vessels of the growth plate (GP), fibrin deposition was sometimes observed (→), phosphotungstic acid haematoxylin (PTAH). (F) Osteonecrosis (→) was often present just beneath the growth plate together with areas of necrotic bone marrow cells (), H&E. (G) Trabeculae with empty lacunae () were typically surrounded by bone resorbing osteoclasts (→), H&E. (H) Multiple S. aureus bacteria were often identified in connection with the capillary loops at the junction between the growth plate (GP) and the metaphysis (MP). Immunostaining for S. aureus.