Porcine Models of Biofilm Infections with Focus on Pathomorphology

Abstract

Bacterial biofilm formation is one of the main reasons for a negative treatment outcome and a high recurrence rate for many chronic infections in humans. The optimal way to study both the biofilm forming bacteria and the host response simultaneously is by using discriminative, reliable, and reproducible animal models of the infections. In this review, the advantages of in vivo studies are compared to in vitro studies of biofilm formation in infectious diseases. The pig is the animal of choice when developing and applying large animal models of infectious diseases due to its similarity of anatomy, physiology, and immune system to humans. Furthermore, conventional pigs spontaneously develop many of the same chronic bacterial infections as seen in humans. Therefore, in this review porcine models of five different infectious diseases all associated with biofilm formation and chronicity in humans are described. The infectious diseases are: chronic wounds, endocarditis, pyelonephritis, hematogenous osteomyelitis, and implant-associated osteomyelitis (IAO).

Keywords: animal model; biofilm; chronic wounds; endocarditis; hematogenous osteomyelitis; implant-associated osteomyelitis; pig; pyelonephritis.

Figure 1

(A) Chronic venous leg ulcer. (B) Biofilm of P. aeruginosa [red stain] and S. aureus [green stain], identified by specific PNA FISH probes, surrounded by host cells (DAPI [blue stain]) in a human chronic wound. (C) CSLM three dimensional imaging of picture B. (D) Enlargement of picture C. The white arrows point to bacterial aggregates and the yellow arrows point to the wound surface (Kirketerp-Møller et al., 2008).

Figure 2

Establishment of four different models in conventional pigs of 30 kg. (A) Implant associated osteomyelitis, a drill hole is created in the right tibia followed by injection of bacteria and insertion of a small metal implant (Jensen et al., 2017). (B) Intravenous inoculation of bacteria for induction of endocarditis. Four days prior to inoculation, a permanent catheter was placed in the left ventricle (Christiansen et al., 2013b). (C) Free dissection of the right ureter, followed by insertion of a catheter used for inoculation of bacteria directly in the renal pelvis (Isling et al., 2011). (D) Four wounds created on the back at different time intervals for bacterial inoculation.

Figure 3

Left column: chronic spontaneous bacterial infections in conventional pigs (A–D) and a human (E). Middle column: experimental porcine models of human infections. Right column (except from picture A3): microscopy of the lesions present in the middle column. Row A: Chronic wounds. A1: Shoulder ulceration. A2: wound located on the back. A3: Bacteria (arrow) in a shoulder ulceration from a conventional pig. Row B: Endocarditis. B1: Left side, thrombotic valvular endocarditis (arrow). B2: A permanent catheter (arrow) inserted into the left ventricle prior to inoculation of bacteria. B3: Immunohistochemical staining of S. aureus (arrow) on the mitral valve (Christiansen et al., 2013b). Row C: Pyelonephritis. C1, C2: Polar located lesions of pyelonephritis (arrows). C3: Immunohistochemical staining of E. coli (arrows) in the proximal tubuli (Isling et al., 2011). Row D: Hematogenous osteomyelitis. D1, D2: Purulent osteomyelitis (O) in the femur. D3: Immunohistochemical staining of S. aureus (arrow) located in the capillary loops of the metaphysis (Johansen et al., 2012b). Row E: Implant-associated osteomyelitis. E1: Infected osteo-syntheses of the ankle. E2: Peri-implant infected bone tissue (double arrow) surrounding the implant cavity (ic), the implant has been removed. E3: Immunohistochemical staining of S. aureus (arrow) and in the insert (Jensen et al., 2017).