A Mouse Model of Implant-Associated Infection

Abstract

Infections of implanted devices are of increasing frequency and importance, representing a significant limitation of many therapeutic modalities. There are puzzling features of implant-associated infection including the changes in microbial flora, the tendency to chronicity and impaired responses to conservative modes of treatment. The concept of the bacterial biofilm as a shielding mechanism generated by bacteria adherent to artificial surfaces has recently been proposed as an explanation for these features. The biofilm is a term applied to a complex comprising the implant surface, adherent bacteria and a specialized matrix enclosing the bacteria. The matrix of the biofilm is an electrostatically charged glue-like extracellular polymer derived by bacterial enzymes acting on tissue carbohydrates, formed by bacteria when adherent to surfaces. This matrix binds the bacteria to the surface providing a sequestration affording selective protection against harmful elements of the environment, especially mechanisms of host defenses and antimicrobial agents. These biological systems are complex to study because of the dynamic interaction of the microbial variables, host defenses, properties of synthetic materials and the biofilm matrix itself. There is a need for a laboratory model in which the variables can be controlled permitting the researcher to examine the outcomes of modifying one variable at a time in a planned and orderly manner. The practical way to attain this end is the conduct of studies in a stable reproducible animal model of localized biofilm-implant infection. Staphylococcus epidermidis is a representative of the class of microorganisms predominant in implant-associated infection. This paper describes the development of a model utilizing an implant-S. epidermidis-biofilm infection localized to the peritoneal cavity of the mouse. The natural history of the infection has been well documented and is stable in all respects for periods exceeding 3 months. This chronicity is especially advantageous in analyzing the impact of long-term therapeutic modalities and necessary periods of recovery and assessment. A representative example of an experimental use of this model to determine the relative efficacy of antibiotic therapeutic regimes is described, demonstrating its scope and efficacy.

A RAT MODEL OF POLYPROPYLENE GRAFT INFECTION CAUSED BY STAPHYLOCOCCUS EPIDERMIDIS

“…There have been few studies in which the foreign body was inoculated before implantation 17,32–35 . Longer incubation periods of 24–72 h allow for extensive bacterial biofilm formation on the surface of foreign body before implantation, which is again not in harmony with the clinical perioperative infection 32–34 . Shorter incubation periods seems to result in a more reliable and reproducible FBI model 17,35 .…”

“…These models consist of direct inoculations of prosthetic materials with bacteria at the time of surgery 36,37 . However, this increased the variability of the data and resulted in unpredictable infection rates in previous studies with small‐animal models 17,34 . Some investigators have claimed successful results using infection models with simultaneous topical bacterial inoculation along with the foreign body implantation in small animals.…”

Evolution of the Internal Fixation of Long Bone Fractures

“…The use of the principle of internal fixation is to minimise and isolate contact of the implant, and its surface must allow adherence of the soft tissue to avoid a fluid-filled dead space as is often seen around conventional electropolished steel implants. 99 The local resistance to infection was studied experimentally using human pathogenic Staphylococcus aureus in simulated internal fixation in the tibia of the rabbit. The study observed the effect of the design, material and application of the implant in relation to the number of colonyforming units required to produce an infection.…”

Estudo do raspado de conjuntiva e margem palpebral de pacientes tratados de retinoblastoma: etapa I - Microflora aeróbica

“…Recentemente, tem sido elaborado o conceito de que a microflora bacteriana em próteses implantadas possui a princí-pio um mecanismo "protetor" gerado por bactérias que aderem às superfícies artificiais, o que seria capaz de explicar por outro lado por que esse tipo de infecção vem crescendo em freqüência e importância, além das alterações na flora microbiana e a tendência à cronicidade (15) .…”