Bioluminescent Imaging of Bacterial Biofilm Infections In Vivo - Bacterial Pathogenesis: Methods and Protocols - page 212

Key Words: Bioluminescent imaging; biophotonic imaging; animal modeling;
in vivo methods; UTI; cvs; catheter; biofilm; chronic; lux ; luciferase; antibiotic; real time;
non-invasive.
1. Introduction
In 1995, Contag et al. (1) first demonstrated the ability to monitor biolumines-
cently engineered bacteria in live mice using whole body biophotonic imaging
(BPI). Subsequent to this publication, a range of both Gram-positive and Gram-
negative bacteria were bioluminescently transformed and tested in vivo in a
number of standard animal models (2,3,4,5) , so establishing this technique as
a platform methodology for basic research and drug development. Most of
these initial studies were focused upon acute models of infection such as soft
tissue, sepsis, and pneumonia (3,4,6) . It was quickly realized, however, that this
technique was especially useful for monitoring chronic and complex infections,
such as biofilm infections (7,8,9,10,11,12,13) . These biofilm methodologies are
the key focus of this chapter.
Modern medical and surgical practice has come to rely increasingly on
various types of prosthetic and implanted devices. Despite sterilization, aseptic
procedures, and improvements in the materials and design of devices, microbial
colonization and biofilm formation on these devices is a common occur-
rence. These biofilm infections represent a serious medical problem, as mature
biofilms are resilient to the host immune response and conventional antibiotic
treatments. Most often such complications lead to failure of the implant and
the need for its complete removal (14,15) . To better understand and control
biofilm infections on indwelling medical devices, new approaches are essential,
especially in in vivo settings. To this end, BPI methodologies have been
developed to allow rapid, continuous real-time monitoring of biofilm infections
in a number of different animal models (7,8,9,10,12,13) . The use of biolumi-
nescent reporters to tag bacterial pathogens allows for the sensitive detection
of only live, metabolically active cells by BPI. Because of its non-destructive
and non-invasive nature, the imaging procedure can be performed repeatedly
without disturbing the integrity of the biofilm structure, as is the case with
procedure that involves detachment of the bacteria. Additionally, BPI experi-
ments can be performed without the loss of contextual influences of the animal's
host defense mechanisms.
Many of the biofilm models described in this chapter resemble characteristics
commonly found in human foreign-body infections, such as the establishment
of infection with low inoculum, persistence of infection without spontaneous
healing, and relapse of disease soon after treatment. This sensitive and quanti-
tative longitudinal monitoring approach is ideally suited to assess disease