Direct Continuous Method for Monitoring Biofilm Infection in a Mouse Model

Abstract

We have developed a rapid, continuous method for real-time monitoring of biofilms, both in vitro and in a mouse infection model, through noninvasive imaging of bioluminescent bacteria colonized on Teflon catheters. Two important biofilm-forming bacterial pathogens, Staphylococcus aureus and Pseudomonas aeruginosa, were made bioluminescent by insertion of a complete lux operon. These bacteria produced significant bioluminescent signals for both in vitro studies and the development of an in vivo model, allowing effective real-time assessment of the physiological state of the biofilms. In vitro viable counts and light output were parallel and highly correlated (S. aureus r ‫؍‬ 0.98; P. aeruginosa r ‫؍‬ 0.99) and could be maintained for 10 days or longer, provided that growth medium was replenished every 12 h. In the murine model, subcutaneous implantation of the catheters (precolonized or postimplant infected) was well tolerated. An infecting dose of 10 3 to 10 5 CFU/catheter for S. aureus and P. aeruginosa resulted in a reproducible, localized infection surrounding the catheter that persisted until the termination of the experiment on day 20. Recovery of the bacteria from the catheters of infected animals showed that the bioluminescent signal corresponded to the CFU and that the lux constructs were highly stable even after many days in vivo. Since the metabolic activity of viable cells could be detected directly on the support matrix, nondestructively, and noninvasively, this method is especially appealing for the study of chronic biofilm infections and drug efficacy studies in vivo.Microbial adhesion and biofilm formation on medical implants is a common occurrence and represents a serious medical problem. Since biofilm microorganisms are difficult to eradicate with antibiotic therapy, chronic, recurrent infections often develop. With the increased use of prosthetic biomedical implants, chronic nosocomial infections have become prevalent in recent years (9,41). Bacterial colonization of indwelling devices can be a prelude to both systemic infection and malfunction of the device.A variety of techniques, such as direct microscopic enumeration, total viable count, metabolically active dyes, radiochemistry, and fluorescence, have been used to investigate microbial biofilms (1,4,8,14,17,18,23,29,33,38). While some of these methods are useful for in vitro studies, they have not proved ideal for the investigation of biofilms in experimental infection models. The difficulty in analyzing biofilms in vivo lies in the lack of tools that allow noninvasive longitudinal study design. Assays developed to date, both direct and indirect, are timeconsuming and laborious and involve the extraction of bacteria from support surfaces. To better understand and control biofilms on medical devices, rapid, direct, nondestructive, realtime quantitative monitoring methods that are adaptable to the clinical situation are needed. These assays may be used to develop new preventive and therapeutic methods to combat biofilm related infections.To ...

The Limitations of In Vitro Experimentation in Understanding Biofilms and Chronic Infection

“…There are a range of in vivo models that simulate chronic infections, such as surface wounds [75,76], subcutaneous wounds [77,78], implant-related (such as catheter, orthopaedic, and dental) [79][80][81][82][83], otitis media [84][85][86], and CF [87][88][89][90] to name but a few. As with all models, some are deemed more applicable than others.…”

“…In vivo models of chronic infection require artificial inoculation, usually at an inflated concentration, and with the aid of foreign bodies, so that the inoculation is not cleared by the host immune system [82,94,95].…”

Staphylococcus aureus promoter-lux reporters for drug discovery

“…7 A highly sensitive assay for the detection of bioactive compounds at low concentrations would be desirable. Bioluminescent reporters, such as lux, have varous applications, ranging from the detection of specific bacteria in foods 8 and model infections 9,10 to the detection of environmental contaminants. 11,12 These assays are extremely sensitive, accurately reflect real-time changes in gene expression and are well suited for monitoring the activity of promoters on an individual or a genome-wide level.…”

cwrA, a gene that specifically responds to cell wall damage in Staphylococcus aureus

“…In order to determine the conditions under which cwrA is expressed we generated two transcriptional fusion constructs in which the bacterial luxABCDE cassette (Kadurugamuwa et al, 2003) was appended downstream of either the putative promoter for cwrA (RN4220lux1) or cwrA itself (RN4220lux2) (Fig. 1a).…”