This concept encompasses three broad areas:

i. The first approach (outlined in Chapters 1-10) involves the use of selected pathogens as effective prophylactic and/or therapeutic agents by replacement technology. The rationale for this "fighting fire with fire" approach being that for most species the strongest niche competitors are often the same or closely related species.

ii. The second approach (outlined in Chapters 11-14) involves the isolation and purification of pathogen-specific immunogenic proteins for direct application, thus removing the necessity for potentially harmful bacterial carrier platforms.

iii. The third approach (outlined in Chapter 15) provides an alternative to either (i) or (ii) above. This approach involves equipping non-pathogenic bacteria with the genetic elements necessary to survive the many stresses encountered outside the host as well as the myriad of antimicrobial hurdles faced during host transit and/or colonisation.