<P> In addition, because of the specific effectiveness of individual phages, for a high chance of success a mixture of phages is often applied . This means that' banks' containing many different phages must be kept and regularly updated with new phages . </P> <P> Further, bacteria can evolve different receptors either before or during treatment; this can prevent phages from completely eradicating bacteria . </P> <P> The need for banks of phages makes regulatory testing for safety harder and more expensive under current rules in most countries . Such a process would make difficult the large - scale use of phage therapy . Additionally, patent issues (specifically on living organisms) may complicate distribution for pharmaceutical companies wishing to have exclusive rights over their "invention", which would discourage a commercial corporation from investing capital in this . </P> <P> As has been known for at least thirty years, mycobacteria such as Mycobacterium tuberculosis have specific bacteriophages . No lytic phage has yet been discovered for Clostridium difficile, which is responsible for many nosocomial diseases, but some temperate phages (integrated in the genome, also called lysogenic) are known for this species; this opens encouraging avenues but with additional risks as discussed below . </P>

Bacteriophage therapy to combat bacterial infections in poultry