Method of determining evolutionary potential of mutant resistance genes and use thereof to screen for drug efficacy

A method of screening a drug for anti-pathogenic activity against a pathogen including a mutant anti-pathogenic resistance gene, the method comprising:

• providing a host cell comprising a mutant anti-pathogenic resistance gene either including two or more mucleic acid modifications or encoding a mutant anti-pathogenic polypeptide which includes two or more amino acid modifications, wherein the mutant anti-pethogenic resistance gene or mutant anti-pathogenic polypeptide confers a selectable advantage to the host cell, the mutant anti-pathogenic resistance gene having been prepared by successive rounds of mutagenesis and selection where each of the rounds confers enhancement of the resistance phenotype until clinical resistance is achieved and having been demonstrated to be likely to evolve through two or more independent mutation events, where each independent mutation event confers an enhancement of the resistance phenotype;
• growing the host cell on a selection media comprising a candidate drug or combinations thereof;
• and
• determining whether the host cell is capable of growing on the selection media, wherein absence of host cell growth and/or proliferation indicates anti-pathogenic activity for the candidate drug or combination thereof.