Combination therapy containing mutated phages and antibiotics is a possible alternative to conventional treatment with antibiotics only. Phages are changed to overexpress selected proteins that regulate a group of genes, or groups of genes that are not directly attacked by antibiotics. In that way, they weaken the bacterial cells, thus enhancing the improved effects of antibiotics. Combination therapy targets nonessential genes, or genes that induce the SOS response in bacterial cells. In the experiment bacteria was treated with mutated phage φlexA3. In this phage, the lexA3 gene was placed under the control of the synthetic PLtetO promoter which caused overexpression of lexA3. φlexA3 suppressed the SOS response induced by antibiotic (quinolones) and improved the bactericidal effect of the same antibiotic. Bactericidal effect of other class of antibiotic (amino glycosides, β-lactam antibiotics) was also considerably improved with usage of lexA3. They also found out that mutated phage φlexA3 is capable of reducing the number of bacterial cells that already have acquired antibiotic resistance. Clinical relevance of mutated phage φlexA3 is visible from its efficacy in preventing death in mice infected with bacteria. Also other gene networks where also targeted to produce effective antibiotic adjuvants (SoxR, CsrA, OmpF) that proved efficient. Mutated bacteriophages are well suited for incorporating multiple targets. The multitarget phage in some surroundings (for example, biofilm) showed better bactericidal effect compared with single-target relatives.