In this study, we propose a phagemid system that harbours the lethal transcription regulator. A few toxins, such as the Bgl II restriction enzyme, О» S holin, Gef and ChpBK, have been studied by researchers for their antibacterial effects ( Hagens & Blasi, 2003 Westwater et al., 2003).

There are a few reports showing the ability of nonlytic bacteriophages encoding lethal proteins that kill their host following amplification without releasing the progeny phage or endotoxins into the environment. To overcome this complication, the use of nonlytic phages as antibacterial agents has been considered. When using lytic phages, rapid lysis of bacteria and the release of endotoxins occur, which can lead to undesired side effects of phage therapy, even when the phages are administered orally ( Slopek et al., 1983). Lytic phage therapy as an alternative approach, however, may pose some clinical problems. Initial studies in phage therapy focused on therapeutic use of lytic phages. Now, as the problem of antibiotic resistance becomes ever more acute, researchers believe that bacteriophages are a promising potential therapy for treatment of bacterial diseases ( Damasko et al., 2005 Tanji et al., 2005). Bacteriophages were first used successfully to treat bacterial infections a decade before penicillin was discovered ( Hanlon, 2007). Phage therapy, the use of bacteriophages as biological therapeutic agents, is one prospective option for controlling pathogenic bacteria ( Matsuzaki et al., 2005 Sulakvelidze, 2005 Skurnik & Strauch, 2006). Furthermore, this problem has driven the search for bacteriophages against pathogenic microorganisms. Consequently, there has been increasing interest in the use of different natural or synthetic compounds to improve the antimicrobial activity of current antibiotics or to develop novel antibiotics ( Viveiros & Amaral, 2001 Shahverdi et al., 2007a, b). The emergence and spread of bacterial resistance to antibiotics is a critical health problem that has led to implementation of strategies to reduce the drawbacks of a large number of antimicrobial agents ( Sulakvelidze et al., 2001). Phage therapy, killing gene, filamentous bacteriophage, lethal catabolite gene activator protein, antibacterial agent Introduction Furthermore, the addition of an inducer to express the lethal protein is not required. The phage was engineered to remain lethal to its bacterial target, but incapable of replicating therein. This study provides a possible strategy for the exploitation of genetically engineered nonlytic phages as bactericidal agents by minimizing the risk of release of progeny phages and endotoxins into the environment.

Our further study using other test strains demonstrated that the host range of lethal phage is limited to E. TimeвЂ“kill assay experiments showed a considerable reduction in the number of surviving bacteria in both LB media and contaminated cow milk. The modified phagemid was propagated in the lethal CAP-resistant strain XA3DII. We constructed a modified nonreplicating M13-derived phage expressing a lethal catabolite gene activator protein (CAP) that is a Glu181Gln mutant of CAP. In vitro experiments were performed to assess the therapeutic value of genetically modified phages for controlling gastrointestinal Escherichia coli O157:H7 cells in LuriaвЂ“Bertani (LB) media and contaminated cow milk. Complications of chemotherapy, such as appearance of multidrug resistance, have persuaded researchers to consider phage therapy as a new method to combat bacterial infections.

Ecological biotechnology activator 2000