الفهرس 
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Abstract
Nosocomial infection is considered as one of significant health care problems because it is associated with elevated morbidity and mortality rates and leads to prolonged hospital stay. In addition to extra economic efforts. Nosocomial infection is closely related to antibiotic resistance due to overdose of antibiotics consumption within hospitals and the misuse outside hospitals leading to the emergence of antibiotic resistant bacteria by multiple mechanisms that subsequently cannot be treated by previously successful regiments. The present investigation was conducted to isolate and characterize some virulent bacteriophages infecting some nosocomial bacteria and study the efficacy of these phages in reduction of bacterial density which is a plateform for finding alternative solution to that problem. To address this aim, antibiotic resistant bacteria were isolated from nosocomial sites of Talkha Central Hospital, then identified morphologically, culturally, biochemical, and molecular. Lytic phages against the isolated bacteria were isolated from sewage water. Both plaque purification and differential centrifugation methods were used to obtain the purified phage, spot test was used in susceptibility test, where double layer agar technique was used in determination of adsorption rate and physical stability of phage. Also bacterial reduction assay was performed. The results indicated that the isolated antibiotic resistant bacteria were identified as Pseudomonas aeruginosa, Escherichia coli, and Proteus mirabilis. The isolated phages from sewage water could be distinguished into 5 types according to plaque morphology and electron microscopy that were designated by PAP1,PAP2, and PAP3 (three phages active against P. aeruginosa), ECP (one phage against E. coli), and PMP (one phage against P. mirabilis). Host range of the isolated phages revealed that they were polyvalent and could infect different bacterial genera. affective at high temperature up to 60°C, stable at wide level of pH from 5.4-10.6, still survive at room temperature from 3 months to more than a year, and become adsorbed in host surface within 4-25 min. Moreover, the new phage was able to make 64- 98% reduction of bacterial count after infection by 20 min. Furthermore, PAP1 phage continued in bacterial reduction through 24 h of incubation period. These properties may make this phage a good candidate as therapeutic agent.