Abstract. Klebsiella became an increasingly important source of community-acquired and nosocomial infections. Extensive
broad-spectrum utilization of antibiotics in hospitalized patients has contributed to both increased carriages of Klebsiella and the
development of multidrug-resistant strains. Many of these strains are extremely virulent and show a strong tendency to spread.
Bacteriophages, viruses that because bacterial lysis can serve as a useful tool for Klebsiella infection control. In this study, two
lytic phages designated as ØKPAS1 and ØKPAS2 infecting multidrug-resistant K. pneumoniae were isolated from sewage
samples collected in Assiut, Egypt. Using transmission electron microscopy, the morphology of isolated phages was characterized,
and their host range was determined. The morphological analysis revealed that both phages belong to the Podoviridae family.
ØKPAS1 has ahead of about 50 ± 5 nm in diameter and a short tail of 20 ± 2 nm in length, while ØKPAS2 has ahead of about 53
± 5 nm in diameter with a short tail of 19 ± 2 nm in length. ØKPAS1 phage showed a broader host range within genus Klebsiella
since it was able to lyse 8 out of 15 different Klebsiella cultures while ØKPAS2 was able to lyse only 5 out of 15. Both phages
could not infect bacteria from other genera such as Escherichia coli and Salmonella typhi. The isolated phage ØKPAS1 was able
to survive at a temperature up to 50 ᵒC and was infective in pH range between 4.0-9.0, while ØKPAS2 was able to survive at a
temperature up to 60 ᵒC and was stable over the pH range of 4,0 to10,0. Both phages were stable in chloroform. One-step growth
curves of ØKPAS1 and ØKPAS2 revealed that the latent period was 10 min for either phage, with burst sizes of about 120 and
245 pfu/ml for ØKPAS1 and ØKPAS2, respectively.