Isolation, morphological characterization and host range determination of Iranian bacteriophages against Salmonella reference collection

Salmonella spp. is important in medicine. Most related infections are self-limited. Antibiotics are used for high risk patients such as children, old individuals and immune-compromised patients. Overuse of antibiotics has led to increased emergence of multi-drug resistant bacteria which are life-threatening. Phage therapy is an alternative method to reduce antibiotic use.
Waste water samples were collected from sewage system of Rasht City twice a month. Prepared suspensions of Salmonella reference collection A (SARA) number 1, 6 (S. typhimurium) and 46, 48, 51 (S. paratyphi B) and double LB broth were mixed with filtrated waste water. After centrifugation and filtration, serial dilutions were prepared and phages were isolated. Morphologic characteristics were determined using TEM (Transmission electron microscopy). Finally, to assess the spectrum effect of the bacteriophages, we determined host range against 19 SARA strains.
Clear plaque formation on double layer LB agar indicated lysis of the test strains by isolated phages. The results of host range showed that some of the phages were able to lyse a number of other bacteria of SARA collection. Imaging with TEM indicated that the isolated phages against SARA collection belonged to Siphoviridae and Podoviridae families.
This is the first report of phage isolation against Salmonella reference collection in Iran. SARA no. 51 (S. paratyphi B) was lysed by S. typhimurium phage. It means that the isolated phage may lyse S. typhi, which is an important human pathogen.