Ana, 

I think it is related to superinfection by two or more phages. (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC356221/pdf/jvirol00283-0119.pdf)

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC376275/pdf/jvirol00288-0036.pdf

http://www.sciencedirect.com/science/article/pii/0042682266902509

The opposite event  - Superinfection Exclusion,  a phenomenon in which a preexisting viral infection prevents a secondary infection with the same or a closely related virus, is much better studied - http://viralzone.expasy.org/all_by_species/3971.html

see some reading:

Cumby N, Edwards AM, Davidson AR, Maxwell KL. The bacteriophage HK97 gp15 moron element encodes a novel superinfection exclusion protein. J Bacteriol. 2012

Sep;194(18):5012-9. doi: 10.1128/JB.00843-12

Thanks Alex, very useful answer. I will go through all you've recommended me. Have a good day

Hi Ana mam , how can you isolated your phages , are u perform plaque assay for confirmation , please send me the procedure for isolation of phages and plaque assay procedure and i am also trying for this three types of phages now.

thank you,,,,

I think that depending on the moi and the type of phages an strains you're using, various phenomena could be involved.: if a cell gets more than one phage type and if the two (or more) phage types share a region of sequence identity (or close to identity) recombination can occur. Many years ago, we for instance observed recombination between two very distant phages of E.coli, Mu and P1, which only share sequence identity in their genome region coding for host range determinants (see PMID: 685175). Or, if the proteins determining host range of the two phage types are related,  phenotypic mixing (e.g. PMID:13325403, PMID:13352781, PMID:4579825) can occur: during viral particle assembly after mixed infection, fibers/host range determinants coded for by one phage type can bind to tails of the other phage type.

If the infected host carries one or more prophage, again with some sequence identity with the infecting phages, transactivation of prophage fiber/host range gene expression could occur with the same outcome as above. Of course recombinant will show stable altered host range while phenotypic mixing is a one shot event: upon further infection this altered host range will be lost and replaced by the original one.