Primer design using Bioinformatics tools.

Hi, 
I am currently working on a project designing a primer template for detecting any pathogenic species of leptospira in a serum sample, but I seem to have hit a roadblock. While the ncbi primer design tool has proven exceedingly useful, I am unable to figure out how to extract a conserved primer (both forward and reverse) that can be used for two different strains of borgpetersenii and three different strains of interoganns. I used mauve to get a comparative genomics profile of the five different strains, and then ran a highly conserved region through the ncbi pcr design tool. Wile it gives me results, these results are good for the particular species that I used. So how could i go about designing a primer that can be used for all these strains, if that is at all possible ? Any help or clarity would be greatly appreciated. Thanks in advance