sentence: Genomic DNA isolated from streptomycin resistant and chloramphenicol sensitive clones were used as a template to screen for replacement of rpsL-cat with the mutant allele with primers JG402 / JG407 for HP0381 , JG378 / JG383 for HP1369 , JG384 / JG389 for HP1471 , JG390 / JG395 for HP1522 , and JG396 / JG401.To perform colonization assays Helicobacter free C57BL / 6 J mice were purchased from the Animal Resource Centre ( Perth , Western Australia ) .