Two new techniques for obtaining consistent results when growing Renibacterium salmoninarum on KDM2 culture medium

We recently showed that the inconsistent performance of the culture medium KDM2 in supporting growth of the fastidious kidney disease agent (Renibacterium sallnoninarurn = Rs) was due to a lot-to-lot variation in the composition of a commercially available peptone used as a medium ingredient.We now report on 2 procedures for obtaining consistent growth of the pathogen on KDM2, regardless of the lot of peptone used in preparing the medium.The first procedure involves the recently described nurse culture technique that has the added advantages of accelerating growth of Rs and of increasing the sensitivity with which the pathogen can be detected.The second procedure is to supplement KDM2 with a small amount of KDM2 broth that has previously been used to grow Rs (= spent broth).A metabolite (or metabolites) produced by the pathogen during its growth in the broth appears to substitute effectively for the nurse culture by providing the Rs growth initiating factor(s) that, apparently, is in short supply in certain lots of peptone.These techmques remove the need to pre-test peptone lots to ensure that they will perform satisfactorily when used in KDM2 for growing Rs.