Unfortunately, the strain used to produce these plasmid vectors is proprietary and may not be shared. In reviewing the literature DH5α and XL1-blue appear to be frequently utilized strains. In addition, please see the link below to a potential product option. https://www.sigmaaldrich.com/product/sigma/cmc0007
To discuss further, please navigate to the link https://www.sigmaaldrich.com/techservice, and click on "Product Technical Inquiries" under the Products Section with all the required information so that a member of the Technical Service team can reach out to assist further.