Exploitation of the diverse insertion sequence element content of dairy Lactobacillus helveticus starters as a rapid method to identify different strains

The species Lactobacillus helveticus is a commonly used thermophilic starter and/or adjunct culture for Swiss and Cheddar cheese manufacture. Its use is normally associated with flavour improvement which is known to be associated with culture traits such as rapid autolysis and high proteolytic activity. The genome of the commercial strain, DPC4571, was recently sequenced and found to have an abundance of IS sequences in terms of both abundance (213 intact) and diversity (21 types). Given this unique diversity for a lactic acid bacterium, we investigated whether PCR-based IS fingerprinting could be used as a discriminatory tool to distinguish between different strains of Lb. helveticus. A set of ten primers targeting five of the most numerous groups (ISL1201, ISLhe65, ISLhe2, ISLhe15 and ISL2) of IS elements was designed. Multiplex-PCR with all primers resulted in 1 – 12 discreet amplicons for each strain tested. The resultant fingerprints (in the 0.5 kb – 3 kb range) were found to be strain specific and reproducible. This approach thus provides a valuable method to distinguish between Lb. helveticus strains while giving some indication of the relative abundance of IS sequences in each strain.