Peptidoglycan hydrolases as species-specific markers to differentiate Lactobacillus helveticus from Lactobacillus gallinarum and other closely related homofermentative lactobacilli.

We propose a new method that allows accurate discrimination of Lactobacillus helveticus from other closely related homofermentative lactobacilli, especially Lactobacillus gallinarum. This method is based on the amplification by PCR of two peptidoglycan hydrolytic genes, Lhv_0190 and Lhv_0191. These genes are ubiquitous and show high homology at the intra-species level. The PCR method gave two specific PCR products, of 542 and 747 bp, for 25 L. helveticus strains coming from various sources. For L. gallinarum, two amplicons were obtained, the specific 542 bp amplicon and another one with a size greater than 1,500 bp. No specific PCR products were obtained for 12 other closely related species of lactobacilli, including the L. acidophilus complex, L. delbrueckii, and L. ultunensis. The developed PCR method provided rapid, precise, and easy identification of L. helveticus. Moreover, it enabled differentiation between the two closely phylogenetically related species L. helveticus and L. gallinarum.