Investigating genetic differences in Listeria strains used for listeriosis vaccine

Announcing a new article publication for Zoonoses journal. Listeriosis is among the most severe food-borne diseases affecting both animals and humans, and it presents a serious threat to public health, animal welfare, and the food industry. Food products contaminated with Listeria monocytogenes (Lm), the causative agent of listeriosis, are recognized as the primary source of infection. Since the late 1960s, the live whole-cell vaccine AUF (LWCV AUF) has been successfully used for the prevention of listeriosis in farm animals in Russian regions affected by the disease. This commercial vaccine is based on manufactured batches of the two ovine parental Lm strains isolated in various regions of the former USSR, Siberia, and Azerbaijan, from distinct animals in different years. This study was aimed at investigating whether these strains might belong to the same phylogenetic lineage and possess identical sequence types (STs).

One Lm vaccine strain was attenuated by multiple ultraviolet irradiation (UFR), whereas the other was obtained through routine techniques involving multiple passages on bacteriological media. Multilocus sequence typing (MLST) analysis was performed with amplification and sequencing of internal fragments of seven housekeeping genes (abcZ, bglA, cat, dapE, dat, ldh, and lhkA). For morphological comparison, both Lm strains were grown on Chromocult Listeria Agar Ottaviani and Agosti bacterial media.

Both attenuated Lm strains belonged to a single phylogenetic lineage (lineage II), and were assigned to different STs (ST124 and ST1538), and clonal complexes (CCs), (CC124 and CC7). In addition, these strains demonstrated different morphological characteristics when grown on bacterial media standard for Lm.

The LWCV AUF is formulated on two manufactured attenuated Lm strains belonging to two genetically different lineages.