Listeriosis is a serious food-borne disease affecting both humans and animals. It poses a significant public health risk, threatens animal welfare, and impacts the food industry. The disease is caused by Listeria monocytogenes (Lm), which contaminates food products and serves as the primary source of infection. The live whole-cell vaccine AUF (LWCV AUF), developed in the late 1960s, has been widely used in Russian regions to prevent listeriosis in farm animals. This vaccine is based on two ovine Lm strains isolated from different animals in distinct regions of the former USSR, Siberia, and Azerbaijan.
Study Aim: Genetic Investigation of Listeria Strains
The objective of this study was to determine if the two Lm strains used in the LWCV AUF vaccine share the same phylogenetic lineage and possess identical sequence types (STs). Researchers aimed to investigate the genetic diversity between these strains and understand their relationship to each other.
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Methodology: MLST and Morphological Analysis
The study employed multilocus sequence typing (MLST) to analyze the genetic structure of the two Lm strains. Internal fragments of seven housekeeping genes (abcZ, bglA, cat, dapE, dat, ldh, and lhkA) were amplified and sequenced for this purpose. The strains were also grown on Chromocult Listeria Agar Ottaviani and Agosti bacterial media to assess their morphological characteristics.
Results: Genetic and Morphological Findings
The results showed that both attenuated Lm strains belonged to the same phylogenetic lineage (lineage II) but were assigned to different sequence types (STs) and clonal complexes (CCs). Specifically, one strain was classified as ST124 and CC124, while the other was ST1538 and CC7. Despite belonging to the same lineage, the strains exhibited distinct genetic profiles.
Additionally, the strains demonstrated different morphological characteristics when cultured on standard Lm bacterial media. These differences underline the genetic divergence between the two strains used in the vaccine formulation.
Conclusion: Genetically Diverse Strains in LWCV AUF
The study concludes that the two attenuated Lm strains used in the LWCV AUF vaccine belong to two genetically distinct lineages. This genetic diversity may have implications for the vaccine’s efficacy and highlights the need for ongoing research into the genetic makeup of Listeria strains used in vaccines.
