AUTHOR=Ramadan Hazem , Al-Ashmawy Maha , Soliman Ahmed M. , Elbediwi Mohammed , Sabeq Islam , Yousef Mona , Algammal Abdelazeem M. , Hiott Lari M. , Berrang Mark E. , Frye Jonathan G. , Jackson Charlene R. 

TITLE=Whole-genome sequencing of Listeria innocua recovered from retail milk and dairy products in Egypt

JOURNAL=Frontiers in Microbiology

VOLUME=14

YEAR=2023

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2023.1160244

DOI=10.3389/fmicb.2023.1160244

ISSN=1664-302X

ABSTRACT=<p>The similarity of the <italic>Listeria innocua</italic> genome with <italic>Listeria monocytogenes</italic> and their presence in the same niche may facilitate gene transfer between them. A better understanding of the mechanisms responsible for bacterial virulence requires an in-depth knowledge of the genetic characteristics of these bacteria. In this context, draft whole genome sequences were completed on five <italic>L. innocua</italic> isolated from milk and dairy products in Egypt. The assembled sequences were screened for antimicrobial resistance and virulence genes, plasmid replicons and multilocus sequence types (MLST); phylogenetic analysis of the sequenced isolates was also performed. The sequencing results revealed the presence of only one antimicrobial resistance gene, <italic>fos</italic>X, in the <italic>L. innocua</italic> isolates. However, the five isolates carried 13 virulence genes involved in adhesion, invasion, surface protein anchoring, peptidoglycan degradation, intracellular survival, and heat stress; all five lacked the <italic>Listeria</italic> Pathogenicity Island 1 (LIPI-1) genes. MLST assigned these five isolates into the same sequence type (ST), ST-1085; however, single nucleotide polymorphism (SNP)-based phylogenetic analysis revealed 422–1,091 SNP differences between our isolates and global lineages of <italic>L. innocua</italic>. The five isolates possessed an ATP-dependent protease (<italic>clp</italic>L) gene, which mediates heat resistance, on a <italic>rep</italic>25 type plasmids. Blast analysis of <italic>clp</italic>L-carrying plasmid contigs showed approximately 99% sequence similarity to the corresponding parts of plasmids of <italic>L. monocytogenes</italic> strains 2015TE24968 and N1-011A previously isolated from Italy and the United States, respectively. Although this plasmid has been linked to <italic>L. monocytogenes</italic> that was responsible for a serious outbreak, this is the first report of <italic>L. innocua</italic> containing <italic>clp</italic>L-carrying plasmids. Various genetic mechanisms of virulence transfer among <italic>Listeria</italic> species and other genera could raise the possibility of the evolution of virulent strains of <italic>L. innocua</italic>. Such strains could challenge processing and preservation protocols and pose health risks from dairy products. Ongoing genomic research is necessary to identify these alarming genetic changes and develop preventive and control measures.</p>