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

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

doi:10.3389/fmicb.2023.1160244

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

Front Microbiol. 2023 May 10:14:1160244. doi: 10.3389/fmicb.2023.1160244. eCollection 2023.

Authors

Affiliations

¹ Hygiene and Zoonoses Department, Faculty of Veterinary Medicine, Mansoura University, Mansoura, Egypt.
² Poultry Microbiological Safety and Processing Research Unit, US National Poultry Research Center, USDA-ARS, Athens, GA, United States.
³ Department of Food Hygiene and Control, Faculty of Veterinary Medicine, Mansoura University, Mansoura, Egypt.
⁴ Department of Microbiology and Immunology, Faculty of Pharmacy, Kafrelsheikh University, Kafr El-Sheikh, Egypt.
⁵ Evolutionary Biology, Institute for Biology, Freie Universität Berlin, Berlin, Germany.
⁶ Animal Health Research Institute, Agriculture Research Center, Cairo, Egypt.
⁷ Department of Food Hygiene and Control, Faculty of Veterinary Medicine, Benha University, Tukh, Qalyubia, Egypt.
⁸ Department of Bacteriology, Immunology and Mycology, Faculty of Veterinary Medicine, Suez Canal University, Ismailia, Egypt.

Abstract

The similarity of the Listeria innocua genome with Listeria monocytogenes 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 L. innocua 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, fosX, in the L. innocua 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 Listeria 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 L. innocua. The five isolates possessed an ATP-dependent protease (clpL) gene, which mediates heat resistance, on a rep25 type plasmids. Blast analysis of clpL-carrying plasmid contigs showed approximately 99% sequence similarity to the corresponding parts of plasmids of L. monocytogenes strains 2015TE24968 and N1-011A previously isolated from Italy and the United States, respectively. Although this plasmid has been linked to L. monocytogenes that was responsible for a serious outbreak, this is the first report of L. innocua containing clpL-carrying plasmids. Various genetic mechanisms of virulence transfer among Listeria species and other genera could raise the possibility of the evolution of virulent strains of L. innocua. 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.

Keywords: Egypt; Listeria innocua; clpL gene; genetic context; milk; phylogenetic analysis; whole-genome sequencing.