Abstract

Listeria monocytogenes is a main foodborne zoonotic pathogen responsible for severe infections in both animals and humans. This study aimed to isolate and characterize L. monocytogenes from clinically affected small ruminants in Salah Aldeen Province, Iraq, and evaluate its molecular and phylogenetic relatedness to global strains. A total of 500 samples, including gallbladder swabs, mastitis samples, neurological lesions, and abortion samples, were collected from goats and sheep. Isolation was carried out via selective enrichment in Half-Fraser and Fraser broth followed by plating on HiCrome™ Listeria Ottaviani–Agosti Agar. A total of 22 isolates (4.4%) were recovered exclusively from encephalitis, abortion, and mastitis patients. Gram staining revealed short gram-positive rods with characteristic morphology. Automated biochemical identification via VITEK-2 confirmed the isolates as L. monocytogenes with a 97% probability. Molecular analysis demonstrated successful amplification of the 16S rRNA, hlyA, and inlA genes in all the isolates, confirming their virulence potential. Partial 16S sequencing and BLAST analysis revealed 95–96% identity with the Nigerian strain MG670095.1. Phylogenetic tree reconstruction further revealed minimal genetic variation among Iraqi isolates, clustering them as a single conserved genotype with a closer relationship to Nigerian strains than to Chinese and Indian isolates. These findings confirm the circulation of pathogenic L. monocytogenes in local dairy-producing small ruminants and highlight a potential zoonotic threat through raw milk consumption. Continued molecular surveillance and improved biosecurity measures are needed to protect animal health and minimize foodborne transmission risks.

Key words: Listeria monocytogenes, small ruminants, 16S rRNA, hlyA, inlA, and ALOA agar