Detection of listeria monocytogenes and atypical hemolytic listeria innocua from mastitis cows’ milk in Baghdad Province

Mastitis is a major problem in the dairy industry globally. No adequate studies are available for detecting Listeria spp in clinical mastitis in Iraq. The current study aimed to determine Listeria spp in clinical cow’s mastitis milk. Fifty clinical cows’ mastitis milk samples were collected from Baghdad farms, Iraq, from September 2023 to March 2024. Identification of bacteria was done by conventional culture methods, biochemical tests, and VITEK2 compact system, followed by molecular confirmation using the Polymerase Chain Reaction (PCR) assay targeting genes followed by nucleotides sequencing. The antimicrobial resistance pattern was studied by the disc diffusion method against eight antibiotics. Listeria isolates were also subjected to PCR to determine the presence of three virulence genes: prfA, actA, and hylA. The results revealed presence of Listeria spp. at 6%, including L. monocytogenes at 4% and atypical hemolytic L. innocua at 2% of the clinical mastitis milk. Listeria spp. were highly resistant to erythromycin, ampicillin, cotrimoxazole (sulfamethoxazole/trimethoprim), chloramphenicol, vancomycin, and tetracycline. At the same time, all the isolates were multidrug resistant (MDR) and had a high multiple antibiotic resistance (MAR) index. In addition, L. monocytogenes isolates harbored L. monocytogenes-associated virulence genes, whereas atypical hemolytic L. innocua, isolated for the first time in Iraq, lacked these genes, but positive for species specific genes. Finally, the study concludes that the presence of virulent and highly antimicrobial resistant L. monocytogenes and atypical hemolytic L. innocua are causative agents of mastitis, and indicates the zoonotic potential of listeriosis and economic losses in dairy cattle.