Comprehensive Phenotypic, MALDI-TOF, and Molecular Characterization of Listeria monocytogenes Isolated from Sheep with Reproductive and Neurological Disorders in Egypt

Listeria monocytogenes is a significant cause of abortion and neurological disorders in sheep, leading to substantial economic losses in livestock production. This study aimed to characterize L. monocytogenes isolated from sheep with reproductive and neurological disorders by assessing their antimicrobial resistance and virulence gene profiles using phenotypic, proteomic, and molecular approaches. Seventy clinical specimens (n=70) were obtained from sheep, including 40 placental tissues/uterine fluids and 30 brain abscesses. The overall prevalence was 14.28%, with slightly higher rates in placental tissues (15%) and brain abscesses (13.33%). Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) detected ten isolates as L. monocytogenes. Polymerase chain reaction (PCR) confirmed that all strains carried the hlyA and inlA genes linked to virulence and the ability to invade host cells. Antimicrobial susceptibility testing showed complete resistance to cefotaxime (100%) and varying levels of resistance to fosfomycin (60%), gentamicin (40%), ciprofloxacin (30%), and meropenem (10%). However, all isolates were susceptible to amoxicillin-clavulanic acid, levofloxacin, amikacin, doxycycline, and linezolid. No multidrug-resistant (MDR) strains were detected for the used antibiotics. These findings emphasize the importance of continued surveillance of L. monocytogenes and prudent antibiotic use in sheep farming systems.