Antimicrobial Susceptibility and Molecular Characterization of Corynebacterium pseudotuberculosis Isolates Recovered From Caseous Lymphadenitis in Sheep

Corynebacterium pseudotuberculosis is a well-recognized etiological agent responsible for caseous lymphadenitis (CLA) and ulcerative lymphangitis (UL) in small and large ruminants, respectively. This pathogen is frequently associated with poor therapeutic outcomes in animals. In the present study, 30 bacterial isolates, recovered from 300 lymph node and pus samples (10%), were identified as Corynebacterium spp. Molecular confirmation using 16S rRNA and pld gene PCR verified 11 of these isolates as C. pseudotuberculosis, while one isolate was identified as C. jeikeium, a first record from sheep in Egypt. The isolates were subjected to antimicrobial susceptibility and genotyping using enterobacterial repetitive intergenic consensus-polymerase chain reaction (ERIC-PCR). Cluster analysis classified the isolates into two major clusters: Cluster 1 (C1) represents C. jeikeium, and cluster 2 (C2) represents C. pseudotuberculosis. Cluster 2 was further subdivided into four subclusters (2A–2D), reflecting epidemiological linkages among livestock in Giza and Cairo governorates. Additionally, the antimicrobial potential of silver nanoparticles (AgNPs) and silver nitazoxanide-loaded nanoparticles (Ag-NPs/NTZ) was assessed against both C. pseudotuberculosis and C. jeikeium. The results revealed extensive multidrug resistance (MDR) among C. pseudotuberculosis and C. jeikeium isolates to several antibiotic classes. However, all C. pseudotuberculosis strains demonstrated 100% sensitivity to vancomycin, amoxicillin–clavulanic acid, gentamicin, and amikacin. These findings support the recommendation of these agents for effective control of CLA. Furthermore, silver nitazoxanide nanoparticles showed a promising in vitro effect against both Corynebacterium spp. recovered in this study and may represent a potential and novel adjunctive approach for managing C. pseudotuberculosis infections.