Isolation and Molecular Characterization of Corynebacterium pseudotuberculosis: Association with Proinflammatory Cytokines in Caseous Lymphadenitis Pyogranulomas

SIMPLE SUMMARY: Caseous lymphadenitis (CLA) is caused by Corynebacterium pseudotuberculosis (C. pseudotuberculosis) and is considered one of the most serious infectious diseases in small ruminants with poor efficacy of treatment. In this study, C. pseudotuberculosis was isolated from 120 abscessed lymph nodes (LNs) and organs at the Matrouh abattoir in Egypt, confirmed by PCR and by intraperitoneal injection of male Guinea pigs, and then characterized for antimicrobial susceptibility and its genetic-relatedness by enterobacterial repetitive intergenic consensus polymerase chain reaction (ERIC-PCR). Gross examination of affected LNs and organs revealed marked enlargement with caseated green pus surrounded by a dense fibrous capsule. Cross section of some LNs exhibited an onion ring-like appearance, which is a pathognomonic feature of CLA. In immunohistochemical staining, IL1β is a more crucial proinflammatory cytokine than TNF in the regulation of C. pseudotuberculosis infection, which is accompanied by marked NF-κB expression. This study aids in the epidemiological investigation and preliminary etiological analysis in the general development of ERIC-PCR for C. pseudotuberculosis genotyping and characterization along with susceptibility to antibiotics to select an appropriate treatment. ABSTRACT: Corynebacterium pseudotuberculosis (C. pseudotuberculosis) is a causative agent of numerous chronic diseases, including caseous lymphadenitis (CLA) in sheep and goats, which has a zoonotic potential in humans in addition to a poor therapeutic response. In this study, out of 120 collected samples, only 12 (10%) were positive for C. pseudotuberculosis by PCR and by intraperitoneal injection of male Guinea pigs and then characterized for antimicrobial susceptibility and its genetic-relatedness by enterobacterial repetitive intergenic consensus polymerase chain reaction (ERIC-PCR), which showed 2–4 bands ranging from 100 to 3000 bp that can be clustered into four clusters (C1–C4). Despite the serotype biovar 1 only infecting sheep and goats, ERIC–PCR reveals intra-subtyping variation. Examination of affected LNs and organs revealed marked enlargement with either thick creamy green pus or multiple abscesses of variable sizes with a central caseated core surrounded by dense fibrous capsule. A histopathological examination revealed a central necrotic core surrounded by a peripheral mantle of mononuclear cells and a fibrous capsule. Positive immune expression of nuclear factor kappa B (NF-κB/p65) and interleukin-1β (IL-1β) and negative expression of tumor necrosis factor (TNF) in CLA is the first report to our knowledge. Conclusion: In CLA pyogranulomas, IL1β is a more crucial proinflammatory cytokine than TNF in the regulation of C. pseudotuberculosis infection, which is accompanied by marked NF-κB immunoexpression. Therefore, the NF-κB/p65 signaling pathway is involved in the activation of IL1β, and additional immunohistochemical studies are required to determine the various roles of NF-κB/p65 in the inflammatory response within CLA pyogranulomas to control this pathogen.