Population structure of the mitochondrial cytochrome b gene region and microbiological analysis of cyst fluids from Coenurus cerebralis and hydatid cysts obtained from sheep in the Southeastern Anatolia Region of Türkiye.

Parasitic diseases are widely observed in different geographical and climatic regions and constitute significant problems in terms of animal health, public health, and livestock-based production systems. This study aimed to determine the molecular characterization and population genetic characteristics of Coenurus cerebralis and hydatid cyst cases observed in sheep in Siirt province, located in the Southeastern Anatolia Region of Türkiye, based on the mitochondrial cytochrome b (cytb) gene region, which was selected due to its ability to provide a balance between conserved structure and sufficient variability for reliable intraspecific discrimination, as well as to determine the presence of bacterial agents in cyst fluids and their antimicrobial susceptibility profiles. Between March and June 2025, 50 C. cerebralis and 50 hydatid cyst samples were collected from a licensed slaughterhouse. The cytb gene region was amplified by PCR from genomic DNA isolated from protoscoleces of hydatid cysts and scolices of C. cerebralis, and phylogenetic and population genetic analyses were performed following sequencing. In addition, bacterial agents were isolated from cyst fluids, and the antimicrobial susceptibilities of the isolates were evaluated. As a result of sequence analyses, reliable sequences of 538 bp in length were obtained in both parasite groups; six different haplotypes were identified in C. cerebralis isolates and eleven in hydatid cyst isolates. Population genetic analyses revealed moderate haplotype diversity (0.698 ± 0.050) and low nucleotide diversity (0.00258 ± 0.00041) with non-significant neutrality tests in the C. cerebralis population, whereas in the hydatid cyst population, both haplotype diversity (0.482 ± 0.087) and nucleotide diversity (0.00152 ± 0.00039) were low; however, significant negative Tajima's D and Fu's Fs values indicated a possible demographic expansion. Microbiological analyses revealed the presence of bacterial agents in 26% of C. cerebralis cysts and 6% of hydatid cysts. Antibiogram results showed that although most isolates were susceptible to some broad-spectrum antimicrobials, antimicrobial resistance was determined in varying levels. In conclusion, the findings shed light on the genetic structure and demographic dynamics of both parasites and demonstrate that cysts may pose a potential risk for secondary bacterial infections, highlighting the importance of antimicrobial susceptibility testing in treatment approaches.