Prevalence, genetic diversity, and antimicrobial resistance of Plesiomonas shigelloides and occurrence of zoonotic parasites in the Türkiye's longest river.

Waterborne diseases continue to pose a major public health threat, particularly in regions where environmental contamination of freshwater sources intersects with agricultural and animal husbandry activities. Plesiomonas shigelloides, an emerging zoonotic bacterium capable of acquiring antimicrobial resistance, remains underrecognized in Türkiye's aquatic ecosystems despite its clinical relevance. This study investigated the occurrence, genetic diversity, and antimicrobial resistance of P. shigelloides and zoonotic parasites in the Kızılırmak River, focusing on a section located within the Kalecik district of Ankara Province that supports intensive agriculture and livestock production. Seventy-eight water samples were collected from seven riverside villages along the Kızılırmak River. A total of 60 P. shigelloides isolates (32.3 %) were confirmed by MALDI-TOF MS and PCR. Notably, most isolates recovered using ISO 21567:2004 Shigella spp. detection protocol. ERIC-PCR fingerprinting revealed high genetic similarity among isolates, while also identifying notable clonal diversity across sampling sites suggesting potential contamination routes between riverside villages. Antimicrobial susceptibility testing showed that 86.6 % of isolates were susceptible to all tested antibiotics (n = 13); however, one isolate was found to be multidrug-resistant (MDR) which displays resistance to amoxicillin-clavulanic acid, trimethoprim-sulfamethoxazole, imipenem, and meropenem. Parasitological analysis revealed the presence of Eimeria spp. (7.7 %), Cryptosporidium spp. (5.1 %), Giardia spp. (1.3 %), Dicrocoelium dendriticum, and Aspiculuris spp. This study is the first to report the presence of P. shigelloides in the Kızılırmak River, highlighting its role as both a reservoir and a transmission route for waterborne zoonotic pathogens, and revealing a low yet notable emergence of antimicrobial resistance in the aquatic ecosystem.