Bacterial resistance is a public and one health problem. Free‐living birds can be reservoirs of multidrug‐resistant bacteria and resistance genes. This study aimed to characterize the antimicrobial resistance of Escherichia coli isolated from free‐living urban pigeons (Columba livia) in South Brazil. Ninety‐two animals were sampled, and one isolate was obtained from each one. The isolates were characterized, and the antimicrobial resistance profile and beta‐lactam and colistin resistance genes were investigated. The isolates were classified as phylogroups B1 (35%), B2 (33%), A (16%) and D (16%), and 14% of the strains had the eae virulence gene. All isolates were resistant to at least one antimicrobial, and 63% of them were multidrug‐resistant. Geographical location where the pigeons were captured and presence of the eae gene were associated with multidrug resistance. blaVIM and mcr‐1 genes were detected in one and two isolates, respectively. This is the first report of these genes in E. coli of pigeons. The blaVIM‐positive isolate was classified as Shiga toxin‐producing E. coli, and the isolates with mcr‐1 were classified as Enterohaemorrhagic E. coli and Enteropathogenic E. coli, which raise additional concerns related to public health since these are zoonotic pathotypes. The results reveal that pigeons carry multidrug‐resistant pathogenic E. coli, which may interest public health. Nonetheless, further studies on whether these animals are sources of contamination for humans must be performed to understand their role in spreading antimicrobial resistance.

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Mammary neoplasms with malignant mesenchymal components are not common in female dogs, and they are poorly understood. As such, this study aimed to describe the clinical presentation, histological findings, and the COX-2 immunohistochemical expression of mammary neoplasms in female dogs with malignant mesenchymal components, as well as verify the relationships between the different neoplasm types and these aspects. We selected 41 female mammary neoplasms (23 carcinosarcomas, 16 sarcomas, and 2 sarcomas in mixed tumors). Medical records were reviewed to obtain clinical data. Subsequently, histological slides were analysed to establish histological parameters, and immunohistochemistry was used to assess the expression of COX-2 receptors. Carcinosarcomas and sarcomas developed as large tumours, mainly in the abdominal and inguinal mammary glands, with frequent intratumoral necrosis and a low frequency of nodal metastasis. Fifty-eight percent of the cases of malignant mesenchymal proliferation were identified as osteosarcomatous, and 24.5% chondrosarcomatous and fibrosarcomastous each. The osteosarcomatous pattern was the most predominant type in sarcomas and carcinosarcomas, and was the only one that resulted in vascular invasion, regional lymph node metastases, and higher histologic grades. High COX-2 expression was detected in 10% of the carcinosarcomas and 25% of the sarcomas. In conclusion, sarcomas and carcinosarcomas showed similar results regarding the clinical and pathological aspects. Discovering carcinosarcomas and sarcomas with high COX-2 expression suggests that, in some cases, these neoplasms may respond to therapy with COX-2 inhibitors.