Beyond bacteria - large agents with analogies to Mimiviruses detected in canine cancers - reexamining Gram staining in cancer diagnostics

Sep 22, 2026

Upload by Aurelia

Gram staining traditionally classifies bacteria by cell-wall properties, yet Mimiviruses and other large mammalian agents can retain Gram-staining signals despite not being typical bacteria. Mimivirus-like agents with Gram-positive staining were previously reported in human malignant samples, suggesting involvement in a distinct carcinogenic pathway. To translate these findings to animals, researchers tested canine malignancies and distinguished analogous Gram-positive agents from conventional bacteria using Gram staining across diverse tumor types.

LanguageEnglish

CategoryHealthcare

FormatPDF

Pages7

Reading Time18 min

AccessFree to download

Key points

Background and rationale

Study design and sampling

Gram-staining findings and differentiation

Implications across species

Introduction

Mimiviruses and revised classifications

Large mammalian agents in human cancers

Need for veterinary/animal validation

Materials and methods

Specimens and tumor categories

TYPE Brief Research Report PUBLISHED 20 February 2026 DOI 10.3389/fvets.2026.1759298 OPEN ACCESS EDITED BY Carlos Eduardo Fonseca-Alves, Paulista University, Brazil REVIEWED BY Fernanda Moura, São Paulo State University, Brazil Paul Tutu, Ion Ionescu de la Brad University of Agricultural Sciences and Veterinary Medicine of Iași, Romania *CORRESPONDENCE Viola Zappone [viola.zappone@unime.it](viola.zappone@unime.it)[ ](viola.zappone@unime.it)Elena Angela Lusi [elenaangelalusi@yahoo.it](elenaangelalusi@yahoo.it)[ ](elenaangelalusi@yahoo.it)RECEIVED 02 December 2025 REVISED 27 January 2026 ACCEPTED 29 January 2026 PUBLISHED 20 February 2026 CITATION Lusi EA, Caicci F, Zappone V, Quartuccio M, Dragà I, Ieni A, Mannarino C, Mazzullo G and Rifici C (2026) Beyond bacteria: large agents with analogies to Mimiviruses detected in canine cancers: reexamining Gram staining in cancer diagnostics. Front. Vet. Sci. 13:1759298 . doi: 10.3389/fvets.2026.1759298 COPYRIGHT © 2026 Lusi, Caicci, Zappone, Quartuccio, Dragà, Ieni, Mannarino, Mazzullo and Rifici. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY) . The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms. Beyond bacteria: large agents with analogies to Mimiviruses detected in canine cancers: reexamining Gram staining in cancer diagnostics Elena Angela Lusi 1*, Federico Caicci 2, Viola Zappone3*, Marco Quartuccio3, Ilaria Dragà3, Antonio Ieni4, Cornelia Mannarino3, Giuseppe Mazzullo3 and Claudia Rifici3 1St Vincent Health Care Group-UCD, Dublin, Ireland, 2Department of Biology, Electron Microscopy Unit, University of Padua, Padua, Italy, 3Department of Veterinary Sciences, University of Messina, Messina, Italy, 4Department of Human Pathology in Adult and Developmental Age "Gaetano Barresi", Section of Pathology, University of Messina, Messina, Italy While Gram staining is traditionally used for classifying bacteria based on their cell wall properties, Mimiviruses and large mammalian agents can also retain the Gram stain, despite not being typical bacteria. In fact, Mimivirus-like agents that exhibit Gram-positive staining were first found in human tissues, particularly in malignant samples, suggesting that these agents may be involved in a unique carcinogenic process. In order to translate the findings published in human medicine to animal models, we evaluated for the first time the presence of analogous Gram-positive agents in canine malignancies and differentiate them from traditional bacteria. Using Gram staining, we analyzed 35 canine tumors across various malignancy types, including 7 sarcomas, 15 carcinomas, and 13 round cell tumors such as mast cell tumors, transmissible venereal tumors and melanomas. Normal tissues and bacteria were used as controls. We were able to identify Gram-positive granulations, exhibiting intracytoplasmic, intra-nuclear and perinuclear patterns, measuring 1–2 μm that were distinct from traditional bacteria. This study, the first of its kind in the veterinary literature, supports comparable published findings in human research and advances our knowledge of the pathophysiology of cancer across species. KEYWORDS canine cancer, Gram staining, human cancer, Mimivirus-like agent, oncogenic agent 1 Introduction The discovery of Mimiviruses, large DNA viruses that infect amoebas, challenged traditional distinctions between viruses and cellular organisms and prompted significant reevaluation in microbiology and virology. In particular, their discovery has challenged existing paradigms regarding the complexity and classification of viruses, introduced the concept that virus

FAQs

Why is Gram staining considered in this research on cancer diagnostics?

Gram staining is used to classify bacteria by cell-wall properties, but the study focuses on large agents that can also retain Gram-staining signals, challenging the assumption that Gram-positive staining indicates only bacteria.

What did the researchers look for in canine tumors?

They evaluated canine malignancies for analogous Gram-positive agents that resemble Mimivirus-related findings in human tissues, and they differentiated these agents from traditional bacteria.

How were the canine tumor samples organized in the study?

Gram staining was applied to 35 canine tumors across multiple malignancy types, including sarcomas, carcinomas, and round cell tumors; normal tissues and bacteria were used as controls.

Sep 22, 2026

Upload by Aurelia