Background: Pets, especially cats and dogs, represent a great potential for zoonotic transmission, leading to major health problems. The purpose of this systematic review was to present the latest developments concerning colistin resistance through mcr genes in pets. The current study also highlights the health risks of the transmission of colistin resistance between pets and humans. Methods: We conducted a systematic review on mcr-positive bacteria in pets and studies reporting their zoonotic transmission to humans. Bibliographic research queries were performed on the following databases: Google Scholar, PubMed, Scopus, Microsoft Academic, and Web of Science. Articles of interest were selected using the PRISMA guideline principles. Results: The analyzed articles from the investigated databases described the presence of mcr gene variants in pets including mcr-1, mcr-2, mcr-3, mcr-4, mcr-5, mcr-8, mcr-9, and mcr-10. Among these articles, four studies reported potential zoonotic transmission of mcr genes between pets and humans. The epidemiological analysis revealed that dogs and cats can be colonized by mcr genes that are beginning to spread in different countries worldwide. Overall, reported articles on this subject highlight the high risk of zoonotic transmission of colistin resistance genes between pets and their owners. Conclusions: This review demonstrated the spread of mcr genes in pets and their transmission to humans, indicating the need for further measures to control this significant threat to public health. Therefore, we suggest here some strategies against this threat such as avoiding zoonotic transmission.

Background: Pets are the closest animals to humans with a considerable risk of zoonotic transmission. This study aimed to screen colistin-resistant bacteria from stools of dogs and cats from Marseille, France. Screening of mcr genes in pets has never been reported in France. Methods: Fecal samples (n = 157) were cultivated on the selective Lucie-Bardet Jean-Marc-Rolain medium (LBJMR). Bacteria were identified using Microflex LS MALDI-TOF. The antibiotic resistance phenotype was investigated for several antibiotics (β-lactams, aminoside, cephalosporine, tetracycline, and sulfonamide). PCR techniques were performed to detect mcr genes. Results: A total of 218 bacteria were identified. For cats, intrinsically colistin-resistant bacteria were significantly higher than mcr-1 gene carriers (n = 4). Dogs had more bacteria with the mcr-1 gene (n = 10). Furthermore, cats had a high prevalence of Gram-positive bacteria (GPB), whereas dogs had GNB equal to GPB. The diversity of identified bacteria was due to the constitution of the pets’ microorganisms. Even though colistin use is monitored in France, pets harbor various colistin-resistant bacteria. Additionally, in this geographical area, bacteria bearing mcr-1 gene from dogs and cats were detected for the first time. Conclusions: The current study opens a new perspective: the spread of colistin resistance is independent of colistin use. What are the most factors related to the emergence of colistin resistance? The surveillance of pets must be considered a priority to avoid the spread of mcr genes. It is important to know the contribution that pets make to the pool of multidrug-resistant mcr-1-containing bacteria.

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