Cephalosporins and polymyxins are employed in antimicrobial protocols to control and treat neonatal infections and post-weaning diarrhoea in swine operations. We conducted a longitudinal study to evaluate the colonization and transmission of antibiotic–resistant Escherichia coli in sows and their piglets in a farrow-to-finish operation, focusing on characterization of Extended Spectrum Beta-Lactamase (ESBL) and mcr genes, virulence traits and genetic relatedness. A total of 293 E. coli isolates were obtained from faecal samples collected in five time points. At birth bla_CTX-M-1group cluster was detected in E. coli isolates from 9 sows and 49 piglets (73.41%), while in the following four’ piglets sampling moments it was detected in 91.8%, 57.6%, 71.4% and 97.4%. The gene mcr-1 was detected in E. coli from one sow and from three piglets from different litters at birth and increased in the first weeks of piglet life (68.85%, 100%, 90% and 8.1%). A new mcr-4 allele, mcr-4.7, was identified in 3.28%, 28.57%, 7.5% of E. coli isolates. Most mcr-positive E. coli isolates (96,7%) carried bla_CTX-M-1Group genes and 93,33% carried both mcr-4 and mcr-1. CTX-M-1 and CTX-M-32 were the most predominant ESBLs. Plasmids belonged to IncI1, IncF and IncN groups. Most isolates belong to phylogenetic group B1; PAI IV₅₃₆ marker was detected in nine isolates. The strains were kept in the different stages of the piglets’ life. The use of ceftiofur and colistin may explain the high prevalence and co-selection of bla_CTX-M-1Group and mcr-1 and/or -4 genes, contributing to the maintenance of resistant and virulent isolates throughout the pig life cycle that may reach the food chain.

Carbapenem-resistant Acinetobacter baumannii is a common pathogen associated with healthcare-acquired infections, and robust infection prevention and control protocols exist in human healthcare settings. In contrast, infection prevention and control (IPC) standards are limited in veterinary medicine, necessitating further investigation. Examine the possible transmission of carbapenem-resistant Acinetobacter spp. in a veterinary practice where a cat was diagnosed with an OXA-23-producing A. baumannii ST2 strain. Environmental samples together with nasal and hand swabs from the veterinary personnel were collected. All swabs were screened for the presence of extended-spectrum-β-lactamase- and carbapenemase-producing Enterobacterales, meticillin-resistant staphylococcus and multi-drug-resistant Acinetobacter spp. Whole-genome sequencing was performed for carbapenemase-producing strains. Of the veterinary staff, 60% carried meticillin-resistant Staphylococcus epidermidis. Environmental evaluation showed that 40% (N=6/15) of the surfaces analysed by contact plates and 40% (N=8/20) by swabs failed the hygiene criteria. Assessment of the surfaces revealed contamination with five OXA-23-producing Acinetobacter spp. strains: an OXA-23-producing Acinetobacter schindleri on the weight scale in the waiting room; and four OXA-23-producing Acinetobacter lwoffii strains, on different surfaces of the treatment room. The bla_OXA-23 gene was located on the same plasmid-carrying Tn2008 across the different Acinetobacter spp. strains. These plasmids closely resemble a previously described OXA-23-encoding plasmid from a human Portuguese nosocomial Acinetobacter pittii isolate. Distinctly, the OXA-23-producing A. baumannii ST2 clinical strain had the resistant gene located on Tn2006, possibly inserted on the chromosome. The detection of an OXA-23-producing A. baumannii ST2 veterinary clinical strain is of concern for companion animal health and infection, prevention and control. This study established the dynamic of transmission of the plasmid-mediated bla_OXA-23 gene on critical surfaces of a small animal veterinary practice. The genetic resemblance to a plasmid found in human nosocomial settings suggests a potential One Health link.

Colistin, a polymyxin antibiotic considered a last-line treatment for multidrug-resistant Gram-negative infections, has been widely used in livestock, promoting resistance in bacterial populations that can disseminate through the environment. Although rarely used in companion animals, dogs and cats can acquire and spread colistin-resistant strains through shared environments, acting as potential reservoirs of resistance. Reliable detection of resistant strains remains challenging due to technical limitations of routine susceptibility tests. Despite these constraints, epidemiological studies demonstrate the global presence of colistin-resistant bacteria in companion animals, with multiple plasmid-mediated colistin-resistant genes (mcr) identified in different bacteria species. Evidence of clonal and plasmid-mediated sharing of resistant strains between companion animals, humans, and, in some cases, food-producing animals highlights the complex and multidirectional nature of transmission. Although the directionality of transmission remains difficult to establish, the detection of colistin-resistant bacteria in companion animals is concerning. Addressing this challenge requires a One Health approach, integrating coordinated surveillance and infection and control measures in veterinary practices to safeguard the effectiveness of this critical last-resort antibiotic. This review summarizes current knowledge on colistin resistance mechanisms, diagnostic challenges, epidemiology, and the potential for interhost transmission, highlighting the role of dogs and cats as potential reservoirs of colistin resistance.

This study assessed longitudinal trends in antimicrobial resistance (AMR) among Enterobacterales causing companion animal infections in Portugal between 2020 and 2023 and characterized carbapenemase-producing Enterobacterales (CPE). A collection of 4155 non-duplicate clinical Enterobacterales isolates underwent antimicrobial susceptibility testing mainly through disk diffusion, targeting β-lactams, fluoroquinolones, aminoglycosides and folate pathway inhibitors. Possible bacteria-AMR associations and temporal trends were statistically assessed. Potential CPE were selected on Brilliance™ CRE Agar, confirmed by multiplex PCR and characterized by whole-genome sequencing (Illumina NovaSeq). In silico MLST was performed and the clonality of the strains was evaluated through maximum likelihood phylogenetic trees and pairwise SNP matrixes. Klebsiella spp. and Enterobacter spp. exhibited a higher likelihood of AMR than Escherichia coli (P < 0.001, ORs between 2.56 and 14.32). Most AMR phenotypes remained stable or declined over time, although fluoroquinolone resistance increased toward the end of the study period. Eighteen CPE mostly associated with high-risk global STs (E. coli ST410 and ST457, Klebsiella pneumoniae ST11, ST147 and ST307, respectively) were detected, carrying bla_KPC-3, bla_NDM-5, bla_OXA-181 or bla_OXA-244. Genomic analysis showed four CPE strain pairs from epidemiologically unrelated sources had < 10 SNPs differences, indicating possible recent clonal transmission of E. coli ST4981 and K. pneumoniae ST147 and ST273 strains. Overall, this study presents longitudinal AMR surveillance data from companion animal Enterobacterales infections and characterizes the genetic diversity of CPE, having detected international high-risk clones and possible transmission events. These findings reinforce the importance of integrating companion animals into One Health surveillance systems and antimicrobial stewardship strategies.