Polymyxin E (colistin) is a medically important active substance both in human and veterinary medicine. Colistin has been used in veterinary medicine since the 1950s. Due to the discovery of the plasmid-borne mcr gene in 2015 and the simultaneously increased importance in human medicine as a last-resort antibiotic, the use of colistin for animals was scrutinised. Though veterinary colistin sales dropped by 76.5% between 2011 to 2020, few studies evaluated real-world data on the use patterns of colistin in different European countries and sectors. A survey among veterinarians revealed that 51.9% did not use or ceased colistin, 33.4% decreased their use, 10.4% stabilised their use, and 2.7% increased use. The most important indications for colistin use were gastrointestinal diseases in pigs followed by septicaemia in poultry. A total of 106 (16.0%) responding veterinarians reported governmental/industry restrictions regarding colistin use, most commonly mentioning “use only after susceptibility testing” (57%). In brief, colistin was perceived as an essential last-resort antibiotic in veterinary medicine for E. coli infections in pigs and poultry, where there is no alternative legal, safe, and efficacious antimicrobial available. To further reduce the need for colistin, synergistic preventive measures, including improved biosecurity, husbandry, and vaccinations, must be employed.

Mycoplasma synoviae is one of the economically most significant avian Mycoplasma species. It can cause great financial losses to the poultry industry by inducing respiratory diseases, infectious synovitis, or eggshell apex abnormalities. There are different approaches to control M. synoviae infection. Although antimicrobial therapy cannot replace long-term solutions, like eradication and vaccination, this strategy can be effective in the short term, as adequate antibiotic treatment can relieve economic losses through the attenuation of clinical signs and reduction of transmission. Using broth microdilution method, minimal inhibitory concentration (MIC) values to fourteen antibiotics related to eight antimicrobial groups were determined in 96 M. synoviae strains. Whole genome sequencing and sequence analysis revealed mutations potentially associated with decreased susceptibility to fluoroquinolones, macrolides and lincomycin. Molecular markers responsible for the high MICs to fluoroquinolones were found in the gyrA, gyrB, parC and parE genes. Besides, single nucleotide polymorphisms identified in genes encoding the 23S rRNA were found to be responsible for high MICs to the 50S inhibitor macrolides and lincomycin, while amino acid change in the 50S ribosomal protein L22 could be associated with decreased susceptibility to macrolides. The revealed mutations can contribute to the extension of knowledge about the genetic background of antibiotic resistance in M. synoviae. Moreover, the explored potentially resistance-related mutations may serve as targets for molecular biological assays providing data of antibiotic susceptibility prior to the laborious and time-consuming isolation of M. synoviae strains.

Some strains of Enterococcus cecorum can cause spondylitis and bacterial osteomyelitis. Translocation and bacteremia are pivotal to the pathogenesis and clinical disease. Virulence typing to distinguish extra-intestinal disease of lesion from cloacal strains remains difficult. We investigated if organoids can be applied to differentiate between E. cecorum strains that are more or less virulent. Floating chicken intestinal organoids combine the complex cell system of the gut with an easily accessible apical-out orientation. The organoids were treated with four E. cecorum strains that differ in original isolation, lesion, or cloacal, and bacterial load was determined after 3 and 6 h by quantitative PCR and bacterial plating. Independent of the inoculum dose or time post inoculation, DNA levels of E. cecorum marginally differed between the strains. To determine if this was caused by adherence of bacteria to the epithelial cells, an invasion assay was developed. The organoids were inoculated with the different E. cecorum strains and after 3 or 6 h treated with an antimicrobial mixture, lysed, and quantified by bacterial plate counting. Significantly higher (p < 0.0001) numbers of bacteria isolated from lesions invaded the organoids compared to cloacal strains in a dose-dependent manner. Higher numbers of bacteria isolated from lesions invaded the organoids compared to cloacal strains in a dose-dependent manner. This study is a major step in the development of a model to study the interaction between E. cecorum and the chicken host and a model to test novel intervention strategies to prevent translocation of bacteria.

This study describes clinical manifestations of highly pathogenic avian influenza (HPAI) H5N1, H5N8 and H5N6 outbreaks between 2014 and 2018 and 2020 and 2022 in the Netherlands for different poultry types and age groups. Adult duck (breeder) farms and juvenile chicken (broiler and laying pullet) farms were not diagnosed before 2020. Outbreaks in ducks decreased in 2020–2022 vs. 2014–2018, but increased for meat-type poultry. Neurological, locomotor and reproductive tract signs were often observed in ducks, whereas laying- and meat-type poultry more often showed mucosal membrane and skin signs, including cyanosis and hemorrhagic conjunctiva. Juveniles (chickens and ducks) showed neurological and locomotor signs more often than adults. Diarrhea occurred more often in adult chickens and juvenile ducks. Mortality increased exponentially within four days before notification in chickens and ducks, with a more fluctuating trend in ducks and meat-type poultry than in layers. For ducks, a mortality ratio (MR) > 3, compared to the average mortality of the previous week, was reached less often than in chickens. A lower percentage of laying flocks with MR > 3 was found for 2020–2022 vs. 2014–2018, but without significant differences in clinical signs. This study provides a basis for improvements in mortality- and clinical-sign-based early warning criteria, especially for juvenile chickens and ducks.

Mycoplasma infections pose a significant challenge in swine production because of their economic impact and the difficulties associated with diagnosis and treatment. Antimicrobials are often the only available option for combating mycoplasmoses despite reports of resistance to several molecules and the frequent chronic nature of infections, which can reduce treatment efficacy. This study aimed to investigate the use of antimicrobials against swine mycoplasmoses through an international field survey and to review the relevant scientific literature and regulatory recommendations. The survey was led by the MyMIC network, whose main objective is to standardise antimicrobial susceptibility testing (AST) methods for livestock mycoplasmas. The responses of 118 swine veterinarians across 25 countries were analysed. No significant variations in practices were observed between countries. Macrolides, tetracyclines, and pleuromutilins were the most prescribed antimicrobial classes (used in more than 40%, 20% and 5% of clinical cases, respectively), which is consistent with current recommendations. Additional diagnosis with laboratory-based methods was commonly reported, with only 2.5% of veterinarians indicating that they never used it. However, AST was not commonly performed; only 30% of respondents reported requesting it in more than half of the cases. Ineffective or critically important antibiotics, such as beta-lactams or fluoroquinolones, were occasionally prescribed (approximately 1% for each). Occasional deviations from the recommended dosages were also noted. These findings raise concerns regarding resistance selection and potential treatment failures. Our results underscore the need for enhanced diagnosis, especially AST, and for a wider dissemination and adoption of treatment guidelines to support the sustainable management of swine health. By developing and promoting harmonised AST protocols and enabling objective, data-driven prescriptions, MyMIC plays a key role in strengthening communication between swine veterinarians and diagnostic laboratories, thereby supporting international antimicrobial stewardship.

Mycoplasmas are major pathogens in cattle, causing respiratory disease, mastitis and arthritis, and leading to significant economic losses. These pathogens’ microbial characteristics complicate diagnosis, treatment, and the performance of certain laboratory assays such as antimicrobial susceptibility testing (AST). Based on a dedicated survey, this study is the first international investigation of diagnostic and treatment strategies used by cattle veterinarians to manage mycoplasma infections. It also assesses how closely these practices align with current scientific evidence and regulatory recommendations. The survey was led by the MyMIC consortium, whose primary objective is to standardize AST methods for livestock mycoplasmas. The survey collected 270 responses from cattle veterinarians across 40 countries worldwide. PCR was the most commonly used diagnostic method, while culture and AST were performed less frequently. Macrolides, florfenicol and tetracyclines were the preferred antimicrobials, in line with current guidelines. However, some prescription practices deviated from recommendations, including the use of ineffective antimicrobial classes (e.g., beta-lactams and trimethoprim/sulfonamides) or of critically important antimicrobial classes as well as inappropriate dosing or duration regimens. These findings emphasize the need for coordinated actions at multiple levels: promoting the use of AST by veterinarians, disseminating updated diagnostic and treatment recommendations, and developing standardized guidelines and procedures for AST in livestock mycoplasmas. The MyMIC consortium has established an inventory of veterinary strategies for antimicrobial use and diagnosis, including resistance surveillance, thereby contributing to improved antimicrobial stewardship and to the health of livestock systems affected by mycoplasmoses. Continued support of this initiative is strongly recommended.