Claire A. M. Becker

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.

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.

Bovine respiratory disease (BRD) is common in calves in Algeria, but to date, Mycoplasma bovis has never been monitored as a potential etiological agent. Here, to assess the presence (direct detection) and circulation (indirect detection) of M. bovis, broncho-alveolar lavage fluids (BALF) and serum samples were collected from 60 veal calf farms in Algeria. A commercial ELISA kit (ID Screen^® ELISA) was used to screen for the presence of specific antibodies against M. bovis in 351 blood sera collected from both diseased and healthy calves, and 69% (241 sera) tested positive. BALFs from the 176 diseased calves were used to screen for M. bovis by real-time-PCR (rt-PCR), and 102 (58%) tested positive. A non-exhaustive set of 53 clones were isolated from 44 calves and further subtyped using polC gene sequencing. No predominant subtype was found, and two clones exhibited a new subtype. Fourteen clones were further characterized by multilocus sequence typing, and results showed a high degree of genetic diversity, with some clones having new alleles and subtypes. The minimum inhibitory concentrations (MICs) of 5 antimicrobials regularly used to treat BRD was determined on 45 clones. Susceptibility profiles showed very broad diversity, confirming the variety of clones actively circulating. We detected clones with high MICs, including increased MICs of enrofloxacin (n = 5). This is the first study to report the presence of M. bovis in Algeria in calves with BRD. This research also finds broad genetic and phenotypic diversity in the actively circulating isolates.

Bovine respiratory diseases (BRD) are widespread in veal calf feedlots. Several pathogens are implicated, both viruses and bacteria, one of which, Mycoplasma bovis, is under-researched. This worldwide-distributed bacterium has been shown to be highly resistant in vitro to the main antimicrobials used to treat BRD. Our objective was to monitor the relative prevalence of M. bovis during BRD episodes, its diversity, and its resistance phenotype in relation to antimicrobial use. For this purpose, a two-year longitudinal follow-up of 25 feedlots was organized and 537 nasal swabs were collected on 358 veal calves at their arrival in the lot, at the BRD peak and 4 weeks after collective antimicrobial treatments. The presence of M. bovis was assessed by real-time PCR and culture. The clones isolated were then subtyped (polC subtyping and PFGE analysis), and their susceptibility to five antimicrobials was determined. The course of the disease and the antimicrobials used had no influence on the genetic diversity of the M. bovis strains: The subtype distribution was the same throughout the BRD episode and similar to that already described in France, with a major narrowly-variable subtype circulating, st2. The same conclusion holds for antimicrobial resistance (AMR) phenotypes: All the clones were already multiresistant to the main antimicrobials used (except for fluoroquinolones) prior to any treatments. By contrast, changes of AMR phenotypes could be suspected for Pasteurellaceae in two cases in relation to the treatments registered.

Q fever is a zoonotic abortive disease of ruminants mostly transmitted by inhalation of aerosols contaminated by Coxiella burnetii. Clusters of cases or even epidemics regularly occur in humans but, to date, there is no consensus about the best way to carry out outbreak investigations in order to identify potential farms at risk. Although environmental samples might be useful during such investigations, there are few baseline data on the presence of C. burnetii in the environment of ruminant farms. We thus investigated dust samples from cattle, sheep and goat farm buildings in order to (a) estimate C. burnetii detection frequency and bacterial loads in the environment, and (b) determine whether this environmental contamination is associated with series of abortions attributed to Q fever. We considered 113 herds with a recent abortive episode potentially related (n = 60) or not (n = 53) to C. burnetii. Dust was sampled using a swab cloth and tested by a quantitative PCR method targeting the IS1111 gene. Coxiella burnetii DNA was detected on 9 of 50 cattle farms, 13 of 19 goat farms and 30 of 40 sheep farms. On 16 cloths, bacterial loads were higher than 10⁸ genome equivalents, levels as high as in infectious materials such as placentas and aborted foetuses. Overall, the probability of detecting C. burnetii DNA was higher on small ruminant farms than cattle farms, in herds suspected of Q fever and in large herds. We conclude that swab cloths are a putative indicator of contamination of ruminant farms by C. burnetii.

Mycoplasma bovis is considered an emerging threat to bovine production in industrialized countries. Its control depends on good husbandry and efficient chemotherapy practices. In France, clinical isolates collected after 2009 showed a drastic loss of susceptibility to most antimicrobials when compared with isolates collected in 1978–1979. The aim of the present study was to analyze the molecular mechanisms underlying the shift toward resistance to macrolides and tetracyclines and to assess whether the clinical origin of the isolates or their molecular subtypes could have influenced their pattern of evolution. We demonstrated that all M. bovis isolates collected as early as 2000 should already be considered resistant to tylosin, tilmicosin, and oxytetracycline, whatever the associated clinical signs. The shift toward resistance happened earlier for oxytetracycline and more progressively for tylosin/tilmicosin. Isolates belonging to the major subtype ST2 ( n = 40) showed a homogeneous genotype for resistance, with combined alterations of G ₇₄₈ A and A ₂₀₅₈ G in the 23S rRNA alleles for tylosin/tilmicosin and of A ₉₆₅ T and A ₉₆₇ T in the 16S rRNA alleles for oxytetracycline. The genotypes of ST3 or ST1 isolates ( n = 9 and 25, respectively) in the process of becoming resistant were more varied. In recent years, the convergence of both ST2 and ST3 isolates toward the same resistance genotype suggests that the corresponding mutations have been selected for providing an appropriate balance between fitness cost and resistance.

Mycoplasma bovis is considered a major contributor to respiratory diseases in young cattle. Resistant M. bovis isolates have increasingly been reported worldwide due to extensive use of antimicrobials to treat bovine pneumonia. The frequency of isolates resistant to fluoroquinolones varies considerably from one country to another. The MICs of isolates collected in France have only increased from “very low” to “low.” The present study was conducted to investigate whether alterations in the quinolone resistance-determining regions (QRDRs) could account for this slight modification in susceptibility. No correlation between QRDR alterations and increased MICs was evidenced in clinical isolates. In addition, all clinical isolates were subtyped, and the tendencies of the different sequence types to develop resistance through mutations in QRDRs under selective pressure in vitro were examined. In vitro , 3 hot spots for mutations in QRDRs (position 83 in GyrA and positions 80 and 84 in ParC) were associated with a high level of resistance when cumulated. We showed that the point mutations in the QRDRs observed in vitro were different (in location and selection rapidity) between the different subtypes. Our in vitro observations were corroborated by the recent detection of a clinical isolate highly resistant to fluoroquinolones (MIC ≥ 16 μg/ml) and belonging to the subtype which easily accumulates QRDR alterations in vitro . The current increased prevalence of this subtype in clinical isolates highlights the urgent need to control fluoroquinolone usage in veterinary medicine.