Digital dermatitis-associated Treponema species detection and quantification in migratory tundra caribou (Rangifer tarandus).

Treponema spp. are associated with infectious lameness in livestock and wild ruminants. While extensive research has been conducted on cattle, investigations in wild ruminants are scarce. Hoof disease is common in caribou populations (Rangifer tarandus), but investigations are limited due to the remoteness of the Arctic. Our study aimed to assess the presence of Treponema spp. associated with bovine digital dermatitis in caribou. DNA was extracted from coronary band tissues from forty-eight caribou without visible hoof lesions and analyzed using two PCR methods (qPCR and nPCR). Treponema spp. were detected in low copy numbers/mg of tissue (3.6 to 6.6 × 101). T. phagedenis was the most prevalent and abundant species in 58% of samples by qPCR, followed by T. medium (44%), and T. pedis (10%). The qPCR and nPCR agreement ranged between 65% and 75% (Cohen's kappa 0.22-0.51). Sanger sequencing of thirteen nPCR products confirmed that treponemes in caribou are remarkably similar to those found in domestic ruminants and wild elk. Our study highlights the colonization of treponemes in healthy hooves of a wild ruminant in the Arctic, where there is no presence of livestock, and expands knowledge on the host range and distribution of treponemes. These findings also emphasize the need for further research into the multifactorial nature of treponema-associated hoof diseases and the putative role of treponemes in infectious lameness affecting caribou.

Proinflammatory CD14highCD16low monocytes/macrophages prevail in Treponema phagedenis-associated bovine digital dermatitis.

Digital dermatitis (DD) is a skin disease in cattle characterized by painful inflammatory ulcerative lesions in the feet, mostly associated with local colonization by Treponema spp., including Treponema phagedenis. The reason why most DD lesions remain actively inflamed and progress to chronic conditions despite antibiotic treatment remains unknown. Herein, we show an abundant infiltration of proinflammatory (CD14highCD16low) monocytes/macrophages in active DD lesions, a skin response that was not mitigated by topical treatment with oxytetracycline. The associated bacterium, T. phagedenis, isolated from DD lesions in cattle, when injected subcutaneously into mice, induced abscesses with a local recruitment of Ly6G+ neutrophils and proinflammatory (Ly6ChighCCR2+) monocytes/macrophages, which appeared at infection onset (4 days post challenge) and persisted for at least 7 days post challenge. When exploring the ability of macrophages to regulate inflammation, we showed that bovine blood-derived macrophages challenged with live T. phagedenis or its structural components secreted IL-1ß via a mechanism dependent on the NLRP3 inflammasome. This study shows that proinflammatory characteristics of monocytes/macrophages and neutrophils dominate active non-healing ulcerative lesions in active DD, thus likely impeding wound healing after antibiotic treatment.

Evaluation of Mycobacterium avium subsp. paratuberculosis isocitrate lyase (IcL) and ABC transporter (BacA) knockout mutants as vaccine candidates.

There has been little success in controlling Johne's disease, caused by Mycobacterium avium subsp. paratuberculosis, due to suboptimal diagnostics and the ineffectiveness of available vaccines. By knocking out BacA and IcL, genes required for MAP survival in dairy calves, two live-attenuated vaccine candidates were created. This study evaluated the host-specific attenuation of MAP IcL and BacA mutants in mouse and calf models, as well as the elicited immune responses. Deletion mutants were generated in MAP strain A1-157 through specialized transduction and found viable in vitro. First, the mutants' attenuation and elicited cytokine secretion were assessed in a mouse model, 3 weeks after intraperitoneal inoculation with MAP strains. Later, vaccine strains were assessed in a natural host infection model where calves received 109CFU oral dose of MAP wild-type or mutant strains at 2 weeks old. Transcription levels of cytokines in PBMCs were evaluated at 12-, 14-, and 16-weeks post-inoculation (WPI) and MAP colonization in tissue was assessed at 4.5 months after inoculation. Whereas both vaccine candidates colonized mouse tissues similarly to wild-type strain, both failed to persist in calf tissues. In either mouse or calf models, gene deletion did not reduce immunogenicity. Instead, inoculation with ΔBacA induced a greater upregulation of proinflammatory cytokines than ΔIcL and wild-type in both models and a greater expansion of cytotoxic and memory T-cells than uninfected control in calves. ΔBacA and wild-type strains significantly increased secretion of IP-10, MIG, TNFα, and RANTES in mice serum compared to uninfected control. This agreed with upregulation of IL-12, IL-17, and TNFα in calves inoculated with ΔBacA at all time points. The ΔBacA also gave rise to greater populations of CD4+CD45RO+, and CD8+ cells than uninfected control calves at 16 WPI. Low survival rate of MAP in macrophages co-incubated with PBMCs isolated from the ΔBacA group indicated that these cell populations are capable of killing MAP. Overall, the immune response elicited by ΔBacA is stronger compared to ΔIcL and it is maintained over two different models and over time in calves. Further investigation is warranted to evaluate the BacA mutant's protection against MAP infection as a live attenuated vaccine candidate.

Expert workshop summary: Advancing toward a standardized murine model to evaluate treatments for antimicrobial resistance lung infections.

The rise in antimicrobial resistance (AMR), and increase in treatment-refractory AMR infections, generates an urgent need to accelerate the discovery and development of novel anti-infectives. Preclinical animal models play a crucial role in assessing the efficacy of novel drugs, informing human dosing regimens and progressing drug candidates into the clinic. The Innovative Medicines Initiative-funded "Collaboration for prevention and treatment of MDR bacterial infections" (COMBINE) consortium is establishing a validated and globally harmonized preclinical model to increase reproducibility and more reliably translate results from animals to humans. Toward this goal, in April 2021, COMBINE organized the expert workshop "Advancing toward a standardized murine model to evaluate treatments for AMR lung infections". This workshop explored the conduct and interpretation of mouse infection models, with presentations on PK/PD and efficacy studies of small molecule antibiotics, combination treatments (ß-lactam/ß-lactamase inhibitor), bacteriophage therapy, monoclonal antibodies and iron sequestering molecules, with a focus on the major Gram-negative AMR respiratory pathogens Pseudomonas aeruginosa, Klebsiella pneumoniae and Acinetobacter baumannii. Here we summarize the factors of variability that we identified in murine lung infection models used for antimicrobial efficacy testing, as well as the workshop presentations, panel discussions and the survey results for the harmonization of key experimental parameters. The resulting recommendations for standard design parameters are presented in this document and will provide the basis for the development of a harmonized and bench-marked efficacy studies in preclinical murine pneumonia model.

Variability of murine bacterial pneumonia models used to evaluate antimicrobial agents.

Antimicrobial resistance has become one of the greatest threats to human health, and new antibacterial treatments are urgently needed. As a tool to develop novel therapies, animal models are essential to bridge the gap between preclinical and clinical research. However, despite common usage of in vivo models that mimic clinical infection, translational challenges remain high. Standardization of in vivo models is deemed necessary to improve the robustness and reproducibility of preclinical studies and thus translational research. The European Innovative Medicines Initiative (IMI)-funded "Collaboration for prevention and treatment of MDR bacterial infections" (COMBINE) consortium, aims to develop a standardized, quality-controlled murine pneumonia model for preclinical efficacy testing of novel anti-infective candidates and to improve tools for the translation of preclinical data to the clinic. In this review of murine pneumonia model data published in the last 10 years, we present our findings of considerable variability in the protocols employed for testing the efficacy of antimicrobial compounds using this in vivo model. Based on specific inclusion criteria, fifty-three studies focusing on antimicrobial assessment against Pseudomonas aeruginosa, Klebsiella pneumoniae and Acinetobacter baumannii were reviewed in detail. The data revealed marked differences in the experimental design of the murine pneumonia models employed in the literature. Notably, several differences were observed in variables that are expected to impact the obtained results, such as the immune status of the animals, the age, infection route and sample processing, highlighting the necessity of a standardized model.

Oral vaccination stimulates neutrophil functionality and exerts protection in a Mycobacterium avium subsp. paratuberculosis infection model.

Mycobacterium avium subsp. paratuberculosis (Map) causes paratuberculosis (PTB), a granulomatous enteritis in ruminants that exerts high economic impact on the dairy industry worldwide. Current vaccines have shown to be cost-effective against Map and in some cases confer beneficial non-specific effects against other pathogens suggesting the existence of trained immunity. Although Map infection is mainly transmitted by the fecal-oral route, oral vaccination has not been deeply studied. Therefore, the aim of this study was to compare the oral route with a set of mycobacterial and non-mycobacterial vaccines with a subcutaneously administered commercially available vaccine. Training effects on polymorphonuclear neutrophils (PMNs) and homologous and heterologous in vivo protection against Map were investigated in the rabbit infection model. Oral vaccination with inactivated or live vaccines was able to activate mucosal immunity as seen by elevation of serum IgA and the expression of IL4 in peripheral blood mononuclear cells (PBMCs). In addition, peripheral PMN phagocytosis against Map was enhanced by vaccination and extracellular trap release against Map and non-related pathogens was modified by both, vaccination and Map-challenge, indicating trained immunity. Finally, PBMCs from vaccinated animals stimulated in vitro with Map antigens showed a rapid innate activation cytokine profile. In conclusion, our data show that oral vaccination against PTB can stimulate neutrophil activity and both innate and adaptive immune responses that correlate with protection.

Effects of different culture media on growth of Treponema spp. isolated from digital dermatitis.

Digital dermatitis (DD) lesions in cattle are characterized by the presence of multiple Treponema species. Current culture media for isolating treponemes generally uses serum supplementation from different animals to target particular Treponema sp.; however, their suitability for DD Treponema isolation has not been fully determined. We studied the effect of culture media (OTEB, NOS and TYGV) and serum supplementation on mixed Treponema spp. dynamics. Bacterial growth was evaluated by direct microscopic count, optical density, wet weight and a species-specific qPCR and the correlations between these independent methods were calculated. Wet weight, optical density and bacterial count correlated best with each other. Different Treponema species performed differently under the tested culture media. T. phagedenis growth was enhanced in OTEB media supplemented with bovine fetal serum (BFS) or horse serum (HS). T. medium had lower generation time when culture media were supplemented with rabbit serum (RS). Lowest generation time for T. pedis and T. denticola were obtained in NOS media supplemented with HS and OTEB media supplemented with BFS, respectively. Detection of cystic forms observed after 5 days of culture did not differ among the culture media. Correlation between different Treponema spp. growth quantification techniques indicated that alternative quantification methods such as qPCR and wet weight could be used depending on the purpose. We conclude that effects of culture media and serum supplementation on mixed Treponema spp. communities should be taken into account when isolating a specific Treponema species.

Treponema spp. Isolated from Bovine Digital Dermatitis Display Different Pathogenicity in a Murine Abscess Model.

Digital dermatitis (DD) causes lameness in cattle with substantial negative impact on sustainability and animal welfare. Although several species of Treponema bacteria have been isolated from various DD stages, their individual or synergistic roles in the initiation or development of lesions remain largely unknown. The objective of this study was to compare effects of the three most common Treponema species isolated from DD lesions in cattle (T. phagedenis, T. medium and T. pedis), both as individual and as mixed inoculations, in a murine abscess model. A total of 109 or 5 × 108Treponema spp. were inoculated subcutaneously, and produced abscess was studied after 7 days post infection. There were no synergistic effects when two or three species were inoculated together; however, T. medium produced the largest abscesses, whereas those produced by T. phagedenis were the smallest and least severe. Treponema species were cultured from skin lesions at 7 days post infection and, additionally, from the kidneys of some mice (2/5), confirming systemic infection may occur. Taken together, these findings suggest that T. medium and T. pedis may have more important roles in DD lesion initiation and development than T. phagedenis.

Alternative Vaccination Routes against Paratuberculosis Modulate Local Immune Response and Interference with Tuberculosis Diagnosis in Laboratory Animal Models.

Paratuberculosis (PTB) is an enteric granulomatous disease caused by Mycobacterium avium subsp. paratuberculosis (MAP) that mainly affects ruminants. Current vaccines have shown to be cost-effective control reagents, although they are restricted due to cross-interference with bovine tuberculosis (bTB). Therefore, novel vaccination strategies are needed and this study is focused on evaluating alternative vaccination routes and their effect on the local immune response. The MAP oral challenge rabbit model was used to evaluate and compare an experimental inactivated MAP vaccine through oral (VOR) and intradermal (VID) routes. The VID group presented the highest proportion of animals with no visible lesions and the lowest proportion of animals with MAP positive tissues. Immunohistochemistry analysis revealed that the VID group presented a dominantly M1 polarized response indicating an ability to control MAP infection. In general, all vaccinated groups showed lower calprotectin levels compared to the non-vaccinated challenged group suggesting less active granulomatous lesions. The VID group showed some degree of skin test reactivity, whereas the same vaccine through oral administration was completely negative. These data show that PTB vaccination has an effect on macrophage polarization and that the route influences infection outcome and can also have an impact on bTB diagnosis. Future evaluation of new immunological products against mycobacterial diseases should consider assaying different vaccination routes.

Synthetic cathelicidin LL-37 reduces Mycobacterium avium subsp. paratuberculosis internalization and pro-inflammatory cytokines in macrophages.

Mycobacterium avium subsp. paratuberculosis (MAP) causes chronic diarrheic intestinal infections in domestic and wild ruminants (paratuberculosis or Johne's disease) for which there is no effective treatment. Critical in the pathogenesis of MAP infection is the invasion and survival into macrophages, immune cells with ability to carry on phagocytosis of microbes. In a search for effective therapeutics, our objective was to determine whether human cathelicidin LL-37, a small peptide secreted by leuckocytes and epithelial cells, enhances the macrophage ability to clear MAP infection. In murine (J774A.1) macrophages, MAP was quickly internalized, as determined by confocal microscopy using green fluorescence protein expressing MAPs. Macrophages infected with MAP had increased transcriptional gene expression of pro-inflammatory TNF-α, IFN-γ, and IL-1ß cytokines and the leukocyte chemoattractant IL-8. Pretreatment of macrophages with synthetic LL-37 reduced MAP load and diminished the transcriptional expression of TNF-α and IFN-γ whereas increased IL-8. Synthetic LL-37 also reduced the gene expression of Toll-like receptor (TLR)-2, key for mycobacterial invasion into macrophages. We concluded that cathelicidin LL-37 enhances MAP clearance into macrophages and suppressed production of tissue-damaging inflammatory cytokines. This cathelicidin peptide could represent a foundational molecule to develop therapeutics for controlling MAP infection.

Oxytetracycline reduces inflammation and treponeme burden whereas vitamin D3 promotes ß-defensin expression in bovine infectious digital dermatitis.

Digital dermatitis (DD), a common ulcerative disease of the bovine foot causing lameness and reducing productivity and animal welfare, is associated with infection by spirochete Treponema bacteria. Topical tetracycline, the most common treatment, has inconsistent cure rates; therefore, new therapeutic options are needed. We compared effects of topical oxytetracycline and vitamin D3 on innate immunity in DD-affected skin. Cows with active DD lesions were treated topically with oxytetracycline or vitamin D3 and skin biopsies were collected from lesions. Tissue samples were examined histologically, transcriptional expression of pro-inflammatory cytokines, Toll-like receptors (TLRs), and host defense peptides assessed, and the presence of specific treponeme species determined. Effects of treatments at a mechanistic level were studied in a human keratinocyte model of treponeme infection. Oxytetracycline promoted hyperplastic scab formation in ulcerated DD lesions and decreased transcriptional expression of Cxcl-8 (neutrophil chemoattractant). Oxytetracycline also reduced numbers of Treponema phagedenis and T. pedis and enhanced Tlr2 mRNA expression. Vitamin D3 did not modify expression of cytokines or Tlrs, or bacterial loads, but enhanced transcription of tracheal antimicrobial peptide (Tap), a key bovine ß-defensin. Combing oxytetracycline and vitamin D3 provides complementary clinical benefits in controlling DD through a combination of antimicrobial, immunomodulatory, and pro-healing activities.

Diet induced changes in the microbiota and cell composition of rabbit gut associated lymphoid tissue (GALT).

The gut associated lymphoid tissue (GALT) is the largest immune organ of the body. Although the gut transient and mucosa-associated microbiota have been largely studied, the microbiota that colonizes the GALT has received less attention. The gut microbiome plays an important role in competitive exclusion of pathogens and in development and maturation of immunity. Diet is a key factor affecting the microbiota composition in the digestive tract. To investigate the relation between diet, microbiota and GALT, microbial and cell composition of vermiform appendix (VA) and sacculus rotundus (SR) were studied in two groups of New Zealand white rabbits on different diets. Diet shifted the lymphoid tissue microbiota affecting the presence and/or absence of certain taxa and their abundances. Immunohistochemistry revealed that a higher fibre content diet resulted in M cell hyperplasia and an increase of recently recruited macrophages, whereas T-cell levels remained unaltered in animals on both high fibre and standard diets. These findings indicate that diet has an impact on the microbiota and cell composition of the GALT, which could act as an important microbial recognition site where interactions with beneficial bacteria can take place favouring microbiota replacement after digestive dysregulations.

A Differential Innate Immune Response in Active and Chronic Stages of Bovine Infectious Digital Dermatitis.

Digital dermatitis (DD) commonly associated with Treponema spp. infection is a prevalent infectious bovine foot disease characterized by ulcerative and necrotic lesions. Lesions associated with DD are often classified using the M-stage scoring system, with M0 indicating healthy heel skin and M4 indicating chronic lesions. Current treatments utilizing antimicrobials or chemical footbaths are often ineffective and rarely cure DD lesions. Understanding the function of the innate immune response in the pathogenesis of DD will help to identify novel therapeutic approaches. In this study, the expression of the local innate host defense peptides cathelicidins and ß-defensins was investigated in cows with DD and associated with the presence of treponemes and inflammatory reactions. Samples from active ulcerative DD lesions (M2) had considerable epidermal neutrophilic infiltration and increased gene expression of ß-defensin tracheal antimicrobial peptides compared to control skin. Samples from acute lesions also had elevated local Cxcl-8 and TLR4 gene expression and abundant treponemes as identified by direct visualization, immunohistochemistry, and culture. Conversely, the anti-inflammatory peptide IL-10 was elevated in skin from chronic (M4) lesions, whereas bovine cathelicidin myeloid antimicrobial peptide 28 (Bmap-28) was increased in skin from oxytetracycline-treated M2 lesions. Experiments using cultured human keratinocytes challenged with Treponema spp. isolated from clinical cases of bovine DD showed that structural products from treponemes are able to initiate the innate immune response, in part through TLR2 signaling. These findings indicate that neutrophil influx, Cxcl-8, and ß-defensin are key markers of active DD. Cathelicidins and IL-10 seem important in response to treatment or during the chronic proliferative stages of the disease.

Tuberculosis Detection in Paratuberculosis Vaccinated Calves: New Alternatives against Interference.

Paratuberculosis vaccination in cattle has been restricted due to its possible interference with the official diagnostic methods used in tuberculosis eradication programs. To overcome this drawback, new possibilities to detect Mycobacterium bovis infected cattle in paratuberculosis vaccinated animals were studied under experimental conditions. Three groups of 5 calves each were included in the experiment: one paratuberculosis vaccinated group, one paratuberculosis vaccinated and M. bovis infected group and one M. bovis infected group. The performance of the IFN-gamma release assay (IGRA) and the skin test using conventional avian and bovine tuberculins (A- and B-PPD) but also other more specific antigens (ESAT-6/CFP10 and Rv3615c) was studied under official and new diagnostic criteria. Regarding the IGRA of vaccinated groups, when A- and B-PPD were used the sensitivity reached 100% at the first post-challenge sampling, dropping down to 40-80% in subsequent samplings. The sensitivity for the specific antigens was 80-100% and the specificity was also improved. After adapting the diagnostic criteria for the conventional antigens in the skin test, the ability to differentiate between M. bovis infected and non-infected animals included in paratuberculosis vaccinated groups was enhanced. Taking for positive a relative skin thickness increase of at least 100%, the single intradermal test specificity and sensitivity yielded 100%. The comparative intradermal test was equally accurate considering a B-PPD relative skin increase of at least 100% and greater than or equal to that produced by A-PPD. Using the specific antigens as a proteic cocktail, the specificity and sensitivity reached 100% considering the new relative and absolute cut-offs in all experimental groups (Δ≥30% and Δmm ≥ 2, respectively). Results suggest that the interference caused by paratuberculosis vaccination in cattle could be completely overcome by applying new approaches to the official tuberculosis diagnostic tests.

Vaccination sequence effects on immunological response and tissue bacterial burden in paratuberculosis infection in a rabbit model.

Paratuberculosis (PTB), a chronic granulomatous enteritis produced by Mycobacterium avium subspecies paratuberculosis (MAP), is considered as one of the diseases with the highest economic impact in the ruminant industry. Vaccination against MAP is recommended during the first months after birth on the basis that protection would be conferred before the first contact with mycobacteria. However, little is known about the therapeutic effect of MAP vaccination in controlled experimental conditions. The current study was designed to evaluate the efficacy of vaccination before and after challenge with MAP in a rabbit infection model. The rabbits were divided into four groups: non-infected control (NIC, n = 4), infected control challenged with MAP (IC, n = 5), vaccinated and challenged 1 month after with MAP (VSI, n = 5) and challenged with MAP and vaccinated 2 months later (IVS, n = 5). The results from this study show a quick increase in IFN-γ release upon stimulation with bovine, avian and johnin PPD in animals vaccinated before MAP challenge. All vaccinated animals show an increased humoral response as seen by western blot and ELISA. The final bacteriology index (considering tissue culture and qPCR) shows that the IC group was the most affected. Vaccination after infection (IVS) produced the lowest bacteriology index showing significant differences with the IC group (p = 0.034). In conclusion, vaccination against MAP shows positive effects in a rabbit model. However, vaccination after infection shows a slightly stronger protective effect compared to vaccination before infection, suggesting a therapeutic effect. This feature could be applied to previously infected adult animals under field conditions.

Mycobacterium avium Subspecies paratuberculosis Infection Modifies Gut Microbiota under Different Dietary Conditions in a Rabbit Model.

Mycobacterium avium subspecies paratuberculosis (MAP) the causative agent of paratuberculosis, produces a chronic granulomatous inflammation of the gastrointestinal tract of ruminants. It has been recently suggested that MAP infection may be associated with dysbiosis of intestinal microbiota in ruminants. Since diet is one of the key factors affecting the balance of microbial populations in the digestive tract, we intended to evaluate the effect of MAP infection in a rabbit model fed a regular or high fiber diet during challenge. The composition of microbiota of the cecal content and the sacculus rotundus was studied in 20 New Zealand white female rabbits. The extracted DNA was subjected to paired-end Illumina sequencing of the V3-V4 hypervariable region of the 16S rRNA gene for microbiota analysis. Microbial richness (Chao1) in the cecal content was significantly increased by MAP infection in regular diet rabbits (p = 0.0043) and marginally increased (p = 0.0503) in the high fiber group. Analysis of beta-diversity showed that MAP infection produces deeper changes in the microbiota of sacculus rotundus than in the cecal content. A lower abundance of Proteobacteria in the cecal content of infected animals fed the high fiber diet and also lower abundance of Bacteroidetes in the sacculus rotundus of infected animals fed the regular diet were observed. Based on OPLS-DA analysis, we observed that some bacteria repeatedly appear to be positively associated with infection in different samples under different diets (families Dehalobacteriaceae, Coriobacteriaceae, and Mogibacteriaceae; genus Anaerofustis). The same phenomenon was observed with some of the bacteria negatively associated with MAP infection (genera Anaerostipes and Coprobacillus). However, other groups of bacteria (Enterobacteriaceae family and ML615J-28 order) were positively associated with infection in some circumstances and negatively associated with infection in others. Data demonstrate that MAP infection and diet changes do interact and result in shifts in the microbiota of the cecal content and sacculus rotundus of rabbits.

Effect of various dietary regimens on oral challenge with Mycobacterium avium subsp. paratuberculosis in a rabbit model.

Rabbits are susceptible to infection by Mycobacterium avium subspecies paratuberculosis (MAP) in both wildlife and experimental conditions. Under the hypotheses that nutrient balance might influence the establishment of infection, we designed an experiment where MAP intestinal colonization was assessed under three dietary regimens: high fiber, high protein, and regular diet in New Zealand white rabbits submitted to oral challenge with MAP. Lowest weight gain (F=5.17, p=0.024), higher tissue culture positivity rates (X(2)=7.43, p=0.024) and especially extended MAP-compatible lesions (F=5.78, p=0.017) were detected in the regular diet. Taken altogether, results indicate that paratuberculosis infection was achieved affecting mostly regular diet animals and showing that dietary changes may modulate the course of the infection.

Detection of Mycobacterium avium subspecies in the gut associated lymphoid tissue of slaughtered rabbits.

BACKGROUND: Rabbits are susceptible to infection by different species of the genus Mycobacterium. Particularly, development of specific lesions and isolation of Mycobacterium avium subsp. avium and Mycobacterium avium subsp. paratuberculosis, both subspecies of the M. avium complex, has been reported in wildlife conditions. Although, rabbit meat production worldwide is 200 million tons per year, microbiological data on this source of meat is lacking and more specifically reports of mycobacterial presence in industrially reared rabbit for human consumption have not been published. To this end, we sought mycobacteria by microbiological and histopathological methods paying special attention to Mycobacterium avium subsp. paratuberculosis in rabbits from commercial rabbitries from the North East of Spain. RESULTS: M. avium subsp. paratuberculosis was not detected either by culture or PCR. However, Mycobacterium avium subsp. avium was detected in 15.15% (10/66) and Mycobacterium avium subsp. hominissuis was detected in 1.51% (1/66) of gut associated lymphoid tissue of sampled animals by PCR, whereas caecal contents were negative. 9% (6/66) of the animals presented gross lesions suggestive of lymphoid activation, 6% (4/66) presented granulomatous lesions and 3% (2/66) contained acid fast bacilli. Mycobacterial isolation from samples was not achieved, although colonies of Thermoactinomycetes sp. were identified by 16s rRNA sequencing in 6% (4/66) of sampled animals. CONCLUSIONS: Apparently healthy farmed rabbits that go to slaughter may carry M. avium subspecies in gut associated lymphoid tissue.