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Murine Mastitis Model Experiment – Preclinical Testing Service for Evaluating Anti‑Infective and Immunomodulatory Compounds

As an ISO/IEC 17025 accredited contract research laboratory, we offer specialised murine mastitis model experimentation services for Bulgarian and international pharmaceutical, biotechnology, and veterinary research organisations. Mastitis – an inflammatory condition of the mammary gland – is a major health concern in both dairy cattle and humans (lactating women). Mouse models of mastitis provide a well‑characterised, cost‑effective, and ethically approved platform for evaluating the efficacy of novel antimicrobial agents, immunomodulators, anti‑inflammatory drugs, and vaccine candidates before advancing to larger animal studies. Our experimental protocols are designed to reproduce the key pathophysiological features of mastitis – including bacterial colonisation, neutrophil infiltration, cytokine release, tissue damage, and impaired lactation – using clinically relevant pathogens such as Staphylococcus aureus, Escherichia coli, and Streptococcus uberis. All procedures are carried out in strict compliance with Directive 2010/63/EU, Bulgarian Animal Welfare Act, and ARRIVE guidelines (Animal Research: Reporting of In Vivo Experiments). Our study reports are recognised by the Bulgarian Food Safety Agency (BFSA), European Medicines Agency (EMA) reference laboratories, and veterinary regulatory authorities for preclinical efficacy and safety assessments.

Mouse Strains and Husbandry Conditions We Use

We employ well‑standardised mouse strains and housing conditions to ensure reproducibility and relevance to human and veterinary mastitis. Typical models include:

• BALB/c and C57BL/6 females – immunocompetent strains widely used for infection and inflammation studies
• Lactating dams (post‑partum days 7‑10) – to simulate natural lactation‑associated mastitis
• Pregnancy‑induced and hormone‑primed models – for non‑lactating studies using oestrogen/progesterone priming
• Transgenic and knock‑out strains – for mechanistic studies of specific immune pathways (e.g., TLR‑deficient, MyD88‑/‑, IL‑17‑/‑)
• SPF (Specific Pathogen‑Free) barrier facilities – with controlled temperature (22 ± 2 °C), humidity (55 ± 10 %), and 12‑hour light/dark cycles, with ad libitum access to standard chow and water
• Bacterial strains – clinically isolated S. aureus (e.g., ATCC 29213), E. coli (e.g., ATCC 25922), and Streptococcus uberis (e.g., ATCC 27958) – prepared as logarithmic‑phase cultures in sterile PBS for inoculation

Induction Protocols – Route, Dose and Timing

We use two well‑validated routes of infection to mimic natural mastitis: the intramammary (trans‑ductal) route and the haematogenous (intravenous) route. The experimental design includes:

• Intramammary inoculation – under light anaesthesia (isoflurane or ketamine/xylazine), the tip of a sterile cannula (blunt 30‑gauge needle) is inserted into the teat canal of the 4th or 5th abdominal mammary gland, and a defined bacterial suspension (typically 10²‑10⁵ CFU in 20‑50 µL sterile PBS) is injected. A sham‑inoculated contralateral gland receives sterile PBS.
• Haematogenous infection – bolus intravenous injection (tail vein) of 10⁷‑10⁸ CFU of S. aureus or E. coli to induce systemic dissemination and subsequent mammary localisation.
• Challenge timing – inoculation is performed on lactation day 7‑10 to ensure maximal milk production and immune responsiveness. The disease course is monitored for 24‑72 hours post‑inoculation, depending on the pathogen and endpoint.
• Dose‑finding studies – preliminary pilot experiments are conducted to define the minimum infectious dose that produces consistent clinical signs (swelling, redness, reduced milk yield) without causing excessive systemic morbidity or mortality.
• Treatment administration – test compounds (antibiotics, anti‑inflammatory agents, immunomodulators, or vaccines) are given at predetermined times (pre‑infection, post‑infection, or both) by oral gavage, intraperitoneal, subcutaneous, or intravenous routes, according to the study design.

Clinical and Pathological Endpoints – Disease Severity Scoring and Sampling

We use a comprehensive set of clinical, bacteriological, histopathological, and molecular endpoints to assess treatment efficacy. The endpoint evaluations include:

• Clinical scoring (daily) – based on mammary gland swelling (0‑4 scale), erythema (0‑3), palpable induration (0‑3), and milk appearance (normal, watery, clot‑containing); a total clinical score is calculated for each animal.
• Body weight and food intake monitoring – daily recording of body weight (g) and qualitative assessment of food consumption as an indicator of systemic illness.
• Milk yield and quality – manual milking of the infected and control glands before necropsy; milk is collected for bacterial enumeration (CFU/mL), somatic cell count (SCC), and cytokine profiling.
• Bacteriology – after euthanasia (CO₂ or cervical dislocation), the mammary glands are aseptically excised, homogenised in sterile PBS, and serial dilutions are plated on selective agar to determine the bacterial load (log₁₀ CFU/g tissue).
• Histopathology – sections of the infected and control glands are fixed in 10 % neutral buffered formalin, paraffin‑embedded, sectioned (4‑6 µm), stained with Haematoxylin & Eosin (H&E), and examined for inflammatory cell infiltration, alveolar damage, necrosis, and fibrosis. Histological scores (0‑4) are assigned based on standardised criteria.
• Molecular analysis – RNA is extracted from gland homogenates for RT‑qPCR analysis of key inflammatory cytokines (IL‑1β, IL‑6, TNF‑α, IL‑10, IL‑17) and antimicrobial peptides (defensins, cathelicidin); protein levels are measured by ELISA or multiplex bead assays.
• Immunophenotyping – flow cytometry is performed on mammary tissue and draining lymph nodes to quantify neutrophil, macrophage, T‑cell, and B‑cell populations (CD45, CD11b, Ly6G, F4/80, CD3, CD4, CD8, B220 markers).

Standardisation and Quality Control – Positive and Negative Controls

To ensure robust and reproducible results, each study includes appropriate control groups and internal quality checks:

• Sham‑inoculated group – receives sterile PBS in the mammary gland to assess any non‑specific inflammation.
• Untreated infected group – receives the bacterial inoculum but no treatment, providing baseline disease severity data.
• Positive treatment control – receives a standard antibiotic (e.g., penicillin/streptomycin for S. aureus, or enrofloxacin for E. coli) to validate the experimental system and demonstrate a known effective response.
• Vehicle control – receives the same formulation (e.g., PBS or solvent) as the test compound, without the active ingredient, to exclude any vehicle‑related effects.
• Batch‑to‑batch consistency – we maintain a master bank of each bacterial strain with documented virulence characteristics (LD₅₀, growth curve, antibiotic susceptibility profile) and perform regular re‑isolation and characterisation to avoid phenotypic drift.

End‑point Readouts and Data Analysis

We provide a comprehensive statistical and graphical analysis of all experimental data, tailored to your study objectives. The core readouts include:

• Bacterial clearance efficacy (log₁₀ reduction) – comparison of bacterial loads in treated vs. untreated groups, expressed as CFU/g tissue reduction.
• Inflammatory response modulation – change in cytokine/chemokine levels (fold‑change or concentration) and white blood cell infiltration scores.
• Histological improvement – reduction in tissue damage score (e.g., from 3 to 1) in treatment groups.
• Clinical recovery rate – time‑to‑resolution of clinical signs (swelling, redness, milk quality) expressed in hours or days.
• Survival rate – for severe sepsis models, the cumulative survival percentage is plotted via Kaplan‑Meier curves.
• Pharmacokinetic (PK) correlation – optional measurement of drug concentrations in plasma and mammary tissue to link exposure to efficacy.
• Pharmacodynamic (PD) modelling – dose‑response curves (ED₅₀ values) are generated for antimicrobial and anti‑inflammatory compounds.

Ethical Compliance, Welfare and Study Approval

All experiments are conducted in accordance with the European Directive 2010/63/EU on the protection of animals used for scientific purposes and the Bulgarian Animal Welfare Act. Our animal facility is registered with the Bulgarian Food Safety Agency (BFSA) and operates under an approved animal welfare body. The study protocol is reviewed and approved by our institutional ethics committee before commencement. We strictly adhere to the 3Rs principles (Replacement, Reduction, Refinement):

• Replacement – we use validated in vitro alternatives where available (e.g., mammary epithelial cell lines) for initial screening, minimising the use of live animals.
• Reduction – we use appropriate sample sizes (power analysis) to obtain statistically significant results with the minimum number of animals; typically, 5‑8 animals per group (based on expected effect size and variance).
• Refinement – we employ humane endpoints (early euthanasia if animals show severe distress, > 20 % body weight loss, or inability to reach food/water) and ensure adequate pain relief (buprenorphine) when required.

Report Acceptance & Compliance with Bulgarian and EU Veterinary Regulatory Frameworks

All murine mastitis model experiments are performed under our ISO/IEC 17025 accreditation and in compliance with Good Laboratory Practice (GLP) principles where required. Our final study reports provide a complete experimental plan (including ethical approval number, study design, and statistical analysis), raw data for all endpoints (clinical scores, bacterial counts, histology, cytokine data), graphical presentations (dose‑response curves, survival plots), a detailed discussion of treatment efficacy and statistical significance, and a clear conclusion on whether the tested compound shows promise for mastitis therapy or prevention. These reports are accepted by the Bulgarian Food Safety Agency (BFSA), the European Medicines Agency (EMA) for veterinary drug registration, and by Bulgarian and international pharmaceutical companies for preclinical decision‑making. Bilingual (Bulgarian/English) versions are available for ease of submission to national and European regulatory bodies.