Outdoor bronze artworks are susceptible to microbial growth, which can lead to discoloration, corrosion, and deterioration over time. To preserve these valuable pieces, several effective methods can be employed.

1. Regular Cleaning: Gently clean bronze surfaces with a soft brush and a mild detergent solution to remove dirt, organic matter, and early microbial colonies. Avoid abrasive materials that can scratch the surface.

2. Wax Coatings: Apply a high-quality microcrystalline wax to create a protective barrier against moisture and microbes. Reapply every 6-12 months depending on environmental conditions.

3. Inhibitive Patinas: Consider applying chemical patinas that contain microbial inhibitors. These specialized coatings can help prevent biological growth while maintaining the artwork's aesthetic appeal.

4. Proper Drainage: Ensure the artwork's base allows for proper water drainage to prevent standing water, which promotes microbial growth.

5. Environmental Controls: Where possible, position artworks in areas with good air circulation and sunlight exposure, as UV light can help inhibit microbial growth.

6. Professional Maintenance: Schedule annual inspections with conservation specialists who can identify early signs of microbial activity and recommend appropriate treatments.

For severe cases of microbial infestation, consult a professional conservator who may recommend specialized biocidal treatments that won't harm the bronze. Remember that prevention is always better than restoration when it comes to preserving outdoor bronze artworks.