Streptococcus pneumoniae: This bacterium is the most common cause of acute otitis media in adults, especially in those with underlying conditions such as diabetes and COPD, which compromise the immune system. The presence of mastoid opacification suggests a severe infection, which is consistent with pneumococcal disease.

Haemophilus influenzae: This bacterium is another common cause of otitis media, particularly in adults with chronic conditions like COPD. It can also cause severe infections, including mastoiditis.
Moraxella catarrhalis: This bacterium is often found in the respiratory tract and can cause otitis media, especially in adults with underlying respiratory conditions like COPD.
Staphylococcus aureus: Although less common, S. aureus can cause otitis media, particularly in patients with compromised immune systems or those with a history of recurrent infections.

Pseudomonas aeruginosa: While less common, P. aeruginosa can cause severe otitis media and mastoiditis, especially in patients with compromised immune systems or those with a history of recurrent infections. Missing this diagnosis could lead to severe consequences due to its resistance to many antibiotics.
Invasive fungal infections (e.g., Aspergillus): In patients with significant immunocompromise, such as those with poorly controlled diabetes, fungal infections can cause otitis media and mastoiditis. These infections are often deadly if not promptly diagnosed and treated.

Gram-negative bacilli (e.g., E. coli, Klebsiella pneumoniae): These bacteria can cause otitis media and mastoiditis, but they are less common causes compared to the bacteria listed above. They might be considered in patients with specific risk factors, such as recent travel or exposure to contaminated water.
Anaerobic bacteria: These bacteria can be involved in chronic otitis media and mastoiditis, especially in cases where there is a history of chronic infection or previous surgery. However, they are less likely to cause acute presentations.