Morphology: Gram-negative diplococcus (resembles Neisseria on Gram stain). Oxidase-positive, DNAse-positive. Grows readily on routine media.
Typical drugs
- #1Amoxicillin-clavulanate— First-line — virtually all Moraxella produce β-lactamase. Amoxicillin alone ALWAYS fails.
- #2Cefpodoxime— Oral cephalosporin alternative — reliably active.
- #3Ceftriaxone— Hospitalized / severe disease.
- #4Azithromycin
- #5Doxycycline
- #6Trimethoprim-sulfamethoxazole
Empiric therapy when resistant
BRO β-lactamase is universal — amoxicillin monotherapy never adequate. Amoxicillin-clavulanate, oral cephalosporin (cefpodoxime, cefuroxime), macrolide, doxycycline, or TMP-SMX all reliably effective. Resistance to second-line agents is rare.
Resistance mechanisms
Enzymatic degradation
BRO-1 / BRO-2 β-lactamase — UNIVERSAL across clinical isolates
Example: Amoxicillin alone fails reliably. Use amox-clav, oral cephalosporin, macrolide, doxycycline, or TMP-SMX.
Resistance notes
100% β-lactamase-positive — amoxicillin alone is wrong by reflex. Otherwise resistance uncommon.
Common syndromes
Pearls
COPD exacerbation classic pathogen (along with H. flu and pneumococcus). Otitis media + sinusitis in children — third most common after pneumococcus and H. flu. ALWAYS β-lactamase-positive — never use amoxicillin alone, always pair with clavulanate or use a different class. Easy to mistake on Gram stain for Neisseria gonorrhoeae or N. meningitidis (both gram-neg diplococci) — clinical context disambiguates.
References
- IDSA/ATS Community-Acquired Pneumonia in Adults (2019)