Does Augmentin Cover Gram-Positive and Gram-Negative Organisms?
Yes, Augmentin (amoxicillin-clavulanate) provides broad-spectrum coverage against both gram-positive and gram-negative organisms, including beta-lactamase-producing strains that would otherwise be resistant to amoxicillin alone. 1, 2
Mechanism and Spectrum of Activity
Augmentin combines amoxicillin (a broad-spectrum penicillin) with clavulanic acid (a beta-lactamase inhibitor), which protects amoxicillin from enzymatic degradation and extends its antimicrobial spectrum to include organisms that produce beta-lactamases 1. This combination possesses the properties of a broad-spectrum antibiotic effective against both gram-positive and gram-negative aerobes, facultative anaerobes, and obligate anaerobes 2.
Gram-Positive Coverage
Augmentin demonstrates robust activity against gram-positive organisms:
- Staphylococcus aureus (both beta-lactamase and non-beta-lactamase-producing strains), though methicillin-resistant strains (MRSA) remain resistant 1
- Streptococcus pneumoniae, including penicillin-susceptible and intermediate strains 3, 4
- Streptococcus species and enterococci 5, 1
- Anaerobic gram-positive cocci including Peptostreptococcus species 6
The American Academy of Otolaryngology-Head and Neck Surgery specifically recommends amoxicillin-clavulanate for coverage of Streptococcus pneumoniae with clinical efficacy rates of 91-92% in both adults and children with acute bacterial rhinosinusitis 3.
Gram-Negative Coverage
Augmentin provides effective coverage against clinically important gram-negative pathogens:
- Haemophilus influenzae (both beta-lactamase and non-beta-lactamase-producing strains), with 20-40% of strains producing beta-lactamase 3, 1
- Moraxella catarrhalis (nearly 100% produce beta-lactamase) 3, 1
- Escherichia coli (beta-lactamase and non-beta-lactamase-producing) 1, 7
- Klebsiella species (all known strains are beta-lactamase-producing) 1, 7
- Proteus mirabilis and other Proteus species 1, 2
- Enterobacter species (though most are resistant in vitro, clinical efficacy has been demonstrated in urinary tract infections) 1
In comparative studies, Augmentin achieved 67% overall bacteriologic success against gram-negative strains compared to only 27% with amoxicillin alone 7.
Anaerobic Coverage
Augmentin provides coverage against Bacteroides fragilis, the predominant anaerobe in intra-abdominal infections, and other anaerobic organisms 5. This makes it particularly useful for polymicrobial infections involving both aerobic and anaerobic bacteria 6.
Critical Limitations
Important pathogens NOT adequately covered by Augmentin include:
- Pseudomonas aeruginosa 3
- Methicillin-resistant Staphylococcus aureus (MRSA) 3, 1
- Atypical respiratory pathogens (Mycoplasma, Chlamydia, Legionella) 3
- Extended-spectrum beta-lactamase (ESBL)-producing organisms 3
For immunocompromised patients requiring coverage for resistant gram-positive bacteria like MRSA, alternative agents such as vancomycin, linezolid, or daptomycin are necessary 6. For resistant gram-negative organisms including Pseudomonas, fluoroquinolones, aminoglycosides, or carbapenems should be considered 6.
Clinical Applications
The Infectious Diseases Society of America and European Society of Clinical Microbiology and Infectious Diseases recommend amoxicillin-clavulanate for:
- Mild to moderate skin and soft tissue infections 8
- Animal and human bite wounds (coverage of oral flora including Pasteurella and anaerobes) 8
- Diabetic foot infections (mild to moderate) 8
- Mild to moderate intra-abdominal infections 8, 5
- Acute otitis media, especially with recent antibiotic exposure 8
Augmentin achieves approximately 70% susceptibility against key pathogens in community-acquired intra-abdominal infections 5.