Common Mechanisms of Antibiotic Resistance

Decreased outer membrane permeability

Loss of outer membrane D2 porin in imipenem-resistant Pseudomonas aeruginosa

Enzymatic inactivation

Production of beta-lactamases that inactivate penicillins in penicillin-resistant Staphylococcus aureus, Haemophilus influenzae, and Escherichia coli

Production of aminoglycoside-inactivating enzymes in gentamicin-resistant enterococci

Changes in target

Decreased affinity of penicillin-binding proteins for beta-lactam antibiotics (eg, in methicillin-resistant Staphylococcus aureus [MRSA] and Streptococcus pneumoniae with reduced penicillin susceptibility)

S. aureus

Enterococcus faecium)

Decreased affinity of DNA gyrase for fluoroquinolones in fluoroquinolone-resistant S. aureus

Increased antibiotic efflux pump

clindamycin, or fluoroquinolones (eg, in S. aureus)

Bypass of antibiotic inhibition and target overproduction