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Table 1 Main resistance mechanisms in Gram-negative pathogens

From: Multidrug Resistant Gram-Negative Bacteria in Community-Acquired Pneumonia

Microorganism Mechanism
Pseudomonas aeruginosa Efflux pumps
Mutant topoisomerases
Modifying enzymes
AmpC/porin reduction combinations
Metallo-b-lactamases
Outer membrane permeability
Extended spectrum β-lactamases
Acinetobacter baumannii β-lactamases
Efflux pumps
Membrane permeability
Aminoglycoside-modifying enzymes
Alteration of target sites
Klebsiella pneumoniae Modifying enzyme
Efflux pumps
Mutant topoisomerases
Extended spectrum β-lactamases
Carbapenemases
Stenotrophomonas maltophilia β-lactamases (L1 and L2)
Multidrug efflux pumps
Antibiotic-modifying enzymes
Mutations of bacterial topoisomerase and gyrase genes
Reduction in outer membrane permeability