The four main mechanisms by which microorganisms exhibit resistance to antimicrobials are: #<unk> ug inactivation or modification: e.g., enzymatic deactivation of Penicillin G in some penicillin-resistant bacteria through the production of β-lactamases. # Alteration of target site: e.g., alteration of PBP — the binding target site of penicillins — in MRSA and other penicillin-resistant bacteria. # Alteration of metabolic pathway: e.g., some sulfonamide-resistant bacteria do not require para-aminobenzoic acid (PABA), an important precursor for the synthesis of folic acid and nucleic acids in bacteria inhibited by sulfonamides. Instead, like mammalian cells, they turn to utilizing preformed folic acid. # Reduced<unk> ug accumulation: by decreasing<unk> ug permeability and/or increasing active efflux (pumping out) of the<unk> ugs across the cell surface. Mechanisms of Acquired<unk> : + Mechanism Antimicrobial Agent<unk> ug Action Mechanism of Resistance Destroy<unk> ug Aminoglycoside Beta-lactam antibiotics (penicillin and cephalosporin) Chloramphenicol Binds to 30S Ribosome subunit, inhibiting protein synthesis Binds to penicillin-binding proteins, Inhibiting peptidoglycan synthesis Bind to 50S ribosome subunit, inhibiting formation of peptide bonds Plasmid encode enzymes that chemically alter the<unk> ug (e.g., by acetylation or phosphorylation), thereby inactivating it. Plasmid encode beta-lactamase, which open the beta-lactam ring, inactivating it. Plasmid encode an enzyme that acetylate the<unk> ug, thereby inactivating it. Alters<unk> ug target Aminoglycosides Beta-lactam antibiotics (penicillin and cephalosporin) Erythromycin Quinolones Rifampin Trimethoprim Binds to 30S Ribosome subunit, inhibiting protein synthesis Binds to penicillin-binding proteins, Inhibiting peptidoglycan synthesis Bind to 50S ribosome subunit, inhibiting protein synthesis Binds to DNA topoisomerase, an enzyme essential for DNA synthesis Binds to the RNA polymerase; inhibiting initiation of RNA synthesis Inhibit the enzyme dihydrofolate reduces, blocking the folic acid pathway Bacteria make an altered 30S ribosomes that does not bind to the<unk> ug. Bacteria make an altered penicillin-binding proteins, that do not bind to the<unk> ug. Bacteria make a form of 50S ribosome that does not binds to the<unk> ug. Bacteria make an altered DNA topoisomerase that does not binds to the<unk> ug. Bacteria make an altered polymerase that does not binds to the<unk> ug. Bacteria make an altered enzyme that does not binds to the<unk> ug. Inhibits<unk> ug entry or removes<unk> ug Penicillin Erythromycin Tetracycline Binds to penicillin-binding proteins, Inhibiting peptidoglycan synthesis Bind to 50S ribosome subunit, inhibiting protein synthesis Binds to 30S Ribosome subunit, inhibiting protein synthesis by blocking tRNA Bacteria change shape of the outer membrane porin proteins, preventing<unk> ug from entering cell. New membrane transport system prevent<unk> ug from entering cell. New membrane transport system pumps<unk> ug out of cell.
Drug resistance
Multiple drug resistance
Antimicrobial resistance
Antibiotic synergy
Resistance 
Vaccine resistance
Infectivity
Host adaptation