MMI133 Lecture Notes - Lecture 8: Methicillin, Aminoglycoside, Oxacillin
2 Feb 2017
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Why don"t antibiotics kill human cells: prokaryotes (vs. eukaryotes) and arsenic. Sulfa humans eukaryotes do not: can produce antibiotics that have selective effect on bacteria and not, penicillin (cid:498)wonder drug(cid:499) Have different ribosomes (70s instead of 80s units) May need to synthesize folic acid for production of dna, rna . Production of the enzyme beta-lactamase or (cid:498)penicillinase(cid:499): inactivation of penicillin by breaking (cid:498)the beta-lactam ring(cid:499) Bacteria rebelled: the active portion of the antibiotic was protected from the enzymes. Mutated again, changing the binding sites on the bacterium to produce a variant that was resistant to methicillin. Penicillin binding protein 2 (pbp 2) mutates to pbp 2a. Pbp 2a has reduced affinity for the penicillin, results in reduced uptake into the cell wall. Penicillin then not effective for inhibiting the cross-linking of peptidoglycan. Ie: mrsa = methicillin resistant s. aureus: note: mssa = methicillin susceptible s. aureus. Bacteriostatic antibiotics: stop the replication of bacteria, do not kill the bacteria already present.
