Medical Pharmacology Chapter 35  Antibacterial Drugs

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  • Penicillin G and Penicillin V Pharmacology and Therapeutics

    • Bacterial Resistance

      • Resistance to penicillin G/V is widespread in many bacteria due to several mechanisms.

        • The most common mechanism is bacterial production of β-lactamase enzymes (penicillinases) that hydrolyze the β-lactam ring, inactivating penicillin.1 

        • Many Staphylococcus aureus strains evolved a penicillinase shortly after was introduced to clinical practice. At present >90% of S. aureus are penicillin-resistant, rendering natural penicillins ineffective for routine staph infections.1

        • Some Gram-negative bacteria (e.g. certain Haemophilus and Bacteroides species) also produce β-lactamases that destroy penicillin.

          • A second resistance mechanism is alteration of the target PBPs so that penicillin binds with less affinity.2

          • For example, penicillin-resistant Streptococcus pneumoniae and Neisseria gonorrhoeae have modified PBPs with reduced β-lactam affinity, requiring higher penicillin concentrations for effect.3  Methicillin-resistant S. aureus (MRSA) carries a novel PBP (PBP2a) that penicillins cannot effectively bind, conferring resistance to all β-lactams.

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References

  1. Penicillin: https://en.wikipedia.org/wiki/Penicillin

  2. Zapuhn A Contreras-Martel C Vernet T Penicillin-binding proteins and Beta-Lactam resistance FemS Microbiology Reviews, Volume 32, Issue 2, March 2008, 361-385. https://academic.oup.com/femsre/article/32/2/361/2684029

  3. Chambers H Penicillin-binding protein-mediated resistance in pneumococci and staphylococci J Infect Dis. 1999 March; 179 Suppl 2:S353-359.

 

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