A 28-year-old female with folliculitis is not responsive to a 10-day treatment course with penicillin. An enzyme produced by the etiologic agent is most likely responsible for this treatment failure. At which site on the molecule shown does this enzyme act to destroy penicillin?
The structural integrity of the b-lactam ring in penicillin is essential for their antimicrobial activity. Many resistant strains of staphylococci produce a b-lactamase (penicillinase) that cleaves the b-lactam ring of penicillin at the carbon-nitrogen bond (4 in diagram). Other organisms, including coliform bacteria and Pseudomonas, produce cephalosporinases, metallo-b-lactamases, and carbapenamases that cleave the b-lactam rings of cephalosporins and/or carbapenems, as well as penicillin, at the same site. Penicillin amidase inactivates penicillin by disrupting the bond between the radical and nitrogen in the free amino group (1 in diagram). Bonds 2, 3, and 5 are not commonly broken by bacterial enzymes.
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