β-Lactamases

β-lactam antibiotics are antibacterial agents that share the structure feature of a β-lactam ring are known to be very diverse (Greenwood, 1995).Resistance to β-lactam antibiotics is due mainly to the production of β-lactamases, enzymes that inactivates these antibiotics by splitting the amide bond of the β-lactam ring. Numerous β-lactamases exist, encoded
either by chromosomal genes or by transferable genes located on plasmids or transposons (Medeiros, 1984).

These enzymes new first detected by Abraham and Chain (1940) in extracts of penicillin-resistant strains of E. Coli and other Gram-negative bacteria, and have since been demonstrated in penicillin- or cephalosporin-resistant strains of most bacterial species.

One of the first-recognized ways for bacteria to resist the actions of antimicrobial agents was the production of enzymes that inactivate a drug. Aminoglycosides and chloramphanicol, have been found to be affected by inactivating enzymes, but the classic example of this phenomenon is β-lactamase production. Since their introduction into clinical practice, the effectiveness of β-lactam antibiotics has been reduced by the occurrence
of bacteria that are resistant to their mode of action. Resistant Staphylococcus aureus strains were reported very soon after the introduction of benzyl penicillin into clinical practice (Abraham and Chain, 1940).

Other than the intrinsic resistance resulting from insusceptible targets or inadequate penetration of the drug through the Gram-negative outer membrane, resistance to this class of antibiotic is most frequently due to the
production of β-lactamase enzymes that hydrolyze the β-lactam bond inthese antibiotics, thus destroying their functionality (Livermore, 1995).

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