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Isolation of beta-lactamase from a penicillin-susceptible strain of Staphylococcus aureus
Abstract:
It is generally accepted that strains of Staphylococcus aureus which are susceptible to penicillin G do not produce beta-lactamase. However, we have found that such a strain susceptible to 0.06 mug of penicillin per ml and 0.56 mug of methicillin per ml produces beta-lactamase(s) which hydrolyzes penicillin G, methicillin, 6-aminopenicillanic acid, and probably cephaloridine. The enzyme which is found only during very early log phase of the growth cycle is not inducible either by penicillin or methicillin and is cell bound and liberated only by disruption of the cell. The rate of enzymatic hydrolysis of methicillin was 60% that of benzylpenicillin. This finding suggests that the elaboration per se of beta-lactamase does not necessarily afford resistance to penicillin in this gram-positive-producing cell.
Insights
Penicillin-susceptible Staphylococcus aureus strains can produce beta-lactamase enzymes. This study identified such a strain, challenging the assumption that beta-lactamase production always confers antibiotic resistance.
Area of Science:
- Microbiology
- Biochemistry
- Antibiotic Resistance
Background:
- Strains of Staphylococcus aureus susceptible to penicillin G are generally not believed to produce beta-lactamase.
- Beta-lactamase enzymes are known to hydrolyze beta-lactam antibiotics, conferring resistance.
Purpose of the Study:
- To investigate the production of beta-lactamase in a strain of Staphylococcus aureus susceptible to penicillin G.
- To characterize the properties of the beta-lactamase produced by this susceptible strain.
Main Methods:
- Susceptibility testing of Staphylococcus aureus to penicillin G and methicillin.
- Detection and characterization of beta-lactamase activity.
- Enzyme assays to determine hydrolysis rates of different beta-lactam antibiotics.
- Investigation of enzyme induction and cellular localization.
Main Results:
- A strain of Staphylococcus aureus susceptible to penicillin G (0.06 µg/ml) and methicillin (0.56 µg/ml) was found to produce beta-lactamase(s).
- The enzyme(s) hydrolyzed penicillin G, methicillin, 6-aminopenicillanic acid, and likely cephaloridine.
- The enzyme was present only in the early log phase of growth, was not inducible by penicillin or methicillin, and was cell-bound.
- The rate of methicillin hydrolysis was 60% of that for benzylpenicillin.
Conclusions:
- Beta-lactamase production in Staphylococcus aureus does not necessarily correlate with resistance to penicillin.
- The presence and activity of beta-lactamase in a susceptible strain suggest a more complex mechanism of antibiotic resistance than previously assumed.