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Activity of clavulanate-potentiated penicillins against methicillin-resistant Staphylococcus aureus
W Graninger1, T Leitha, K Griffin
1Department of Chemotherapy, University of Vienna, Austria.
Abstract:
It has been suggested that combinations of penicillins with clavulanate may be useful in treatment of infections by methicillin-resistant strains of Staphylococcus aureus (MRSA). To determine the potentiating effect of clavulanate on the antibacterial activity of penicillins, we studied MRSA in vitro by an agar-dilution method. A total of 124 clinical isolates of MRSA were tested for sensitivity to benzylpenicillin, amoxycillin, and ticarcillin alone and in combination with 1.25, 2.5, 5.0 and 10.0 mg/l of clavulanate. Most of the strains were not typable by the international reference set of bacteriophages of human staphylococci but showed typical properties of nosocomial strains. A reduction in the MIC90 of benzylpenicillin and amoxycillin to 25 mg/l was seen in the presence of 2.5 mg/l of clavulanate. The effect was less pronounced with ticarcillin. In spite of some increase in the susceptibility of MRSA to benzylpenicillin and amoxycillin produced by clavulanate, these combinations seem to be inappropriate in infections due to MRSA.
Insights
Clavulanate showed limited potentiation of penicillin activity against methicillin-resistant Staphylococcus aureus (MRSA) in vitro. These penicillin-clavulanate combinations are likely inappropriate for treating MRSA infections.
Area of Science:
- Microbiology
- Infectious Diseases
- Pharmacology
Background:
- Methicillin-resistant Staphylococcus aureus (MRSA) poses a significant threat in healthcare settings.
- Combinations of penicillins with clavulanate have been explored for treating MRSA infections.
Purpose of the Study:
- To evaluate the in vitro potentiating effect of clavulanate on the antibacterial activity of penicillins against MRSA.
- To determine the minimum inhibitory concentrations (MIC90) of penicillin-clavulanate combinations against clinical MRSA isolates.
Main Methods:
- An agar-dilution method was employed to test 124 clinical MRSA isolates.
- Strains were tested against benzylpenicillin, amoxycillin, and ticarcillin alone and with varying concentrations of clavulanate (1.25–10.0 mg/l).
Main Results:
- Clavulanate (2.5 mg/l) reduced the MIC90 of benzylpenicillin and amoxycillin to 25 mg/l.
- The potentiating effect of clavulanate was less pronounced with ticarcillin.
- Some increase in MRSA susceptibility to benzylpenicillin and amoxycillin was observed.
Conclusions:
- While clavulanate demonstrated some in vitro potentiation, the observed effect was modest.
- Penicillin-clavulanate combinations appear unsuitable for effective treatment of MRSA infections.
- Further research into alternative treatment strategies for MRSA is warranted.