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Production of low-affinity penicillin-binding protein by low- and high-resistance groups of methicillin-resistant
1Shionogi Research Laboratories, Shionogi and Co., Ltd., Osaka, Japan.
Abstract:
Methicillin- and cephem-resistant Staphylococcus aureus (137 strains) for which the cefazolin MICs are at least 25 micrograms/ml could be classified into low-resistance (83% of strains) and high-resistance (the remaining 17%) groups by the MIC of flomoxef (6315-S), a 1-oxacephalosporin. The MICs were less than 6.3 micrograms/ml and more than 12.5 micrograms/ml in the low- and high-resistance groups, respectively. All strains produced penicillin-binding protein 2' (PBP 2'), which has been associated with methicillin resistance and which has very low affinity for beta-lactam antibiotics. Production of PBP 2' was regulated differently in low- and high-resistance strains. With penicillinase-producing strains of the low-resistance group, cefazolin, cefamandole, and cefmetazole induced PBP 2' production about 5-fold, while flomoxef induced production 2.4-fold or less. In contrast, penicillinase-negative variants of low-resistance strains produced PBP 2' constitutively in large amounts and induction did not occur. With high-resistance strains, flomoxef induced PBP 2' to an extent similar to that of cefazolin in both penicillinase-producing and -negative strains, except for one strain in which the induction did not occur. The amount of PBP 2' induced by beta-lactam antibiotics in penicillinase-producing strains of the low-resistance group correlated well with resistance to each antibiotic. Large amounts of PBP 2' in penicillinase-negative variants of the low-resistance group did not raise the MICs of beta-lactam compounds, although these strains were more resistant when challenged with flomoxef for 2 h. Different regulation of PBP 2' production was demonstrated in the high- and low-resistance groups, and factor(s) other than PBP 2' were suggested to be involved in the methicillin resistance of high-resistance strains.
Insights
Flomoxef effectively differentiates Staphylococcus aureus strains with low or high resistance to methicillin and cephem antibiotics. Penicillin-binding protein 2
Area of Science:
- Microbiology
- Infectious Diseases
- Pharmacology
Background:
- Methicillin-resistant Staphylococcus aureus (MRSA) poses a significant public health threat due to its resistance to beta-lactam antibiotics.
- Penicillin-binding protein 2' (PBP 2') is a key determinant of methicillin resistance in S. aureus, exhibiting low affinity for beta-lactam agents.
- Understanding the differential regulation of PBP 2' production is crucial for developing effective therapeutic strategies against MRSA.
Purpose of the Study:
- To investigate the utility of flomoxef in classifying MRSA strains based on their resistance levels.
- To explore the differential regulation of PBP 2' production in response to various beta-lactam antibiotics in low- and high-resistance MRSA strains.
- To identify potential factors beyond PBP 2' that contribute to high-level methicillin resistance.
Main Methods:
- Classification of 137 MRSA strains into low- and high-resistance groups using cefazolin and flomoxef minimum inhibitory concentrations (MICs).
- Assessment of PBP 2' production in response to different beta-lactam antibiotics (cefazolin, cefamandole, cefmetazole, flomoxef) using induction assays.
- Correlation analysis between PBP 2' levels and antibiotic resistance in penicillinase-producing and -negative MRSA strains.
Main Results:
- Flomoxef MICs effectively categorized MRSA strains into low- (83%) and high-resistance (17%) groups.
- PBP 2' production was differentially regulated: induced by cefazolin in low-resistance penicillinase-producing strains, but constitutively produced in penicillinase-negative strains.
- High-resistance strains showed similar PBP 2' induction by flomoxef and cefazolin, suggesting additional resistance mechanisms.
Conclusions:
- Flomoxef serves as a valuable tool for stratifying MRSA resistance.
- Differential regulation of PBP 2' production plays a role in varying levels of beta-lactam resistance.
- Factors other than PBP 2' likely contribute to high-level methicillin resistance in certain MRSA strains.