Related Experiment Videos
Role of an altered penicillin-binding protein in methicillin- and cephem-resistant Staphylococcus aureus
Abstract:
About 80% of methicillin- and cefazolin-resistant strains of Staphylococcus aureus isolated clinically in Japan in 1982 retained their resistance even after elimination of penicillinase-encoding plasmids. The penicillin-binding proteins (PBPs) of the penicillinase-free, methicillin- and cephem-resistant subclones of Staphylococcus aureus (MRSA) were compared with those of spontaneous susceptible revertants which had been obtained by the replica method after 10 subcultures in drug-free media. A new PBP fraction (PBP2') having a molecular weight of 78,000 and low binding affinities for various beta-lactam antibiotics was found in MRSA exclusively. The levels of resistance of MRSA strains were reduced markedly by culturing them at 43 degrees C or at pH 5.2 or both. We found that the binding capacity of PBP2' for 14C-labeled penicillin G was decreased by preincubation of the membrane fractions of MRSA strains at 43 degrees C for 60 min and that the amount of PBP2' in MRSA strains grown at pH 5.2 was less than that the amount of PBP2' in MRSA strains grown at pH 7.0. Temperature- and pH-dependent expression of resistance in MRSA is likely to reflect the temperature sensitivity and neutral pH-dependent production of the specific PBP fraction (PBP2'). We suggest that MRSA strains can grow in the presence of beta-lactam antibiotics because of the low affinities of the specific PBP2' fraction for various beta-lactam antibiotics.
Insights
Methicillin-resistant Staphylococcus aureus (MRSA) retains resistance via a unique penicillin-binding protein (PBP2') with low beta-lactam affinity. Environmental factors like temperature and pH influence PBP2' expression and MRSA resistance levels.
Area of Science:
- Microbiology
- Molecular Biology
- Drug Resistance
Background:
- Approximately 80% of clinical methicillin- and cefazolin-resistant Staphylococcus aureus (MRSA) strains isolated in Japan in 1982 maintained resistance after plasmid elimination.
- This suggests intrinsic resistance mechanisms independent of penicillinase-encoding plasmids.
Purpose of the Study:
- To investigate the penicillin-binding proteins (PBPs) in MRSA strains lacking plasmids.
- To identify the molecular basis for beta-lactam antibiotic resistance in these MRSA strains.
Main Methods:
- Comparison of PBPs between MRSA subclones and susceptible revertants.
- Analysis of PBP binding affinities for beta-lactam antibiotics.
- Assessment of resistance levels under varying temperature (43°C) and pH (5.2) conditions.
Main Results:
- A novel PBP fraction, PBP2', with a molecular weight of 78,000 and low affinity for beta-lactam antibiotics, was exclusively found in MRSA.
- MRSA resistance significantly decreased at 43°C or pH 5.2.
- PBP2' binding affinity for penicillin G decreased after incubation at 43°C, and its production was lower at pH 5.2 compared to pH 7.0.
Conclusions:
- The temperature- and pH-dependent expression of resistance in MRSA is linked to the temperature sensitivity and pH-dependent production of PBP2'.
- MRSA's ability to grow in the presence of beta-lactam antibiotics is attributed to the low binding affinity of PBP2' for these drugs.