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FemA, a host-mediated factor essential for methicillin resistance in Staphylococcus aureus: molecular cloning and
B Berger-Bächi1, L Barberis-Maino, A Strässle
1Institute of Medical Microbiology, University of Zürich, Switzerland.
Abstract:
The methicillin resistance determinant (mec) in Staphylococcus aureus resides on additional DNA not present in isogenic sensitive cells. However, besides mec, other chromosomally determined factors are essential for expression of methicillin resistance. We cloned and characterized a chromosomally determined gene which encodes a factor essential for the expression of methicillin resistance (femA) in S. aureus. femA mapped in chromosomal segment number 18, genetically very distant from the methicillin resistance determinant (mec). The product of femA was a protein of an apparent size of 48 kDa. FemA restored methicillin resistance in S. aureus that had become sensitive to methicillin by insertion of omega 2003 (femA::Tn551). Although FemA was needed for cell growth in the presence of beta-lactam antibiotics, it had no influence on the synthesis of the low affinity, additional penicillin-binding protein (PBP2') encoded by mec and known to be essential for cell wall synthesis in the presence of inhibitory concentrations of methicillin. Nucleotide sequence analysis, Northern RNA blotting and S1 nuclease RNA mapping suggested that femA was transcribed on a polycistronic mRNA. This mRNA contained the coding region (ORF419) producing a protein of 47 kDa. The nucleotide and amino acid sequence of FemA showed homologies with ORF419, suggesting that these genes arose by gene duplication. In addition we present evidence for a second chromosomal factor, femB, involved in expression of methicillin resistance which maps close to femA.
Insights
Researchers identified femA, a crucial gene for methicillin resistance in Staphylococcus aureus. This gene, distinct from the mec determinant, is essential for bacterial survival in the presence of beta-lactam antibiotics.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Methicillin resistance in Staphylococcus aureus is complex, involving the methicillin resistance determinant (mec) and other chromosomal factors.
- The precise mechanisms and genetic elements contributing to methicillin resistance expression require further elucidation.
Purpose of the Study:
- To clone and characterize a novel chromosomal gene, femA, essential for methicillin resistance expression in S. aureus.
- To investigate the role of femA in the context of methicillin resistance and its relationship with the mec determinant.
Main Methods:
- Gene cloning and characterization of femA in S. aureus.
- Genetic mapping of femA on the S. aureus chromosome.
- Complementation studies to restore methicillin resistance in femA-deficient mutants.
- Analysis of protein size, nucleotide sequence, and gene transcription (Northern blotting, S1 nuclease mapping).
Main Results:
- The femA gene was cloned and mapped to a chromosomal segment distant from mec.
- The femA product, a 48 kDa protein, restored methicillin resistance in sensitive S. aureus strains.
- FemA is essential for growth in beta-lactam antibiotics but does not affect PBP2' synthesis.
- Evidence suggests femA is transcribed as part of a polycistronic mRNA and shows homology to ORF419, indicating potential gene duplication.
- A second gene, femB, involved in methicillin resistance, was identified near femA.
Conclusions:
- FemA is a critical chromosomal factor, independent of mec, required for the expression of methicillin resistance in S. aureus.
- FemA's function is vital for bacterial survival against beta-lactam antibiotics.
- The discovery of femA and femB highlights the complex genetic basis of methicillin resistance in S. aureus.