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Apt (Adenine Phosphoribosyltransferase) Mutation in Laboratory-Selected Vancomycin-Intermediate Staphylococcus aureus
Reena Lamichhane-Khadka1,2, Santosh Dulal1, Jesus A Cuaron1
1Department of Biology, New Mexico State University, Las Cruces, NM 88003, USA.
Abstract:
Comparative genomic sequencing of laboratory-derived vancomycin-intermediate Staphylococcusaureus (VISA) (MM66-3 and MM66-4) revealed unique mutations in both MM66-3 (in apt and ssaA6), and MM66-4 (in apt and walK), compared to hetero-VISA parent strain MM66. Transcriptional profiling revealed that both MM66 VISA shared 79 upregulated genes and eight downregulated genes. Of these, 30.4% of the upregulated genes were associated with the cell envelope, whereas 75% of the downregulated genes were associated with virulence. In concordance with mutations and transcriptome alterations, both VISA strains demonstrated reduced autolysis, reduced growth in the presence of salt and reduced virulence factor activity. In addition to mutations in genes linked to cell wall metabolism (ssaA6 and walK), the same mutation in apt which encodes adenine phosphoribosyltransferase, was confirmed in both MM66 VISA. Apt plays a role in both adenine metabolism and accumulation and both MM66 VISA grew better than MM66 in the presence of adenine or 2-fluoroadenine indicating a reduction in the accumulation of these growth inhibiting compounds in the VISA strains. MM66 apt mutants isolated via 2-fluoroadenine selection also demonstrated reduced susceptibility to the cell wall lytic dye Congo red and vancomycin. Finding that apt mutations contribute to reduced vancomycin susceptibility once again suggests a role for altered purine metabolism in a VISA mechanism.
Insights
Mutations in the adenine phosphoribosyltransferase (apt) gene contribute to reduced vancomycin susceptibility in Staphylococcus aureus. This finding suggests altered purine metabolism plays a role in vancomycin-intermediate Staphylococcus aureus (VISA) development.
Area of Science:
- Microbiology
- Genomics
- Molecular Biology
Background:
- Vancomycin is a critical antibiotic for treating Staphylococcus aureus infections.
- Emergence of vancomycin-intermediate Staphylococcus aureus (VISA) poses a significant public health threat.
- Mechanisms underlying VISA development are not fully understood.
Purpose of the Study:
- To investigate the genomic and transcriptomic changes associated with laboratory-derived vancomycin-intermediate Staphylococcus aureus (VISA) strains.
- To identify specific genetic mutations and altered gene expression patterns contributing to vancomycin resistance.
Main Methods:
- Comparative genomic sequencing of VISA strains (MM66-3, MM66-4) and their hetero-VISA parent (MM66).
- Transcriptional profiling to analyze gene expression changes in VISA strains.
- Phenotypic characterization including autolysis, growth in salt, virulence factor activity, and susceptibility to Congo red and vancomycin.
Main Results:
- Unique mutations were identified in apt, ssaA6, and walK genes in VISA strains.
- Shared transcriptional changes included upregulation of cell envelope genes and downregulation of virulence genes.
- VISA strains exhibited reduced autolysis, salt tolerance, and virulence factor activity.
- Mutations in apt were linked to improved growth in adenine/2-fluoroadenine and reduced vancomycin susceptibility.
Conclusions:
- The adenine phosphoribosyltransferase (apt) gene mutation is a key factor in reduced vancomycin susceptibility.
- Altered purine metabolism, influenced by apt mutations, contributes to the VISA phenotype.
- These findings offer new insights into VISA mechanisms and potential therapeutic targets.
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