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Differential expression of methicillin resistance by different biofilm-negative Staphylococcus epidermidis transposon
Dietrich Mack1, Axel Sabottke, Sabine Dobinsky
1Institut für Medizinische Mikrobiologie und Immunologie, Universitätsklinikum Hamburg-Eppendorf, 20246 Hamburg, Federal Republic of Germany. dmack@uke.uni-hamburg.de
Abstract:
Biofilm formation mediated by polysaccharide intercellular adhesin (PIA) is the major virulence factor of Staphylococcus epidermidis and is often associated with methicillin resistance. Transposon Tn917 insertions leading to a biofilm-negative phenotype in the biofilm-producing S. epidermidis strain 1457 (mecA-negative) were transferred into the methicillin-resistant, biofilm-producing S. epidermidis 1057 (mecA-positive) by transduction. According to their phenotypes and genotypes, the mutants could be separated into genetic classes I to IV (D. Mack, H. Rohde, S. Dobinsky, J. Riedewald, M. Nedelmann, J. K. M. Knobloch, H.-A. Elsner, and H. H. Feucht, Infect. Immun. 68:3799-3807, 2000). All transductants of S. epidermidis 1057 had phenotypes for biofilm formation similar to those of the corresponding mutants of S. epidermidis 1457. With a mecA-specific probe, identical hybridization patterns were observed for wild-type S. epidermidis 1057 and all the transductants. There were minor changes in oxacillin MICs for Class II and III transductants compared to those for wild-type S. epidermidis 1057. On population analysis, S. epidermidis 1057 displayed a heterogeneous expression type of resistance with an oxacillin MIC of > or =6 microg/ml for more than 90% of the cells. An almost identical profile was observed with biofilm-negative class I mutants, where the transposon insertions inactivate the icaADBC gene locus essential for PIA synthesis. In contrast, class III mutants were more sensitive to oxacillin with a MIC of < or =1 microg/ml for more than 90% of the cells. The class IV mutant displayed homogeneous resistance with a MIC of > or =50 microg/ml for more than 90% of the cells. On oxacillin gradient plates, the class II mutant displayed decreased resistance. Apparently, different independent mutations leading to a biofilm-negative phenotype of S. epidermidis by influencing expression of icaADBC on the level of transcription significantly influence the expression of methicillin resistance. However, transcription of mecA was not significantly altered in the different transductants compared to the wild type, independent of mecA induction with oxacillin, indicating that other mechanisms influencing phenotypic expression of methicillin resistance are involved.
Insights
Mutations affecting polysaccharide intercellular adhesin (PIA) production in Staphylococcus epidermidis significantly influence methicillin resistance. Biofilm-negative mutants showed altered oxacillin resistance, indicating complex regulatory mechanisms.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Polysaccharide intercellular adhesin (PIA) is a key virulence factor in Staphylococcus epidermidis biofilm formation.
- PIA-mediated biofilm formation is frequently associated with methicillin resistance in S. epidermidis.
- Understanding the interplay between biofilm formation and antibiotic resistance is crucial for clinical management.
Purpose of the Study:
- To investigate the impact of mutations affecting PIA synthesis on methicillin resistance in Staphylococcus epidermidis.
- To analyze the genetic and phenotypic characteristics of S. epidermidis mutants with altered biofilm formation.
- To explore the relationship between biofilm-negative phenotypes and oxacillin resistance expression.
Main Methods:
- Transduction of transposon Tn917 insertions from a mecA-negative strain into a mecA-positive S. epidermidis strain.
- Phenotypic analysis of biofilm formation and oxacillin susceptibility (MICs).
- Genotypic characterization using mecA-specific probes and population analysis.
Main Results:
- Transductants exhibited biofilm-negative phenotypes similar to the original mutants.
- Mutations inactivating the icaADBC locus (essential for PIA) significantly influenced oxacillin resistance.
- Class III mutants showed increased oxacillin sensitivity, while Class IV mutants displayed homogeneous resistance.
- Class II mutants exhibited decreased oxacillin resistance.
Conclusions:
- Independent mutations leading to a biofilm-negative phenotype in S. epidermidis can significantly alter methicillin resistance expression.
- These mutations appear to affect the transcription of the icaADBC locus, influencing phenotypic methicillin resistance.
- The mecA gene transcription was not significantly altered, suggesting alternative mechanisms regulate phenotypic methicillin resistance.