title: Differential expression of methicillin resistance by different biofilm-negative Staphylococcus epidermidis transposon mutant classes.
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.
authors.affiliation: Institut für Medizinische Mikrobiologie und Immunologie, Universitätsklinikum Hamburg-Eppendorf, 20246 Hamburg, Federal Republic of Germany. dmack@uke.uni-hamburg.de
authors.forename: Dietrich
authors.initials: D
authors.lastname: Mack
authors.forename: Axel
authors.initials: A
authors.lastname: Sabottke
authors.forename: Sabine
authors.initials: S
authors.lastname: Dobinsky
authors.forename: Holger
authors.initials: H
authors.lastname: Rohde
authors.forename: Matthias A
authors.initials: MA
authors.lastname: Horstkotte
authors.forename: Johannes K-M
authors.initials: JK
authors.lastname: Knobloch
mesh_terms: D001426:Bacterial Proteins; D018441:Biofilms; D002352:Carrier Proteins / Q000032:analysis / Q000235:genetics; D004251:DNA Transposable Elements / Q000235:genetics*; D006602:Hexosyltransferases; D016106:Methicillin Resistance / Q000235:genetics*; D008826:Microbial Sensitivity Tests; D002267:Muramoylpentapeptide Carboxypeptidase / Q000032:analysis / Q000235:genetics; D010068:Oxacillin / Q000494:pharmacology; D046915:Penicillin-Binding Proteins; D010406:Penicillins / Q000494:pharmacology; D010458:Peptidyl Transferases; D013212:Staphylococcus epidermidis / Q000187:drug effects / Q000235:genetics*
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; D004251:DNA Transposable Elements; D046915:Penicillin-Binding Proteins; D010406:Penicillins; C083616:mecA protein, Bacillus subtilis; D010458:Peptidyl Transferases; D006602:Hexosyltransferases; D002267:Muramoylpentapeptide Carboxypeptidase; D010068:Oxacillin