Biomedical subjects

Holger Rohde

Publications and source records attributed to Holger Rohde.

22 records · Page 2Linked to original sources

PubMed2002

Minimal attachment killing (MAK): a versatile method for susceptibility testing of attached biofilm-positive and -negative Staphylococcus epidermidis.

Due to its ability to attach to polymeric surfaces Staphylococcus epidermidis is a common pathogen in chronic, medical device-associated infections. Attached S. epidermidis displays reduced susceptibility against a variety of antimicrobial substances, and little correlation between standard susceptibility test results and clinical outcome of antibiotic treatment is observed. In this study we established a new, versatile, and easy method of antimicrobial susceptibility testing for attached Staphylococcus epidermidis, suitable for both biofilm-negative and biofilm-positive attached bacteria using readily available equipment. For three biofilm-positive wild-type strains and their biofilm-negative mutants minimal attachment killing concentrations (MAK) of penicillin, oxacillin, vancomycin, and gentamicin were determined. Depending on strain and investigated antibiotics, a heterogeneous MAK (MAK(hetero)) could be differentiated from a homogeneous resistance (MAK(homo)), favoring a model of few persisters within attached cells under antibiotic treatment. For the biofilm-negative mutants, a lower MAK(homo) was detected than for the corresponding wild types for some of the tested antibiotics, which probably resulted from higher bacterial inocula of wild-type strains, whereas the MAK(hetero) were comparable for mutants and wild types for most of the tested antibiotics and strains. These data indicate that biofilm formation is not a necessary prerequisite for persistence of attached S. epidermidis cells under antibiotic treatment, which could explain therapeutic failure in foreign body-associated infections due to biofilm-negative S. epidermidis isolates. The highly individual resistance phenotypes of the investigated strains with different antibiotics suggests that MAK determination could help to predict the therapeutic outcome of foreign body-associated infections with both biofilm-positive and biofilm-negative S. epidermidis.

Anti-Bacterial Agents↗

PubMed2002

Alcoholic ingredients in skin disinfectants increase biofilm expression of Staphylococcus epidermidis.

The pathogenesis of Staphylococcus epidermidis is correlated with biofilm formation. We investigated the effect of three common alcoholic skin disinfectants, ethanol, n-propanol and isopropanol, on the biofilm formation of 37 clinical, icaADBC-positive S. epidermidis isolates. In alcohol-supplemented media 18 strains displayed increased biofilm expression. Sixteen of 19 strains were generally incapable of biofilm formation. In three representative isolates, the increase in biofilm formation was paralleled by increased polysaccharide intercellular adhesin synthesis. Regarding the widespread use of alcoholic skin disinfectants, it is possible that the alcohol-inducible biofilm phenotype of S. epidermidis could add to the development of foreign body-related infections.

Biofilms↗

PubMed2002

Differential expression of methicillin resistance by different biofilm-negative Staphylococcus epidermidis transposon mutant classes.

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.

Bacterial Proteins↗

PubMed2002

Rapid detection of methicillin resistance in coagulase-negative Staphylococci with the VITEK 2 system.

The aim of the present study was to evaluate the accuracy of the new VITEK 2 system (bioMérieux, Marcy l' Etoile, France) for the detection of methicillin resistance in coagulase-negative staphylococci (CoNS) by using AST-P515 and AST-P523 test cards. Analyses of the VITEK 2 oxacillin MIC determination evaluated according to the actual breakpoint (>/=0.5 micro g/ml) of the National Committee for Clinical Laboratory Standards resulted in a high sensitivity of 99.2% but a moderate specificity of 80%. The newly included oxacillin resistance (OR) test of the VITEK 2 system displayed a high sensitivity and a high specificity of 97.5 and 98.7%, respectively. Concordance between the results of the mecA PCR and the VITEK 2 oxacillin MIC was observed for almost all Staphylococcus epidermidis strains, but the reduced specificity was attributable to higher oxacillin MICs for mecA-negative non-S. epidermidis strains, especially S. saprophyticus, S. lugdunensis, and S. cohnii. Evaluation of alternative oxacillin MIC breakpoints of 1, 2, or 4 micro g/ml resulted in improved degrees of specificity of 84, 90.7, and 97.3%, respectively. Only minor changes occurred in the corresponding sensitivity values, which were 98.4, 97.5, and 97.5%, respectively. Methicillin resistance in CoNS was detected after 7 and 8 h in 91.1 and 93.5% of the mecA-positive strains, respectively, by the VITEK 2 OR test and in 86.3 and 89.5% of the mecA-positive strains, respectively, by VITEK 2 oxacillin MIC determination. After 7 and 8 h the VITEK 2 OR test classified 59.2 and 78.9% of the mecA-negative strains, respectively, as susceptible to oxacillin, whereas comparable values were obtained 2 h later by VITEK 2 oxacillin MIC determination. The results of our study encourage the use of the VITEK 2 system, which proved to be a highly reliable and rapid phenotypic method for the detection of methicillin resistance in CoNS.

Bacterial Proteins↗