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Karsten Becker

Publications and source records attributed to Karsten Becker.

31 records · Page 2Linked to original sources
PubMed2004

Effect of trimethoprim-sulfamethoxazole prophylaxis in AIDS patients on the formation of the small colony variant phenotype of Staphylococcus aureus.

Emergence of Staphylococcus aureus small colony variants (SCVs) has been associated with antibiotic use, particularly with trimethoprim-sulfamethoxazole (TMP-SMZ). In this study, 634 specimens of 125 patients with AIDS were prospectively screened for S. aureus with normal phenotype and for S. aureus SCVs. Charts of these patients were reviewed for previous prophylaxis with TMP-SMZ often used as long-term pneumocystosis prophylaxis. Thirty-seven patients (29.6%) harbored S. aureus in their anterior nares, three of these patients (8.1%) had S. aureus SCVs. Interestingly, TMP-SMZ does not appear to select for S. aureus SCVs in nasal swabs of these patients.

AIDS-Related Opportunistic Infections↗
PubMed2004

Prevalence of genes encoding for members of the staphylococcal leukotoxin family among clinical isolates of Staphylococcus aureus.

Well-characterized Staphylococcus aureus nasal and blood isolates (N = 429) were tested by polymerase chain reaction for the prevalence of genes that encode leukocidal toxins. The leukotoxin genes lukE+lukD were found at high prevalence, significantly more so in blood (82%) than in nasal isolates (60.5%). Although almost all isolates were positive for the gamma-hemolysin gene, none was positive for lukM. Genes encoding Panton-Valentine leukocidin (PVL) components were very rare in either nasal or blood isolates. The lukE+lukD-negative isolates were significantly more likely to be positive for the staphylococcal enterotoxin gene combination seg/sei (89.5%) and the toxic shock syndrome toxin-1 gene (39.3%) than lukE+lukD-positive isolates (41.7% and 12.7%, respectively). The lukE+lukD-negative isolates were also more likely to show positivity for the accessory gene regulatory locus agr III, but less likely to be positive for the agr II locus. The co-possession of different virulence factors and their probable synergy should receive more attention in order to better understand their role in pathogenicity.

Bacterial Proteins↗
PubMed2004

Development and evaluation of a quality-controlled ribosomal sequence database for 16S ribosomal DNA-based identification of Staphylococcus species.

To establish an improved ribosomal gene sequence database as part of the Ribosomal Differentiation of Microorganisms (RIDOM) project and to overcome the drawbacks of phenotypic identification systems and publicly accessible sequence databases, both strands of the 5' end of the 16S ribosomal DNA (rDNA) of 81 type and reference strains comprising all validly described staphylococcal (sub)species were sequenced. Assuming a normal distribution for pairwise distances of all unique staphylococcal sequences and choosing a reporting criterion of > or =98.7% similarity for a "distinct species," a statistical error probability of 1.0% was calculated. To evaluate this database, a 16S rDNA fragment (corresponding to Escherichia coli positions 54 to 510) of 55 clinical Staphylococcus isolates (including those of the small-colony variant phenotype) were sequenced and analyzed by the RIDOM approach. Of these isolates, 54 (98.2%) had a similarity score above the proposed threshold using RIDOM; 48 (87.3%) of the sequences gave a perfect match, whereas 83.6% were found by searching National Center for Biotechnology Information (NCBI) database entries. In contrast to RIDOM, which showed four ambiguities at the species level (mainly concerning Staphylococcus intermedius versus Staphylococcus delphini), the NCBI database search yielded 18 taxon-related ambiguities and showed numerous matches exhibiting redundant or unspecified entries. Comparing molecular results with those of biochemical procedures, ID 32 Staph (bioMerieux, Marcy I'Etoile, France) and VITEK 2 (bioMerieux) failed to identify 13 (23.6%) and 19 (34.5%) isolates, respectively, due to incorrect identification and/or categorization below acceptable values. In contrast to phenotypic methods and the NCBI database, the novel high-quality RIDOM sequence database provides excellent identification of staphylococci, including rarely isolated species and phenotypic variants.

Bacterial Typing Techniques↗
PubMed2004

Evaluation of different methods to detect methicillin resistance in small-colony variants of Staphylococcus aureus.

To evaluate different methods for their abilities to detect methicillin resistance in small-colony variants (SCVs) of Staphylococcus aureus, 11 different methicillin-resistant S. aureus (MRSA) clones with the SCV phenotype were used in this study. The slow growth of SCVs often makes testing by disk diffusion or by automated methods invalid. Only detection of the mecA gene by PCR and the MRSA-Screen latex agglutination test using a higher colony number were shown to be reliable methods to rapidly detect methicillin resistance in these variants.

Genetic Variation↗
PubMed2004

Cellular prion protein acquires resistance to proteolytic degradation following copper ion binding.

The conversion of cellular prion protein (PrP(C)) into its pathological isoform (PrP(Sc)) conveys an increase in hydrophobicity and induces a partial resistance to proteinase K (PK). Interestingly, co-incubation with high copper ion concentrations also modifies the solubility of PrP(c) and induces a partial PK resistance which was reminiscent of PrP(Sc). However, concerns were raised whether this effect was not due to a copper-induced inhibition of the PK itself. We have therefore analyzed the kinetics of the formation of PK-resistant PrP(C) and excluded possible interference effects by removing unbound copper ions prior to the addition of PK by methanol precipitation or immobilization of PrP(C) followed by washing steps. We found that preincubation of PrPc with copper ions at concentrations as low as 50 microM indeed rendered these proteins completely PK resistant, while control substrates were proteolyzed. No other divalent cations induced a similar effect. However, in addition to this specific stabilizing effect on PrP(C), higher copper ion concentrations in solution (>200 microM) directly blocked the enzymatic activity of PK, possibly by replacing the Ca2+ ions in the active center of the enzyme. Therefore, as a result of this inhibition the proteolytic degradation of PrP(C) as well as PrP(Sc) molecules was suppressed.

Animals↗
PubMed2003

Bacteria and granulation tissue associated with Montgomery T-tubes.

OBJECTIVES: Although complications (infection, development of granulation tissue) of silicone Montgomery T-tubes have been reported, the microbiological consequences and the origin of granulation tissue have not yet been evaluated. STUDY DESIGN: A prospective trial. METHODS: Twenty-three Montgomery T-tubes from 10 patients were analyzed with regard to the development of granulation tissue, bacterial growth (including genotyping with polymerase chain reaction), and results of sensitivity testing. Furthermore, stent sterilization (n = 6) was investigated. RESULTS: Granulation tissue occurred with 74% of the stents, and all specimens showed signs of infection but no foreign body reaction. The predominant organisms were Staphylococcus aureus (35%) and Pseudomonas aeruginosa (17%). The differences between groups with and without granulation tissue were significant for P aeruginosa. Polymerase chain reaction fingerprinting of the S aureus obtained from 15 stents (n = 3 patients) revealed a total of seven different genotypes. Whereas two of these patients harbored six different genotypes of S aureus, the third patient was persistently colonized by S aureus over a 15-month period with the identical genotype. Susceptibility testing showed most commonly (65%) sensitivity to a combination of amoxicillin-clavulanate and ofloxacin. After sterilization, 92% of analyzed stent segments showed no bacterial growth. CONCLUSIONS: Granulation tissue commonly occurred next to the silicone (subglottic area, stoma) where S aureus and P aeruginosa were commonly isolated. A combination of mechanical irritation and bacterial infection seems to account for the development of granulation tissue. Polymerase chain reaction fingerprinting showed both prolonged persistence and a change of colonizing strains after multiple stent replacements. A combination of amoxicillin-clavulanate and ofloxacin is the most effective antibiotic therapy. Sterilization of the cost-intensive silicone stents is feasible, and reuse in the same patient is justifiable from economic aspects.

Adult↗
PubMed2003

In vitro activity of recombinant lysostaphin against Staphylococcus aureus isolates from anterior nares and blood.

The in vitro activity of recombinant lysostaphin was tested against a collection of well-characterized clinical Staphylococcus aureus isolates by disk diffusion (429 isolates) and minimum bactericidal concentration (10 isolates) assays. Minimum bactericidal concentrations of 0.16 microg/ml and zones of inhibition ranging between 15 and 21 mm in diameter demonstrate that lysostaphin was highly active against all isolates tested.

Anti-Bacterial Agents↗
PubMed2003

agr-dependent bacterial interference has no impact on long-term colonization of Staphylococcus aureus during persistent airway infection of cystic fibrosis patients.

The agr specificity group distribution of persistent Staphylococcus aureus clones recovered from the airways of cystic fibrosis (CF) patients did not differ from that of isolates recovered from various clinical infections and healthy nasal carriers. The success of CF clones in terms of cocolonization and/or infection with S. aureus, prevalence of clones, or persistence appeared to be independent of agr group specificity.

Antibiosis↗
PubMed2003

Prevalence of genes encoding pyrogenic toxin superantigens and exfoliative toxins among strains of Staphylococcus aureus isolated from blood and nasal specimens.

A total of 429 different Staphylococcus aureus isolates encompassing 219 blood isolates and 210 isolates taken from anterior nares were systematically searched by two multiplex PCR-DNA enzyme immunoassays (PCR-DEIA) for exfoliative toxin (ET) genes eta and etb, as well as for the classical members of the pyrogenic toxin superantigen (PTSAg) gene family comprising the staphylococcal enterotoxin (SE) genes sea-see and the toxic shock syndrome toxin 1 gene tst. In addition, a third PCR-DEIA was established to investigate the possession of four recently described SE genes, viz. seg-sej. The most frequent PTSAg/ET genes amplified were seg and sei, which were found strictly in combination in 55.0% of the S. aureus isolates tested. Other frequently detected toxin genes were tst (20.3%), sea (15.9%), and sec (11.2%). Only five isolates harbored ET genes. Regarding the origin of the S. aureus isolates, a significant difference (P = 0.037) was found for the possession of the sed/sej gene combination (10.5% of blood isolates versus 3.3% of nasal strains). Overall, about half of S. aureus isolates tested harbored genes of the classical members of the PTSAg family and ETs (50.8%), whereas 73.0% of S. aureus isolates were toxin gene positive if the recently described SE genes were included. This notable higher prevalence indicates that the possession of PTSAg genes in particular seems to be a habitual feature of S. aureus. Moreover, mainly due to the fixed combinations of seg plus sei, as well as sed plus sej, the possession of multiple PTSAg genes (62.9%) is more frequent than assumed so far.

Bacteremia↗
PubMed2002

Methicillin-resistant Staphylococcus aureus keratitis after excimer laser photorefractive keratectomy1.

A 43-year-old woman in good health was admitted to the hospital 3 days after photorefractive keratectomy (PRK) in the left eye with postoperative bandage contact lens application. She had developed a severe keratitis with ulceration and hypopyon. Upon the patient's admission to the hospital, the contact lens was removed. Ofloxacin eyedrops were prescribed 4 times a day. In the hospital, the patient was successfully treated with immediate thermocautery application, followed by full-thickness keratoplasty the next day and intensive systemic and topical antibiotics. Cultures were positive for methicillin-resistant Staphylococcus aureus (MRSA). Severe MRSA keratitis is a rare cause of infection after PRK.

Adult↗
PubMed2002

Kytococcus schroeteri sp. nov., a novel Gram-positive actinobacterium isolated from a human clinical source.

A strain of a gram-positive, coccoid, yellow-pigmented bacterium was isolated from human blood. The bacterium was aerobic, non-encapsulated and non-motile. Phenotypically, the bacterium closely resembled Kytococcus sedentarius, but could be distinguished from this species by physiological tests and chemotaxonomic investigations. The peptidoglycan type is L-Lys-Glu2, variation A4alpha. The predominant menaquinones are MK-8 and MK-7. The major cellular fatty acids are iso-C17:1, iso-C17:0, iso-C15:0 and anteiso-C17:0. The strain contains catalase and does not produce acid from carbohydrates. The ability to hydrolyse Tween 80 and the lack of alpha-glucosidase activity are the most characteristic features. The results of comparative 16S rDNA analysis revealed that the strain represents a novel species within the genus Kytococcus, for which the name Kytococcus schroeteri sp. nov. is proposed. The type strain is strain Muenster 2000T (= DSM 13884T = CCM 4918T).

Actinomycetales↗