Christiane König

DNA end resection by CtIP and exonuclease 1 prevents genomic instability.

End resection of DNA—which is essential for the repair of DNA double‐strand breaks (DSBs) by homologous recombination—relies first on the partnership between MRE11–RAD50–NBS1 (MRN) and CtIP, followed by a processive step involving helicases and exonucleases such as exonuclease 1 (EXO1). In this study, we show that the localization of EXO1 to DSBs depends on both CtIP and MRN. We also establish that CtIP interacts with EXO1 and restrains its exonucleolytic activity in vitro. Finally, we show that on exposure to camptothecin, depletion of EXO1 in CtIP‐deficient cells increases the frequency of DNA–PK‐dependent radial chromosome formation. Thus, our study identifies new functions of CtIP and EXO1 in DNA end resection and provides new information on the regulation of DSB repair pathways, which is a key factor in the maintenance of genome integrity.

Factors compromising antibiotic activity against biofilms of Staphylococcus epidermidis.

Abstract Several factors associated with bacterial biofilms were studied for their role in phenotypic resistance to antibiotics. These factors included bacterial slime extracted from biofilms, reduced growth rates of biofilm-embedded bacteria and high bacterial inocula. Antibiotic activity against suspended bacteria in the presence of these factors, either alone or combined, was compared with activity against adherent biofilms. All MICs, determined by standard susceptibility tests, were below the sensitivity breakpoints for Staphylococcus epidermidis strain V2. The addition of bacterial slime to suspended bacteria reduced the bactericidal activity of glycopeptides but had less or no effect on the activity of the other antibiotics tested. High bacterial inocula affected the activity of flucloxacillin and quinolones only moderately or not at all, though a more pronounced effect on glycopeptides was observed. In contrast, the bactericidal activity of most antibiotics was severely compromised when adherent bacterial biofilms were used as inocula. In conclusion, the presence of slime, slow growth rates and high bacterial counts may explain the poor activity of glycopeptides against biofilm-embedded organisms, but these factors, either alone or in combination, do not explain the lack of bactericidal activity of other drugs against biofilms. Thus, additional factors need to be identified.

Autosterilization of biodegradable implants by injection molding process

Sterilization of degradable implants by standard procedures may damage the parts due to the labile chemical nature of the polymers. This study examined whether the injection molding process used for the production of polymeric parts may itself sterilize the implant due to high temperature, pressure, and shear forces applied. Poly-D,L-lactic acid (PDLLA) and poly-L-lactic acid (PLLA) granules were contaminated with thermoresistant spores of Bacillus stearothermophilus (>10(5) spores/g). Sterile and contaminated granules of both polymers were injection molded and tested for sterility. All 27 samples produced with sterile PDLLA and processed at 120 degrees C and all 18 samples produced with sterile PLLA at 200 degrees C remained sterile after injection molding and handling. However, in five out of 28 PDLLA samples and in one out of 26 PLLA samples produced with contaminated material, spores had survived the process. In conclusion, the injection molding process could not reliably sterilize parts produced with polylactic acid granules that were heavily contaminated with thermoresistant organisms. However, the number of viable spores was significantly reduced by more than 99.99%. Thus, the injection molding process might allow the autosterilization of parts produced with raw material that is not heavily contaminated.

Effect of pathological changes of pH, pO2 and pCO2 on the activity of antimicrobial agents in vitro

Since standard susceptibility tests reflect the physiological rather than the pathological conditions prevailing within an infected abdomen, as recently documented, the effect of reduced pH and pO2 and increased pCO2 on the activity of antibiotics in vitro was studied. MICs were determined in vitro under standard culture conditions (MICstandard) and modified conditions (MICmodification) simulating the previously determined pathological values. Various classes of antibiotics were affected differently by the modified conditions. However, within an antibiotic class similar results were obtained for gram-negative and gram-positive pathogens. Median MICmodification/MICstandard ratios were 4 for aminoglycosides, 2 for quinolones and clindamycin, 1 for cephalosporins, and 0.5 for penicillins and vancomycin. Anaerobic conditions and a pH of 6.4 further increased the ratio of aminoglycosides to 8. Ratios were similar within an antibiotic class at inocula of 105 or 107 cfu/ml. All MICs determined in tests with imipenem against gram-negative and gram-positive bacteria and with vancomycin against gram-positive organisms were below the susceptibility breakpoint, whatever conditions and inocula were employed. In contrast, the percentage of MICs in susceptibility range using high inocula and modified conditions decreased to 78 % for penicillins, 73 % for cephalosporins, 22 % for aminoglycosides, 11 % for quinolones and 0 % for clindamycin. In conclusion, routine susceptibility testing may overestimate the activity of aminoglycosides and underestimate the activity of beta-lactams under the conditions prevailing during abdominal infection.