Radiation damage in protein crystals is reduced with a micron-sized X-ray beam.

Radiation damage is a major limitation in crystallography of biological macromolecules, even for cryocooled samples, and is particularly acute in microdiffraction. For the X-ray energies most commonly used for protein crystallography at synchrotron sources, photoelectrons are the predominant source of radiation damage. If the beam size is small relative to the photoelectron path length, then the photoelectron may escape the beam footprint, resulting in less damage in the illuminated volume. Thus, it may be possible to exploit this phenomenon to reduce radiation-induced damage during data measurement for techniques such as diffraction, spectroscopy, and imaging that use X-rays to probe both crystalline and noncrystalline biological samples. In a systematic and direct experimental demonstration of reduced radiation damage in protein crystals with small beams, damage was measured as a function of micron-sized X-ray beams of decreasing dimensions. The damage rate normalized for dose was reduced by a factor of three from the largest (15.6 µm) to the smallest (0.84 µm) X-ray beam used. Radiation-induced damage to protein crystals was also mapped parallel and perpendicular to the polarization direction of an incident 1-µm X-ray beam. Damage was greatest at the beam center and decreased monotonically to zero at a distance of about 4 µm, establishing the range of photoelectrons. The observed damage is less anisotropic than photoelectron emission probability, consistent with photoelectron trajectory simulations. These experimental results provide the basis for data collection protocols to mitigate with micron-sized X-ray beams the effects of radiation damage.

Bacterial contamination of the anterior chamber during phacoemulsification cataract surgery.

PURPOSE: To determine the incidence of bacterial contamination of the anterior chamber after phacoemulsification cataract surgery with intraocular lens (IOL) implantation. SETTING: Department of Ophthalmology, Royal Prince Alfred Hospital, Sydney, Australia. METHODS: Ninety-eight consecutive eyes of 96 patients having phacoemulsification cataract surgery with IOL implantation were included in this prospective study. Two intraoperative anterior chamber aspirates were obtained from each patient, 1 taken at the start and the other at the conclusion of surgery. In addition, preoperative and postoperative conjunctival swabs were acquired. The 4 specimens were cultured using direct culturing techniques under aerobic and anaerobic conditions for 14 days. No preoperative antibiotics were used. RESULTS: The incidence of intraoperative anterior chamber contamination was 0% (95% confidence interval, 0%-3.7%) as all intraoperative anterior chamber samples proved culture negative. Sixty-five percent of the preoperative conjunctival swabs were positive for growth, with corynebacteria, coagulase-negative staphylococci, and Propionibacterium acnes being the most frequently cultured organisms. Sixteen percent of the postoperative conjunctival swabs were positive for growth, with corynebacteria and coagulase-negative staphylococci being the most common bacteria. One patient developed culture-positive postoperative endophthalmitis; using pulsed-field gel electrophoresis for further typing, the implicated Staphylococcus epidermidis was indistinguishable from that isolated from the patient's preoperative conjunctival swab. CONCLUSIONS: The bacterial contamination rate of the anterior chamber after phacoemulsification and IOL implantation was extremely low. Additional findings support the conjunctiva as being a primary source of bacteria causing postoperative endophthalmitis as well as the ability of povidone-iodine to reduce the conjunctival bacterial load.