Impact of non-Gaussian electron energy heating upon the performance of a seeded free-electron laser

Laser-heater systems have been demonstrated to be an important component for the accelerators that drive high gain free electron laser (FEL) facilities. These heater systems suppress longitudinal microbunching instabilities by inducing a small and controllable slice energy spread to the electron beam. For transversely uniform heating, the energy spread augmentation is characterized by a non-Gaussian distribution. In this Letter, we demonstrate experimentally that in addition to suppression of the microbunching instability, the laser heater-induced energy distribution can be preserved to the FEL undulator entrance, significantly impacting the performance of high-gain harmonic generation (HGHG) FELs, especially at soft x-ray wavelengths. In particular, we show that the FEL intensity has several local maxima as a function of the induced heating caused by the non-Gaussian energy distribution together with a strong enhancement of the power at high harmonics relative to that expected for an electron beam with an equivalent Gaussian energy spread at an undulator entrance. These results suggest that a single stage HGHG FEL can produce scientifically interesting power levels at harmonic numbers m ≥ 25 and with current seed laser technology could reach output photon energies above 100 eV or greater.

Epidemiology of Clostridium difficile infections in a tertiary-care hospital in Korea

To survey healthcare-associated Clostridium difficile infection (HA-CDI) in a 900-bed tertiary-care hospital, we prospectively investigated the epidemiology of CDI and distribution of PCR-ribotypes. From February 2009 through January 2010, all patients with HA-CDI were enrolled. Epidemiological information and prescription records for antibiotics were collected. The C. difficile isolates were characterized using reference strains and were tested for antibiotic susceptibility. During the survey, incidence of HA-CDI was 71.6 per 100 000 patient-days. In total, 140 C. difficile isolates were obtained from 166 patients with HA-CDI. The PCR-ribotyping yielded 38 distinct ribotypes. The three most frequently found ribotypes made up 56.4% of all isolates; they comprised 37 isolates (26.4%) of PCR-ribotype 018, 22 (15.7%) of toxin A-negative PCR-ribotype 017, and 20 (14.3%) of PCR-ribotype 001. Clostridium difficile PCR-ribotype 018 was present in all departments throughout the hospital during the 11 months, whereas ribotype 017 and ribotype 001 appeared mostly in the pulmonary department. Hypervirulent C. difficile PCR-ribotype 027 was detected in 1 month on two wards. The incidence of CDI in each department showed a seven-fold difference, which correlated significantly with the amount of prescribed clindamycin (R = 0.783, p 0.013) or moxifloxacin (R = 0.733, p 0.025) in the departments. The rates of resistance of the three commonest ribotypes to clindamycin and moxifloxacin were significantly higher than those of other strains (92.1% versus 38.2% and 89.5% versus 27.3%, respectively). CDI is an important nosocomially acquired infection and this study emphasizes the importance of implementing country-wide surveillance to detect and control CDI in Korea.

Prospective evaluation of environmental contamination by Clostridium difficile in isolation side rooms

We determined prospectively the frequency, persistence and molecular epidemiology of Clostridium difficile environmental contamination after detergent-based cleaning in side rooms used to isolate patients with C. difficile diarrhoea. Approximately one-quarter of all environmental sites in side rooms sampled over four-week periods were contaminated with C. difficile. The overall side room prevalence of environmental C. difficile declined from 35% initially, to 24% in week 2, 18% in week 3, and 16% in week 4. The bed frame was the most common site from which C. difficile was recovered, although the floor was the most contaminated site in terms of total numbers of colonies. C. difficile was recovered significantly more frequently from swabs plated directly on to C. difficile selective media containing lysozyme than from enrichment broth (P< 0.001), emphasizing the benefit of lysozyme supplementation. The great majority of C. difficile isolates (87% of all isolates, 84% of patient isolates) was indistinguishable from the UK epidemic strain (PCR ribotype 1). It thus could not be determined whether environmental contamination was a cause or a consequence of diarrhoea. Our findings highlight the need for improved approaches to hospital environmental hygiene, and call into question current UK guidelines that recommend detergent-based cleaning to remove environmental C. difficile. In particular, improved cleaning of frequently touched sites in the immediate bed space area is required.

In vitro activity of new generation fluoroquinolones against genotypically distinct and indistinguishable Clostridium difficile isolates

We compared the activities of ciprofloxacin and levofloxacin with those of the newer fluoroquinolones grepafloxacin, moxifloxacin, sparfloxacin and trovafloxacin against Clostridium difficile isolates. As there is good evidence of marked clonal spread of C. difficile, we studied both genotypically distinct (n = 26) and indistinguishable (n = 28) isolates as determined by random amplified polymorphic DNA and ribosomal spacer PCR fingerprinting. The indistinguishable strains examined represent the main UK epidemic C. difficile clone. For 17 of 54 strains (31%) we were unable to read MICs following inocula preparation using Mueller-Hinton broth. Using Schaedler's broth for inocula preparation 93% of strains had readable MICs, although geometric mean MICs were uniformly higher (2.5- to 5.4-fold) compared with results using Mueller-Hinton broth. Moxifloxacin and trovafloxacin, followed by grepafloxacin, were the most active fluoroquinolones tested and were 3- to 4-fold more active than older agents such as ciprofloxacin by both MIC methods. Unexpectedly, clonal C. difficile strains had markedly reduced susceptibility compared with the distinct strains to each of the fluoroquinolones tested. Clonal strains were more than seven-fold or 12- to 29-fold less susceptible (according to geometric mean MICs) than distinct strains to both moxifloxacin and trovafloxacin, depending on the MIC method used. It remains to be seen whether the enhanced activity of new fluoroquinolones such as moxifloxacin in comparison with other fluoroquinolones against C. difficile implies that these agents are unlikely to be associated with C. difficile infection. However, clinical use of new generation fluoroquinolones in elderly hospitalized patients where C. difficile is endemic requires further study, particularly given the reduced antibiotic susceptibility to all fluoroquinolones of the readily transmissible UK C. difficile clone.