Evaluation of linezolid for the treatment of Clostridium difficile infection caused by epidemic strains using an in vitro human gut model.

OBJECTIVES: Therapeutic options in Clostridium difficile infection (CDI) are limited. We examined linezolid activity in vitro and potential therapeutic efficacy using a gut model of CDI. METHODS: MICs were determined by agar incorporation for 118 diverse C. difficile faecal isolates, including epidemic strains and strains with reduced susceptibility to metronidazole. CDI was established in two gut model experiments using C. difficile epidemic strains (ribotypes 027 and 106) and linezolid was dosed to achieve human gut concentrations. RESULTS: Linezolid demonstrated good in vitro activity against 98% of the isolates. Two isolates (PCR ribotypes 023 and 067) demonstrated resistance to linezolid, although supplementary susceptibility testing of ribotype 023 isolates did not detect further resistance. In a gut model that simulates CDI, linezolid reduced the duration of cytotoxin production by C. difficile PCR ribotype 027 without influencing viable counts of vegetative forms of the organism. C. difficile PCR ribotype 106 viable counts declined at a faster rate than those of PCR ribotype 027 following dosing with linezolid, but cytotoxin titres declined at a similar rate to an untreated control. Gut flora perturbation occurring on linezolid exposure reversed after drug cessation. Recrudescence of spore germination with subsequent cytotoxin was seen with the C. difficile ribotype 106 strain. Resistance to linezolid was not detected either during linezolid instillation or post-dosing. CONCLUSIONS: Linezolid may reduce toxin levels, as reported in staphylococci and streptococci. Further evaluation is warranted of the effect of linezolid on expression of C. difficile toxin, and to investigate potential recurrence of CDI following cessation of linezolid.

Does laboratory antibiotic susceptibility reporting influence primary care prescribing in urinary tract infection and other infections?

OBJECTIVES: Using a prospective interrupted time series design, our goal was to determine whether a change in urine antibiotic susceptibility reporting from co-amoxiclav to cefalexin to community clinicians served by Southmead General Hospital led to a change in antibiotic prescribing. METHODS: We used longitudinal data on antibiotic prescribing using a clinician questionnaire to identify prescribing for urinary tract infections (UTIs) when a urine specimen was submitted to microbiology; MIQUEST computer search in general practices for prescribing for all UTIs in the community; and Prescribing Analysis and Cost (PACT) data to determine antibiotic prescribing for all infections. RESULTS: Cefalexin and cephalosporin prescribing increased when cefalexin was reported and co-amoxiclav prescribing decreased when co-amoxiclav was not reported by the laboratory. This was seen for episodes of UTI in which a general practitioner (GP) sent a specimen as determined with: the questionnaire results (9-fold rise in cephalosporins, 70% fall in co-amoxiclav); episodes of UTI identified by MIQUEST searches in the practice (50% increase in cefalexin, 25% reduction in co-amoxiclav); and overall antibiotic prescribing in the practice determined with PACT data (20% increase in cefalexin, 8% reduction in co-amoxiclav). MIQUEST data indicated that prescribing reverted to pre-intervention levels once the change in antibiotic reporting had stopped. CONCLUSIONS: Our data provide more evidence that changing laboratory antibiotic susceptibility reporting has a direct effect on antibiotic prescribing by GPs. Our data indicate that much of the change in prescribing was attributable to the use of cefalexin and co-amoxiclav for persistent or recurrent infections. Microbiology laboratories can influence antibiotic use by selectively reporting antibiotics they would prefer GPs to prescribe.

Phasing in the presence of radiation damage.

In the accurate estimation of small signals, redundancy of observations is often seen as an essential tool for the experimenter. This is particularly true during macromolecular structure determination by single-wavelength anomalous dispersion (SAD), where the exploitable signal can be less than a few percent. At the most intense undulator synchrotron beamlines, the effect of radiation damage can be such that all usable signal is obscured. Here the magnitude of this effect in experiments performed at the Se K-edge is quantified. Six successive data sets were collected on the same crystal, interspersed with two exposures to the X-ray beam during which data were not collected. It is shown that the very first data set has excellent phasing statistics, whereas these statistics degrade for the later data sets. Merging several data sets into one, highly redundant, data set only gave moderate improvements as a result of the presence of radiation damage. Part of the damage could be corrected for using a linear interpolation scheme. Interpolation of the data to a low-dose as well as to a high-dose data set allowed us to combine the SAD method with the radiation-damage induced phasing (RIP) technique, which further improved the experimental phases, especially after density modification. Some recommendations are given on how to mitigate the effect of radiation damage during structure determination.

Topical vancomycin applied on closure of the sternotomy wound does not prevent high levels of systemic vancomycin.

OBJECTIVE: Vancomycin is effective in reducing the risk of mediastinits and topical vancomycin has been hypothesised to give high local dose concentrations while avoiding high systemic levels, thus avoiding the risk of bacterial resistance to this second-line antibiotic. However, this theory has never been tested and the degree to which vancomycin is absorbed systemically is unknown. METHODS: Fourteen patients undergoing elective coronary artery bypass grafts (CABG) received 500mg of topical vancomycin prior to sternotomy closure. Serum samples were taken at 30, 60, 120, 180 and 720min post-operatively. In addition, samples were taken from the drain bottles and urine samples taken daily for 5 days. Vancomycin levels were measured by fluorescence polarisation immunoassay, using the reverse dilution method to give a detection limit of 0.8mg/l. RESULTS: Vancomycin was detected in almost all serum samples. Peak concentration was at 30min and the mean value was 2.96mg/l (range, 0.99-5.00mg/l). This mean fell to 1.32mg/l at 6h. Of the 500mg of vancomycin applied, a mean of only 8.8mg was found to have been lost into the drain bottles in the first 24h (range, 0.17-12.5mg). When 5 consecutive days of urine collection was achieved, a mean of 151mg of vancomycin was excreted (range, 40-195mg) and vancomycin was detectable in the urine till day 5. The mean concentration of vancomycin in the urine was maximal on day 1 and was 24.4mg/l (range, 4.49-44.98mg/l). CONCLUSIONS: Topical vancomycin causes significant systemic concentrations in the 6h post-surgery and can be detected in the urine for up to 5 days post-surgery.