Fimbriation in enterobacteria

1. It has been possible to transduce the property of fimbriation to a number of permanently non-fimbriate strains of Salmonella typhimurium, using pellicle formation, which occurs on serial subculture in aerobic, static broth, as a selection mechanism. The transduction rate, using lysates prepared on wild -type fimbriate S.typhimurium strains, was calculated as 1 per 5 x 10[7] - 10[8] infected cells. It was shown that before successful transduction was effected, the recipient strain was required to be motile. This requirement was not satisfied by the presence of paralysed flagella, and is a reflection of the need for positive aerotactic movements by the recipient strain, which will result in its transport to the broth surface.2. Among 140 naturally -isolated non-fimbriate strains of S.typhimurium, evidence of non -identical allelism in the fim segment of the chromosome was shown. Reciprocal transduction among the mutants suggested the existence of five transductional groups. The order of the mutations involved in these different groups was not ascertained because of limitations in the selection method and physiological differences inherent in the mutants.3. Reciprocal transduction among 132 non -fimbriate strains of Salmonella typhimurium classified as FIRN, i.e. fin - inl - rha - , did not reveal recombination either to fin+ or rha+. These strains, although epidemiologically independent, are thought to have identical or overlapping mutations in fin and rha. The hypothesis was presented that these arose from a common fin - rha - parent, and that present-day FIRN strains represent a world -wide, successfully distributed typhimurium type.4. There was no evidence of a close linkage between fin and any other markers tested, so that the initial hypothesis of a close genetic linkage between fin and rha, to explain the almost absolute correlation of these characters in S.typhimurium strains, was not valid. With the non-fimbriate, non-flagellate derivatives of S.typhimurium LT -2 by ethyl methane sulphonate treatment, called Dubnau strains, indications of cotransduction of fin and fla were presented, but this phenomenon was not examined in detail.5. One non-fimbriate strain, S.typhimurium Sa 519, produced a small colony fimbriate revertant. Genetic analysis suggested that this was due to suppressor mutation.6. Induced reversion to a fimbriate state was achieved wi the mutagens ultra- violet light and manganous chloride. Limited tests with ethyl methane sulphonate did not induce fimbriate revertants. Of the seven fin - rha + strains of S.typhimurium, three strains reverted to a fimbriate state - Sa 749, 1436 and 1566b. Six of the 132 FIRN strains revert to fimbriate state, and were characterised as FIRN derivat- ives. The value of these findings is discussed. Spon- taneous mutation to fimbriation was never detected with any non -fimbriate S.typhimurium mutants.7. A number of fimbriate, non- haemagglutinating strains of S.paratyphi B was transduced to a haemagglutinating state with traneducing lysates from wild -type fimbriate strains o Salmonella tyohimurium. This was judged indicative of a gene Ha controlling fimbrial function, but alternate inter- pretations were discussed.8. Attempts to demonstrate the presence of a fin episome controlling phase variation in Salmonella typhimurium were without success. Another theory to explain the fin phase variation was presented, and discussed also in relation to the larger number of fimbriate and non-fimbriate types Escherichia coli.9. Competition experiments were devised to investigate the transduction procedure for fimbriate cells on a quantitative basis. Small numbers of fimbriate cells were used to challenge large numbers of non-fimbriate cells, both strains being flagellate, in mixed culture under a range of environmental conditions - static broths incubated (a) aerobically, (b) anaerobically, (c) microaerophilically, artificially aerated broths (d) on a reciprocating shaker at 100 oscillations per min. and (e) on a rotator at 12 rotations per min., and, finally, (f) on agar plates. Buffered and unbuffered media were used. The strains used were naturally isolated fimbriate and non-fimbriate strains of Salmonella typhimurium, and pairs of fimbriate and non-fimbriate strains isolated from a transduction mixture. Under conditions favourable to the formation of a fimbrial pellicle, the fimbriate cells outgrew the non -fimbriate cells and formed as much as 80% of the final population after 48 hr. A small outgrowth by naturally isolated fimbriate strains was sometimes detected, not associated with the formation of a fimbrial pellicle, and due to physiological strain differences. The possible mechanisms of this out- growth are discussed.10. Similar competition experiments in which the challenger fimbriate cells were non -motile showed that, if the challenger cell was phenotypically fimbriate, it could outgrow large numbers of non -fimbriate, non- flagellated challenged cells even in the absence of motility. This outgrowth was accompanied by the formation of a fimbrial pellicle in the later stages of growth.11. Competition experiments also revealed the importance of flagella alone. Small numbers of flagellate, motile cells outgrew large numbers of non -motile cells under aerobic static conditions by their ability to form a flagellar pellicle. The outgrowth, however, was less significant than that associated with the formation of a fimbrial pellicle.12. From these competition experiments and the parallel growth experiments between S.paratyphi B strains with functional and non -functional fimbriae, the advantage bestowed on a cell by its ability to form a pellicle was seen. It is considered that these experiments provide quantitative experimental data supporting the hypothesis that fimbriae are organs of survival.13. Fimbriae from Escherichia coli were isolated in a pure form by differential centrifugation and by chromatography on DEAE-cellulose exchanger at a neutral pH, and elution with a salt gradient. The fimbriae were judged pure by five criteria - electron microscopy, ultraviolet spectrophotometry, chemical analysis, agar gel diffusion and biological activity. The relative values of these criteria are discussed.14. Chemical analysis reîealed that fimbriae were protein structures, unrelated to cell wall, capsule or flagella.15. The range of amino acids detected on two -dimensional chromatography was not suggestive of an atypical protein. The adsorption of fimbriae to DEAE - but not to CM- cellulose suggests a preponderance of acidic amino acids in their structure. The relevance of this finding is discussed in relation to their agglutinating properties and to their resistance to proteolytic enzymes.16. Chromatography of fimbriae from Shigella flexneri FIaI showed a behaviour different from E.coli 2v,. The possible relevance of this to sharing of fimbrial antigens is discussed

Instream and riparian implications of weed cutting in a chalk river

Macrophyte growth is extensive in the iconic chalk streams that are concentrated in southern and eastern England. Widespread and frequent weed cutting is undertaken to maintain their key functions (e.g. flood water conveyance and maintenance of viable fisheries). In this study, a multidisciplinary approach was adopted to quantify coincident physico-chemical responses (instream and riparian) that result from weed cutting and to discuss their potential implications. Three weed cuts were monitored at a site on the River Lambourn (The CEH River Lambourn Observatory) and major instream and riparian impacts were observed. Measurements clearly demonstrated how weed cutting enhanced flood flow conveyance, reduced water levels (river and wetland), increased river velocities, and mobilised suspended sediment (with associated chemicals) and reduced the capacity for its retention within the river channel. Potential implications in relation to flood risk, water resources, downstream water quality, instream and riparian ecology, amenity value of the river, and wetland greenhouse gas emissions were considered. Provided the major influence of macrophytes on instream and riparian environments is fully understood then the manipulation of macrophytes represents an effective management tool that demonstrates the great potential of working with nature

The Cholecystectomy As A Day Case (CAAD) Score: A Validated Score of Preoperative Predictors of Successful Day-Case Cholecystectomy Using the CholeS Data Set

Background Day-case surgery is associated with significant patient and cost benefits. However, only 43% of cholecystectomy patients are discharged home the same day. One hypothesis is day-case cholecystectomy rates, defined as patients discharged the same day as their operation, may be improved by better assessment of patients using standard preoperative variables. Methods Data were extracted from a prospectively collected data set of cholecystectomy patients from 166 UK and Irish hospitals (CholeS). Cholecystectomies performed as elective procedures were divided into main (75%) and validation (25%) data sets. Preoperative predictors were identified, and a risk score of failed day case was devised using multivariate logistic regression. Receiver operating curve analysis was used to validate the score in the validation data set. Results Of the 7426 elective cholecystectomies performed, 49% of these were discharged home the same day. Same-day discharge following cholecystectomy was less likely with older patients (OR 0.18, 95% CI 0.15–0.23), higher ASA scores (OR 0.19, 95% CI 0.15–0.23), complicated cholelithiasis (OR 0.38, 95% CI 0.31 to 0.48), male gender (OR 0.66, 95% CI 0.58–0.74), previous acute gallstone-related admissions (OR 0.54, 95% CI 0.48–0.60) and preoperative endoscopic intervention (OR 0.40, 95% CI 0.34–0.47). The CAAD score was developed using these variables. When applied to the validation subgroup, a CAAD score of ≤5 was associated with 80.8% successful day-case cholecystectomy compared with 19.2% associated with a CAAD score >5 (p < 0.001). Conclusions The CAAD score which utilises data readily available from clinic letters and electronic sources can predict same-day discharges following cholecystectomy

Imaging of hydrological processes in a lowland wetland of the Lambourn river, Berkshire, UK (abstract only)

The River Lambourn and the associated wetlands comprise some of the least impacted chalk river systems in Britain. The associated lowland wetlands, due to their hydrological characteristics, may form a key conduit for, or barrier to, aqueous fluxes between land, rivers and groundwater. At Boxford, Berkshire, UK, a research site has been monitored for a number of years to establish the degree of groundwater and surface water interaction. Recently, two geoelectric monitoring lines have been added and measurements have been repeated every month