Evaluation of carriers used in the test methods of the Association of Official Analytical Chemists

Revision of the official test method for the determination of the tuberculocidal activity of disinfectants is being undertaken. The current procedure lacks precision and accuracy and is not quantitative. Variability associated with carriers and the lack of temperature control were evaluated in this paper. The use of porcelain versus stainless steel carriers was also evaluated. When carriers of either type were contaminated with Mycobacterium bovis BCG, the number of organisms on the carriers varied by as much as 1.0 on the log10 scale. The average number of organisms attached to each porcelain carried was 1.10 x 10(5) CFU (range, 2.7 x 10(4) to 2.7 x 10(5) CFU), whereas the average number of organisms attached to each stainless steel carrier was 1.38 x 10(5) CFU (range, 2.9 x 10(4) to 4.0 x 10(5) CFU). The average number of cells attached to the carrier was directly proportional to the number of cells in the contaminating cell suspension. Variations in drying time did not alter the number of cells attached to the carrier. When porcelain carriers were placed in a test solution, the average number of organisms washed from the carriers was 55% of the total, with a range of 19 to 80%, whereas for stainless steel carriers, the average number was 82% of the total, with a range of 52 to 96%. Data for B. subtilis spores were similar to those for M. bovis BCG, suggesting that there may be similar problems with the Association of Official Analytical Chemists sporicidal test, which uses carriers. It was also found that the lack of an exacting temperature control could influence the outcome of the test. Changes in temperature as little as 1 degree C could influence the rate of killing of M. bovis BCG.     

Das Lp-System

Ohne ZusammenfassungDeutschlandaufenthalt mit Stipendium des Deutschen Akademischen Austauschdienstes und der Aktieselskabet Freia Chocolade Fabriks Medicinske Fond     

Aggregation and fibril formation of plasma fibronectin by heparin

The precipitation of plasma fibronectin by heparin in dependence on various parameters was investigated. Rising heparin concentration augmented the precipitates up to a maximum beyond which precipitation decreased. Yields close to 80% were obtained at low temperatures, but some precipitation was observed at 37 degrees C as well. Insolubilization was considerably dependent on the ionic strength, indicating that electrostatic forces play a major role in the aggregation of fibronectin. Calcium already prevented precipitation by heparin at low concentrations. If precipitation was performed on hydrophobized glass cover slides, the formation of fibrils visible by phase-contrast microscopy was observed. On hydrophilic surfaces amorphous precipitates were generally obtained, most likely due to trapping of aggregates by adsorption prior to their arrangement to fibrils. The results are discussed on the basis of a model assuming that heparin induces a conformational rearrangement of plasma fibronectin so that masked binding sites responsible for self-association become exposed.     

Separation of Three Species of Ditylenchus and Some Host Races of D. dipsaci by Restriction Fragment Length Polymorphism

This study examined the ribosomal cistron of Ditylenchus destructor, D. myceliophagus and seven host races of D. dipsaci from different geographic locations. The three species showed restriction fragment length polymorphisms (RFLPs) in the ribosomal cistron, the 18S rDNA gene, and the ribosomal internal transcribed spacer (ITS). Southern blot analysis with a 7.5-kb ribosomal cistron probe differentiated the five host races of D. dipsaci examined. Polymerase chain reaction (PCR) amplification of the ITS, followed by digestion with some restriction endonucleases (but not others), produced restriction fragments diagnostic of the giant race. Because the PCR product from D. myceliophagus and the host races of D. dipsaci was about 900 base pairs and the ITS size in D. destructor populations was 1,200 base pairs, mixtures of populations could be detected by PCR amplification. ITS fragments differentiated between D. dipsaci and Aphelenchoides rhyntium in mixed populations. This study establishes the feasibility of differentiation of the host races of D. dipsaci by probing Southern blots with the whole ribosomal cistron.     

Tetradiidae — First evidence of aragonitic mineralogy in tabulate corals

Tabulate corals exhibit well preserved microstructures when observed at low magnifications, but reveal various degrees of diagenetic overprint when analyzed at high SEM magnifications. This evidence suggests an original Mg-calcitic mineralogy. In contrast to all other examined genera of the order, the skeletons of the family Tetradiidae are completely replaced by neomorphic spar, indicating an original aragonitic composition.