A Matlab library for solving quasi-static volume conduction problems using the boundary element method.

The boundary element method (BEM) is commonly used in the modeling of bioelectromagnetic phenomena. The Matlab language is increasingly popular among students and researchers, but there is no free, easy-to-use Matlab library for boundary element computations. We present a hands-on, freely available Matlab BEM source code for solving bioelectromagnetic volume conduction problems and any (quasi-)static potential problems that obey the Laplace equation. The basic principle of the BEM is presented and discretization of the surface integral equation for electric potential is worked through in detail. Contents and design of the library are described, and results of example computations in spherical volume conductors are validated against analytical solutions. Three application examples are also presented. Further information, source code for application examples, and information on obtaining the library are available in the WWW-page of the library: (http://biomed.tkk.fi/BEM).

A polyphasic study on the taxonomic position of industrial sour dough yeasts.

The sour dough bread making process is extensively used to produce wholesome palatable rye bread. The process is traditionally done using a back-slopping procedure. Traditional sour doughs in Finland comprise of lactic acid bacteria and yeasts. The yeasts present in these doughs have been enriched in the doughs due to their metabolic activities, e.g. acid tolerance. We characterized the yeasts in five major sour bread bakeries in Finland. We found that most of the commercial sour doughs contained yeasts which were similar to Candida milleri on the basis of 18S rDNA and EF-3 PCR-RFLP patterns and metabolic activities. Some of the bakery yeasts exhibited extensive karyotype polymorphism. The minimum growth temperature was 8 degrees C for C. milleri and also for most of sour dough yeasts.

MPN-PCR-quantification method for staphylococcal enterotoxin c1 gene from fresh cheese.

PCR detection methods have been extensively used in diagnostic microbiology. However, a lack of a simple and reliable method for quantification of the PCR products has partly hindered the use of PCR in routine food laboratories. The quantification of PCR products can be done by combining the principles of MPN statistics and PCR technique. We have developed a simple and sensitive MPN-PCR assay for detection and enumeration of enterotoxin C producing Staphylococcus aureus NCTC 10655 from fresh cheese. By amplifying single copy chromosomal enterotoxin C gene fragment, we could detect as little as 20 cfu/g. By Moran's test, most of the DNA dilution series appeared to fulfill the basic mathematical assumptions of ordinary MPN methods. The analysis with MPN-PCR took one day to perform compared with three days analysis time with plate counting. This MPN-PCR method can be readily applied with different primer systems without extensive development work.

A rapid PCR-based DNA test for enterotoxic Bacillus cereus.

The occurrence of DNA sequences encoding the hemolysin HblA complex and Bacillus cereus enterotoxin BceT, which have recently been confirmed as enterotoxins, was studied in Bacillus spp. To amplify these DNA sequences, PCR primer systems for the B component of hblA and for bceT DNA sequences were developed. The results from the amplification of hblA sequences correlated well with results obtained with the B. cereus enterotoxin (diarrheal type) test kit (RPLA kit), but not with the results of the Bacillus diarrheal enterotoxin visual immunoassay (BDE kit). Except for two thermophilic strains, all strains that were positive in PCR amplification assays with the hblA primers were also positive when tested with the RPLA kit. The hblA DNA sequence was found in 33 strains, and these strains were closely related according to 16S rDNA-RFLP analysis, except B. pasteurii. In PCR amplifications with the bceT primers only the model strain gave a positive signal. It is concluded that screening of the hemolysin HblA complex by the PCR method allows faster detection of enterotoxin production than does testing with the RPLA enterotoxin kit.