Study on the antimicrobial effect of silver-containing inner liners in refrigerators.

AIMS: To investigate the effect of silver-based antimicrobial material incorporated in the inner liners of refrigerators on food safety and quality. METHODS AND RESULTS: In the first stage, the bactericidal effect was tested in the laboratory. Silver-containing samples and control plates were inoculated with different bacterial suspensions and stored at various temperatures. After defined storage periods the bacterial reduction was calculated by comparing viable cell count on reference plates and on silver-containing plates. The reduction caused by the silver-containing material varied between 1.0 and 5.9 log(10) units, depending on bacterial strain, incubation time and temperature. In the second stage, food storage experiments have been carried out. Thus, perishable foods were stored in coated and untreated refrigerators. After certain time periods the products were analysed for their sensorial and microbiological characteristics. A clear drop in viable counts both on the refrigerator wall and on the food was demonstrated using the silver-based antimicrobial material. CONCLUSIONS: Silver prevents refrigerators from being a hot spot for contaminants that could be transferred upon contact with food. SIGNIFICANCE AND IMPACT OF THE STUDY: This study provides original results regarding the antimicrobial activity of silver-containing refrigerator surfaces.

Isolation, characterization, and identification of bacterial contaminants in semifinal gelatin extracts.

Bacterial contamination of gelatin is of great concern. Indeed, this animal colloid has many industrial applications, mainly in food and pharmaceutical products. In a previous study (E. De Clerck and P. De Vos, Syst. Appl. Microbiol. 25:611-618), contamination of a gelatin production process with a variety of gram-positive and gram-negative bacteria was demonstrated. In this study, bacterial contamination of semifinal gelatin extracts from several production plants was examined. Since these extracts are subjected to harsh conditions during production and a final ultrahigh-temperature treatment, the bacterial load at this stage is expected to be greatly reduced. In total, 1,129 isolates were obtained from a total of 73 gelatin batches originating from six different production plants. Each of these batches was suspected of having bacterial contamination based on quality control testing at the production plant from which it originated. For characterization and identification of the 1,129 bacterial isolates, repetitive-element PCR was used to obtain manageable groups. Representative strains were identified by means of 16S rRNA gene sequencing, species-specific gyrB PCR, and gyrA and rpoB sequencing and were tested for gelatinase activity. The majority of isolates belonged to members of Bacillus or related endospore-forming genera. Representative strains were identified as Bacillus cereus, Bacillus coagulans, Bacillus fumarioli, Bacillus amyloliquefaciens, Bacillus licheniformis, Bacillus pumilus, Bacillus sonorensis, Bacillus subtilis, Bacillus gelatini, Bacillus thermoamylovorans, Anoxybacillus contaminans, Anoxybacillus flavithermus, Brevibacillus agri, Brevibacillus borstelensis, and Geobacillus stearothermophilus. The majority of these species include strains exhibiting gelatinase activity. Moreover, some of these species have known pathogenic properties. These findings are of great concern with regard to the safety and quality of gelatin and its applications.

Design of a 5' exonuclease-based real-time PCR assay for simultaneous detection of Bacillus licheniformis, members of the 'B. cereus group' and B. fumarioli in gelatine.

AIMS: The design of a fast, sensitive and specific detection method for Bacillus licheniformis, members of the 'B. cereus group' and B. fumarioli in gelatine. METHODS AND RESULTS: Specific Taqman probes were designed and tested in a real-time PCR setting. A specific fluorescent signal could be obtained for all gelatine isolates attributed to these species in one single real-time PCR reaction. After sample preparation, a gelatine sample spiked with 1 CFU provided enough template DNA for a significant signal. CONCLUSION: The potential of a real-time PCR assay for simultaneous detection of B. licheniformis, members of the 'B. cereus group' and B. fumarioli in gelatine is demonstrated. SIGNIFICANCE AND IMPACT OF THE STUDY: Implementation of the assay in gelatine producing plants may shorten delivery terms and inform on hazards to public health and suitable remediation procedures.

Screening of bacterial contamination during gelatine production by means of denaturing gradient gel electrophoresis, focussed on Bacillus and related endospore-forming genera.

AIMS: To screen for bacterial contamination during gelatine production by means of denaturing gradient gel electrophoresis (DGGE). As members of Bacillus and related genera were found to persist in the final product, this study focussed on these taxa. METHODS AND RESULTS: Template DNA was extracted from gelatine samples at five crucial points of a gelatine production process. A primer specific for Bacillus and related genera was designed and used in a selective PCR, followed by a nested DGGE-PCR targeting the V9 region of the 16S rDNA. DGGE analysis of the resulting amplicons, and sequence analysis of selected bands, showed high sequence similarities of these bands with Bacillus fumarioli, B. licheniformis, B. coagulans and Clostridium perfringens. When the selective PCR was omitted, primarily Lactobacillus bands were retrieved. CONCLUSIONS: PCR-DGGE analysis of gelatine extracts can be used for tracing and screening of bacterial contamination during gelatine production. A selective PCR, nested with DGGE-PCR, gave much more accurate information about endospore-forming contaminants than did the direct DGGE procedure alone. SIGNIFICANCE AND IMPACT OF THE STUDY: Use of this nested DGGE-PCR protocol may provide important information about possible hazards to the final microbiological quality and/or safety of gelatine, so allowing production parameters and/or remediation procedures may be adjusted on-line.

Controlled comparison of commercial media for human in-vitro fertilization: Ménézo B2 medium versus Medi-Cult universal and BM1 medium.

For many years, we have been using Ménézo B2 medium in our human in-vitro fertilization (IVF) programme. Ménézo B2 contains bovine serum albumin, which has in the meantime become less popular. The search for a valid alternative has therefore been initiated. In a first study from December 1993 to June 1994, we compared Ménézo B2 medium to Medi-Cult (Medi-Cult Universal IVF medium). In this auto-controlled study, sibling oocytes cultured in Ménézo B2 showed a normal fertilization rate similar to that for those cultured in Medi-Cult: 62.9 +/- 33.3 and 61.0 +/- 33.0% respectively (NS; paired t-test). In a second auto-controlled study conducted from November 1995 to March 1996, we compared Ménézo B2 to BM1 (Ellios Bio-Media) medium. The normal fertilization rate in the sibling oocytes was similar for those cultured in Ménézo B2 and in BM1: 66.9 +/- 27.5 versus 62.0 +/- 31.7% (NS; paired t-test). After further culture of the fertilized oocytes, no difference was apparent in either study as regards the morphological characteristics of the embryos cultured in the different media. The speed of development, however, did differ. In both studies, we observed a higher proportion of the embryos reaching at least the three- to four-cell stage at approximately 41 h post-insemination in Ménézo B2 medium than in either Medi-Cult or BM1. As regards the implantation potency of the embryos obtained in the different media, data were collected from the non-randomized transfers. These data indicate no difference between the media tested. This study indicates that the three commercial media with a different composition are equally able to sustain fertilization and embryo development until transfer.

Site-directed mutagenesis of the small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase from Anacystis nidulans.

Using oligonucleotide-directed mutagenesis of the gene encoding the small subunit (rbcS) from Anacystis nidulans mutant enzymes have been generated with either Trp-54 of the small subunit replaced by a Phe residue, or with Trp-57 replaced by a Phe residue, whereas both Trp-54 and Trp-57 have been replaced by Phe residues in a double mutant. Trp-54 and Trp-57 are conserved in all amino acid sequences or the small subunit (S) that are known at present. The wild-type and mutant forms of Rubisco have all been purified to homogeneity. The wild-type enzyme, purified from Escherichia coli is indistinguishable from enzyme similarly purified from A. nidulans in subunit composition, subunit molecular mass and kinetic parameters (Vmax CO2 = 2.9 U/mg, Km CO2 = 155 microM). The single Trp mutants are indistinguishable from the wild-type enzyme by criteria (a) and (b). However, whereas, Km CO2 is also unchanged, Vmax CO2 is 2.5-fold smaller than the value for the wild-type enzyme for both mutants, demonstrating for the first time that single amino acid replacements in the non-catalytic small subunit influence the catalytic rate of the enzyme. The specificity factor tau, which measures the partitioning of the active site between the carboxylase and oxygenase reactions, was found to be invariant. Since tau is not affected by these mutations we conclude that S is an activating not a regulating subunit.