The Journal of applied bacteriology最新文献

Five strains of Bacillus stearothermophilus have been studied to identify a spore strain to be used as a biological indicator organism for low temperature steam and formaldehyde sterilization. Three strains gave poor reproducibility of batch size and growth index and were discarded. The other two strains gave good reproducibility with a high growth index and gave rise to linear survivor curves when exposed to 5% aqueous formaldehyde. However, only NCIMB 8224 sporulates on a simpler medium and as it was the most resistant to formaldehyde, it was further studied. Tests were carried out in a modified miniclave and factors studied included temperature of the steam and formaldehyde concentration. All studies confirmed the suitability of this strain as a biological indicator organism.

Pulsed-field gel electrophoresis (PFGE) was used to characterize Aeromonas hydrophila strains isolated from a cluster of hospital-acquired infections that occurred over approximately 1 month in a French hospital. Five isolates from patients and 10 isolates from the water supply were characterized by biotyping and antibiotic susceptibility patterns and compared with 10 epidemiologically unrelated strains isolated from patients and rivers, by PFGE of digests of chromosomal DNA. Five environmental and four clinical isolates belonged to the same biotype and antibiotic susceptibility pattern type. The endonucleases XbaI, SpeI and SwaI gave satisfactory profiles whereas DraI did not. The profiles were stable, reproducible and discriminatory. The 10 epidemiologically unrelated strains exhibited 10 different patterns after digestion with XbaI, the least expensive, suitable endonuclease. PFGE is a rapid and discriminatory technique for the typing of Aeromonas hydrophila where a common origin of infection is suspected.

In this work, the death of Clostridium botulinum 213B was measured at temperatures between 101 degrees C and 121 degrees C. It was found that at all temperatures tested, survivor curves deviated from log-linearity which prevented their description using traditional first order kinetics. The survivor curves were better described using a vitalistic approach and the log-logistic transformation proposed by Cole et al. (1993). A single equation was derived to describe all survivor curves over the temperature range tested and a comparison of predicted and measured data showed good correlation. The implications of the use of the vitalistic approach to the validity of the 'minimum botulinum cook' is discussed.

Escherichia coli grown in high or low phosphate medium was inoculated into a lake water starvation medium. The viable count decreased at 37 degrees C but not at the lower temperatures over 70 d. Alkaline phosphatase was monitored using a colorimetric assay with pNPP as the substrate. Derepression of the enzyme occurred in cultures starved for > 30 d in the lake water and within 5 d in lake water microcosms supplemented with carbon and nitrogen sources where there was rarely an increase in viable count. Chloramphenicol prevented the synthesis of alkaline phosphatase suggesting that, even under starvation conditions, de novo synthesis of the enzyme occurs.

The survival of a genetically-marked Aeromonas hydrophila strain was studied in water microcosms using viable counts. Aeromonas hydrophila AWWX1 was shown to survive without decline in viable counts for at least 10 d in three of four filtered-autoclaved freshwaters (surface water and groundwater) and in all examined filtered-autoclaved nutrient-poor waters (bottled spring water, Milli-Q and tap water). However, in the unfiltered waters, a rapid decrease in viable counts of Aer. hydrophila AWWX1 was observed after 1-5 d. The survival of Aer. hydrophila AWWX1 in nutrient-poor waters was compared with that of Pseudomonas fluorescens P17 and Spirillum strain NOX. Survival characteristics were organism- and water-dependent. In the filtered-autoclaved waters, viable counts of Spirillum strain NOX were ca 1 log-unit higher than for Aer. hydrophila AWWX1 and Ps. fluorescens P17. The tested strains Aer. hydrophila AWWX1 and Ps. fluorescens P17 survived 3 to 20, respectively 2 to 4 times better in the filtered-autoclaved waters compared to the unfiltered waters. Apparently, any inherent capability of these micro-organisms to adapt to low-nutrient environments was undone by the presence of the autochthonous microbiota. The present findings that Aer. hydrophila survives very poorly in several drinking waters is of utmost importance towards public health and arises questions about the mechanisms involved.

A rapid and sensitive method for detection of Salmonella typhi would help in preventing the spread of outbreaks and in clinical diagnosis. In order to develop unique PCR primers to detect Salm. typhi, ribosomal RNA genes from Salm. typhi (Rawlings) were cloned in pUC18. The resulting clone was confirmed by sequencing. The cloned DNA fragment contained the 5S, part of the 23S rRNA genes and the 5S-23S spacer region (EMBL/GenBank accession No. U04734). It was expected that the 5S-23S spacer region is divergent unlike the highly conserved 23S + 5S genes. This was confirmed by comparison with the rRNA gene sequences in the EMBL/GenBank database. A pair of PCR primers specific for Salm. typhi was obtained, based on this spacer region sequence. The specificity of this pair of primers was tested with 54 Salm. typhi strains (of 27 different phage types). All these Salm. typhi strains showed the positive 300 bp PCR product with this pair of primers. Six other Salmonella species as well as six other non-Salmonella bacteria were tested and none showed the 300 bp PCR product. The sensitivity of the detection level was 0.1 pg of pure Salm. typhi genomic DNA, or approximately 40 Salm. typhi cells in a spiked food sample. This pair of primers therefore has the potential for development into a diagnostic tool for the rapid diagnosis of typhoid fever.

The random amplified polymorphic DNA (RAPD) assay and the restriction enzyme analysis of PCR amplified rDNA are compared for the identification of the common spoilage yeasts Zygosaccharomyces bailii, Z. rouxii, Saccharomyces cerevisiae, Candida valida and C. lipolytica. Both techniques proved to be adequate tools for yeast identification. Since the RAPD does provide less stable patterns than restriction enzyme analysis of PCR amplified rDNA, and a large amount of data had to be compared without data reduction, Principal Component Analysis (PCA) was applied successfully for clustering the RAPD patterns. The success of PCA is highly influenced by the primer used in RAPD and the amount of reference samples. A large amount of reference samples improves the performance of clustering in PCA. The primer of choice was shown to be important with respect to the discriminatory power of the RAPD method. Some primers used enabled discrimination on the subspecies level. The results collected with both typing methods justify the conclusion that the present typing system can be applied for taxonomical purposes.

A new, rapid method for the determination of biodegradable dissolved organic carbon (BDOC), especially suited to water industry needs, was recently proposed by the authors. This dynamic method measured the BDOC of circulating water continuously pumped over a biofilm attached to a special support (sinterized porous glass) that fills a system of two glass columns. The BDOC value corresponds to the difference in dissolved organic carbon (DOC) between inflow and outflow water samples. The analytical results are not significantly different from those of other bioassays that use indigenous bacteria, and the total duration of the analysis is less than 3 h. However, a problem common to all the BDOC methods based on attached bacteria is the extent to which the decrease in DOC during the BDOC analysis is due to true biodegradation or to adsorption of organic matter to the reactor. In the present study, a reasonable support is provided for the hypothesis that this decrease, at least in the dynamic method, is predominantly due to microbiological activity. After comparing the support (sinterized porous glass) with a good physical adsorbent (granular activated carbon), the influence of temperature, residual chlorine and sodium azide on the reactor performance was tested, and a sensitivity only attributable to biological activity was observed. Another set of experiments were performed to assess the fate and specific elimination of different organic substances, explicable assuming that biodegradation processes were involved.