The Journal of applied bacteriology最新文献

Cobalt- and iodide-enriched (adapted, tolerant) strains of the protein-rich cyanobacterium, Spirulina platensis, were produced by repeated sub-culturing in increasing concentrations of the two trace elements. The strains enriched with cobalt and iodide showed higher uptake of these elements than the controls. The LD50 values for the parent and cobalt-adapted strains were 95 and 231 mumol l-1 CO2+, respectively. Likewise, the LD50 values for parent and iodide-adapted strains were 12 and 42 mmol l-1 I-. The carotenoid:chlorophyll a ratio of the parent strains increased after cobalt addition. The cobalt-adapted strain showed a much higher ratio than the cobalt-grown parent (sensitive) cells which remained unchanged after cobalt addition. Intracellular CO2+ uptake by the cells was concentration-dependent and followed Michaelis-Menten kinetics with saturation in uptake occurring in the parent and adapted strains at 126 and 189 mumol l-1 Co2+, respectively. At saturating concentrations, the maximum CO2+ uptake was 39.73 and 158.43 nmol CO2+ mg-1 protein, respectively for the parent and adapted strains. The adapted strain also showed greater cobalt adsorption. The Km of intracellular CO2+ uptake was lower in the case of adapted cells as compared with the parent, whereas Vmax showed an opposite trend. Thus, the adapted cells appear to be more efficient than the parent strain in intracellular uptake of cobalt. Differences between kinetic constants of both the strains suggest that the strains may be physiologically different. Likewise, iodide uptake was significantly higher in iodide-adapted cells than in controls.

The effect of carbon dioxide (100%), nitrogen (100%), carbon dioxide/oxygen (20%:80%) or vacuum pack at 3 and 10 degrees C was studied on the microbial flora, in skinless poultry breast fillets or thigh meat. Lactic acid bacteria and Brochothrix thermosphacta were the predominant organisms in samples stored in vacuum packs, carbon dioxide and nitrogen. Pseudomonads grew only in oxygen/carbon dioxide packaging systems. The concentration of lactate diminished in both thigh and breast meat during storage at 3 and 10 degrees C. This decrease was more pronounced in thigh meat stored under 20%:80% carbon dioxide/oxygen. Acetate increased to varying degrees in all samples regardless of the storage conditions.

The potential of lactic acid bacteria, isolated from a variety of foods, to inhibit indicators representative of spoilage and pathogenic bacteria associated with food products was examined. Fruit and vegetables were a poor source of lactic acid bacteria but large numbers were readily isolated on MRS agar from cheese, milk and meat samples. Approximately 1000 isolates from each of the food samples were examined by the deferred antagonism procedure to determine their ability to inhibit Staphylococcus aureus, Listeria innocua and Pseudomonas fragi. Listeria innocua was the bacterium predominantly inhibited by isolates from the cheese, milk and meats, but antagonism was also observed to a lesser extent against the other indicators. The only inhibition observed for isolates from vegetable material was directed against Staph. aureus. The majority of inhibitor producers were effective against only one of the indicators but a small number were isolated which inhibited two or three.

The formation of water soluble vitamins (vitamin B12, vitamin B6, riboflavin, thiamine, nicotinic acid and nicotinamide) during the tempe solid substrate fermentation was investigated. The role of several strains of Rhizopus oligosporus, R. arrhizus, and R. stolonifer and the role of several bacteria in the vitamin formation process were checked. All fungal and bacterial strains were isolated from Indonesian tempe and soaking water samples. The Rhizopus strains formed riboflavin, nicotinic acid, nicotinamide and vitamin B6. The final concentrations of these substances depended on the different strains involved and on the fermentation time. Isolates of R. oligosporus were generally the best vitamin formers. The moulds did not produce physiologically active vitamin B12. The thiamine content decreased during fermentation. The addition of bacteria, which had been selected in a screening for vitamin B12 production, resulted in an increase of physiologically active vitamin B12. Citrobacter freundii and Klebsiella pneumoniae showed the best formation capabilities. Furthermore, the bacteria produced riboflavin and vitamin B6 in addition to the moulds. The influence of Rhizopus on the vitamin B12 formation of Cit. freundii was also investigated. The vitamin content of tempe that was fermented with the mould and the bacterium was three times as high as a control fermentation with Cit. freundii only.

The type strains of the 57 phage types of Salmonella virchow have been characterized by plasmid profile and by distribution of the insertion sequence IS200. Thirty-two strains carried plasmids and 21 profile types were identified; 17 strains were resistant to antimicrobial agents. In contrast only six of the type strains carried IS200 elements and three patterns were identified. Within Salm. virchow phage type 31, five of 10 wild-type isolates carried plasmids and two plasmid profiles were identified; in contrast, an IS200 element was identified in the genome of only one of these strains. It is concluded that for Salm. virchow, IS200 is unlikely to significantly extend the degree of discrimination achieved by phage typing which may be supplemented when appropriate by plasmid profile typing.

Three rapid microbiological methods, impedance, the direct epifluorescence technique (DEFT-MEM) and ATP bioluminescence (ATP-B) were evaluated for their applicability to preservative efficacy testing (PET) of pharmaceuticals and cosmetics. A good correlation between rapid method response and total colony counts was obtained for untreated suspensions of Staphylococcus aureus, Pseudomonas aeruginosa and Candida albicans with all three methods but, for Aspergillus niger, with impedance only. For chlorhexidine-treated suspensions of Staph. Aureus and C. albicans, a good dose-response curve was obtained with impedance, but ATP-B and DEFT-MEM methods underestimated the kill by the order of 1-6 logs. From the results of this study it is concluded that impedance offers an alternative method to colony counting methods for PET but, at their present level of method development, neither DEFT-MEM nor ATP-B can be considered as satisfactory.

Two DNA probes and a number of oligonucleotide probes were designed from the virulence factor genes of Bacillus anthracis. These probes were tested for specificity against 52 B. anthracis strains and 233 Bacillus strains encompassing 23 other species. A rapid slot blotting technique was used for screening the large numbers of isolates involved. All probes tested appeared to be specific for B. anthracis under high stringency conditions. These probes could differentiate between virulent and avirulent strains. The probes were also applied to the detection of B. anthracis in routine environmental and clinical samples. A non-radioactive hybridization and detection system based on digoxigenin-11-dUTP was developed.

The antibacterial cell-binding properties of lactoferricin B, a potent bactericidal peptide derived from bovine lactoferrin, were investigated for the first time. To facilitate measurements of binding the peptide was radiolabelled by reduction and treatment with iodo-[1-14C]acetamide. 14C-lactoferricin B bound rapidly to the surface of Escherichia coli and Bacillus subtilis. The rate of binding was consistent with the rapid rate of killing caused by this peptide. The extent of binding was reduced in the presence of Mg2+ or Ca2+ ions which act to reduce its antimicrobial effectiveness. The optimal pH for binding was strain-dependent and the killing effect was maximal near the optimal pH for cell binding with each strain tested. These observations indicate that direct interaction of lactoferricin B with the cell surface is necessary for its lethal effect. The number of peptide molecules bound (> 10(6) per cell) was more than would be expected for binding to specific protein receptors. Lactoferricin B inhibited bacterial uptake of 3H-proline with effectiveness similar to polymyxin B, a known membrane-disruptive agent. The cell-binding event appears to lead to a disruption of normal permeability functions of the cytoplasmic membrane.