| 1. |
- Andersson, Annika, et al.
(författare)
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Adhesion and removal of dormant, heat-activated, and germinated spores of three strains of Bacillus cereus
- 1998
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Ingår i: Biofouling (Print). - 0892-7014 .- 1029-2454. ; 13:1, s. 51-67
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Tidskriftsartikel (refereegranskat)abstract
- As the spores of Bacillus cereus are known to be very adhesive, the cleaning processes used to eliminate them are often inefficient. This study investigated how adhesion and removal of spores varied among strains of the species B. cereus. The adhesion and removal of spores during their life cycle were also examined. Spores of three different strains of B. cereus, viz. NVH 61, 1AM 1110 and NCTC 2599, were used. IAM 1110 spores adhered in greater numbers than spores of the other two strains and were the most hydrophobic; four times as many spores of this strain adhered than of the least adhesive spores, NCTC 2599. Spores of both these strains have an exosporium and appendages, but as the relative hydrophobicity varies, there are probably differences in their chemical composition. It was also found that dormant spores were 33-48% more adhesive than germinated spores. There were no obvious differences in adhesion between dormant and heat-activated spores. Up to 80% of the germinated spores could be removed from the surfaces tested. Dormant and heat-activated spores on the other hand were difficult to remove from the surfaces. When siliconized glass surfaces were coated with milk, germinated spores were still the easiest to remove but the difference was not as marked as before. Therefore, this work suggests that cleaning processes should take into consideration factors that boost spore germination in order to improve the cleaning.
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| 2. |
- Andersson, Annika, et al.
(författare)
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Comparison between automatic ribotyping and random amplified polymorphic DNA analysis of Bacillus cereus isolates from the dairy industry
- 1998
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Ingår i: International journal of food microbiology. - 0346-718X. ; 47:1-2, s. 147-51
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Tidskriftsartikel (refereegranskat)abstract
- Discrimination by automatic ribotyping and random amplified polymorphic DNA PCR, RAPD, was compared for 40 different B. cereus dairy isolates, 4 different B. mycoides isolates and 6 culture collection strains. RAPD-PCR has previously shown to be useful for tracing contamination routes of B. cereus to milk. Automatic ribotyping using EcoRI and PvuII separated the B. cereus and B. mycoides isolates/strains into 36 different ribotypes. RAPD-typing with primer 1 (5?-CCGAGTCCA-3?) and primer 2 (5?-CCGGCGGCG-3?) generated 40 different RAPD-profiles. However, 17 isolates clustered into 8 groups, irrespective of the primer and restriction enzyme used and in all but one case, the isolates with the same pattern were isolated from the same dairy. To conclude RAPD-typing was only slightly more discriminatory than automatic ribotyping and therefore automatic ribotyping proved to be a useful, standardized and quick method to discriminate between B. cereus strains. As the two methods are based on completely different genetic properties, one of the methods can be used to confirm the results from the other method, when identity among isolates needs to be verified.
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| 3. |
- Andersson, Annika, et al.
(författare)
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Comparison between automatic ribotyping and random amplified polymorphic DNA analysis of Bacillus cereus isolates from the dairy industry
- 1999
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Ingår i: International Journal of Food Microbiology. - 0168-1605 .- 1879-3460. ; 47:42006, s. 147-151
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Tidskriftsartikel (refereegranskat)abstract
- Discrimination by automatic ribotyping and random amplified polymorphic DNA PCR, RAPD, was compared for 40 different B. cereus dairy isolates, 4 different B. mycoides isolates and 6 culture collection strains. RAPD-PCR has previously shown to be useful for tracing contamination routes of B. cereus to milk. Automatic ribotyping using EcoRI and PvuII separated the B. cereus and B. mycoides isolates/strains into 36 different ribotypes. RAPD-typing with primers generated 40 different RAPD-profiles. However, 17 isolates clustered into eight groups, irrespective of the primer and restriction enzyme used, and in all but one case, the isolates with the same pattern were isolated from the same dairy. Automatic ribotyping proved to be a useful, standardized and quick method to discriminate between B. cereus strains, only slightly less discriminatory than RAPD-typing.
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| 4. |
- Andersson, Annika, et al.
(författare)
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The adhesion of Bacillus cereus spores to epithelial cells might be an additional virulence mechanism
- 1998
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Ingår i: International Journal of Food Microbiology. - 0168-1605 .- 1879-3460. ; 39:1-2, s. 93-9
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Tidskriftsartikel (refereegranskat)abstract
- Four out of ten Bacillus cereus strains produced spores able to adhere to monolayers of Caco-2 cells (human epithelial cells). One of these strains has been involved in an outbreak of food poisoning where the symptoms were more severe and persisted for longer than a normal B. cereus food poisoning. The hydrophobicity of the spores is a contributing factor for the adhesion to occur. The spores are able to germinate in an environment similar to that of the small intestine and then the vegetative cells can produce the enterotoxin directly at the target place. A concentrated and active form of the enterotoxin will be taken up by the epithelial cells in the small intestine. Spore adhesion could be an important virulence factor for some B. cereus strains.
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| 5. |
- Andersson, Annika, et al.
(författare)
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What problems does the food industry have with the spore-forming pathogens Bacillus cereus and Clostridium perfringens?
- 1995
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Ingår i: International Journal of Food Microbiology. - 0346-718X. ; 28:2, s. 14-55
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Tidskriftsartikel (refereegranskat)abstract
- Spore-forming Bacillus cereus and Clostridium perfringens bacteria are special problems for the dairy and meat industry, respectively. Proper cleaning and disinfection with hypochlorite is essential to avoid high numbers of these bacteria in food products. It is impossible for B. cereus and C. perfringens to cause food poisoning with cooking and rapid cooling, and proper reheating. It is also important to note that the generation time for C. perfringens can be as short as 8 min under optimal conditions, so temperatures between 10 and 47 °C in any meat product must be restricted. B. cereus food poisoning through milk and milk products can be avoided with a low number of spores in the products and proper cooling.
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| 6. |
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| 7. |
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| 8. |
- Aronsson, Kristina, et al.
(författare)
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Growth of pulsed electric field exposed Escherichia coli in relation to inactivation and environmental factors
- 2004
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Ingår i: International Journal of Food Microbiology. - 0168-1605 .- 1879-3460. ; 93:1, s. 1-10
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Tidskriftsartikel (refereegranskat)abstract
- Pulsed electric fields (PEF) have been proven to inactivate microorganisms during nonthermal conditions and have the potential to replace thermal processing as a method for food preservation. However, there is a need to understand the recovery and growth of survivors and potentially injured microorganisms following PEF processing. The purpose of this investigation was to study the growth of Escherichia coli at 10°C following exposure to electrical field strengths (15, 22.5 and 30 kV/cm) in relation to inactivation and the amount of potentially sublethally injured cells. One medium was used as both a treatment medium and an incubation medium, to study the influence of environmental factors on the inactivation and the growth of the surviving population. The pH (5.0, 6.0 and 7.0) and water activity (1.00, 0.985 and 0.97) of the medium was varied by adding HCl and glycerol, respectively. Growth was followed continuously by measuring the optical density. The time-to-detection (td) and the maximum specific growth rate (?max) were calculated from these data. Results showed that the PEF process did not cause any obvious sublethal injury to the E. coli cells. The number of survivors was a consequence of the combination of electrical field strength and environmental factors, with pH being the most prominent. Interestingly, the ?max of subsequent growth was influenced by the applied electrical field strength during the process, with an increased ?max at more intense electrical field strengths. In addition, the ?max was also influenced by the pH and water activity. The td, which could theoretically be considered as an increase in shelf life, was found to depend on a complex correlation between electrical field strength, pH and water activity. That could be explained by the fact that the td is a combination of the number of survivors, the recovery of sublethal injured cells and the growth rate of the survivors. © 2003 Published by Elsevier B.V.
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| 9. |
- Aronsson, Kristina, et al.
(författare)
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Inactivation of Escherichia coli, Listeria innocua and Saccharomyces cerevisiae in relation to membrane permeabilization and subsequent leakage of intracellular compounds due to pulsed electric field processing
- 2005
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Ingår i: International Journal of Food Microbiology. - : Elsevier BV. - 0168-1605 .- 1879-3460. ; 99:1, s. 19-32
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Tidskriftsartikel (refereegranskat)abstract
- Membrane permeabilization, caused by pulsed electric field (PEF) processing of microbial cells, was investigated by measurement of propidium iodide (PI) uptake with flow cytometry. Inactivation of Escherichia coli, Listeria innocua and Saccharomyces cerevisiae was determined by viable counts, and leakage of intracellular compounds, such as ATP and UV-absorbing substances, was measured in the extracellular environment. Electrical field strength and pulse duration influenced membrane permeabilization of all three tested organisms of which S. cerevisiae was the most PEF sensitive, followed by E. coli and L. innocua. It was shown by viable counts, PI uptake and leakage of intracellular compounds that L. innocua was the most resistant. Increased inactivation corresponded to greater numbers of permeabilized cells, which were reflected by increased PI uptake and larger amounts of intracellular compounds leaking from cells. For E. coli and L. innocua, a linear relationship was observed between the number of inactivated cells (determined as CFU) and cells with permeated membranes (determined by PI uptake), with higher number of inactivated cells than permeated cells. Increased leakage of intracellular compounds with increasing treatment severity provided further evidence that cells were permeabilized. For S. cerevisiae, there was higher PI uptake after PEF treatments, although very little or no inactivation was observed. Results suggest that E. coli and L. innocua cells, which took up PI, lost their ability to multiply, whereas cells of S. cerevisiae, which also took up PI, were not necessarily lethally permeabilized. © 2004 Elsevier B.V. All rights reserved.
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| 10. |
- Aronsson, Kristina, et al.
(författare)
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Inactivation of microorganisms using pulsed electric fields : The influence of process parameters on Escherichia coli, Listeria innocua, Leuconostoc mesenteroides and Saccharomyces cerevisiae
- 2001
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Ingår i: Innovative Food Science & Emerging Technologies. - 1466-8564 .- 1878-5522. ; 2:1, s. 41-54
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Tidskriftsartikel (refereegranskat)abstract
- This study examines the killing effect of pulsed electric fields (PEF) on four organisms suspended in a model medium. Escherichia coli, Listeria innocua, Leuconostoc mesenteroides and Saccharomyces cerevisiae differ in size, shape and cell wall construction. The electric field strength, pulse duration and number of pulses were varied in the ranges of 25-35 kV/cm, 2-4 ?s and 20-40 pulses, respectively. The results showed that S. cerevisiae was the most sensitive organism with a 6-log reduction, followed by E. coli with a 5.4-log reduction, when they were exposed to 30 kV/cm, and 20 pulses with 4 ?s duration. The most resistant organisms were L. innocua and L. mesenteroides with only a 3-log reduction, however, by increasing the parameters to 35 kV/cm and 40 pulses with 4 ?s pulse duration; marked viability reductions of 8 and 7 log, respectively, were observed. Heat, which is generated during the process, has limited killing effect on the cells, hence the observed reduction can be ascribed to the PEF treatment. Although transmission electron microscopy of PEF treated cells did not confirm membrane damage, observations suggest that PEF treatments have profound direct or indirect effects on the intracellular organisation of microorganisms. © 2001 Elsevier Science Ltd.
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| 11. |
- Aronsson, Kristina, et al.
(författare)
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Influence of pH, water activity and temperature on the inactivation of Escherichia coli and Saccharomyces cerevisiae by pulsed electric fields
- 2001
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Ingår i: Innovative Food Science & Emerging Technologies. - 1466-8564 .- 1878-5522. ; 2:2, s. 105-112
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to examine the influence of pH, water activity (aw) and temperature on the killing effect of pulsed electric fields (PEF). Escherichia coli and Saccharomyces cerevisiae suspended in a model media were subjected to 20 pulses with 4 ?s duration in a continuous PEF system, during which the effects of pH (4.0-7.0), aw (1.00-0.94) and inlet temperature (10°C and 30°C) could easily be studied. Electrical field strengths were set to 25 kV/cm for S. cerevisiae and 30 kV/cm for E. coli and the highest outlet temperature was monitored to 44°C. A synergy of low pH values, high temperatures and PEF processing was observed. A drop in pH value from 7.0 to 4.0 resulted in the reduction of E. coli by four additional log units, whereas for S. cerevisiae, the pH effect was less pronounced. Lowering aw seems to protect both E. coli and S. cerevisiae from PEF processing. © 2001 Elsevier Science Ltd.
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| 12. |
- Husmark, U., et al.
(författare)
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Bacillus spores and moulding with TTC agar: A useful method for the assessment of food processing equipment cleanability
- 1999
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Ingår i: Biofouling (Print). - 0892-7014 .- 1029-2454. ; 14:1, s. 15-24
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Tidskriftsartikel (refereegranskat)abstract
- In the present work a powerful and practical method for the assessment of food processing equipment cleanability is described. Surfaces were soiled with Bacillus spores. After cleaning, surfaces were overlaid with agar containing a tetrazolium salt (TTC) which stained the growing colonies red. Stained colonies could be readily detected and counted. The poorer hygienically designed areas were easily observed and contamination levels could be defined. The TTC method was compared to other classical techniques such as contact plates, direct epifluorescence microscopy (DEM) and Shapton and Hindes (SH) agar. Recovery of bacteria using the TTC method was found to be a good complement to DEM and more accurate than contact plates and SH agar. Cleanability tests on closed equipment are also reported showing the utility of the TTC method.
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| 13. |
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| 14. |
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| 15. |
- Lowenadler, J., et al.
(författare)
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Determination of dissolved carbon dioxide by coulometric titration in modified atmosphere systems
- 1994
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Ingår i: Letters in Applied Microbiology. - 0266-8254 .- 1472-765X. ; 18:5, s. 285-288
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Tidskriftsartikel (refereegranskat)abstract
- The solubility of carbon dioxide (CO2) in microbiological media at different pH values, water activities (a,), temperatures, buffering capacities and ratios of headspace to media volumes was determined by using a coulometer. Buffering capacity and ratio of headspace to media volume were shown to be the major factors influencing the solubility of CO, in modified atmosphere model systems. The growth inhibitory effects of different dissolved CO2 concentrations (0-50 ?mol ml-1) were determined for Pseudomanas fragi at 8°C and 22°C. Pseudomonas fragi was shown to be strongly affected by the CO2 concentration in the media. A carbon dioxide concentration of 40 ?mol ml-1 was needed to inhibit Ps. fragi at 8°C. The importance of measuring dissolved CO2 Concentrations in modified atmosphere packaging applications was shown and the coulometer proved to be an excellent tool for this purpose.
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