Identification of a New Heavy-Metal-Resistant Strain of Geobacillus stearothermophilus Isolated from a Hydrothermally Active Volcanic Area in Southern Italy

Microorganisms thriving in hot springs and hydrothermally active volcanic areas are dynamically involved in heavy-metal biogeochemical cycles; they have developed peculiar resistance systems to cope with such metals which nowadays can be considered among the most permanent and toxic pollutants for humans and the environment. For this reason, their exploitation is functional to unravel mechanisms of toxic-metal detoxification and to address bioremediation of heavy-metal pollution with eco-sustainable approaches. In this work, we isolated a novel strain of the thermophilic bacterium Geobacillus stearothermophilus from the solfataric mud pool in Pisciarelli, a well-known hydrothermally active zone of the Campi Flegrei volcano located near Naples in Italy, and characterized it by ribotyping, 16S rRNA sequencing and mass spectrometry analyses. The minimal inhibitory concentration (MIC) toward several heavy-metal ions indicated that the novel G. stearothermophilus isolate is particularly resistant to some of them. Functional and morphological analyses suggest that it is endowed with metal resistance systems for arsenic and cadmium detoxification.

A Comparative Study of Ethylene Oxide Gas, Hydrogen Peroxide Gas Plasma, and Low-Temperature Steam Formaldehyde Sterilization

Objective:

To compare the efficacies of ethylene oxide gas (EOG), hydrogen peroxide gas plasma (PLASMA), and low-temperature steam formaldehyde (LTSF) sterilization methods.

Methods:

The efficacies of EOG, PLASMA, and LTSF sterilization were tested using metal and plastic plates, common medical instruments, and three process challenge devices with narrow lumens. All items were contaminated with Bacillus stearothermophilus spores or used a standard biological indicator.

Results:

EOG and LTSF demonstrated effective killing of B. stearothermophilus spores, with or without serum, on plates, on instruments, and in process challenge devices. PLASMA failed to adequately sterilize materials on multiple trials in several experiments, including two of three plates, two of three instruments, and all process challenge devices.

Conclusions:

Our results suggest that PLASMA sterilization may be unsuccessful under certain conditions, particularly when used for items with complex shapes and narrow lumens. Alternatively, LTSF sterilization demonstrates excellent efficacy and is comparable to EOG sterilization. LTSF could potentially act as a substitute if EOG becomes unavailable due to environmental concerns.

Ozone Gas as a Benign Sterilization Treatment for PLGA Nanofiber Scaffolds

The use of electrospun nanofibers for tissue engineering and regenerative medicine applications is a growing trend as they provide improved support for cell proliferation and survival due, in part, to their morphology mimicking that of the extracellular matrix. Sterilization is a critical step in the fabrication process of implantable biomaterial scaffolds for clinical use, but many of the existing methods used to date can negatively affect scaffold properties and performance. Poly(lactic-co-glycolic acid) (PLGA) has been widely used as a biodegradable polymer for 3D scaffolds and can be significantly affected by current sterilization techniques. The aim of this study was to investigate pulsed ozone gas as an alternative method for sterilizing PLGA nanofibers. The morphology, mechanical properties, physicochemical properties, and response of cells to PLGA nanofiber scaffolds were assessed following different degrees of ozone gas sterilization. This treatment killed Geobacillus stearothermophilus spores, the most common biological indicator used for validation of sterilization processes. In addition, the method preserved all of the characteristics of nonsterilized PLGA nanofibers at all degrees of sterilization tested. These findings suggest that ozone gas can be applied as an alternative method for sterilizing electrospun PLGA nanofiber scaffolds without detrimental effects.

Kinetics of germination of individual spores of Geobacillus stearothermophilus as measured by raman spectroscopy and differential interference contrast microscopy

Geobacillus stearothermophilus is a gram-positive, thermophilic bacterium, spores of which are very heat resistant. Raman spectroscopy and differential interference contrast microscopy were used to monitor the kinetics of germination of individual spores of G. stearothermophilus at different temperatures, and major conclusions from this work were as follows. 1) The CaDPA level of individual G. stearothermophilus spores was similar to that of Bacillus spores. However, the Raman spectra of protein amide bands suggested there are differences in protein structure in spores of G. stearothermophilus and Bacillus species. 2) During nutrient germination of G. stearothermophilus spores, CaDPA was released beginning after a lag time (T_lag) between addition of nutrient germinants and initiation of CaDPA release. CaDPA release was complete at T_release, and ΔT_release (T_release – T_lag) was 1–2 min. 3) Activation by heat or sodium nitrite was essential for efficient nutrient germination of G. stearothermophilus spores, primarily by decreasing T_lag values. 4) Values of T_lag and T_release were heterogeneous among individual spores, but ΔT_release values were relatively constant. 5) Temperature had major effects on nutrient germination of G. stearothermophilus spores, as at temperatures below 65°C, average T_lag values increased significantly. 6) G. stearothermophilus spore germination with exogenous CaDPA or dodecylamine was fastest at 65°C, with longer T_lag values at lower temperatures. 7) Decoating of G. stearothermophilus spores slowed nutrient germination slightly and CaDPA germination significantly, but increased dodecylamine germination markedly. These results indicate that the dynamics and heterogeneity of the germination of individual G. stearothermophilus spores are generally similar to that of Bacillus species.

Effect of dielectric and liquid on plasma sterilization using dielectric barrier discharge plasma

Plasma sterilization offers a faster, less toxic and versatile alternative to conventional sterilization methods. Using a relatively small, low temperature, atmospheric, dielectric barrier discharge surface plasma generator, we achieved ≥6 log reduction in concentration of vegetative bacterial and yeast cells within 4 minutes and ≥6 log reduction of Geobacillus stearothermophilus spores within 20 minutes. Plasma sterilization is influenced by a wide variety of factors. Two factors studied in this particular paper are the effect of using different dielectric substrates and the significance of the amount of liquid on the dielectric surface. Of the two dielectric substrates tested (FR4 and semi-ceramic (SC)), it is noted that the FR4 is more efficient in terms of time taken for complete inactivation. FR4 is more efficient at generating plasma as shown by the intensity of spectral peaks, amount of ozone generated, the power used and the speed of killing vegetative cells. The surface temperature during plasma generation is also higher in the case of FR4. An inoculated FR4 or SC device produces less ozone than the respective clean devices. Temperature studies show that the surface temperatures reached during plasma generation are in the range of 30°C–66°C (for FR4) and 20°C–49°C (for SC). Surface temperatures during plasma generation of inoculated devices are lower than the corresponding temperatures of clean devices. pH studies indicate a slight reduction in pH value due to plasma generation, which implies that while temperature and acidification may play a minor role in DBD plasma sterilization, the presence of the liquid on the dielectric surface hampers sterilization and as the liquid evaporates, sterilization improves.

Thermal inactivation of Bacillus anthracis surrogate spores in a bench-scale enclosed landfill gas flare

A bench-scale landfill flare system was designed and built to test the potential for landfilled biological spores that migrate from the waste into the landfill gas to pass through the flare and exit into the environment as viable. The residence times and temperatures of the flare were characterized and compared to full-scale systems. Geobacillus stearothermophilus and Bacillus atrophaeus, nonpathogenic spores that may serve as surrogates for Bacillus anthracis, the causative agent for anthrax, were investigated to determine whether these organisms would be inactivated or remain viable after passing through a simulated landfill flare. High concentration spore solutions were aerosolized, dried, and sent through a bench-scale system to simulate the fate of biological weapon (BW)-grade spores in a landfill gas flare. Sampling was conducted downstream of the flare using a bioaerosol collection device containing sterile white mineral oil. The samples were cultured, incubated for seven days, and assessed for viability. Results showed that the bench-scale system exhibited good similarity to the real-world conditions of an enclosed standard combustor flare stack with a single orifice, forced-draft diffusion burner. All spores of G. stearothermophilus and B. atrophaeus were inactivated in the flare, indicating that spores that become re-entrained in landfill gas may not escape the landfill as viable, apparently becoming completely inactivated as they exit through a landfill flare.

Mechanisms of allosteric gene regulation by NMR quantification of microsecond-millisecond protein dynamics

The trp RNA-binding attenuation protein (TRAP) is a paradigmatic allosteric protein that regulates the tryptophan biosynthetic genes associated with the trp operon in bacilli. The ring-shaped 11-mer TRAP is activated for recognition of a specific trp-mRNA target by binding up to 11 tryptophan molecules. To characterize the mechanisms of tryptophan-induced TRAP activation, we have performed methyl relaxation dispersion (MRD) nuclear magnetic resonance (NMR) experiments that probe the time-dependent structure of TRAP in the microsecond-to-millisecond "chemical exchange" time window. We find significant side chain flexibility localized to the RNA and tryptophan binding sites of the apo protein and that these dynamics are dramatically reduced upon ligand binding. Analysis of the MRD NMR data provides insights into the structural nature of transiently populated conformations sampled in solution by apo TRAP. The MRD data are inconsistent with global two-state exchange, indicating that conformational sampling in apo TRAP is asynchronous. These findings imply a temporally heterogeneous population of structures that are incompatible with RNA binding and substantiate the study of TRAP as a paradigm for probing and understanding essential dynamics in allosteric, regulatory proteins.

Evaluation of steam sterilization processes: comparing calculations using temperature data and biointegrator reduction data and calculation of theoretical temperature difference

When calculating of the physical F121.1 degrees c-value by the equation F121.1 degrees C = t x 10(T-121.1/z the temperature (T), in combination with the z-value, influences the F121.1 degrees c-value exponentially. Because the z-value for spores of Geobacillus stearothermophilus often varies between 6 and 9, the biological F-value (F(Bio) will not always correspond to the F0-value based on temperature records from the sterilization process calculated with a z-value of 10, even if the calibration of both of them are correct. Consequently an error in calibration of thermocouples and difference in z-values influences the F121.1 degrees c-values logarithmically. The paper describes how results from measurements with different z-values can be compared. The first part describes the mathematics of a calculation program, which makes it easily possible to compare F0-values based on temperature records with the F(BIO)-value based on analysis of bioindicators such as glycerin-water-suspension sensors. For biological measurements, a suitable bioindicator with a high D121-value can be used (such a bioindicator can be manufactured as described in the article "A Method of Increasing Test Range and Accuracy of Bioindicators-Geobacillus stearothermophilus Spores"). By the mathematics and calculations described in this macro program it is possible to calculate for every position the theoretical temperature difference (deltaT(th)) needed to explain the difference in results between the thermocouple and the biointegrator. Since the temperature difference is a linear function and constant all over the process this value is an indication of the magnitude of an error. A graph and table from these calculations gives a picture of the run. The second part deals with product characteristics, the sterilization processes, loading patterns. Appropriate safety margins have to be chosen in the development phase of a sterilization process to achieve acceptable safety limits. Case studies are discussed and experiences are shared.

Post-transcriptional regulation of the xynA expression by a novel mRNA binding protein, XaiF

XaiF, a novel 32kDa protein encoded by the ORF located in the immediate downstream of the xynA gene of Bacillus stearothermophilus No. 236, was identified to be the xylanase-specific trans-activator. In this study, the positive effect of XaiF was confirmed to be xylanase-specific, and the results from Northern blot and in vitro transcription assays showed that the XaiF increased the xynA transcripts at post-transcriptional step. Moreover, analysis of the mRNA decay rate led to the assertion that the XaiF functions to stabilize the xynA mRNA. Intriguingly, in vitro RNA-protein binding assay and analysis using gst-xynA 3'-UTR chimeric gene constructs demonstrated that the XaiF stabilizes xynA mRNA by direct binding onto the 3'-UTR of the mRNA.

In vivo molecular evolution reveals biophysical origins of organismal fitness

In nature, evolution occurs through the continuous adaptation of a population to its environment. At the molecular level, adaptive changes in protein sequence and expression impact organismal fitness and, consequently, dictate population dynamics. Here, we have used a "weak link" method to favor variations in one gene, allowing adaptation to thermostability to be studied in molecular detail as bacteria were grown continuously for approximately 1500 generations. Surprisingly, only six mutant alleles, representing less than 1% of the possible missense mutations, were observed, suggesting a highly constrained molecular landscape during protein evolution. The changes in organismal fitness were linked directly to incremental increases in enzyme stability and activity maxima and corresponded to the narrow temperature ranges where each mutant enjoyed success within the overall population. Thus, continuous evolution of a single gene permits a quantitative approach that extends from the phenotypes of the microbial populations to their underlying biophysical basis.

Inactivation of Bacillus spores by the combination of moderate heat and low hydrostatic pressure in ketchup and potage

The combination effect of moderate heat and low hydrostatic pressure (MHP) on the reduction of Bacillus subtilis, Bacillus coagulans and Geobacillus stearothermophilus spores in food materials (potage and ketchup) was investigated. These bacterial spores were suspended in potage (pH 7), acidified potage (pH 4), neutralized ketchup (pH 7) and ketchup (pH 4). The suspensions were treated with and without pressure (100 MPa) and temperatures of 65-85 degrees C for 3 to 12 h. The bacterial spores were inactivated by 4-8 log cycles during MHP treatment in potage, acidified potage and ketchup, whereas the spores were highly resistant to long time heat treatment in potage and neutralized ketchup. The degrees of spore destruction were mostly dependent on pH and medium composition during MHP treatment. The inactivation effect in MHP treatment was higher at the pH 7 than at pH 4 both in ketchup and potage. The bacterial spores showed higher inactivation in potage than ketchup during MHP treatment.

Application of artificial neural networks to describe the combined effect of pH and NaCl on the heat resistance of Bacillus stearothermophilus

A model for prediction of bacterial spore inactivation was developed. The influence of temperature, pH and NaCl on the heat resistance of Bacillus stearothermophilus spores was described using low-complexity, black box models based on artificial neural networks. Literature data were used to build and train the neural network, and new experimental data were used to evaluate it. The neural network models gave better predictions than the classical quadratic response surface model in all the experiments tried. When the neural networks were evaluated using new experimental data, also good predictions were obtained, providing fail-safe predictions of D values in all cases. The weights and biases values of neurons of the neural network that gave the best results are presented, so the reader can use the model for their own purposes. The use of this non-linear modelling technique makes it possible to describe more accurately interacting effects of environmental factors when compared with classical predictive microbial models.

Proteomics viewed on stress response of thermophilic bacteriumBacillus stearothermophilus TLS33

Thermophilic bacterium Bacillus stearothermophilus TLS33, isolated from a hot spring in Chiang Mai, Thailand, usually produces many enzymes that are very useful for industrial applications. However, the functional properties and mechanisms of this bacterium under stress conditions are rarely reported and still need more understanding on how the bacterium can survive in stress environments. In this study, we examined the oxidative stress induced proteins of this bacterium by proteomic approach combining two-dimensional electrophoresis and mass spectrometry. When the bacterium encountered oxidative stress, peroxiredoxin, as an antioxidant enzyme, is one of the interesting stressed proteins which appeared to be systematically increased with different pI. There are four isoforms of peroxiredoxin, denoted as Prx I, Prx II, Prx III and Prx IV, which are observed at the same molecular weight of 27 kDa but differ in pI values of 5.0, 4.87, 4.81 and 4.79, respectively. The H2O2 concentration directly increased Prx II, Prx III and Prx IV intensities, but decreased Prx I intensity. These shifting of peroxiredoxin isoforms may occur by a post-translational modification. Otherwise, the longer time of oxidative stress had not affected the expression level of peroxiredoxin isoforms. Therefore, this finding of peroxiredoxin intends to know the bacterial adaptation under oxidative stress. Otherwise, this protein plays an important role in many physiological processes and able to use in the industrial applications.

Assessing survival of dairy propionibacteria in gastrointestinal conditions and adherence to intestinal epithelia

The genus Propionibacterium consists of two principal groups, cutaneous and classical or dairy. Cutaneous species are predominant members of the microbial population of human skin and have also been isolated from the feces of humans and other vertebrate animals. They are often considered opportunistic organisms and have been occasionally associated with infections in humans. Dairy propionibacteria are microorganisms extensively used in the industry for manufacture of Swiss-type cheeses and biological production of propionic acid and vitamin B12. They can be isolated from soil, vegetables, silage, raw milk, and dairy products such as kefir and different cheeses with "eyes."In the last decade, several studies have demonstrated probiotic properties for members of the genus Propionibacterium. The effects claimed are based on the production of bacteriocins, vitamins, stimulation of growth of other colonic bacteria like bifidobacteria, beneficial modification of the composition and metabolic activities of the intestinal microflora, immunomodulation, and antimutagenic activity. It is thought that to produce many of these health benefits, the probiotic microorganisms must be able to survive the transit through the hostile conditions of the gastrointestinal tract (GIT) and remain at high levels in the intestine, avoiding removal by peristaltic contractions of the gut. In this sense, microorganisms with a short generation time or the ability to adhere to the intestinal mucosa will survive for prolonged periods in the body of the host. Therefore, two desirable properties for probiotic microorganisms are (1) resistance to gastric acidity, bile, and pancreatic enzymes; and (2) adhesion ability to mucosal surfaces. Dairy bacteria are traditionally not considered to persist as normal inhabitants of the human intestinal tract. Therefore, survival under GIT conditions and adherence are important properties to be considered, and tests to study them would be useful tools. In the present chapter we describe the methods used in our laboratory to assess survival, metabolic activity, and adhesion of dairy propionibacteria to intestinal epithelial cells after gastrointestinal digestion.

Effect of media on spore yield and thermal resistance of Bacillus stearothermophilus

The interference of eight components in the yield of sporulation and thermal resistance to moist heat (121 degrees C) of Bacillus stearothermophilus spores suspended in 0.02 M calcium acetate solution and inoculated on paper strips previously treated with calcium acetate/calcium hydroxide was studied. The spore yield of 1.0 x 10(8)mL was developed at 62 degrees C in 17 media containing different concentrations of D-glucose, sodium chloride, L-glutamic acid, yeast extract, peptone, manganese sulfate, potassium phosphate, and ammonium phosphate. The combined effects of yeast extract, peptone, and glucose contributed positively to the spore yield and to the stability of the thermal resistance of both spores in suspension and on strips.

The effect of composition of parenteral solution on the thermal resistance of Bacillus stearothermophilus and Bacillus subtilis spores

Large-volume parenteral solutions were submitted to heat treatments after being inoculated with Bacillus stearothermophilus ATCC 7953 (Tr = 121 degrees C) and Bacillus subtilis ATCC 9372 (Tr = 104.5 degrees C) spores. The average decimal reduction time for B. stearothermophilus ranged from a D121 degrees C value of 1.31 to 3.14 min, in glucophysiologic and Ringer's solutions respectively. For B. subtilis, D104.5 degrees C value increased from 0.69 to 1.37 min, in Ringer's (pH=5.91) and 50% glucose (pH 3.05) solutions respectively. The z value ranged from 7.95 degrees C (20% mannitol solution) to 13.14 degrees C (50% glucose solution), corresponding to an activation energy (Ea) of 81.48 and 49.30 kcal/mol, respectively.

The effect of bioindicator preparation and storage on thermal resistance of Bacillus stearothermophilus spores

Paper strips inoculated with spores of Bacillus stearothermophilus ATCC 7953 were conventionally dried (lot 1) and lyophilized (lot 2); stored in defined environments of 32 and 86% relative humidity at 10, 25 and 33 degrees C for 210 d; and submitted to moist heat treatments at 121 degrees C. A significant decrease in thermal resistance from initial starting levels was found for lyophilized bioindicators stored at 86% relative humidity. The respective average D121 degrees C values were 1.55+/-0.05 and 1.37+/-0.10 min for lyophilized bioindicators stored at 32 and 86% relative humidity; and 1.65+/-0.15 min and 1.57+/-0.11 min for dried bioindicators stored in the same environments.

[Isolation and screening of beneficial endophytic bacteria to control bacterial ring rot of potato]

One hundred and thirty-three bacterial strains were isolated from inner tissue of potato tubers collected from Datong, Taiyuan and Inner Mongolia Autonomous regions. On the basis of antagonistic examination in vitro, greenhouse and field tests, five strains named as 069, 085, 110, 116 and 118 were chosen for their suppression of bacterial ring rot or their growth promotion. Strain 118 is an endophytic bacterium with three effects of colonization, growth promotion and suppression of the pathogenic bacteria, showing good prospects for commercial use.

The thermostability of DNA-binding protein HU from mesophilic, thermophilic, and extreme thermophilic bacteria

Based on primary structure comparison between four highly homologous DNA-binding proteins (HUs) displaying differential thermostability, we have employed in vitro site-directed mutagenesis to decipher their thermostability mechanism at the molecular level. The contribution of the 11 amino acids that differ between the thermophilic HUBst from Bacillus stearothermophilus (Tm = 61.6 degrees C) and the mesophilic HUBsu from Bacillus subtilis (Tm = 39.7 degrees C) was evaluated by replacing these amino acids in HUBst with their mesophilic counterparts. Among 11 amino acids, three residues, Gly-15, Glu-34, and Val-42, which are highly conserved in the thermophilic HUs, have been found to be responsible for the thermostability of HUBst. These amino acids in combination (HUBst-G15E/E34D/V42I) reduce the thermostability of the protein (Tm = 45.1 degrees C) at the level of its mesophilic homologue HUBsu. By replacing these amino acids in HUBsu with their thermophilic counterparts, the HUBsu-E15G/D34E/142V mutant was generated with thermostability (Tm = 57.8 degrees C) at the level of thermophilic HUBst. Employing the same strategy, we generated several mutants in the extremely thermophilic HUTmar from Thermotoga maritima (Tm = 80.5 degrees C), and obtained data consistent with the previous results. The triplet mutant HUTmar-G15E/E34D/V421 (Tm = 35.9 degrees C) converted the extremely thermophilic protein HUTmar to mesophilic. The various forms of HU proteins were overproduced in Escherichia coli, highly purified, and the thermostability of the mutants confirmed by circular dichroism spectroscopy. The results presented here were elucidated on the basis of the X-ray structure of HUBst and HUTmar (our unpublished results), and their mechanism was proposed at the molecular level. The results clearly show that three individual local interactions located at the helix-turn-helix part of the protein are responsible for the stability of HU proteins by acting cooperatively in a common mechanism for thermostability.

Modeling the combined effect of pH and temperature on the heat resistance of Bacillus stearothermophilus spores heated in a multicomponent food extract

The combined effect of pH and temperature on the heat resistance of Bacillus stearothermophilus spores heated in an extract of complex food was studied. The results showed that, in general, reducing the pH reduced the heat resistance of the spores. Similarly, the value for the D parameter in the nonacidified extract was between 30 and 70% lower than the one obtained with double-distilled water. This result once again shows the importance of the substrate in inactivation studies of microorganisms. The experimental data were used to carry out a comparison of two predictive mathematical models of inactivation, one based on a multiparametric regression obtained in this study and the other obtained from the bibliography and based on a linear-Bigelow equation. Both models predict reasonably well, although the multiparametric model presented a slightly better accuracy factor (1.11) than the one obtained with the linear-Bigelow equation (1.13).

Protocol for detection of biofilms on needleless connectors attached to central venous catheters

Central venous catheter needleless connectors (NCs) have been shown to develop microbial contamination. A protocol was developed for the collection, processing, and examination of NCs to detect and measure biofilms on these devices. Sixty-three percent of 24 NCs collected from a bone marrow transplant center contained biofilms comprised primarily of coagulase-negative staphylococci.

Effect of pH on the heat resistance of spores comparison of two models

All published models describing the effect of pH on the heat resistance of spores can be regarded either as a linear first degree equation or a linear second degree equation. This work aimed to compare both models from three sets of published data for, Clostridium sporogenes and Bacillus stearothermophilus, respectively. The relative quality of fit of each model with respect to the other depends on the species, the strain and the heating temperature. Parameter estimation was more reliable for the second degree model than for of the simple first degree equation. However, in the case of acidic foodstuffs, predictions obtained from the second degree model are more sensitive toward errors of parameter values. The second degree model is better from the point of view of safety at most frequent ranges of pH of foods. Moreover, for Clostridium botulinum the goodness of fit of this model is clearly higher than that of the first degree equation. If this observation is confirmed by further work, the second degree model in application of standard calculations of heat processes of foods would be preferred.

Effect of calcium in assay medium on D value of Bacillus stearothermophilus ATCC 7953 spores

The D value of commercial biological indicator spore strips using Bacillus stearothermophilus ATCC 7953 was increased by higher calcium concentrations in assay media. The calcium concentration in assay media varied among the manufacturers. The calcium concentration in assay media is an important factor to consider to minimize the variation of D value.

Lipid composition and dynamics of cell membranes of Bacillus stearothermophilus adapted to amiodarone

Bacillus stearothermophilus, a useful model to evaluate membrane interactions of lipophilic drugs, adapts to the presence of amiodarone in the growth medium. Drug concentrations in the range of 1-2 microM depress growth and 3 microM completely suppresses growth. Adaptation to the presence of amiodarone is reflected in lipid composition changes either in the phospholipid classes or in the acyl chain moieties. Significant changes are observed at 2 microM and expressed by a decrease of phosphatidylethanolamine (relative decrease of 23.3%) and phosphatidylglycerol (17.9%) and by the increase of phosphoglycolipid (162%). The changes in phospholipid acyl chains are expressed by a decrease of straight-chain saturated fatty acids (relative decrease of 12.2%) and anteiso-acids (22%) with a parallel increase of the iso-acids (9.8%). Consequently, the ratio straight-chain/branched iso-chain fatty acids decreases from 0. 38 (control cultures) to 0.30 (cultures adapted to 2 microM amiodarone). The physical consequences of the lipid composition changes induced by the drug were studied by fluorescence polarization of diphenylhexatriene and diphenylhexatriene-propionic acid, and by differential scanning calorimetry. The thermotropic profiles of polar lipid dispersions of amiodarone-adapted cells are more similar to control cultures (without amiodarone) than those resulting from a direct interaction of the drug with lipids, i.e., when amiodarone was added directly to liposome suspensions. It is suggested that lipid composition changes promoted by amiodarone occur as adaptations to drug tolerance, providing the membrane with physico-chemical properties compatible with membrane function, counteracting the effects of the drug.

The effect of media composition on the thermal resistance of Bacillus stearothermophilus

Spores of Bacillus stearothermophilus ATCC 7953 were developed at 62 degrees C on 32 media composed of various amounts of 11 components: D-glucose, L-glutamic acid, yeast extract, peptone, sodium chloride, magnesium sulfate, ammonium phosphate, potassium phosphate, calcium chloride, ferrous sulfate and manganese sulfate. Statistical models were used and demonstrated a strong interaction of yeast/peptone/ammonium phosphate, contributing positively to the best sporulation yield (6-7 log10 spores). The most influential medium components on the thermal resistance (at 121 degrees C) of spores in suspension (calcium acetate, pH 9.7) were yeast extract (positively) and potassium phosphate (negatively), both creating the positive interaction, for spores from a 6-day incubation period. However, the strong negative effect of sodium chloride decreased the D-value from 1.81 min to 0.57 min upon increasing the incubation period (62 degrees C) from 3 days to 6 days. The D-glucose and peptone exhibited greater effects than the yeast extract and potassium phosphate interaction on D-values for 3-day spores on strip, just as the highly joint-positive peptone/sodium chloride effect maintained the thermal resistance of 6-day spores on strips. The spores on strip system showed less stability than the spores in suspension. The most stable spore system confirmed D-values at 121 degrees C at a range between 1.5 min and 1.9 min, which were obtained by keeping sodium chloride and potassium phosphate at minimum concentrations and yeast extract and peptone at maximum concentrations, regardless of the 3- to 6-day sporulation.

[Thermophilic endospores in the environment of a sugar mill in Jujuy]

Twenty six samples from green and scorched sugarcane stems and leaves, sugarmill air dust and raw sugar were analyzed. Thirty nine thermophilic bacilli strains were isolated. Physiological and morphological examinations were carried out according to Bergey's Manual. The strains were identified as B. licheniformis (66.7%), B. coagulans (17.9%), B. stearothermophilus (10.3%) y B. subtilis (5.1%).

Domain swapping in the sporulation response regulator Spo0A

Adaptive responses of micro-organisms, such as chemotaxis and sporulation, are governed by two-component systems consisting of sensor kinases, that interpret environmental signals, and response regulators which activate the appropriate physiological responses. Signal transduction via response regulator proteins is mediated through transient phosphorylation of aspartic acid residues. In Spo0A, the key regulator of development (sporulation) in Bacillus, phosphorylation of the N-terminal receiver domain (N-Spo0A) at aspartate-55 switches on the transcription activation functions residing in the C-terminal effector domain. Here we report the crystal structure of N-Spo0A from Bacillus stearothermophilus at 1.6 A spacing, revealing a dimer formed by an alpha-helix swap. Comparison of this structure with the recently described structure of phosphorylated N-Spo0A shows that dimer formation results from a cis-trans isomerization of the Lys106--Pro107 peptide bond. The quaternary reorganization is associated with alterations in the active site stereochemistry which may have implications for signalling. Remarkably, this 3-D domain swapped N-Spo0A dimer has an identical topology to a hypothetical CheY-like dimer, recently proposed as an intermediate in the evolution of the family of periplasmic substrate binding proteins.

Effect of acidification and oil on the thermal resistance of Bacillus stearothermophilus spores heated in food substrate

The effect of the addition of vinegar and/or oil to a food homogenate (tomato sauce, tuna and vegetables) on the thermal resistance of Bacillus stearothermophilus spores was studied. The results indicated that the food substrate without the addition of vinegar and oil and a pH value of 5.28 reduced the thermal resistance of B. stearothermophilus spores compared with that obtained in double-distilled water, (D121 = 1.41 and 3.08 min respectively). The addition of vinegar reduced the pH of the substrate (4.81) and consequently the D values were reduced (D121 = 1.28 min). The addition of soya oil and vinegar to substrate until a pH of 4.81, further reduced the thermal resistance of the spores, giving a D121 value of 0.93 min.

Bacterial cell envelopes (ghosts) but not S-layers activate human endothelial cells (HUVECs) through sCD14 and LBP mechanism

Bacterial cell-envelopes (called ghosts) and surface layers (S-layers) are discussed to be used as vaccines and/or adjuvants, consequently it is necessary to find out which immunomodulatory mediators are induced in human cells. The present work focuses on the effects of ghosts (Escherichia coli O26:B6), S-layers (Bacillus stearothermophilus) in comparison with LPS and antibiotic-inactivated whole bacteria (E. coli O26:B6) on human umbilical vein endothelial cells (HUVEC) with regard to the release of interleukin 6 (IL-6) and the expression of surface E-selectin and the role of lipopolysaccharide binding protein (LBP), soluble CD14 (sCD14) and serum for this activation. Endothelial cells responded to ghosts, whole bacteria and LPS with IL-6 release up to 15000 pg/ml and surface E-selectin expression, while in contrast the response to S-layers with IL-6 release up to 500 pg/ml was very weak. Compared to LPS, 10-100-fold higher concentrations of bacterial ghosts and whole bacteria were required to induce the cytokine synthesis and E-selectin expression. IL-6 release and E-selectin expression of HUVECs were reduced in the absence of serum and equivalent to unstimulated samples. We have also studied the role of CD14 and LBP for the activation of endothelial cells using antiCD14 and antiLBP antibodies (Ab). AntiCD14 and antiLBP Ab both inhibited IL-6 release and E-selectin expression in a dose dependent manner after stimulation with ghosts, whole bacteria and LPS but had no effect on S-layers stimulated cells. AntiCD14 Ab inhibited more effectively than antiLBP Ab. These findings suggest that bacterial ghosts but not S-layers activate HUVECs through sCD14 and LBP dependent mechanisms.

Morpho-structural variations of bacterial spores after treatment in steam vacuum assisted autoclave

This study intended to verify, through microbiological techniques and TEM investigations, the killing of bacterial spores after treatment in steam autoclave, and to propose strictly morphological considerations about the target of this sterilisation process. Autoclave is the most common device for sterilising instruments in order to prevent cross infections in dental offices. The autoclave efficiency has been improved in the last years and part of this improvement is related to both a better and more correct use of the autoclave system and to the technological innovations introduced in the last generation of devices. However, associations as ADA or CDC suggest to regularly verify the process of 'autoclaving' through biological indicators (BI). The most commonly used BI are made of spores strips or suspensions of Bacillus Subtilis (pb 168) and Bacillus Stearothermophilus (ATCC 10149). They visually prove, changing colours on enzymatic base, the death of micro-organism and if the physical parameters, necessary for sterilisation, have been achieved. These two strains of endospore-forming bacteria were processed and prepared following two different techniques: Karnovsky fixed and epon embedded--phosphotungstic acid fixed for direct observation. The kind and the extent of analysed modifications are extremely various: from deep lacerations, which changed the spore structure, to little clefts which let the cytoplasm go out.

Thermal inactivation kinetics of Bacillus stearothermophilus spores using a linear temperature program

A systematic study of the inactivation kinetics of Bacillus stearothermophilus spores was carried out in nonisothermic heating conditions using a linear temperature increase program and analyzing the experimental data by means of a one-step nonlinear regression. The D and z values estimated are close to those obtained in isothermic conditions and estimated by using a two-step model, first D values are calculated, and then in the second step a z value is deduced (D(121 degrees C) = 3.08 and 4.38 min, respectively, and z = 7 and 7.9 degrees C, respectively). No convergence problems were observed when using the one-step nonlinear regression proposed. The results indicated that the methodology applied in this study can be used to obtain kinetic data for bacterial spores, which could mean a significant reduction in the amount of experimental work employed to generate these data.

Sporicidal activity of a new low-temperature sterilization technology: the Sterrad 50 sterilizer

This study was undertaken to evaluate the efficacy of a new low-temperature sterilization system that recently has been cleared by the Food and Drug Administration, the Sterrad 50. Flat stainless steel carriers were inoculated with approximately 10(6) Bacillus stearothermophilus spores. These carriers were placed aseptically in the middle of 40-cm-long stainless steel-lumened test units of varying diameters (1 mm, 2 mm, and 3 mm). After inoculation, the test units were processed in the Sterrad 50. After sterilization, the carriers were assayed for growth of the B. stearothermophilus spores. Our data demonstrated that the Sterrad 50 was highly effective in killing the B. stearothermophilus spores (no positive carriers with 30 tests of each lumen-diameter test unit). The Sterrad 50 is likely to be clinically useful for the sterilization of heat-sensitive medical equipment.

Thermal resistance of bacterial spores in milk-based beverages supplemented with nisin

The effect of nisin, added in the form of Nisaplin, on the thermal resistance of bacterial spores and the effects of medium composition, exposure time, and pH on nisin enhancement of heat sensitivity were evaluated. Nisin apparently required specific nutrients to sensitize spores to heat. For example, D130 degrees C values of approximately 10 s were observed in sodium phosphate buffer with and without 6% sucrose with no significant (P> or =0.05) differences detected as a result of increased nisin concentration. In a nutrient-rich chocolate milk model system (CMMS), increasing either the time of exposure to nisin (5, 15, or 24 h) before heating or nisin concentration (0, 2,000, or 4,000 IU/ml) increased the sensitivity of Bacillus stearothermophilus spores to heat. In the CMMS with 10 to 12% fat cocoa powder, increasing nisin concentration (at 5 h of exposure) significantly (P< or =0.05) reduced D130 degrees C values; D130 degrees C values were 21.7, 17.2, and 17.8 s, respectively, for the 0-, 2,000-, and 4,000-IU/ ml nisin treatments. Fifteen and 24 h of exposure further reduced D130 degrees C values in the nisin-containing treatments compared to the control (0 IU of nisin per ml). A lower-fat CMMS (0 to 1% fat cocoa powder) had lower D130 degrees C values (19.3, 15.8, and 14.7 s for the 0-, 2,000-, and 4,000-IU/ml nisin treatments, respectively). Nisin activity was enhanced by lowering pH in the CMMS (10 to 12% fat cocoa powder), with reductions in D130 degrees C values across all pH values (ranging from 18.0% at pH 6.4 to 41.9% at pH 5.0). zD values were 9.6, 9.0, and 8.4 degrees C for the 0-, 2,000-, and 4,000-IU/ml nisin treatments, respectively. Spores of B. licheniformis yielded results similar to those obtained with B. stearothermophilus. For example, decreasing CMMS (10 to 12% fat cocoa powder) pH values from 6.4 to 5.0 produced D100 degrees C values of 3.3, 2.8, and 2.8 min (pH 6.4) and 1.0, 0.8, and 0.8 min (pH 5.0) for the 0-, 2,000-, and 4,000-IU/ml nisin treatments. This study clearly verified that the addition of Nisaplin to dairy-based beverages, such as a chocolate milk drink, or other foods intended to be heated reduces the thermal resistance of selected bacterial spores. Increased spore sensitivity to heat may provide food processors with an opportunity to reduce their thermal processes and expenses while maintaining product quality, functionality, and shelf stability.

Nisin in milk sensitizes Bacillus spores to heat and prevents recovery of survivors

Decimal reduction times (D values) were determined for Bacillus cereus T spores and B. stearothermophilus ATCC 12980 spores in skim milk supplemented with various concentrations (0, 2,000, and 4,000 IU/ml) of the bacteriocin nisin by using an immersed, sealed capillary tube procedure. For both organisms, the addition of nisin lowered the apparent D values. For B. cereus, the addition of 2,000 IU of nisin per ml to skim milk before heating significantly (P< or =0.05) lowered the apparent D value compared to the control treatment. The D values at 97 degrees C were 7.0, 4.8, and 4.7 min for the control and 2,000- and 4,000-IU/ml nisin treatments, respectively. At 103 degrees C, the D values were 1.5, 0.85, and 0.88 min for the control and 2,000-and 4,000-IU/ml nisin treatments. When calculated across both nisin treatments, the mean reductions in apparent D values at 97, 100, and 103 degrees C due to addition of nisin in comparison to the controls were 32, 20, and 42%, respectively. The zD values for B. cereus ranged from 8.0 to 8.9 degrees C. With B. stearothermophilus, the apparent D values at 130 degrees C were reduced by 13 and 21% respectively, because of the presence of 2,000 or 4,000 IU of nisin per ml. The D values were 16.0, 13.8, and 12.5 s for the control and 2,000- and 4,000-IU/ml nisin treatments, respectively. There was a significant (P< or =0.05) decrease in the apparent D value between the control and 4,000-IU/ml treatment. Overall, log populations of survivors for B. stearothermophilus compared to the control were lower at any given sampling time due to the presence of nisin. The results of these studies suggest that spore control is likely due to enhanced sensitivity of spores to heat and the presence of residual nisin in the recovery medium that could prevent outgrowth of survivors.

Phylogenetic analysis of transformable strains of thermophilic Bacillus species

Few strains of thermophilic Bacillus spp are readily transformable with plasmid DNA. Given the considerable phylogenetic and phenotypic diversity amongst thermophilic bacilli, we have examined whether transformability is a trait associated with a particular phylogenetic group, by sequencing the 16S ribosomal RNA genes from transformable strains NUB3621, K1041, and NRRL1174. Although all of these strains were described in the literature as B. stearothermophilus, only NRRL1174 is closely related to the type strain of this species. Based on its 16S rDNA sequence and physiological data K1041 appeared to belong to the species B. thermodenitrificans, while NUB3621 showed a slightly closer relationship to B. thermoglucosidasius than to B. stearothermophilus. Therefore we conclude that the trait of transformability, though possibly strain-specific, is not limited to a single species of thermophilic Bacillus.

Microbiological efficacy of superheated steam. I. Communication: results with spores of Bacillus subtilis and Bacillus stearothermophilus and with spore earth

For the spores of Bacillus subtilis and Bacillus stearothermophilus as well as for spore earth (acc. DIN 58,946 Part 4 of August 1982), the dependence of resistance on the superheating of the steam used to kill germs was determined. A material (glass fibre fleece) was used as the germ carrier which does not superheat on contact with steam. The temperature of the saturated steam was 100 degrees C (B. subtilis) and 120 degrees C (B. stearothermophilus and spore earth). The yardstick for the resistance of the spores or bioindicators was the exposure period of the saturated or superheated steam at which 50% of the treated test objects no longer showed any viable test germs. The spores of Bacillus subtilis were far more sensitive to superheating of steam and reacted far more than the spores of Bacillus stearothermophilus and the germs in the spore earth. When superheating by 4 Kelvin the spores of Bacillus subtilis were approximately 2.5 times more resistant than they were to saturated steam. The resistance of Bacillus stearothermophilus and spore earth was only slightly higher up to superheating by 10 Kelvin. The spores of Bacillus subtilis had the highest resistance during superheating by 29 Kelvin; they were 119 times more resistant than they were to saturated steam. The resistance maximum of the spores of Bacillus stearothermophilus was at an superheating by around 22 Kelvin. However, the spores were only 4.1 times more resistant than they were to saturated steam. When using steam to kill germs, we must expect superheated steam. This raises the question whether the spores of Bacillus stearothermophilus, with their weaker reaction to the superheating of steam, are suitable as test germs for sterilisation with steam in all cases.

Biological indicators for steam sterilization: characterization of a rapid biological indicator utilizing Bacillus stearothermophilus spore-associated alpha-glucosidase enzyme

The alpha-glucosidase enzyme was isolated from vegetative cells and spores of Bacillus stearothermophilus, ATCC 7953. Spore-associated enzyme had a molecular weight of approximately 92,700, a temperature optimum of 60 degrees C, and a pH optimum of 7.0-7.5. The enzyme in crude aqueous spore extract was stable for 30 min up to a temperature of 65 degrees C, above which the enzyme was rapidly denatured. The optimal pH for stability of the enzyme was approximately 7.2. The alpha-glucosidase in crude vegetative cell extract had similar characteristics to the spore-associated enzyme but its molecular weight was 86,700. The vegetative cell and spore-associated enzymes were cross-reactive. The enzymes are postulated to derive from a single gene product, which undergoes modification to produce the spore-associated form. The location of alpha-glucosidase in the spore coats (outside the spore protoplast) is consistent with the location of most enzymes involved in activation, germination and outgrowth.

Predictive model to describe the combined effect of pH and NaCl on apparent heat resistance of Bacillus stearothermophilus

The combined effect of pH and NaCl on the apparent thermal resistance of Bacillus stearothermophilus ATCC 12980 spores was studied. Spores were heated at different temperatures (115-125 degrees C) in mushroom substrate, acidified using glucono-delta-lactone to different pH levels (from 5.75 to 6.7), which contained concentrations of NaCl that ranged from 0.5 to 3% (w/v). The recovery medium was acidified to the same pH level and contained the same NaCl concentration as the heating menstruum. A factorial experimental design allowed a predictive model to be developed, which described the combined effect of heating temperature, pH and NaCl on the thermal resistance of B. stearothermophilus spores. Predictions from the model provided a valid description of the data used to generate the model, and agreed with observations from the literature and from an independent experiment performed using asparagus and bean substrates.

Bacillus stearothermophilus sporulation response to different composition media

To evaluate the effectiveness of 11 commonly used ingredients to improve Bacillus stearothermophilus ATCC 7953 sporulation, with high spore yields in a short period of incubation, 32 composition media were set up by a fractional factorial 2IV11-6 design at two levels: D-glucose (0.018-0.25%), L-glutamic acid (0.040-0.10%), yeast extract (0.050-0.40%), peptone (0.30-0.50%), sodium chloride (0.001-1.0%), magnesium sulfate (0.001-0.20%), ammonium phosphate (0.010-0.035%), potassium phosphate monobasic (0.050-0.25%), calcium chloride (0.001-0.05%), ferrous sulfate (0.0003-0.002%), manganese sulfate (0.001-0.50%). The largest variation on Log10 CFU response took place due to sodium chloride main effect, by changing it from low to high levels. Magnesium sulfate, calcium chloride, and ferrous sulfate were split and exerted no detectable main effect influence on sporulation. Setting up two 16 runs for sodium chloride effect, in each of which the remainder levels were kept constant, other components contribution was studied. At low sodium chloride, best average 7.25 Log10 CFU yielded by fastening yeast extract and peptone at high level, and remainders at low level. Considering high level of sodium chloride, peptone, yeast extract and ammonium phosphate kept at high level and remainders at low level confirmed the best sporulation yield. Adjusted models evidenced a strong influence of joint yeast/peptone effect, associated to ammonium phosphate contributing positively. The reduced incubation period from 15 days to 3-6 days at 62 degrees C was attained for all 32 experimental runs.

Comparative evaluation of the sporicidal activity of new low-temperature sterilization technologies: ethylene oxide, 2 plasma sterilization systems, and liquid peracetic acid

OBJECTIVE

This study was undertaken to evaluate the efficacy of 4 new low-temperature sterilization technologies: ethylene oxide with hydrochlorofluorocarbons, a liquid peracetic acid immersion system (Steris System 1 Processor), and 2 plasma sterilization processes that use vaporized hydrogen peroxide (Sterrad 100 and the Sterrad 100S). The Sterrad 100S system potentially improves sterilizer efficacy by using 2 cycles of a diffusion stage and a plasma stage per sterilization cycle.

METHODS

Flat stainless steel carriers were inoculated with approximately 10(6) Bacillus stearothermophilus spores. These carriers were aseptically placed in the middle of 40 cm long stainless steel lumens (hollow tubes). Two types of lumen were used:(1) a lumen test unit with a removable 5 cm center piece (1.2 cm diameter) of stainless steel sealed to the narrower steel tubing by hard rubber septums and (2) a straight lumen. Three different diameters of the lumen test unit (1, 2, and 3 mm) and a single diameter of the straight lumen (3 mm) were studied. At least 40 replicates were performed for each type of lumen and sterilization method. After inoculation, the test unit was evaluated in 1 of the low-temperature sterilization technologies. After sterilization, the carriers were cultured in trypticase soy broth for 14 days at 55 degrees C and assessed for growth of B stearothermophilus spores.

RESULTS

Our results demonstrated that ethylene oxide with hydrochlorofluorocarbons, the Sterrad 100s, and the Sterrad 100S half cycle were highly effective in killing approximately 10(6) B stearothermophilus spores present in the center of narrow-lumen stainless steel tubes. As the lumen diameter decreased with the lumen test unit, the Sterrad 100 demonstrated reduced ability to kill B stearothermophilus spores present on the carrier. At the smallest diameter tested (1 mm), the Sterrad 100 system failed 74% of the time. The Steris System 1 was not effective in completely eliminating the 10(6) inoculum under test conditions.

CONCLUSION

The Sterrad 100S was significantly superior to the Sterrad 100 system and equivalent to ethylene oxide with hydrochlorofluorocarbons. Introduction of this new Sterrad 100S system should improve the margin of safety and reduce processing costs by its use of a shorter cycle time. The Steris System 1 is limited by diffusion of the chemical sterilant into the interior of the lumen test unit.

Effect of lyophilization on the mechanical characteristics of a large particle and on the behavior of immobilized bacterial spores

The mechanical stability of the carrier and the behavior of the sensor element of a time-temperature integrator (TTI) after lyophilization and storage for 60 days at room temperature were studied. The results indicated that particles containing added starch at concentrations from 2 to 12% had good handling characteristics for use as TTI carriers, although mechanical resistance was lower by comparison with freshly prepared particles. Lyophilization reduced the number of viable microorganisms by 17 to 25%, depending on the length of the storage period. Variations were also observed in the count of surviving microorganisms after heating at 121 degrees C for 12 min. These variations, expressed as decimal reductions in the number of microorganisms, might reflect an effect of lyophilization on the thermal resistance of the immobilized spores.

S-layered Aneurinibacillus and Bacillus spp. are susceptible to the lytic action of Pseudomonas aeruginosa membrane vesicles

When S-layered strains of Bacillus stearothermophilus and Aneurinibacillus thermoaerophilus, possessing S-layers of different lattice type and lattice constant as well as S-(glyco)protein chemistry, and isogenic S-layerless variants were subjected to membrane vesicles (MVs) from P. aeruginosa during plaque assays on plates or CFU measurements on cell suspensions, all bacterial types lysed. Electron microscopy of negative stains, thin sections, and immunogold-labelled MV preparations revealed that the vesicles adhered to all bacterial surfaces, broke open, and digested the underlying peptidoglycan-containing cell wall of all cell types. Reassembled S-layer did not appear to be affected by MVs, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis showed that the S-(glyco)proteins remained intact. meso-Diaminopimelic acid, as a peptidoglycan breakdown product, was found in all culture supernatants after MV attack These results suggest that even though MVs are much larger than the channels which penetrate these proteinaceous arrays, S-layers on gram-positive bacteria do not form a defensive barrier against the lytic action of MVs. The primary mode of attack is by the liberation from the MVs of a peptidoglycan hydrolase, which penetrates through the S-layer to digest the underlying peptidoglycan-containing cell wall. The S-layer is not affected by MV protease.

Heat transfer and lethality considerations in aseptic processing of liquid/particle mixtures: a review

Consumer awareness and demand for nutritious yet inexpensive food products call for innovative processing techniques that have both safety and quality as primary objectives. These challenges appear to have been met by aseptic processing techniques, especially for liquid and high-acid foods. However, the extension of aseptic processing principles to low-acid foods containing discrete particles in viscous sauces has not been approved by regulatory agencies, particularly in North America. This apparent limitation is due primarily to the lack of adequate temperature monitoring devices to keep track of particles in dynamic motion, as well as to the residence time distribution of particles flowing in the continuous heat-hold-cool sections of the aseptic processing system. These problems have prompted active research to describe the phenomenal behavior of particulates through sound mathematical modeling and computer simulators. The accuracy of mathematical models depends heavily on how accurate input parametric values are. These parameters include the thermophysical properties of the carrier fluid and particles, as well as the aseptic processing system characteristics in relation to residence time distribution and the fluid-to-particle interfacial heat transfer coefficient. Apparently, several contradictory findings have been reported in the literature with respect to the effect of various processing parameters on the above-mentioned input parametric values. The need therefore arises for more collaborative studies involving the industry and academia. This review brings to perspective, the current status on the aseptic processing of particulate foods with respect to the critical processing parameters which affect the fluid-to-particle convective heat transfer coefficient associated with particulate laden products.

[Suitability of Bacillus subtilis and Bacillus stearothermophilus spores as test organism bioindicators for detecting superheating of steam]

Biological indicators used to test sterilisation procedures for their efficacy consist of a so-called germ carrier to which the microorganisms used as test organisms adhere. In previous papers we demonstrated that carriers made of filter paper on contact with saturated steam show superheating while carriers made of glass fibre fleece as well as wetted filter paper do not. Using spores of Bacillus subtilis and Bacillus stearothermophilus as test organisms we have now investigated whether and to what extent carrier superheating affects the characteristic values (t50%) of these biological indicators. The indicators were exposed to saturated steam at 100 degrees C (B. subtilis) or 120 degrees C (B. stearothermophilus) under three different exposure conditions: 1. dry (i.e. conditioned to 45% relative humidity before introduction into the sterilising chamber), freely accessible; 2. dry with a substratum and a cover of filter card-board; 3. wet (moistened with twice distilled water before introduction into the sterilising chamber), freely accessible. For previously selected exposure periods, the incidence of indicators with surviving test organisms was determined. The reaction pattern of bioindicators with spores of B. stearothermophilus was different from that of bioindicators with spores of B. subtilis. For B. subtilis, the incidence of bioindicators exhibiting surviving test organisms depended on the nature of the carries as well as on the exposure conditions. On filter paper carriers, t50% increased in the order "wet, freely accessible", "dry, freely accessible", "dry, between filter card-board". On dry and wetted glass fibre fleece, resistance was approximately the same; when the indicators were sandwiched between layers of filter card-board, t50% increased. For B. stearothermophilus, t50% was largely dependent on the carrier material alone. The values obtained for filter paper were invariably much lower than those for glass fibre fleece. As the results show, using spores of B. subtilis it is possible to detect superheating, but the steam resistance of the spores is relatively low. Spores of B. stearothermophilus are of high steam resistance but they are practically unsuitable for detecting superheating. It is imperative to search for a test organism the resistance of which against steam is sufficiently high and which at the same time is capable of reacting to superheating (equivalent to reduced humidity) by a sufficiently large increase in resistance.

Thermal resistance of Bacillus stearothermophilus spores in different heating systems containing some approved food additives

The effects of different heating systems on the heat resistance of Bacillus stearothermophilus spores (ATCC 7953, 12980, 15951 and 15952) were investigated. Spores were heated in distilled water, Sorensen buffer (0.18 mol 1-1), McIlvaine buffer (0.0025-0.18 mol 1-1), and several solutions containing sodium chloride (0.06-12%), sodium nitrite (125 ppm), potassium sorbate (0.1%) and sodium benzoate (0.1%) over a wide range of temperatures (115-140 degrees C). D-values obtained for McIlvaine and Sorensen buffers, at the same molarities, were not significantly different (P > 0.05), but decimal reduction times increased as phosphate concentrations in the solutions decreased. The concentrations, in which statistically significant differences (P < 0.05) were obtained, varied among strains. Among the additives assayed, only sodium chloride reduced heat resistance, being effective at concentrations as low as 0.06%. The z-values calculated in this study ranged from 6.99 to 8.40 with a mean value of 7.60 +/- 0.45. Although z-values observed for salt and buffers (180 mol 1-1) were slightly higher than obtained in the other conditions assayed, the difference was not statistically significant (P > 0.05).

Thermal resistance of Bacillus stearothermophilus spores on strips previously treated with calcium

Moist thermal resistance parameters of spores of B. stearothermophilus ATCC 7953, inoculated in aqueous suspensions and on strips, were evaluated at 118 degrees C and 121 degrees C, by the proposed serum-bottle-mini-autoclave method. The present work studied the effect of alkaline calcium exchange-inducing storage treatments on the viability and moist heat-resistance of B. stearothermophilus spores, stored at -18 degrees C, following impregnation into filter paper strips which had been previously treated by immersion in alkaline 0.02 M calcium acetate. The thermal resistance of B. stearothermophilus spores on strip at set work conditions as biological indicator exhibited an average medium D (121 degrees C) of 1.92 min for concentrations of 10(5)-10(6) spores per strip over 360 days of storage in a freezer. The serum-bottle-mini-autoclave measuring system resulted in reasonably accurate and reproducible BIs calibration, before using them in an equipment validation program. The calcium acetate-strip system demonstrated a very high stability (Ea = 49.95 kcal/mol) to keep the spore viability and thermoresistance over steam cycles and storage. The heat activation kinetics of spores were also studied.

[Factors modulating the sensitivity of bacterial spores to steam under pressure]

The sensitivity of spores B. subtilis and B. stearothermophilus to steam under pressure depended on the growth medium and duration of cultivation. B. subtilis and B. stearothermophilus produced the largest number of spores on medium with Mn and yeast extract. However the spores grown on the medium were not the most resistant. The resistant spores was growing up with the age of cultures. The highest level of resistance was obtained in the case of the medium with Ca, after 7-10 days of cultivation. The sporicidal effect of steam under pressure depended on the number of spores on the test.

Biological indicators for low temperature steam and formaldehyde sterilization: the effect of defined media on sporulation, growth index and formaldehyde resistance of spores of Bacillus stearothermophilus strains

Preliminary screening was carried out on spores of 29 strains of Bacillus stearothermophilus to determine their potential as biological indicator organisms for low temperature steam and formaldehyde sterilization. Each strain was sporulated on four chemically defined media. Fourteen strains produced satisfactory sporulation on one or more of the media but there was considerable variation in the extent of sporulation. The growth index of the spores, which was dependent on both the strain of organism and the sporulation medium, ranged from 1% to 90%. The spores were appraised on the basis of their resistance to inactivation by 0.5% w/v formaldehyde in aqueous solution at 70 degrees C. The survivor curves obtained could be characterized into five types on the basis of the shape of the curve. Only five strains of Bacillus stearothermophilus produced spores with the characteristics of high resistance, linear semi-logarithmic survivor curve and high growth index that would be required of a potential biological indicator organism.

[Microbial resistance to formaldehyde. III> Dependence of the microbial effect on Staphylococcus aureus, Enterococcus faecium and spores of Bacillus stearothermophilus on temperature]

Temperature dependence of microbicidal efficacy of formaldehyde was examined with suspension tests (pH 7.0). Test germs were Staphylococcus aureus, Enterococcus faecium and spores of Bacillus stearothermophilus. The methodology was nearly the same as in previous investigations (5, 7). At given exposure periods and temperatures formaldehyde concentrations necessary to produce a microbicidal effect of log (N/N0) = -4.0 (concentrations of equal efficacy) were determined. N and N0 represent the numbers of colony-forming units in suspensions with and without formaldehyde, respectively. On rectangular graphic representation with the reciprocal value of absolute temperature on the abscissa and with the logarithm of the formaldehyde concentration on the ordinate, the formaldehyde concentrations of equal efficacy fitted straight lines. Lines referring to different exposure periods nearly paralleled each other. With increasing exposure periods the steepness of the lines decreased slightly. This effect was most pronounced with Staphylococcus aureus as a test germ. The ratio of formaldehyde concentrations of equal efficacy for exposure periods of 120 minutes at 20 degrees C and 30 degrees C, respectively, was 3.1:1 with Staphylococcus aureus, and 2.8:1 with Enterococcus faecium. The corresponding ratio obtained with spores of Bacillus stearothermophilus and referring to 60 degrees C and 70 degrees C, respectively, was 3.6:1. The logarithms of these ratios decreased with temperature in the same measure as the pertinent absolute temperatures increased. On the basis of the previously presented three-dimensional model of the relations between concentration, period of action and efficacy of microbicidal agents, it could be shown that deviations of the results from a linear and parallel course reflect an inconstant concentration exponent. When low formaldehyde concentration, long exposure period and "high" temperature coincide, the efficacy of formaldehyde is lower than calculated for a linear and parallel course of the relation.

Effect of rubber stopper composition, preservative pretreatment and rinse water temperature on the moist heat resistance of Bacillus stearothermophilus ATCC 12980

Bacillus stearothermophilus spores (liquid suspension) were inoculated onto rubber stoppers and exposed to sublethal steam sterilization cycles at 120 degrees C. The D-values were determined using the fraction-negative method. An increase in heat resistance (D-value) of 200%-400% was observed when the spore suspension was inoculated onto rubber stoppers. The D-values ranged from 4.90-6.96 minutes 120 degrees C. No significant effect was seen when different preservatives were added to the stoppers nor when hot or cold rinse water temperatures were used after processing.