Does proximity to neighbours affect germination of spores of non-proteolytic Clostridium botulinum?

It is recognised that inoculum size affects the rate and extent of bacterial spore germination. It has been proposed that this is due to spores interacting: molecules released from germinated spores trigger germination of dormant neighbours. This study investigated whether changes to the total number of spores in a system or proximity to other spores (local spore density) had a more significant effect on interaction between spores of non-proteolytic Clostridium botulinum strain Eklund 17B attached to defined areas of microscope slides. Both the number of spores attached to the slides and local spore density (number of spores per mm²) were varied by a factor of nine. Germination was observed microscopically at 15 °C for 8 h and the probability of, and time to, germination calculated from image analysis measurements. Statistical analysis revealed that the effect of total spore number on the probability of germination within 8 h was more significant than that of proximity to neighbours (local spore density); its influence on germination probability was approximately four-times greater. Total spore number had an even more significant affect on time to germination; it had a nine-fold greater influence than proximity to neighbours. The applied models provide a means to characterise, quantitatively, the effect of the total spore number on spore germination relative to the effect of proximity to neighbouring spores.     

Germination and growth from spores: variability and uncertainty in the assessment of food borne hazards

We have developed a model for the variability of spore lag times and shown that variability has an important role in the quantitative assessment of risks associated with spore forming bacteria in food. The model includes two sequential independent delay times that contribute to the lag time for a single spore. We have shown that a population of variable spores also has a variable lag time, and we have emphasised the significance of this variability in quantitative representations of population dynamics for small populations. We have made a Bayesian estimate for the extent of the variability in spore lag times and made a comparison with direct microscopic observations of individual spores of nonproteolytic Clostridium botulinum. We conclude that Bayesian inference is a practical method for quantifying variability and hence a significant element in the development of quantitative risk assessments for hazards associated with spore forming bacteria.     

Calculation of the total lethality of conductive heat in cylindrical cans sterilization using linear and non linear survival kinetic models

There is growing evidence suggesting that inactivation of bacterial spores may follow the Weibullian model, of which the log linear relationship between survival ratio and time is just a special case. Where true, the time and not only the temperature dependence of the rate must be taken into account. Also, it is of interest to estimate spores survival not only at the coldest point but also throughout the whole container's volume.Numerical calculation on changing survival ratios was performed by combining the conductive heat transfer model with that of the nonlinear inactivation kinetics. Results are based on published linear and non linear inactivation parameters of Clostridium botulinum spores, typical thermal properties of solid foods and realistic thermal processing conditions. Results could be used to quantify the efficacy of thermal processes of solid products in terms of spores' residual survival ratio at the coldest point and in the container as a whole.     

The content of agaritine in spores from Agaricus bisporus

Agaritine (l-glutamic acid, 5-(2-(4-(hydroxymethyl)phenyl)hydrazide)) was identified and quantified in spores of Agaricus bisporus by high resolution liquid chromatography with mass spectrometric detection using negative electrospray ionisation. The spores were collected from mushrooms purchased at the open marked in Oslo, and the agaritine was extracted in pure water before analyses. On average the agaritine content was 0.304 ± 0.003% of the spores.     

Effectiveness of Portable Indoor Air Cleaners: Sensory Testing Results

The objective of this study was to test the effectiveness of individual commercially available portable indoor air cleaning units in removing dust particulates, tobacco smoke particulate and vapor phase constituents (nicotine and vinyl pyridine), viable and total fungal spores, pollen, and gaseous contaminants (carbon monoxide[CO], nitrogen dioxide[NO²], and formaldehyde[HCHO]), in a clean air test chamber. The air cleaner chamber results presented here represent initial-use results. In general, High Efficiency Particulate Air (HEPA) and electrostatic precipitator systems demonstrated the highest efficiencies with respect to particulate, contaminants, followed closely by electret filter systems. Ionizers and ozone generators were least effective in particulate removal. Systems which included sufficient sorbent material (i.e. activated carbon or potassium permanganate) were marginally effective at gaseous contaminant removal. None of the systems tested were effective at carbon monoxide removal. Sensory testing was conducted to discern potential correlation between human perceptive response and measured air cleaner performance (with respect to tobacco smoke removal). An electret filter (EF) loaded with carbon sorbent received the best ratings with respect to odor strength, nasal irritation, eye irritation, and overall air acceptability.     

Relevant factors affecting microbial surface decontamination by pulsed light

Pulsed Light (PL) uses intense flashes of white light rich in ultraviolet (UV) light for decontamination. A log-reduction higher than 5 was obtained in one flash and at fluences lower than 1.8 J/cm² on spores of a range of spore-forming bacteria, of vegetative cells of non-spore-forming bacteria and on yeasts spread on agar media. Vegetative cells were more sensitive than spores. The inactivation by PL of Bacillus subtilis, B. atrophaeus, B. cereus, Geobacillus stearothermophilus, and Aspergillus niger spores sprayed on polystyrene was similar. The inactivation by PL of B. subtilis and A. niger spores sprayed on glass was slightly lower than on polystyrene. No alteration of the spore structures was detected by scanning electron microscopy for both PL treated B. subtilis and A. niger spores. The inactivation of spores of B. subtilis, B. atrophaeus, B. cereus and B. pumilus by PL or by continuous UV-C at identical fluences was not different, and was much higher by PL for A. niger spores. The increase in the input voltage of the lamps (which also increases the UV-C %) resulted in a higher inactivation. There was no correlation between the resistance to heat and the resistance to PL. The relative effect of UV-C radiations and light thermal energy on PL inactivation was discussed.     

Accelerated inactivation of Geobacillus stearothermophilus spores by ohmic heating

Until recently, ohmic heating was commonly thought to kill microorganisms through a thermal effect. However a growing body of evidence suggests that non-thermal effects may occur. Our aim was to determine the kinetics of inactivation of Geobacillus stearothermophilus spores (ATCC 7953) under ohmic and conventional heating using a specially constructed test chamber with capillary sized cells to eliminate potential sources of error and ensure that identical thermal histories were experienced both by conventionally and ohmically heated samples. Ohmic treatments at frequencies of 60 Hz and 10 kHz were compared with conventional heating at 121, 125 and 130 °C for four different holding times. Both ohmic treatments showed a general trend of accelerated spore inactivation. It is hypothesized that vibration of polar dipicolinic acid molecules (DPA) and spore proteins to electric fields at high temperature conditions may result in the accelerated inactivation.     

Sporulation dynamics and spore heat resistance in wet and dry biofilms of Bacillus cereus

Environmental conditions and growth history can affect the sporulation process as well as subsequent properties of formed spores. The sporulation dynamics was studied in wet and air-dried biofilms formed on stainless steel (SS) and polystyrene (PS) for Bacillus cereus ATCC 10987 and the undomesticated food isolate B. cereus NIZO 4080. After harvesting and maturation, the wet heat resistance of spores obtained from these biofilms was tested and compared to planktonic and agar plate-derived spores. Drying/air exposure of the preformed 24 h old biofilms accelerated spore formation for both strains and resulted in higher final spore percentages. Prolonged dry incubation of more than three days triggered germination of spores in the biofilms of ATCC 10987. Spores harvested from wet biofilms on SS displayed the highest heat resistance compared to liquid, agar plate and PS biofilm derived spores. The D_95 °C values for these spores were 17 and 22 min for NIZO 4080 and ATCC 10987, respectively, which was 2 and 1.2 fold higher compared to planktonic spores of these strains. Spores obtained from dried biofilms of ATCC 10987 displayed reduced heat resistance compared to wet biofilm spores. The results indicate that environmental conditions encountered by biofilms affect sporulation dynamics and spore heat resistance, thus affecting subsequent quality issues and safety risks related to these biofilms.     

Solar and photocatalytic disinfection of protozoan, fungal and bacterial microbes in drinking water

The ability of solar disinfection (SODIS) and solar photocatalytic (TiO(2)) disinfection (SPC-DIS) batch-process reactors to inactivate waterborne protozoan, fungal and bacterial microbes was evaluated. After 8 h simulated solar exposure (870 W/m(2) in the 300 nm-10 microm range, 200 W/m(2) in the 300-400 nm UV range), both SPC-DIS and SODIS achieved at least a 4 log unit reduction in viability against protozoa (the trophozoite stage of Acanthamoeba polyphaga), fungi (Candida albicans, Fusarium solani) and bacteria (Pseudomonas aeruginosa, Escherichia coli). A reduction of only 1.7 log units was recorded for spores of Bacillus subtilis. Both SODIS and SPC-DIS were ineffective against the cyst stage of A. polyphaga.     

Diversity of Bacillus megaterium isolates cultured from honeys

Bacillus megaterium isolates recovered from Argentinean honeys (n = 48) were compared with isolates recovered from honey from other countries (n = 4) and with strain NRRL B-939. All the isolates and the NRRL strain were characterized using rep-PCR fingerprinting with primers BOX-, REP- and ERIC-; restriction fragment length polymorphism analysis of a 16S rRNA gene fragment (16S rRNA PCR/RFLP), and morphological and biochemical tests. There was a high degree of diversity, both phenotypic and genotypic among the isolates of B. megaterium. Our results not only show considerable levels of diversity among isolates of B. megaterium analyzed here but also that repetitive sequences such as BOX, ERIC and REP are reliable tools to characterize isolates at the genomic level. Haemolytic activity was shown by 77% of the isolates, as β-haemolysis (40 isolates) or α-haemolysis (one isolate). Within the β-haemolytic group, 10% of isolates produced a discontinuous haemolytic pattern, which is usually correlated with enterotoxin activity in other bacterial species. In addition, coagulase activity was detected in 74% of 53 isolates tested suggesting a pathogenic activity not ordinarily reported as a property of B. megaterium. According to our knowledge, this is the first report of phenotypic and genotypic characterization of B. megaterium isolates from honey.