Modelling the effect of pH, acidulant and temperature on the growth rate of Yersinia enterocolitica

Growth of two pathogenic and one environmental serotype of Yersinia enterocolitica under acidic conditions and at 4 and 25 degrees C was investigated. At both temperatures the maximum growth inhibitory pH depended on the acidulant used and was in the order acetic greater than lactic greater than citric greater than sulphuric. At the lower temperature the maximum growth inhibitory pH was 0.3-0.5 pH units higher than at 25 degrees C. No difference was observed between the behaviour of pathogenic and environmental serotypes in this respect. Measurement of growth at a number of sub-optimal temperatures and pH values showed that the variation of growth rate with temperature could be represented by a square root plot. The effect of different pH values could be incorporated into the model by replacing the regression coefficient b by its relationship with pH. Values of maximum growth inhibitory pH derived from the model were in good agreement with experimental values with the exception of acetic acid.     

The effect of pH, acidulant and temperature on the survival of Yersinia enterocolitica

The survival of Yersinia enterocolitica at sub-optimal temperatures (0–23°C) and growth inhibitory pH values, achieved using a range of acidulants, was investigated. At a given pH, survival was greater the lower the temperature. Sulphuric and citric acids had lower bactericidal activity than acetic and lactic acids and in nearly all cases where the four acids could be compared at the same pH the order of bactericidal activity was acetic > lactic > citric > sulphuric. Attempts to model this behaviour by a negative square root relationship gave good correlation coefficients for plots of the square root of death rate against temperature at different combinations of pH and acidulant but so too did several other functions of death rate. The high coefficient of variation for T ₀ determined from square root plots prevented construction of a combined temperature/pH model similar to that already described for growth.     

The influence of pH, temperature and organic acids on the initiation of growth of Yersinia enterocolitica

The influence of incubation temperature, and of acetic, lactic and citric acids on the minimum pH for the initiation of growth of six strains of Yersinia enterocolitica was determined. The strains included two of serotype O : 9, two of serotype O : 3, and one each of serotypes O : 8 and O : 5, 27. In a culture medium acidified with HC1 to pH values between 4.0 and 6.0 at intervals of approximately 0.1 unit the minimum pH at which growth was detected after incubation at 20°, 10°, 7° and 4°C for 21 d was in the ranges 4.18–4.36, 4.26–4.50, 4.36–4.83 and 4.42–4.80, respectively. The minimum pH for growth was also determined in media that contained 17, 33 and 50 mmol/1 acetic acid adjusted to pH values between 5.1 and 5.9 at intervals of approximately 0.2 unit, 24, 48 and 95 mmol/1 citric acid adjusted to pH values between 41 and 4.9 at intervals of approximately 0.2 unit, and 22, 44, and 111 mmol/1 lactic acid adjusted to pH values between 4.3 and 5.7 at intervals of approximately 0.4 or 0.5 unit. The effect of these concentrations of organic acids was, in most cases, to increase the minimum pH that allowed growth. The order of effectiveness of the organic acids in raising the minimum pH for growth was acetic > lactic > citric and the minimum inhibitory concentrations were greater at higher temperatures.     

The Biology of Trypanosoma diemyctyli, Tobey. III. Factors influencing the cycle of Trypanosoma diemyctyli in the vertebrate host Triturus v. viridescens.

SYNOPSIS. The effects of some environmental influences on the cycle of Trypanosoma diemyctyli in Triturus v. viridescens are described. Bleeding of the host produced a reduction in the number of trypanosomes but did not affect their growth rate. The temperature at which the host was maintained affected the cycle of the trypanosomes. The length of the post-inoculation latent stage increased from 24 hours at 25°C. to an indefinitely long time at 5°C. The trypanosomes were found to be dimorphic. Adult parasites of the short form had a range of 45–75 μ and those of the long form of 76–116 μ. Growth rate of the trypanosomes was inhibited or greatly retarded at temperatures of 10°C. or lower and was greatest at 25°C. The size attained by the parasites and the number of parasites were greatest at 15°C. At this temperature the infection was pathogenic and the dimorphic parasites were in their long form. At the higher temperatures (20–25°C.) the infection was non-pathogenic with the trypanosomes in their short form.
The infection is primarily one of adult newts. Experiments indicated that the larvae were resistant to the trypanosomes at all temperatures while the red efts were not. The latter are usually free from the trypanosomes because they are not exposed to them. Attempts to infect other newts and to locate any cryptic stages by the injection of blood and tissues from infected newts gave negative results.
Starvation, sodium salicylate, and treatments used to control fungus infection of the newts had no detectable effects on the trypanosomes.     

Significance of temperature and preincubation temperature on survival of Listeriamonocytogenes at pH 4·8

Listeria monocytogenes is a food-borne pathogenic bacterium that can be found in softcheese. At the beginning of cheese ripening, the pH is about 4·85–4·90. The aimof this work was to study the influence of temperature, preincubation temperature (temperature atwhich the inoculum was cultivated) and initial bacterial concentration on the survival of L.monocytogenes (strain Scott A) at pH 4·8. It was demonstrated in an earlier study thatthese factors did influence growth kinetics. Survival studies of L. monocytogenes weredone in a laboratory broth simulating cheese composition. Four test temperatures (2, 6, 10 and14°C) and two preincubation temperatures were studied (30°C or the test temperature). Listeria monocytogenes (strain Scott A) was unable to grow at pH 4·8 under allconditions tested. The time for 10% survival was about 11 and 2 d, at 2°C with preincubationat 2°C and 30°C, respectively; 9 d at 6°C with preincubation at 6°C; 4 d at 6°Cwith preincubation at 30°C; and 1 d at 14°C with preincubation at 14°C or at 30°C.The results show that survival of L. monocytogenes (strain Scott A) at pH 4·8 is notdependent on initial bacterial concentration but on both the test and preincubation temperatures.     

Hydrogen ion concentration in the gastrointestinal tract of channel catfish

Hydrogen ion concentrations (pH) of the digestive tracts of channel catfish were determined for fish of two sizes (892 and 134 g average weight) at two environmental temperatures (28 and 23°C). Acidic conditions (pH 2–4) were present in the stomach contents of all catfish with slightly higher pH values in stomachs of fish at 28°C. The pH increased to slightly alkaline values (pH 7–9) in the duodenum and reached a maximum level (pH 8.6) in the upper intestinal region and then decreased in the lower segments to approach neutrality in the colon. The pH of the bile ranged from 6.1 to 7.5 and was higher in fish maintained at 28°C. Higher environmental temperatures (28°C) resulted in a slightly lower pH throughout the intestinal and colon segments. The larger catfish had lower intestinal length/body weight ratios than smaller catfish. As the result of distension due to increased food consumption, catfish maintained at 28°C had shorter intestinal tracts than catfish maintained at 23°C.     

Effects of temperature and ration level on the growth and food conversion efficiency of Salmo gairdneri, Richardson

The effects of temperature and ration size on the growth rate and gross efficiency of food conversion of juvenile rainbow trout Salmo gairdneri were evaluated during 25-day seasonal experiments. Rations ranged from near-starvation to repletion levels. Test temperatures were 3 and 6°C higher than the controls which fluctuated dielly and seasonally. At rations near maintenance, elevated temperatures decreased trout growth. As the feeding rate increased the detrimental effect of temperature on growth was ameliorated. At repletion feeding levels, elevated temperature up to 17°C improved trout growth by increasing the maximum food consumption rate. With a temperature increase from 6.9 to 22.5°C maintenance rations increased from 2.2 to 7.5 % body weight per day. Gross efficiency was dependent upon ration level and temperature. As the food consumption rate increased, efficiency increased to a maximum, then generally declined at repletion levels. Elevated temperatures resulted in reduced efficiencies at low consumption rates but temperatures had little effect at high ration levels. A field study provided estimates of the food consumption relationships established in the laboratory, suggested any substantial increase of stream temperature without a concomitant increase of food abundance would result in decreased trout production.     

Influence of acidity and initial substrate temperature on germination of Rhizopus oligosporus sporangiospores during tempe manufacture

J.C. DE REU, F.M. ROMBOUTS AND M.J.R. NOUT. 1995. During the soaking of soya beans according to an accelerated acidification method organic acids were formed, resulting in a pH decrease from 6·0 to 3·9. After 24 h of fermentation at 30°C, lactic acid was the major organic acid (2·1% w/v soak water), while acetic acid (0·3% w/v soak water) and citric acid (0·5% w/v soak water) were also found. During cooking with fresh water (ratio raw beans: water, 1: 6·5) the concentrations of lactate/lactic acid and acetate/acetic acid in the beans were reduced by 45% and 51%, respectively.
The effect of organic acids on the germination of Rhizopus olgosporus sporangiospores was studied in liquid media and on soya beans. Germination in aqueous suspensions was delayed by acetic acid: within 6 h no germination occurred at concentrations higher than 0·05% (w/v incubation medium), at pH 4·0. When soya beans were soaked in the presence of acetic acid, the inhibitory concentration depended on the pH after soaking. Lactic acid and citric acid enhanced germination in liquid medium, but not in tempe.
Inoculation of soya beans with R. oligosporus at various temperatures followed by incubation at 30°C resulted in both increased and decreased periods for the lag phase of fungal growth. A maximum difference of 3 h lag phase was found between initial bean temperatures of 25 and 37°C.
When pure cultures of homofermentative lactic acid bacteria were used in the initial soaking process, less lactic acid and acetic acid was formed during soaking than when the accelerated acidification method was used. This resulted in a reduction of the lag phase before growth of R. oligosporus by up to 4·7 h.     

Cold-tolerant (psychrotrophic) moulds and blue stain fungi from softwood in Sweden. Growth rates in relation to pH and temperature

Seventy isolates of moulds and blue stain fungi ( Zygomycota and Deuteromycota ), isolated from discoloured outdoor softwood in Sweden, comprising of 27 different species, (the two largest genera Penicillium and Cladosporium ) were investigated for their linear growth at three different start-pH values (5, 7 and 9.5) at two temperatures (2°C and 24°C) on malt extract agar (MEA). At 24°C all isolates showed growth at all three start-pH values except for one isolate which did not grow at initial-pH 9.5. After 21 days at 2°C at the three start pH-values, only six isolates showed no growth indicating that 64 of the isolates were cold-tolerant (psychrotrophic). Of these 64 strains, 58 showed growth at an initial pH of 9.5. Lower pH optima at 2°C than at 24°C were found for most of the isolates. The reduction of the linear growth at initial pH 9.5 in relation to the growth at optimal pH was more pronounced (higher) at the low temperature.     

The effects of temperature and pH on the growth of yeast species during the fermentation of grape juice

The effects of temperature and pH on the survival and growth of Saccharomyces cerevisiae, Kloeckera apiculata, Candida stellata, Candida krusei, Candida pulcherrima and Hansenula anomala were examined during mixed culture in grape juice. At 25°C, pH 3.0 and pH 3.5, S. cerevisiae dominated the fermentation and the other species died off before fermentation was completed. Saccharomyces cerevisiae also dominated the fermentation at 20°C but there was increased growth and survival of the other species. At 10°C the fermentation was dominated by the growth of both S. cerevisiae and K. apiculata and there was extended growth and survival of C. stellata and C. krusei. Juices fermented at 10°C exhibited ethanol concentrations between 7.4 and 13.4% and populations of K. apiculata, C. stellata and C. krusei in the range 10⁶-10⁸ cells/ml. However, these species produced maximum ethanol concentrations in the range 2.7–6.6% when grown as single cultures in grape juice.     

Isolation of a Pseudomonas species from fish intestine that produces a protease active at low temperature

A psychrotrophic bacterium producing a protease active at low temperatures was isolated from fish intestine and identified as a Pseudomonas species. Optimum growth and protease-producing temperatures of this strain were 15°C and 10°C, respectively. The maximum temperature for proteolytic activity was 25°C, an unusually low temperature.     

Effects of environmental factors on survival, growth, and production of American shad larvae

Episodic increases in temperature of 5°C above 20° C, over 48 h or declines in pH of 1·0 unit from pH 7·0 reduced survival of yolk-sac and feeding-stage larvae of American shad Alosa sapidissima . Over 16 days all measures of survival, growth, and production were more favourable at each higher temperature in the 15–25° C range. More favourable responses were also obtained at the higher prey level (500 v . 50 Artemia nauplii l^-1) and at the higher pH (7·5 v . 6·5). Combinations of high temperature and high prey levels, at pH 7·5, led to highest larval production. Little growth or production occurred at 15° C, regardless of pH or prey level. The effect of pH was strong with respect to survival, but weak with respect to growth. In attempts to restore American shad populations by larval stocking, release times and sites can be critical to optimize survival and eventual returns. Releases of larvae potentially will be most effective when made at temperatures >20° C, pH>7·0, and prey levels >50 1^-1. These conditions are most likely to occur in Maryland tributaries of Chesapeake Bay between mid-May and early June.     

Effect of temperature and pH onCandida blankii in chemostat culture

The growth characteristics ofCandida blankii as a function of temperature and pH in a simulated bagasse hemicellulose hydrolysate were determined in chemostat culture. The highest maximum specific growth rate of 0.44h^–1 was reached at 38°C and at pH 5.5, with a sharp decrease in growth rate on either side of this temperature. Growth occurred at 46°C but not at 48°C. The protein and cell yields varied little below 40°C and the respective values were 0.22 and 0.5 g/g at 38°C. At the lower pH values, a severe linear decrease in cell and protein yields occurred, whereas a small increase in these yields at decreasing pH values was found when acetic acid was omitted from the medium. In the presence of acetic acid, a very sharp decrease in the growth rate at pH values below pH 4.5 was noted, despite the very low residual acetic acid concentrations, of less than 50 mg/l, in the culture.     

Water temperature fluctuations and territoriality in the intertidal zone: two possible explanations for the elevational distribution of body size in Graus nigra

On the central coast of Chile, distribution of body size in Graus nigra varied with tidal pool height. With the objective of determining whether environmental temperature is one of the possible causes which explains the observed distribution pattern, two behavioural responses were analysed during an experimental period of increasing water temperature: number of opercular movements (an indirect measure of energy expenditure) and activity levels. The interactions of temperature × time and body size × time had a significant effect on the number of opercular movements. At low temperatures (13–15° C), large fish reached a maximum number of opercular movements, while small fish reached a maximum only at high temperatures (23–25° C). The interaction temperature × time had a significant effect on activity levels of different body sizes. In general, large fish appeared to be less active than small fish, however, at very high temperatures (24–26° C) all individuals increased their activity levels. These data indicate that small fish are acclimatized to live in a wider range of temperatures (13–23° C), and, for fish of all body sizes, the highest temperatures (23–26° C) probably constitute a suboptimal microhabitat. Strong territoriality was observed, with large individuals displacing smaller individuals. These data suggest that temperature is an important factor in explaining why large individuals are not present in high tidal pools (high temperatures), whereas territoriality explains why small individuals are not in low tidal pools (habitat of large individuals).     

The effect of temperature and ageing on root apical meristems during seedling growth of Triticum aestivum L.: a specific effect on nucleoli

Abstract. Growth and cytology of root apical meristems of Chinese Spring wheat were studied in relation to temperature. The maximum rate of growth increased with temperature, a marked rise occurring between 10°C and 12°C. At all temperatures studied nucleolar volume increased to a maximum and then declined. The maximum nucleolar size achieved showed particular temperature sensitivity, higher volumes being attained at lower temperatures. The peak at 5°C was 70% higher than at 20°C. However, in comparison, cell and nuclear volumes were only 38% and 47% larger, respectively. Ultrastructural analysis of the nucleoli revealed a temperature-dependent relationship between the proportion of granular component and dense fibrillar component. The results are discussed in relation to the regulation of ribosome synthesis and function during growth and development at different temperatures.     

The combination effect of pH, SO2, ethanol and temperature on the growth of Leuconostoc oenos

A factorial design was used to determine the main effects and interactions of pH (3.6, 3.8 and 4.0), SO₂ (25 and 50 mg/l), ethanol (7%, 10% and 13%, v/v) and temperature (15°C and 25°C) on the growth of 54 Leuconostoc oenos strains. These differed greatly in their ability to survive adverse conditions. Under the test conditions, temperature had a profound effect on growth. The power pH values of 3.6 and 3.8 had a marked inhibitory effect on growth, as did at the lower temperature of 15°C. The higher concentrations of SO₂ (50 mg/l) and ethanol (13%) had the greatest inhibitory effect on growth, and with a synergistic effect when both SO₂ and ethanol were added to the test medium. Based on these results, five strains were selected that were best capable of surviving the adverse conditions studied. These strains will be used for further study on the induction of malolactic fermentation in wine.     

Evaluation of the effects of various culture conditions on Cr(VI) reduction by Shewanella oneidensis MR-1 in a novel high-throughput mini-bioreactor

The growth and Cr(VI) reduction by Shewanella oneidensis MR-1 was examined using a mini-bioreactor system that independently monitors and controls pH, dissolved oxygen (DO), and temperature for each of its 24, 10-mL reactors. Independent monitoring and control of each reactor in the cassette allows the exploration of a matrix of environmental conditions known to influence S. oneidensis chromium reduction. S. oneidensis MR-1 grew in minimal medium without amino acid or vitamin supplementation under aerobic conditions but required serine and glycine supplementation under anaerobic conditions. Growth was inhibited by DO concentrations >80%. Lactate transformation to acetate was enhanced by low concentration of DO during the logarithmic growth phase. Between 11 and 35 degrees C, the growth rate obeyed the Arrhenius reaction rate-temperature relationship, with a maximum growth rate occurring at 35 degrees C. S. oneidensis MR-1 was able to grow over a wide range of pH (6-9). At neutral pH and temperatures ranging from 30 to 35 degrees C, S. oneidensis MR-1 reduced 100 microM Cr(VI) to Cr(III) within 20 min in the exponential growth phase, and the growth rate was not affected by the addition of chromate; it reduced chromate even faster at temperatures between 35 and 39 degrees C. At low temperatures (<25 degrees C), acidic (pH < 6.5), or alkaline (pH > 8.5) conditions, 100 microM Cr(VI) strongly inhibited growth and chromate reduction. The mini-bioreactor system enabled the rapid determination of these parameters reproducibly and easily by performing very few experiments. Besides its use for examining parameters of interest to environmental remediation, the device will also allow one to quickly assess parameters for optimal production of recombinant proteins or secondary metabolites.     

Antimicrobial activity of food-related Penicillium sp. against pathogenic bacteria in laboratory media and a cheese model system

Food-related Penicillium species ( n ep fy1 = rs 34) and Geotrichum candidum ( n = 11) grown on Czapek Dox and brie agar were tested for their ability to suppress growth of pathogenic bacteria. Ten out of 13 P. camemberti showed antagonistic activity while the other species did not interact significantly with the bacterial growth. The order of inhibition was: Gram-negative bacteria and Bacillus cereus > Listeria monocytogenes , Lactococcus sp. > Micrococcus sp. whereas Lactobacillus sp., Staphylococcus aureus and some Micrococcus sp. were unaffected. When Salmonella typhimurium was inoculated together with P. camemberti P25 in brie agar, bacterial growth was inhibited during the first 6 d of incubation whereafter growth started. The inhibition of L. monocytogenes was similar but less pronounced. The antimicrobial activity produced by P. camemberti P25 and L84 was enhanced with increasing amount of sucrose in the medium. The activity was increased at low pH and destroyed at pH above 8. It was detectable at 15°C but not at 37°C indicating that volatile metabolites might be involved. No significant accumulation of organic acids and no secondary metabolites such as mycotoxins were detected. HSGC-MS analysis indicated that acetaldehyde, benzaldehyde, 3-methylbutanal and 1-octen-3-ol were produced by P. camemberti during the period when inhibitory activity was observed. Pure acetaldehyde and benzaldehyde were shown to be inhibitory to L. monocytogenes and Salm. typhimurium when grown at 15°C and pH 5·5 and 7·0.     

Modelling the effectiveness of a natural antimicrobial on Salmonella enteritidis as a function of concentration, temperature and pH, using conductance measurements

The growth of Salmonella enteritidis in a brain heart infusion medium was monitored using the traditional viable count method and by conductance measurements using a Rabit impedance instrument. Growth curves (log₁₀ cfu ml⁻¹ vs time) at three different concentrations of oleuropein (0, 0·2 and 0·8%), pH values in the range of 5–8 and incubation temperatures from 22 to 42 °C were modelled using the Gompertz equation. A good correlation between the maximum growth rate from the viable count method and the maximum slope of the conductance curve from the impedance instrument was established. Based on this correlation, the maximum specific growth rate of Salm. enteritidis was modelled as a function of the oleuropein concentration, initial pH values and the incubation temperature with a quadratic equation, using a new, larger dataset of growth measurements by conductance. The developed model was validated by statistical comparison of predicted growth rates with growth rates determined by the viable count method, within the limits of the antimicrobial, pH and temperature domain.     

Temperature influences walking speed and walking activity of Trichogramma brassicae (Hym., Trichogrammatidae)

Walking speeds and walking activities (walking time divided by total time) of Trichogramma brassicae were determined at 12, 16, 20 and 25°C. Walking speed was measured during a 5-min period, and walking activity over a 4-day period. Both walking speed and walking activity were strongly influenced by temperature. Walking speed increased linearly with the temperature and was twice as high at 20 as at 12°C. At 25°C, walking activity was high during the whole day, at 20 and 16°C it decreased during the afternoon, whereas at 12°C the wasps became most active only at noon or later. At low temperatures, there was a strong individual variation in walking activity. At 25°C, T. brassicae was active most of the time, so the area searched per time unit can only increase at temperatures above 25°C if walking speed increases. At temperatures below 20°C, searching was more restricted by low walking activity than by low walking speed. Even disregarding other effects of temperature, the reduction in walking speed and walking activity at suboptimal temperatures means that T. brassicae can only search half of the area at 20°C, and only one-seventh at 15°C that it can search at 25°C.