The effect of transient temperatures on the growth of Salmonella typhimurium LT2. I: cycling within the growth region

The effect of fluctuating temperatures on microbial growth is important in the passage of foods through the food chain. Suspensions of Salmonella typhimurium were subjected to sinusoidally time-varying temperatures of periods from 40 to 480 min within their growth temperature range. The change in the numbers of viable bacteria was measured with time and the experimental growth curves and average generation times compared with predictions based on isothermal growth data. The experimental average generation times exceeded the predictions by less than 30%, although the discrepancy increased with cycle frequency. Instantaneous growth rates obtained for the 480 min cycles were in agreement with those predicted from isothermal behaviour.     

Expanded response surface model for predicting the effects of temperatures, pH, sodium chloride contents and sodium nitrite concentrations on the growth rate of Yersinia enterocolitica

The previously reported data set for the low temperature (5, 12 and 19°C) of Yersinia enterocolitica was expanded to include higher abusive temperature (28, 37 and 42°C). In addition to temperature, the data set included the effects and interactions of pH (4.5–8.5), sodium chloride (0.5-5%) and sodium nitrite (0-200 μg ml^-1) on the aerobic growth of Y. enterocolitica in brain heart infusion broth. Growth curves were modeled by fitting viable count data to the Gompertz equation. Quadratic models of natural logarithm transformations of the Gompertz B and M values and the derived values for lag phase durations and generation times were obtained using response surface analyses. Predictions based on the models for B and M values were comparable to predictions based on the derived values. These revised models provide an expanded means for rapidly estimating how the bacterium is likely to respond to any combination of the four variables within the specified ranges.     

The effect of step changes in sucrose concentration on the growth of Salmonella typhimurium LT2

Water activity is a method of preservation that can affect microbial growth in foods and that may fluctuate during their processing, distribution and storage. Sucrose has been used to change the water activity of microbiological culture media. Suspensions of Salmonella typhimurium LT2 in the exponential phase of growth have been subjected to step changes in sucrose concentration at 20°C. The changes in the numbers of viable bacteria were measured with time and the experimental growth curves compared with predictions based on growth data obtained at constant sucrose concentrations. Steps down in sucrose concentration showed some apparent loss of viability after the step followed by growth at a rate close to the expected value. Steps up in sucrose concentration resulted in a greater apparent loss of viability after the step and either growth or the inducement of lag, depending on the final concentration of sucrose. A series of small steps up in sucrose concentration to 45% (w/v) was able to sustain growth where it was not possible by inoculation directly into this concentration. Improved recovery of bacteria subject to osmotic stress was possible with a medium containing sodium chloride.     

Effect of temperature on sulphate reduction, growth rate and growth yield in five psychrophilic sulphate-reducing bacteria from Arctic sediments

Five psychrophilic sulphate-reducing bacteria (strains ASv26, LSv21, PSv29, LSv54 and LSv514) isolated from Arctic sediments were examined for their adaptation to permanently low temperatures. All strains grew at −1.8°C, the freezing point of sea water, but their optimum temperature for growth ( T _opt) were 7°C (PSv29), 10°C (ASv26, LSv54) and 18°C (LSv21, LSv514). Although T _opt was considerably above the in situ temperatures of their habitats (−1.7°C and 2.6°C), relative growth rates were still high at 0°C, accounting for 25–41% of those at T _opt. Short-term incubations of exponentially growing cultures showed that the highest sulphate reduction rates occurred 2–9°C above T _opt. In contrast to growth and sulphate reduction rates, growth yields of strains ASv26, LSv54 and PSv29 were almost constant between −1.8°C and T _opt. For strains LSv21 and LSv514, however, growth yields were highest at the lowest temperatures, around 0°C. The results indicate that psychrophilic sulphate-reducing bacteria are specially adapted to permanently low temperatures by high relative growth rates and high growth yields at in situ conditions.     

The effect of incubation temperature, sodium chloride and ascorbic acid on the growth kinetics of Aeromonas hydrophila

The effects of temperature, sodium chloride and ascorbic acid on the aerobic growth kinetics of a clinical strain of Aeromonas hydrophila were evaluated. At 5°C, ascorbic acid (1 mmol l^-1) and sodium chloride (3% w/v) inhibited the growth of the organism. At 10°C, ascorbic acid depressed only the maximum population densities (A) by approximately 2 log cycles, but not maximum specific growth rate (μ_m) or the lag time (Λ). On the contrary, NaCl caused A to increase, with the effect being greatest when the NaCl content was 1.5%. Temperature increase from 10 to 15°C resulted in an approximate doubling of μ_m and unexpectedly an apparent increase in Λ However, this apparent increase resulted from the particular manner in which the lag phase was mathematically calculated.     

Embryonic development, larval growth and life cycle of Coenagrion puella (Odonata: Zygoptera) from an Austrian pond

SUMMARY. 1. Newly-laid eggs of Coenagrion puella (L.) from a pond near Herzogenburg (Lower Austria) were kept at constant water temperatures (range c .3.5°C to c .28°C)in the laboratory. Hatching success varied with temperature; no eggs hatched below 12°C and nearly all hatched at c .l6°C. Hatching time decreased with increasing temperature and the relationship between the two variables within the range 12–28 °C was well described by a power law. The length of the hatching period was less than 12 days. Hatching times estimated from the power-law equations and those obtained in the field experiments were similar. Therefore both the hatching time and the length of the hatching period in the field could be estimated from the laboratory data for the range 12–28°C.
2. The maximum number of instars from egg to imago was 11; the average body length increment (mm) per moult was proportionately constant at c .26% and Dyar's rule was applicable. The interval between moults decreased with increasing temperature up to the seventh instar and the relationship between the two variables within the range 12–28°C was well described by a power law. The moulting interval for instars 8–11 ranged from 23 to 48 days and was relatively independent of temperature. No moulting occurred at temperatures below 12°C.
3. Larval growth was logistic in the laboratory and variations in mean logistic growth rate (range 0–2.5% length day⁻¹) were related to mean temperature with no growth at temperatures <12°C. Larval growth rates in pond experiments were similar to those estimated from laboratory data, and therefore the regression equations obtained from the laboratory experiments are probably applicable to larval growth in the field.
4. Information on the life cycle of C. puella is briefly reviewed and it is concluded that C. puella from the pond near Herzogenburg has an univoltine life cycle.     

The study of Salmonellaenteritidis growth kinetics using Rapid Automated Bacterial Impedance Technique

In order to study strain-specific differences in their growth behaviour at different, and particularly lower, temperatures, generation times for 45 strains of Salmonella enteritidis isolated from food were determined impedimetrically over a temperature range from 7 to 42 °C. In practical terms, 7 °C is the minimum requirement for Salm. enteritidis growth, and generation time variability increases markedly as this temperature is reached. Reports in the literature describing psychrotrophic behaviour and multiplication at lower temperatures cannot be confirmed. Generation time variability increased as temperature moved away from the optimal range with variation coefficients tending to rise as temperature fell. The great variability of multiplication parameters near the growth limit found in Salm. enteritidis may also be a characteristic of other bacterial species. It is therefore imperative to commence studies on larger numbers of strains to allow prediction of their behaviour at lower temperatures.     

Characteristics of micrococci from the surface of Roquefort cheese

Five different Micrococcus spp. were isolated from the surface of Roquefort cheese: M. roseus, M. sedentarius, M. lylae, M. luteus and M. varians. During culture on synthetic medium these bacteria produced acetic acid as the main volatile fatty acid and propanol as the main alcohol. On a complex medium these isolates synthesized additional volatile fatty acids. Studies were made of the effect of pH, of water activity adjusted with sodium chloride or sorbitol, and of temperature on growth rates. All five isolates were inhibited at a pH lower than 5.5 and grew at temperatures from 4° to 44°C; they were halotolerant and multiplied at NaCl concentrations up to 20%, corresponding to a water activity of 0.884.     

Efficacy of high sodium chloride concentrations for the destruction of Listeria monocytogenes

The effect of sodium chloride concentrations (6, 16 and 26% (w/v) NaCl) on the survival of Listeria monocytogenes at low temperatures (10°C and under refrigeration, average 2°C) and frozen (- 18°C) was investigated. All salt concentrations tested were ineffective in reducing numbers over 6 h incubation at low temperatures. Over a longer time (33 d) at low temperatures, the organism grew in 6% NaCl, numbers remained the same in 16% NaCl and numbers declined in 26% NaCl. Although L. monocytogenes was destroyed in 26% NaCl, numbers declined too slowly for immersion in cold brine at this concentration to be a useful bacteriocidal treatment. Storage at - 18°C for 33 d caused no significant reduction in numbers at any of the NaCl concentrations tested.     

The effect of temperature on growth and reproduction of Scytosiphon complanatus (Fucophyceae) from Greenland

Scytosiphon complanatus from Greenland was grown under long-day conditions on a temperature-gradient device with a temperature range from 5.4°C to 31.8°C. Growth was optimal between 16.0°C and 20.9°C. In a four week experimental period at 5.4°C and 7.5°C growth was slow and not measurable. The inoculated germlings died at temperatures between 24.0°C and 27.5°C. Under all temperatures the prostrate systems, knot filaments or ralfsioid thalli, as well as the parenchymatous macrothalli remained sterile during the experimental period. Prolongation of the growth period showed that formation of swarmers was prevented at temperatures above 18.6°C. The geographic distribution is discussed in relation to these results.     

Minimum water activity for the growth of Aeromonas hydrophila as affected by strain, temperature and humectant

The influence of water activity (adjusted with three humectants: sodium chloride, glycerol and polyethylene glycol) on the growth of three strains of Aeromonas hydrophila at 28, 10 and 3.8°C was studied. Minimum water activity for growth (MWAG) of Aer. hydrophila varied with strain, temperature and type of humectant. MWAG ranged from 0.940 to 0.973 (28°C), 0.959 to 0.980 (10°C) and 0.975 to 0.980 (3.8°C).     

Growth of Listeria monocytogenes at refrigeration temperatures

The growth of three strains of Listeria monocytogenes at refrigeration temperatures (-0.5 to 9.3°C) in chicken broth and/or UHT milk was determined using a rocking temperature gradient incubator. Minimum growth temperatures ranged from -0.1 to -0.4°C for the three strains. Lag times of 1–3 d and 3 to >34 d were observed with incubation at 5 and 0°C respectively. Corresponding generation times ranged from 13–24 h at 5°C and 62–131 h at 0°C. The type of culture medium had an influence on both the rate and extent of growth. Incubation of cultures at 4°C before inoculation caused a marked reduction in the lag time when compared with cultures which had been previously incubated at 30°C.     

Effect of temperature on larval growth of Ecdyonurus dispar (Ephemeroptera: Heptageniidae) from two English lakes

SUMMARY. Mature larvae of Ecdyonurus dispar were collected from Ennerdale Water and Windermere (English Lake District) and reared to adult males and females in the laboratory. The females were then fertilized artificially and their progeny were kept at constant temperatures (range 4.2–20.2°C). Larvae collected directly from the two lakes were also reared under the same conditions.
The maximum number of instars from egg to subimago was 25, the average body length increment (mm) per moult was proportionately constant at c . 15% and Dyar's rule was applicable. The interval between moults decreased with increasing temperature and the relationship between the two variables within the temperature range 4.2–19.8°C was described by a power law. Larval growth was exponential and variations in mean specific growth rate (range 0.23–5.23% length day⁻¹) were related to mean temperature which was the major factor affecting growth in the laboratory. A few experiments were also performed in the lake to test the adequacy of the estimated values for larval growth at different temperatures in the laboratory. There was agreement between the estimates and the actual growth rates in the lake. Therefore, the regression equations obtained from the laboratory experiments are probably applicable to larval growth in the field.
Values for daily production in the laboratory ranged from 0.53 to 9.33 mg dry wt day⁻¹ m⁻². The lowest value was obtained at 8.9°C and the highest at 20°C.
Information on different life cycles of E. dispar is briefly reviewed and it is concluded that E. dispar from the lakes can only achieve one generation per year.     

Upper thermal limits for feeding and growth of 0+ Arctic charr

When Arctic charr Salvelinus alpinus from two diVerent stocks were fed live Neomysis integer , the upper thermal limits for feeding and growth were established in the range 21·5–21·8° C. These critical temperatures might have been underestimates, because fish tend to show increased sensitivity to handling at high experimental temperatures. In the second experiment, the proportion of feeding undisturbed charr from four stocks decreased initially as temperature was raised in steps from 18 to 22° C. At the lower temperatures, 18 and 20) C, almost all fish resumed feeding, but the recovery time was longer and more fish ceased to feed at 20) C than at 18° C. When the temperature was increased to 21° C, 50% of the fish ceased feeding permanently, and all fish ceased feeding within 2 days at 22° C. It is concluded that 0+ charr cease to feed and grow at c .21·5) C and that the critical temperatures for feeding and growth coincide.     

Minimum water activity requirements for the growth of Listeria monocytogenes

The ability of five strains of Listeria monocytogenes to initiate growth at five different temperatures in brain heart infusion (BHI) broth adjusted to various water activity ( a _w) values with either sodium chloride (NaCl), sucrose or glycerol was investigated. Glycerol was the least toxic of the three solutes studied, with three of five strains of L. monocytogenes capable of growing in BHI broth adjusted with glycerol to an a w value of 0.90 at 30 C, compared to a w minima of 0.93 and 0.92 in broth adjusted with sucrose and sodium chloride, respectively. The minimum a w value required for growth generally increased as the incubation temperature decreased. Listeria monocytogenes appeared to tolerate glycerol and NaCl best when growing at 30 and 15°C, respectively, while for sucrose, temperature did not appear to influence growth of the organism. Listeria monocytogenes is one of the few food-borne pathogens that can grow at an a w value below 0.93.     

Thermophilic sulfate-reducing bacteria in cold marine sediment

Abstract Sulfate reduction was measured with the ³⁵SO₄²⁻ -tracer technique in slurries of sediment from Aarhus Bay, Denmark, where seasonal temperatures range from 0° to 15°C. The incubations were made at temperatures from 0°C to 80°C in temperature increments of 2°C to search for presence of psychrophilic, mesophilic and thermophilic sulfate-reducing bacteria. Detectable activity was initially only in the mesophilic range, but after a lag phase sulfate reduction by thermophilic sulfate-reducing bacteria were observed. No distinct activity of psychrophilic sulfate-reducing bacteria was detected. Time course experiments showed constant sulfate reduction rates at 4°C and 30°C, whereas the activity at 60°C increased exponentially after a lag period of one day. Thermophilic, endospore-forming sulfate-reducing bacteria, designated strain P60, were isolated and characterized as D esulfotomaculum kuznetsovii . The temperature response of growth and respiration of strain P60 agreed well with the measured sulfate reduction at 50°–70°C. Bacteria similar to strain P60 could thus be responsible for the measured thermophilic activity. The viable population of thermophilic sulfate-reducing bacteria and the density of their spores was determined in most probable number (MPN) dilutions. The density was 2.8·10⁴ cells·.g⁻¹ fresh sediment, and the enumerations suggested that they were all present as spores. This result agrees well with the observed lag period in sulfate reduction above 50°C. No environment with temperatures supporting the growth of these thermophiles is known in the region around Aarhus Bay.     

The effect of temperature on the growth of non-proteolytic type B Clostridium botulinum

The effect of temperature between 4 and 35°C on the growth rate of a non-proteolytic type B strain of Clostridium botulinum was examined. Growth was in culture media at pH 6.7 and was measured by viable counts using the Most Probable Number (MPN) method. Doubling times were derived from the curve fitting model of Baranyi et al. (1992) and ranged from 42.3 h at 3.9°C to 22 min at 35°C.     

Factors affecting the growth of Listeria monocytogenes on minimally processed fresh endive

The influence of various factors on the fate of Listeria monocytogenes on cut leaves of broad-leaved endive has been studied. Factors considered were temperature, characteristics of the leaves (age, quantity and quality of the epiphytic microflora) and characteristics of the L. monocytogenes inoculum (concentration, strain). The increases in numbers of L. monocytogenes were lower than those of the aerobic mesophilic microflora at 3°, 6°, 10° and 20°C. Doubling times of the populations of L. monocytogenes were in the same order of magnitude as those of aerobic bacteria at 10° and 20°C, but longer at 3° and 6°C. There were positive significant correlations between growth of L. monocytogenes and populations of aerobic bacteria, and between growth of L. monocytogenes and extent of spoilage on the leaves.
Of 225 bacteria isolated from the leaves, 84% were identified as fluorescent pseudomonads; there was no difference in the species isolated from leaves that showed a low growth of L. monocytogenes and leaves that showed a high growth of L. monocytogenes. Populations of L. monocytogenes increased faster during the first 2 and 4 d of storage at 10°C on leaves inoculated with 10–10³ cfu g^-1 than on leaves inoculated with about 10⁵ cfu g^-1, but the population reached after 7 d was lower. The behaviour of L. monocytogenes was similar among the three strains tested.     

Effect of freezing of water samples on viable counts of environmental mycobacteria

The effect of prolonged storage on mycobacteria and other heterotrophic bacteria in brook water samples was examined by determination of viable counts from fresh samples and again after water concentrates had been stored in nutrient broth at —75°C for 15 months. The counts of mycobacteria were on average three times higher after storage (range of ratio 0·9–10·4). In contrast, the viable counts of other heterotrophic bacteria were reduced by 69%. The increase in mycobacterial counts was probably due to break-up of microcolonies or release of attached bacteria from particles. The possibility of cultivating mycobacteria from frozen samples is of practical help in large-scale field surveys.     

Use of the Direct Epifluorescent Filter Technique for predicting the keeping quality of pasteurized milk within 24 hours

The keeping quality (KQ) of pasteurized milk stored at 5°C and 11°C was predicted within 24 h by pre-incubating samples and counting bacteria by the Direct Epifluorescent Filter Technique (DEFT). For samples from 5°C storage, 0.03% (w/v) benzalkonium chloride and 0.002% (w/v) crystal violet (final concentration) were added to inhibit the growth of Gram positive bacteria during pre-incubation. The samples from milk stored at 11°C were pre-incubated without the addition of inhibitors. After pre-incubation there was a satisfactory relationship between the DEFT count and the KQ of milks at both 5°C and 11°C. The DEFT count following pre-incubation correctly classified > 80% of pasteurized milks on the basis of KQ.