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PubMed1998

Mechanical modulation of stretch-induced premature ventricular beats: induction of mechanoelectric adaptation period.

OBJECTIVE: Mechanoelectric Feedback, a mechanical intervention inducing an electrical change, is gaining credence as a cause of cardiac arrhythmia in the clinical situation. However, the precise mechanism is unknown. To elucidate this we investigated mechanical and chemical modulation of stretch-induced premature ventricular beats. METHODS: We positioned a balloon in the left ventricle of an isolated heart (New Zealand White rabbit), perfused by the Langendorff technique. Balloon inflation regularly produces premature ventricular beats. Monophasic action potentials, ECG's and pressure recordings monitored changes, during mechanical intervention. The hearts were subjected to (i) variations in the degree of preload and duration of inflation, and (ii) cytoskeletal disrupters, colchicine and cytochalasin-B. RESULTS: Mechanical dilation of the left ventricle can not only induce premature ventricular beats, but also induce a period during which premature beats cannot be re-induced on a subsequent inflation, i.e. a mechanoelectric adaptation period. The trigger for the mechanoelectric adaptation period seems to occur immediately on balloon inflation and required up to 60 s to recover. This period started with an undershoot in the diastolic component of the monophasic action potential as well as in the peak systolic pressure, with return to control levels within the period. Deflation produced an overshoot (rather than undershoot) in the monophasic action potential duration, but this also returned to control levels within the period. Changes in preload, duration of inflation and disruption of the cytoskeleton failed to modulate the mechanically induced premature beats, or the mechanoelectric adaptation period. CONCLUSIONS: Transient ventricular stretch produces arrhythmia, followed by an antiarrhythmic adaptive period. Possible mechanisms are related to a mechanical influence on stretch-activated channels, changes in ionic concentration or diffusion, or second messenger systems, which influence membrane potential. The arrhythmic adaptation does not appear to be related to the mechanical properties of the cytoskeleton. Final elucidation of the mechanism of the mechanoelectric adaptation period demonstrated, may prove important in determining the mechanism of stretch-induced premature ventricular beats and consequently arrhythmia management.

Action Potentials↗
PubMed2001

Adaptive physiological processes in the host during gastrointestinal parasitism.

Parasite infection of the gastrointestinal tract with helminths or protozoa induces detrimental effects on host tissues and host physiology, which have been extensively studied and reviewed. However, parasitism of the digestive system is also associated with adaptive, compensatory phenomena based on changes in host physiology or structures and which tend to counterbalance the negative consequences. The objective of this review is to describe these adaptive processes and their possible underlying mechanisms. Different processes which tend to attenuate the effect of either the loss of appetite, the intestinal malabsorption or the increased tissue losses have been assessed. These processes have been reported both for helminth and protozoan infections, where they present similar characteristics. The mechanisms involved in the adaptation to parasitism remain largely unidentified. The role of feedback mechanisms based on host regulation, possibly through gastrointestinal hormones, has been raised. On the other hand, some data support the proposal that parasites themselves may initiate some of the adaptive processes and consequently favour their own survival. These adaptive phenomena appear to be an essential component in the dynamic balance between host and parasites. Also, parasite infections represent unique models to study the adaptation of the gastrointestinal tract to aggressors.

Adaptation, Physiological↗
PubMed1997

Adaptation to changes in dietary phosphorus intake in health and in renal failure.

Phosphate (Pi) homeostasis is maintained by the ability of the kidneys to adjust the tubular reabsorption of Pi to changes in the dietary intake of phosphorus. Renal tubular Pi reabsorption increases with the ingestion of a low-phosphorus diet (LPD) and decreases when a high-phosphorus diet (HPD) is consumed. A similar adaptive mechanism is also operative at the intestinal microvillus. The adaptive changes in Pi reabsorption are independent of parathyroid hormone production and are paralleled by similar changes in the Na+-dependent Pi transport at the brush border membrane (BBM). Type II Na+-Pi cotransporters (NaPi-2) are mainly involved in such regulatory mechanisms. Chronic dietary phosphorus restriction leads to increased Na+-Pi cotransport rate, along with increased NaPi-2 protein and mRNA abundance. In acute dietary phosphorus restriction, transport rate and NaPi-2 protein are also increased, but mRNA abundance remains unchanged. A shuttling mechanism involving translocation of cotransporters from intracellular pools to the BBM is involved in the rapid proximal tubular adaptation. The intestinal adaptation to changes in dietary phosphorus are similar to those described for the renal Pi transport, but the molecular structure of the intestinal Na+-Pi cotransporter is not known. When nephron mass is reduced, phosphate homeostasis is maintained through enhanced Pi excretion by residual nephrons. The adaptation to renal mass reduction is mediated by increased parathyroid hormone (PTH) production and by PTH-independent mechanisms, including increased intrarenal dopamine production. The adaptive changes of Pi transport to dietary phosphorus restriction can counteract the effect of dietary phosphorus reduction often prescribed in patients with renal failure. However, because of the reduced filtered load of Pi, the overall impact on serum Pi concentration is minimal.

Adaptation, Physiological↗
PubMed2000

The role of apoptosis during intestinal adaptation after small bowel resection.

BACKGROUND/PURPOSE: Adaptation after small bowel resection (SBR) is characterised by a new set point in the balance of enterocyte proliferation and apoptosis. Apoptosis is gene directed. The authors hypothesised that the adaptive response is influenced positively by antiapoptotic gene products (eg, bcl-2 gene-produced protein). The authors tested this hypothesis by studying the effect of bcl-2 overexpression on intestinal adaptation after SBR. METHODS: Male bcl-2 transgenic mice, overexpressing bcl-2 in the small intestinal epithelium, and wild type control mice underwent either a 75% mid-SBR, or a sham operation. The 4 experimental groups consisted of resection wild type (n = 8), transection wild type (n = 6), resection bcl-2 transgenic (n = 8), and transection bcl-2 transgenic (n = 8). Seven days postoperatively small bowel was harvested; total weight, mucosal weight, and mucosal protein, DNA, and RNA content in jejunal and ileal tissue were determined to quantitate the hyperplastic response. RESULTS: Compared with sham-operated animals, SBR resulted in increased total jejunal weight; mucosal weight; and mucosal protein, DNA, and RNA content. Furthermore, in the SBR groups, the jejunal mucosal weight and mucosal protein and DNA content were significantly higher in the bcl-2 transgenic mice compared with the wild-type mice. No differences were observed between any of these parameters in the transection wild-type and transgenic mice. In the ileum, similar changes were observed. The differences between resected and transected wild-type mice were less pronounced, and only total ileal weight and mucosal protein content reached statistical significance. In the transgenic animals, all ileal variables, with the exception of mucosal RNA content, were significantly higher in the SBR group than in the transected group. SBR in the transgenic mice resulted in higher ileal mucosal weight and mucosal protein, DNA, and RNA content compared with the wild-type mice. CONCLUSIONS: The results show that the murine SBR model is a true representation of the process of adaptation after SBR. Furthermore, major components of the adaptive response, both in the jejunum and in the ileum, are significantly more pronounced in the bcl-2 transgenic mice than in the wild-type control animals. Thus, it can be concluded that intestinal hyperplasia after SBR is significantly enhanced by overexpression of the anti-apoptotic bcl-2 gene product. This finding should prompt further research on the effects of antiapoptotic interventions on adaptation after SBR.

Adaptation, Physiological↗
PubMed1998

Intestinal adaptation is enhanced by epidermal growth factor independent of increased ileal epidermal growth factor receptor expression.

BACKGROUND/PURPOSE: Intestinal adaptation after massive small bowel resection (SBR) is augmented by epidermal growth factor (EGF) via an unknown mechanism. We recently have observed that EGF increases the expression of EGF receptor mRNA and protein content in the remnant ileum after SBR. The purpose of this study was to determine whether the magnitude of EGF-induced receptor expression correlates with intestinal adaptation. METHODS: A 50% proximal SBR or sham operation (bowel transection with reanastomosis) was performed on male ICR mice. Animals from each group were then selected randomly to receive either human recombinant EGF (150 microg/kg/d) or saline by twice daily intraperitoneal injections. The remnant ileum was harvested at 1 week, and parameters of adaptation measured as changes in protein content. Ileal EGF receptor mRNA was quantitated using a ribonuclease protection assay. Changes in the expression ileal EGF receptor protein were determined by Western blot after immunoprecipitation. Comparisons of mean values between groups was performed using analysis of variance (ANOVA) and a P value of less than .05 was considered significant. Values are presented as mean +/- SEM. RESULTS: EGF was mitogenic to the ileum after sham operation as monitored by increases in ileal protein content (2.21 +/- 0.002 mg/cm Sham v 2.97 +/- 0.25 mg/cm Sham +/- EGF; P < .05). After SBR, adaptation resulted in increased ileal protein content (4.45 +/- 0.27 mg/cm), which was substantially boosted by EGF (5.98 +/- 0.39 mg/cm; P < .05). No differences were detected in ileal EGF receptor mRNA or protein expression between Sham or SBR groups that did not receive EGF. However, EGF significantly enhanced the expression of ileal EGF receptor mRNA to an equal extent after both sham and SBR (approximately threefold). The magnitude of this increase in EGF receptor protein (four- to sixfold) was similar in both EGF groups as shown by Western blotting. CONCLUSIONS: Changes in ileal EGF receptor expression are not mandatory for adaptation to occur. EGF upregulates the expression of mRNA and protein for its own intestinal receptor in vivo. Because EGF-induced receptor expression was comparable after both SBR and Sham operation, the beneficial effect of EGF during adaptation is likely caused by other factors in addition to increased receptor expression.

Adaptation, Physiological↗
PubMed1989

Efficiency and the role of adaptation in klinokinesis.

Klinokinesis is a behavioral mechanism in which an organism moves toward or away from a stimulus source by altering its frequency of change of direction without biasing its turns with respect to the stimulus field. Computer simulation was used to study the efficiency of, and the effect of sensory adaptation on, this behavioral strategy. In modeling an organism with perfect performance (no error in determining the intensity of the stimulus and ability to move in perfectly straight lines) efficiency was about 70% without adaptation, and declined as the rate of adaptation increased. In contrast, models with non-perfect (noisy) performance were frequently able to double or triple their reduced efficiency by adapting to the stimulus intensity. Three types of noise that degraded performance were simulated: (1) intensity noise described random fluctuations in the intensity of the stimulus that were not associated with movement of the organism in the stimulus field; (2) motor noise described random fluctuations in the direction of locomotion as the organism moved along; (3) developmental noise described random differences between individuals in a constant tendency to turn to a certain degree as they moved forward. Adaptation had similar effects with any of the three types of noise. If a particular type of noise was strong enough to degrade performance significantly, then optimal performance occurred with an adaptation rate of about 0.2 per step.

Adaptation, Physiological↗
PubMed2002

Investigations on the mechanism of hyperbaric oxygen (HBO)-induced adaptive protection against oxidative stress.

Hyperbaric oxygen (HBO) treatment of cell cultures is a well suited model for studying genetic and cellular consequences of oxidative stress. We have previously shown that exposure of isolated human lymphocytes to HBO induces DNA damage and leads to the development of an adaptive response which protects lymphocytes from oxidative DNA damage induced by a repeated HBO exposure or by treatment with H(2)O(2). Our earlier studies also provided evidence for a functional involvement of the inducible enzyme heme oxygenase-1 (HO-1) in this adaptive protection. In contrast, V79 Chinese hamster cells did neither show a comparable adaptive protection nor an induction of HO-1 after HBO exposure. We now investigated possible mechanism(s) by which HO-1 contributes to an enhanced resistance of lymphocytes against oxidative stress. HO-1 catalyzes the rate-limiting step in heme degradation to form carbon monoxide (CO), biliverdin and free iron. We can now show that supplementation with exogenous CO does not protect V79 cells from HBO-induced oxidative DNA damage suggesting that increased generation of CO cannot account for the observed adaptive protection. On the other hand, HBO-exposed lymphocytes showed a small but reproducible increase in cellular ferritin levels, which might indicate that the underlying protective mechanism is based on an induction of ferritin, which may act antioxidatively by preventing the generation of the DNA-damaging hydroxyl radical via Fenton reaction. Our results further show that isolated lymphocytes also induce HO-1 and develop an adaptive protection when the first HBO exposure does not induce DNA damage, indicating that DNA damage is not the trigger for the development of the adaptive protection.

Adaptation, Physiological↗
PubMed2003

Simulating unilateral neglect in normals using prism adaptation: implications for theory.

Rightward deviation on line bisection is considered one of the most classic clinical signs of unilateral visual neglect--a cognitive disorder of spatial processing that commonly follows right brain damage. Recently, short-term adaptation to wedge prisms has been shown to significantly reduce neglect on this and other conventional diagnostic tasks. Our previous study has shown that visuomotor adaptation in normals produces a similar pattern of directional bias on a line bisection task. Based on the good working knowledge of how neglect patients perform on different versions of the standard diagnostic task, we showed here that using leftward-deviating prisms in normals, it is possible to produce: (1) a reliable bias on line bisection, (2) a rightward specific deviation, (3) a modulation of rightward deviation, which depends on the relative spatial location of the target lines and (4) a line length effect. A final experiment confirmed that these after-effects are specific to prism adaptation rather than passive prism exposure. Collectively, these findings confirm that adaptation to left-deviating prisms in normals produces a reliable right-sided bias and as shown by a previous visuospatial judgement task, these findings cannot be adequately explained by the symmetric sensori-motor effects of prism adaptation. Taken together with the improvement of spatial neglect shown by right-deviating prisms only, the present study suggests that low level sensori-motor adaptations play a greater role in right hemisphere organisation for spatial cognition than previously thought.

Adaptation, Physiological↗
PubMed2000

Asymmetries in the time-course of chromatic adaptation and the significance of contrast.

The time-course of chromatic adaptation was determined as a function of the spectral content of the adaptation-light and of image-contrast. The adaptation-lights varied along the chromatic cardinal axes or one of their intermediate axes in an equiluminant plane in colour-space. We found an asymmetry in the initial time-course of adaptation (0.2-10 s) in that adaptation to middle-wavelength light was significantly faster than adaptation to short- and long-wavelength light. The asymmetry was only observed in the presence of a spatially complex pattern. It was fully supported by luminance and chromatic contrast and present under haploscopic stimulus conditions.

Adaptation, Physiological↗
PubMed1999

Integration after adaptation to transparent motion: static and dynamic test patterns result in different aftereffect directions.

One of the many interesting questions in motion aftereffect (MAE) research is concerned with the location(s) along the pathway of visual processing at which certain perceptual manifestations of this illusory motion originate. One such manifestation is the unidirectionality of the MAE after adaptation to moving plaids or transparent motion. This unidirectionality has led to the suggestion that the origin of this MAE might be a single source (gain control) located at, or beyond areas that are believed to be responsible for the integration of motion signals. In this report we present evidence against this suggestion using a simple experiment. For the same adaptation pattern, which consisted of two orthogonally moving transparent patterns with different speeds, we show that the direction of the resulting unidirectional MAE depends on the nature of the test stimulus. We used two kinds of test patterns: static and dynamic. For exactly the same adaptation conditions, the difference in MAE direction between testing with static and dynamic patterns can be as large as 50 degrees. This finding suggests that this MAE is not just a perceptual manifestation of a passive recovery of adapted motion sensors but an active integrative process using the output of different gain controls. A process which takes place after adaptation. These findings are in line with the idea that there are several sites of adaptation along the pathway of visual motion processing and that the nature of the test pattern determines the fate of our perceptual experience of the MAE.

Adaptation, Psychological↗
PubMed2001

Brain preparations for maternity--adaptive changes in behavioral and neuroendocrine systems during pregnancy and lactation. An overview.

Pregnancy, parturition and lactation comprise a continuum of adaptive changes necessary for the development and maintenance of the offspring. The endocrine changes that are driven by the conceptus and are essential for the maintenance of pregnancy and are involved in the preparations for motherhood are outlined. These changes include large increases in the secretion of sex steroid hormones, and the secretion of peptide hormones that are unique to pregnancy. The ability of these pregnancy hormones to alter several aspects of brain function in pregnancy is considered, and the adaptive importance of some of these changes is discussed, for example in metabolic and body fluid adjustments, and the induction of maternal behavior. The importance of sex steroids in determining the timing of the various adaptive changes in preparing for parturition and maternal behavior is emphasized, and the concept that the actions of prolactin and oxytocin, quintessential mammalian motherhood neuropeptides, can serve to coordinate a spectrum of adaptive changes is discussed. The part played by oxytocin neurons and their regulatory mechanisms is reviewed to illustrate how neural systems involved in maternity are prepared in pregnancy via changes in phenotype, synaptic organization and in the relative importance of their different inputs, to function optimally when needed. For oxytocin neurons secreting from the posterior pituitary, important in parturition and essential in lactation, these changes include mechanisms to restrain their premature activation, and adaptations to support synchronized burst firing for pulsatile oxytocin secretion in response to stimulation via afferents from the birth canal, olfactory system or suckled nipples. Within the brain, expression of oxytocin receptors permits centrally released oxytocin to facilitate the expression of maternal behavior. Changes in other neuroendocrine systems are similarly extensive, leading to lactation, suppression of ovulation, reduced stress responses and increased appetite; these changes in lactation are driven by the suckling stimulus. The possible link between these adaptations and changes in cognition and mood in pregnancy and post partum are considered, as well as the dysfunctions that lead to common problems of depression and puerperal psychoses.

Adaptation, Physiological↗
PubMed2003

Bottom-up transfer of sensory-motor plasticity to recovery of spatial cognition: visuomotor adaptation and spatial neglect.

A large proportion of right-hemisphere stroke patients show hemispatial neglect, a neurological deficit of perception, attention, representation, and/or performing actions within their left-sided space, inducing many functional debilitating effects on everyday life, and responsible for poor functional recovery and ability to benefit from treatment. This spatial cognition disorder affects the orientation of behavior with a shift of proprioceptive representations toward the lesion side. This shift is similar to that produced by psychophysical manipulations as a wedge-prism exposure in normal healthy subjects. In both subjects, one major compensative effect of short-term prism adaptation is a shift of proprioceptive representations, demonstrated by a shift in manual straight-ahead pointing in the dark, in a direction opposite to the visual shift. In neglect patients, prism adaptation involves the shift of proprioceptive representations to the left with a reduction of rightward bias observed in neglect patients in visuo-manual tasks as line-bisection, line-cancellation or copy drawing. Improvement of neglect is also observed in no visuo-manual tasks as mental imagery, auditory extinction or posture. This generalization of prism adaptation effects at different neglect level symptoms suggests that the process of prism adaptation may activate brain functions related to multisensory integration and higher spatial representations. Moreover the positive effects found for both sensorimotor and more cognitive spatial functions lasted for at least two or more hours after prism removal. Unlike reduction of neglect through sensory stimulations, the long-lasting improvement of neglect after prism adaptation suggests the activation of short-term plasticity of brain functions related to coordinate transformations and space representations. Lastly, the duration of these effects could be useful in rehabilitation programs, as suggested by the effects of prism adaptation on disabling neglect symptoms as wheelchair driving, posture or writing.

Adaptation, Physiological↗
PubMed2001

Processes underlying adaptation to tempo changes in sensorimotor synchronization.

In synchronizing finger taps with an auditory sequence, a small sudden tempo ("step") change in the sequence tends to be followed by rapid adaptation of the tapping period but slow adaptation of the relative phase of the taps, whereas a larger step change leads to initial period overshoot followed by rapid adaptation of both period and phase [M.H. Thaut, R.A. Miller, L.M. Schauer, Biological Cybernetics 79 (1998a) 241-250]. Experiment 1 replicated these findings and showed that the transition between the two patterns of adaptation occurs near the perceptual detection threshold for a tempo change. A reasonable explanation of these data was provided by a dual-process model of internal error correction [J. Mates, Biological Cybernetics 70 (1994a) 463-473, 70 (1994b) 475-484], with the added assumption that one process (period correction) depends on conscious awareness of a tempo change whereas the other (phase correction) does not. This assumption received support in Experiment 2, where a synchronization-continuation tapping task was used in combination with perceptual judgments to probe into the process of period correction following step changes. The results led to the conclusion that rapid adaptation of the tapping period to a small, undetected tempo change is in fact due to rapid internal phase correction, whereas slow adaptation of the relative phase of the taps is due to slow internal period correction.

Adaptation, Physiological↗
PubMed2003

Adaptation to display rotation and display gain distortions during drawing.

The relationship between movement extent and movement direction coding mechanisms was investigated using a visuomotor adaptation paradigm. To determine if these mechanisms are either modular or interdependent, young healthy college students were tested while they performed a visually guided drawing task that incorporated varying combinations of movement distance and direction distortions. Analysis of participants' standardized movement duration, initial directional error, and movement length over the course of the adaptation process revealed a certain degree of interdependence between direction and extent coding mechanisms. Specifically, changes in final adaptation levels and after-effects depended on the order of introduction of the visual distortions. This interaction can be characterized as unidirectional, where alterations in rotational feedback interfere with subsequent adaptation to gain changes, whereas alterations in "display gain" do not significantly impede the adaptation to "display rotation". Moreover, simultaneous exposure to gain and rotational distortions resulted in better learning. The results argue against an independent coding of movement direction and extent during adaptation by the central nervous system.

Adaptation, Physiological↗
PubMed1998

Adaptive modifications of post-saccadic smooth pursuit eye movements and their interaction with saccades and the vestibulo-ocular reflex in the primate.

Adaptation of the horizontal smooth pursuit eye movement was examined using step-ramp moving target paradigms in chronically prepared Macaca fuscata. Monkeys were trained to pursue a small target which moved in the horizontal plane in a 3 degrees step-10 degrees/s ramp or a 0 degrees step-10 degrees/s ramp mode for 300-400 ms. When the target moved from central fixation point in a step-ramp mode, the monkeys usually responded with an initial pursuit eye movement (latency, 100-120 ms) which reached to a nearly constant velocity of 4 degrees/s in 50 100 ms, followed by a 1-3.5 degrees catch-up saccade (latency, 170-230 ms). The catch-up saccade was followed by a 7-8 degrees/s post-saccadic pursuit. The post-saccadic pursuit velocity was measured 40-90 ms after the end of the catch-up saccade. When the target velocity was doubled (20 degrees/s) for 100-200 ms immediately after the onset of the catch-up saccade, the post-saccadic pursuit velocity increased by 40%. When the target velocity was decreased by half (5 degrees/s) immediately after the onset of the catch-up saccade for 150 ms, the post-saccadic pursuit velocity decreased by 30%. These increases or decreases of post-saccadic pursuit were observable within just 50-150 trials. The adaptation of post-saccadic pursuit occurred independent of the position of the target. The amplitude and latency of the catch-up saccade also increased correspondingly when the post-saccadic pursuit velocity was adaptively increased. Adaptation of smooth pursuit did not affect the dynamics of reflex eye movements, including the horizontal vestibulo-ocular reflex (HVOR) gain and phase measured by 0.33 Hz-10 degrees (peak-to-peak) turntable oscillations in darkness. Conversely, adaptation of the HVOR gain induced by a 2 h sustained oscillation of the turntable and screen in reversed direction at 0.33 Hz-10 degrees affected little the velocity of post-saccadic pursuit or the amplitude of the catch-up saccade. These results suggest that different neural mechanisms are respectively involved for the adaptation of horizontal smooth pursuit and HVOR in the primate.

Adaptation, Physiological↗
PubMed2001

Acid adaptation and temperature effect on the survival of E. coli O157:H7 in acidic fruit juice and lactic fermented milk product.

In this study, two strains of Escherichia coli O157:H7, (ATCC 43889 and ATCC 43895) were acid adapted at pH 5.0 in tryptic soy broth (TSB) for 4 h. Commercial products of mango juice (pH 3.2), asparagus juice (pH 3.6), Yakult--a diluted milk fermented drink (pH 3.6), and low-fat yoghurt (pH 3.9) were inoculated with acid-adapted or nonadapted cells of E. coli O157:H7. Survival of the inoculated E. coli O157:H7 in these commercial food products during storage at 25 or 7 degrees C was examined. It was found that although survival of the acid-adapted and nonadapted E. coli O157:H7 ATCC 43895 in asparagus juice during storage at 7 degrees C did not show marked difference, in general, acid adaptation and low temperature enhanced the survival of E. coli O157:H7 in both the commercial fruit juices tested. On the contrary, acid adaptation reduced the survival of both the strains of the test organism in Yakult and low-fat yoghurt stored at 7 degrees C. Besides, E. coli O157:H7 ATCC 43895 survived longer than ATCC 43889 in all the products examined, regardless of the storage temperature and acid adaptation.

Adaptation, Physiological↗
PubMed2003

Influence of marinades on survival during storage of acid-adapted and nonadapted Listeria monocytogenes inoculated post-drying on beef jerky.

The objective of the present study was to investigate the survival of acid-adapted and nonadapted Listeria monocytogenes inoculated post-drying on dried beef slices (beef jerky), which were treated (24 h, 4 degrees C) with the following marinades before drying at 60 degrees C for 10 h: (1) control (C), (2) traditional marinade (TM), (3) modified marinade; double the amount of TM with added 1.2% sodium lactate, 9% acetic acid, and 68% soy sauce with 5% ethanol (MM), (4) dipping into 5% acetic acid and then TM (AATM), and (5) dipping into 1% Tween 20 and then into 5% acetic acid followed by the TM (TWTM). Dried meat slices were inoculated with acid-adapted or nonadapted L. monocytogenes (ca. 5.7 log CFU/cm(2)) prior to aerobic storage at 25 degrees C for 60 days. Survivors were determined using tryptic soy agar with 0.1% pyruvate (TSAP) and PALCAM agar. Results showed that surviving bacterial populations on TWTM, AATM, and MM treatments were significantly (P<0.05) lower than those surviving on C and TM until 42 days of storage. By the end of 60 days of storage, bacterial populations in all treatments were not different regardless of acid adaptation or recovery media, except for treatment C inoculated with nonadapted cultures, which had significantly higher TSAP counts than other treatments. There was no significant (P> or =0.05) difference in survival of previously acid-adapted and nonadapted bacterial populations in samples of TWTM, AATM, and MM treatments. However, bacterial populations that were nonadapted were significantly higher than those that were acid-adapted on products of C and TM treatments on days 60 and 24, respectively. The earliest complete elimination (enrichment negative) of the pathogen occurred by day 28 (AATM) in products inoculated with acid-adapted cultures and by day 42 (TWTM and AATM) in products inoculated with nonadapted cultures. These results indicate that use of modified marinades in jerky processing and low water activity provided antimicrobial effects against possible post-processing contamination with L. monocytogenes.

Adaptation, Physiological↗
PubMed2003

Cold adaptation of Escherichia coli: microbiological and proteomic approaches.

The aim of this work was to use two approaches (microbiological and proteomic) to study the effect of cold adaptation (3 h at 4 degrees C) on the survival of two Escherichia coli strains, I2 and R3, following freezing at -20 degrees C for 24 h and thawing for 45 min at 37 degrees C. The effect of cold adaptation on cell survival after freezing was determined by measuring viable counts on selective (PTX) and nonselective media (TSA). The beneficial effect of the cold treatment was more pronounced for the freezing-sensitive R3 strain: Prior to adaptation, differences between the two media were 3.5 log10 for R3 and 0.4 log10 for I2. After adaptation, the differences were 2.5 log10 and 0.1 log10 for R3 and I2, respectively. The proteins from two cell compartments, cytoplasm and outer membrane, were separated by two-dimensional electrophoresis and identified by mass spectrometry or Edman sequencing. The adaptation resulted in changes in the expression of certain proteins. Among the principal changes to protein profiles in strain R3 following cold adaptation, we observed an over-expression of the EF-TU elongation factor in the outer membrane, and an under-expression of flagellin (FLIC) in the cytoplasm. Very few changes were observed in strain I2.

Adaptation, Physiological↗