Membrane damage and viability loss of Escherichia coli K-12 in apple juice treated with radio frequency electric field

The need for a nonthermal intervention technology that can achieve microbial safety without altering nutritional quality of liquid foods led to the development of a radio frequency electric fields (RFEF) process. In order to understand the mechanism of inactivation of bacteria by RFEF, apple juice purchased from a wholesale distributor was inoculated with Escherichia coli K-12 at 7.8 log CFU/ml and then treated with RFEF. The inoculated apple juice was passed through an RFEF chamber operated at 20 kHz, 15 kV/cm for 170 micros at a flow rate of 540 ml/min. Treatment condition was periodically adjusted to achieve outlet temperatures of 40, 45, 50, 55, and 60 degrees C. Samples at each outlet temperature were plated (0.1 ml) and the number of CFU per milliliter determined on nonselective and selective agar media was used to calculate the viability loss. Bacterial inactivation and viability loss occurred at all temperatures tested with 55 degrees C treatment, leading to 4-log reductions. No significant effect was observed on bacterial population in control samples treated at 55 degrees C with a low-RFEF (0.15 kV/cm) field strength. These observations suggest that the 4-log reduction in samples treated at 15 kV/cm was entirely due to nonthermal effect. RFEF treatment resulted in membrane damage of the bacteria, leading to the efflux of intracellular ATP and UV-absorbing materials. Populations of injured bacteria recovered immediately (<30 min) from the treated apple juice averaged 0.43 log and were below detection after 1 h of RFEF treatment and determination using selective plates (tryptic soy agar containing 5% sodium chloride). The results of this study suggest that mechanism of inactivation of RFEF is by disruption of the bacterial surface structure leading to the damage and leakage of intracellular biological active compounds.     

Propylparaben sensitizes heat-resistant Salmonella Enteritidis and Salmonella Oranienburg to thermal inactivation in liquid egg albumen

Propyl p-hydroxybenzoic acid (propylparaben [PRPA]) is a phenolic antioxidant, known to occur in nature and used as a microbiostat in foods, feeds, pharmaceuticals, cosmetics, and medications. The U.S. Department of Agriculture, Food Safety and Inspection Service (FSIS) requires that liquid egg white (LEW) be pasteurized at 56.7°C for 3.5 min. This study evaluated the effects of PRPA on the pasteurization sensitivity of Salmonella in LEW. When LEW (pH 7.8) was pasteurized under FSIS conditions, salmonellae declined by 0.5, 4.6, 4.5, > 7.0, and > 7.0 log CFU/ml, with 0, 125, 250, 500, or 1,000 ppm of PRPA, respectively, and D(56.7°C)-values were 2.99, 1.05, 0.68, 0.26 and ≤0.16 min. Albumen (pH 8.9) pasteurized under FSIS standards incurred salmonellae reductions of 3.3, 2.8, 5.2, > 7.0, and > 7.0 log CFU/ml, with 0, 125, 250, 500, or 1,000 ppm of PRPA, respectively, while D(56.7°C)-values were 0.87, 0.99, 0.66, 0.22, and 0.09 min. Adding 500 ppm of PRPA to albumen (pH 7.8) reduced D(56.7°C)-values more than 11-fold, and reduced the time to achieve a 5-log reduction from 15.0 to only 1.3 min. A 7-log reduction in plain LEW (pH 7.8) at 56.7°C required 20.9 min, versus only 1.8 and 1.1 min with 500 and 1,000 ppm of PRPA, respectively. Furthermore, a 7-log reduction in plain LEW (pH 8.9) required 6.1 min, versus only 1.5 and 0.6 min with 500 and 1,000 ppm of PRPA, respectively. This study is the first to report the efficacy of PRPA (pK(a) = 8.4) in sensitizing Salmonella in LEW to thermal pasteurization, while documenting that PRPA retains its antibacterial efficacy at pH levels as high as 8.9.     

Destruction of Escherichia coli O157:H7 and Salmonella enteritidis in cow manure composting

Application of cow manure and composted manure in agricultural practice could potentially cause contamination of foodstuffs with pathogenic bacteria such as Salmonella Enteritidis and Escherichia coli O157:H7. In this study, rifampicin-resistant (RifR) E. coli O157:H7 and Salmonella Enteritidis at a level of 7 log CFU/g of raw compost feed were used to determine the effect of a bench-scale composting system on their survival. RifR E. coli O157:H7 was not detected after 72 h of composting at 45 degrees C, and RifR Salmonella Enteritidis was not detected after 48 h. The use of selective media for enrichment failed to recover in the composting samples held at 45 degrees C for 96 h. However, the pathogens showed no change in bacterial numbers when the composting system was held at room temperature. Thus, properly composted manure can be safely used in food crop production while minimizing the likelihood of microbial contamination.     

Estimation of the biofilm formation of Escherichia coli K-12 by the cell number

We developed a method of estimating the biofilm formation of Escherichia coli K-12 strains in microtiter-plate wells by the cell number. Regression lines between the cell number and absorbance of crystal violet that stained the E. coli biofilm consisted of high and low slope lines, respectively.     

Inactivation of Salmonella enteritidis and Salmonella senftenberg in liquid whole egg using generally recognized as safe additives, ionizing radiation, and heat

The effect of combining irradiation and heat (i.e., irradiation followed by heat [IR-H]) on Salmonella Enteritidis and Salmonella Senftenberg inoculated into liquid whole egg (LWE) with added nisin, EDTA, sorbic acid, carvacrol, or combinations of these GRAS (generally recognized as safe) additives was investigated. Synergistic reductions of Salmonella populations were observed when LWE samples containing GRAS additives were treated by gamma radiation (0.3 and 1.0 kGy), heat (57 and 60 degrees C), or IR-H. The presence of additives reduced the initial radiation Dgamma -values (radiation doses required to eliminate 90% of the viable cells) by 1.2- to 1.5-fold, the thermal decimal reduction times (D,-values) by up to 3.5- and 1.8-fold at 57 and 60 degrees C, respectively, and the thermal D,-values after irradiation treatments by up to 3.4- and 1.5-fold at 57 and 60 degrees C, respectively, for both Salmonella serovars. Of all the additives investigated, nisin at a concentration of 100 IU/ml was the most effective at reducing the heat treatment times needed to obtain a 5-log reduction of Salmonella. Thus, while treatments of 21.6 min at 57 degrees C or of 5 min at 60 degrees C should be applied to achieve a 5-log reduction for Salmonella in LWE, only 5.5 min at 57 degrees C or 2.3 min at 60 degrees C after a 0.3-kGy radiation pretreatment was required when nisin at a concentration of 100 IU/ml was used. The synergistic reduction of Salmonella viability by IR-H treatments in the presence of GRAS additives could enable LWE producers to reduce the temperature or processing time of thermal treatments (current standards are 60'C for 3.5 min in the United States) or to increase the level of Salmonella inactivation.     

Antimicrobial activity of essential oils on Salmonella enteritidis, Escherichia coli, and Listeria innocua in fruit juices

The antimicrobial properties of essential oils (EOs) and their derivatives have been known for years. However, the information published about the minimal effective concentration of EOs against microorganisms in fruit juices is scarce. In this study, both MIC and MBC of six EOs (lemongrass, cinnamon, geraniol, palmarosa, or benzaldehyde) against Salmonella Enteritidis, Escherichia coli, and Listeria innocua were determined by the agar and broth dilution methods, respectively. All of the six EOs inhibited the microbial (Salmonella Enteritidis, E. coli, and L. innocua) growth at a concentration from 1 microl/ ml (MIC). These studies led to choosing the three most effective EOs. Lemongrass, cinnamon, and geraniol were found to be most effective in inhibiting the growth of the microorganisms and thus were used for the MBC analysis. On this last point, significant differences (P < 0.05) among EOs, their concentrations, and culture media (apple, pear, and melon juices, or tryptone soy broth medium) were found after comparing the results on MBC for each microorganism. A concentration of 2 microl/ml from lemongrass, cinnamon, or geraniol was enough to inactivate Salmonella Enteritidis, E. coli, and L. innocua in apple and pear juices. However, in melon juice and tryptone soy broth medium, concentrations of 8 and 10 microl/ml from cinnamon, respectively, or 6 microl/ml from geraniol were necessary to eliminate the three microorganisms, whereas lemongrass required only 5 micro/ml to inactivate them. These results suggest that EOs represent a good alternative to eliminate microorganisms that can be a hazard for the consumer in unpasteurized fruit juices. The present study contributes to the knowledge of MBC of EOs against pathogenic bacteria on fruit juices.     

Laying season and egg shell cracks on the growth of Salmonella enteritidis in the egg albumen during storage

We studied the effects of laying seasons and egg shell cracks on the ability of egg albumen to support the growth of Salmonella Enteritidis (SE) in eggs. Hens eggs used were those laid in February, June, and October in a farm in Japan and stored at 10, 20, and 30 degrees C, and at 30 degrees C after storage at 10 degrees C, immediately after receipt or after cracking the shell. At several-day intervals during storage, the egg contents were poured into a dish, SE was inoculated into albumen, and then the growth of SE during 3 days incubation at 18 degrees C was measured. The results demonstrated that storage temperature and laying season affected the growth of SE in the egg albumen. The proportion of eggs upon which albumen allowed the growth of SE was higher in the eggs stored at 30 degrees C than those stored at 10 degrees C. The growth of SE in eggs was lowest in the following order of laying: February, October, and June. SE grew preferably in albumen of cracked eggs than intact eggs.     

Synergistic effect of sonication and high osmotic pressure enhances membrane damage and viability loss of Salmonella in orange juice

The efficacy of using sonication (50 ± 0.2 W, 20 kHz), combined with subsequent concentration and storage at high osmotic pressure, has been evaluated to reduce levels of Salmonella bacteria in different solutions (PBS, sucrose and orange juice) at varying concentrations. To visualize the impact on cell membranes, we used a staining protocol (propidium iodide [PI] and 4′,6′-diamidino-2-phenylindole [DAPI]). Sonication alone did not cause significant membrane damage. Storage alone, for 48 h and at high osmotic pressure (10.9 MPa), affected membrane permeability in 20% of cells. However, sonication, combined with storage, considerably increased loss of membrane integrity, resulting in a significant logarithmic reduction of microorganisms. When the combination was applied to contaminated orange juice, a 5 log₁₀ cfu ml^?1 reduction of Salmonella spp. was obtained. “Osmosonication”—the synergistic combination of sonication and subsequent storage at high osmotic pressure—is an innovative alternative for the non-thermal decontamination of liquid foods.     

Detection of Salmonella enteritidis in shell and liquid eggs using enrichment and plating

Detection methods using various enrichment and plating media and immunoconcentration for Salmonella enteritidis in shell and liquid eggs were evaluated. For liquid egg samples naturally contaminated with S. enteritidis, pre-enrichment in 225 ml of buffered peptone water with cysteine followed by selective enrichment in 10 ml of tetrathionate broth was the superior, resulting in the detection of S. enteritidis in all samples on six of the seven types of selective agar substrate investigated. This enrichment procedure also enabled detection of S. enteritidis in most of artificially inoculated shell egg and pasteurized liquid egg samples.     

Modeling the thermal inactivation kinetics of heat-resistant Salmonella Enteritidis and Oranienburg in 10 percent salted liquid egg yolk

There is no suitable model for predicting thermal inactivation kinetics of Salmonella spp. for many types of liquid egg products, including salted liquid egg yolk, for use in updating U.S. Department of Agriculture (USDA) pasteurization guidelines. This is because, in part, of the variations in Salmonella strains and the changes in the processing of liquid egg products over the past 40 years. The objectives of the present study were to determine the thermal inactivation kinetics and to create a general thermal inactivation kinetics model that can be used for estimating log reductions of salmonellae in 10% salted liquid egg yolk for temperatures between 62.2 and 69°C. This model can be used by processors to help ensure adequate pasteurization. This was accomplished by studying the inactivation kinetics of a three-strain composite of heat-resistant Salmonella serovars Enteritidis and Oranienburg, inoculated into commercially processed 10% salted liquid egg yolk. The survival curves were convex, with asymptotic D-values. From these curves, a general model was developed to predict log reductions for given times at specified temperatures. For example, at a temperature of 67.3°C (153.1°F) for 3.5 min, our model predicts a 5-log reduction would be obtained, whereas with the current USDA minimum required pasteurization regimen (63.33°C [146°F] for 3.5 min), our model predicts that a reduction of only 2.7 log would be obtained. The results of this study provide information that can be used by processors to aid in producing safe, pasteurized egg yolk products, and for satisfying USDA pasteurization performance standards and developing industry guidance.     

Inactivation of Salmonella serovars in liquid whole egg by heat following irradiation treatments

Salmonella is a frequent contaminant on eggs and is responsible for foodborne illnesses in humans. Ionizing radiation and thermal processing can be used to inactivate Salmonella in liquid whole egg, but when restricted to doses that do not affect egg quality, these technologies are only partially effective in reducing Salmonella populations. In this study, the effect of ionizing radiation in combination with thermal treatment on the survival of Salmonella serovars was investigated. Of the six Salmonella serovars tested, Salmonella Senftenberg was the most resistant to radiation (Dgamma = 0.65 kGy) and heat (D(55 degrees C) = 11.31 min, z = 4.9 degrees C). Irradiation followed by thermal treatment at 55 or 57 degrees C improved the pasteurization process. Radiation doses as low as 0.1 kGy prior to thermal treatments synergistically reduced the D(55 degrees C) and D(57 degrees C) of Salmonella Senftenberg 3.6- and 2.5-fold, respectively. The D(55 degrees C) and D(57 degrees C) of Salmonella Typhimurium were reduced 2- and 1.4-fold and those of Salmonella Enteritidis were reduced 2- and 1.6-fold, respectively. Irradiation prior to thermal treatment would enable the reduction of heat treatment times by 86 and 30% at 55 and 57 degrees C, respectively, and would inactivate 9 log units of Salmonella serovars.     

Survival of Escherichia coli O157:H7, Salmonella enteritidis, Staphylococcus aureus, and Listeria monocytogenes in Kimchi

The survival of gram-positive and gram-negative foodborne pathogens in both commercial and laboratory-prepared kimchi (a traditional fermented food widely consumed in Japan) was investigated. It was found that Escherichia coli O157:H7, Salmonella Enteritidis, Staphylococcus aureus, and Listeria monocytogenes could survive in both commercial and laboratory-prepared kimchi inoculated with these pathogens and incubated at 10 degrees C for 7 days. However, when incubation was prolonged, the S. aureus level decreased rapidly from the initial inoculum level to the minimum detectable level within 12 days, whereas Salmonella Enteritidis and L. monocytogenes took 16 days to reach similar levels in commercial kimchi. On the other hand, E. coli O157:H7 remained at high levels throughout the incubation period. For laboratory-prepared kimchi, the S. aureus level decreased rapidly from the initial inoculum level to the minimum detectable level within 12 days, and L. monocytogenes took 20 days to reach a similar level. E. coli O157:H7 and Salmonella Enteritidis remained at high levels throughout the incubation period. The results of this study suggest that the contamination of kimchi with E. coli O157:H7, Salmonella Enteritidis, S. aureus, or L. monocytogenes at any stage of production or marketing could pose a potential risk.     

Inactivation of Salmonella Typhimurium and Staphylococcus aureus by pulsed electric fields in liquid whole egg

In this study, the lethal effectiveness of pulsed electric fields (PEF) on the inactivation of Salmonella enterica subs. enterica ser. Typhimurium and Staphylococcus aureus in liquid whole egg (LWE) has been investigated. Maximum inactivation levels of 4 and 3 Log₁₀ cycles of the population of Salmonella Typhimurium and S. aureus were achieved with treatments of 45 kV/cm, 30 μs and 419 kJ/kg, and 40 kV/cm for 15 μs and 166 kJ/kg, respectively. The non-linear kinetics of inactivation observed for both microorganisms at all the investigated electric field strengths were described by mathematical equations based on the Weibull distribution. The developed equations enabled to compare the microbial resistance to PEF and to establish the most suitable treatment conditions to achieve a determined level of microbial inactivation. PEF treatments varying from 30 kV/cm, 67 µs and 393 kJ/kg to 45 kV/cm, 19 µs and 285 kJ/kg allow to reduce 3 Log₁₀ cycles the population of the microorganism of concern in PEF food processing of LWE, Salmonella Typhimurium.Industrial relevanceThe data presented in this investigation in terms of electric field strength, specific energy and treatment time result of relevance to evaluate the possibilities of PEF technology to pasteurize LWE with this technology. The models developed in this study can be applied to engineering design, and for the evaluation and optimization of the PEF technology as a new technique to obtain Salmonella free LWE.Based on our results it is not recommended to apply treatments of energy levels higher than 250 kJ/kg, since PEF lethality hardly increased but markedly augmented the energetic costs. For these energy values, PEF technology by itself is not sufficient (3 Log10 cycles in the best case scenario) to assure the safe security of LWE. Therefore, intelligent combinations of PEF with other preservation technologies have to be developed in order to use pulsed electric fields as an alternative to heat pasteurization of LWE.     

Simple quantitative analysis of Escherichia coli K-12 internalized in baby spinach using Fourier Transform Infrared spectroscopy

Bacterial contamination continues to be a serious concern for food safety. Although washing fresh produce helps in reducing pathogen levels, pathogen internalization often limits the effectiveness of washing. When pathogens internalize in leafy vegetables, the method of identification and quantitative measurement would be called into question. This study was aimed to use Fourier Transform Infrared (FTIR) spectroscopy integrated with an attenuated total reflectance kit for quantification of Escherichia coli K-12 internalized in baby spinach. The bacteria were inoculated into vascular and intracellar tissues of spinach leaves by syringe injection and the distribution of internalized E. coli K-12 cells was confirmed under scanning electron microscopy (SEM). FTIR measurement following the preparation of bacterial suspension from spinach leaves with high speed pulverizing enabled to detect the absorbance peaks in the amide II region between 1590 and 1490 cm⁻¹ as a fingerprint for the microbes. It was found that the estimated concentrations of E. coli K-12 agreed well with the concentrations determined by plate counting with R² values of 0.98 and 0.97 in peptone water and spinach extracts, respectively. The results demonstrated that FTIR can identify and quantify E. coli K-12 in baby spinach extracts at a limit of detection of approximately 100 CFU/mL in 5 min. The developed method is expected to be suitable for the analysis of pathogenic E. coli strains and other bacterial species in fresh vegetables.     

Inactivation of Escherichia coli K-12 exposed to pressures in excess of 300 MPa in a high-pressure homogenizer

Homogenization is used widely in the dairy industry to improve product stability and quality. High-pressure homogenization (HPH) of fluid foods up to pressures of 300 MPa has demonstrated excellent potential for microbial inactivation. Microbial inactivation can be enhanced during HPH with the inclusion of antimicrobial compounds. Escherichia coli K-12 cells, grown statically or in chemostat, were exposed to HPH processing pressures of 50 to 350 MPa in the absence or presence of the antimicrobial nisin. Valve temperature was regulated by a water bath and pressure, and temperature data were recorded continuously after process initiation. Survivors were enumerated via plating on nonselective growth media. Pressure and temperature at the valve outlet port exhibited a quadratic relationship (R(2) = 0.9617, P < 0.05). Significant HPH-induced inactivation of the gram-negative microorganism was observed in the range of 100 to 250 MPa. Above 300 MPa, heat was the main factor promoting microbial inactivation, regardless of whether cells were grown in chemostat or statically. Chemostat-grown cells were significantly (P < 0.05) more resistant to HPH processing than were statically grown cells. Data indicate potential synergistic effects of nisin and HPH on the inactivation of bacterial contaminants. This study represents the first report of inactivation of a bacterium with HPH pressures in excess of 300 MPa in the presence and absence of an antimicrobial.     

Combined effect of high hydrostatic pressure treatment and hydrogen peroxide on Salmonella Enteritidis in liquid whole egg

The effects of high hydrostatic pressure treatment (HHP) of 250, 350, 450 MPa and hydrogen peroxide additions at different concentrations of 0.1, 0.5, 1% in liquid whole egg following high hydrostatic pressure treatment at 250 MPa at 20 °C on Salmonella Enteritidis PT4 in liquid whole egg were investigated. At 20 °C for 5 min treatment, 56.63 and 49.38% injury were determined for the treatment pressures of 250 and 350 MPa, respectively. Injury was not detected and total destruction of Salmonella Enteritidis PT4 was obtained for 5 min treatment at 450 MPa. The obtained results indicated that HHP was a more effective treatment than preheating for the enhancement of the effectiveness of H₂O₂. In order to minimize the adverse effect of HHP on food texture, the HHP treatment of 250 MPa was used throughout this study. Therefore, treating with 0.5% H₂O₂ following 5 min HHP at 250 MPa was determined as an effective way of Salmonella Enteritidis destruction in liquid whole egg. The catalase activity retention was determined as 62.26±0.6% after 3.5 min treatment of LWE at 60 °C. A 5-min treatment at 250 and 450 MPa at 20 °C of LWE resulted in a 78.67±2.1 and 65.01±1.8% retention of catalase activity, respectively.     

Antimicrobial properties of lactic acid bacteria and yeast-LAB cultures isolated from traditional fermented milk against pathogenic Escherichia coli and Salmonella enteritidis strains

The survival and growth of Escherichia coli 3339 and Salmonella enteritidis 949575 isolated from human clinical samples, in milk fermented with lactic acid bacteria (LAB) and yeast strains previously isolated from Zimbabwean naturally fermented milk (NFM) was studied. The LAB starter cultures used were Lactococcus lactis subsp. lactis biovar. diacetylactis C1 alone (C1) or in combination with Candida kefyr 23 (C1/23), L. lactis subsp. lactis Lc261 alone (LC261) or in combination with C. kefyr 23 (Lc261/23). The growth of the same pathogens in milk fermented with a commercial DL culture (CH-N 22) and spontaneously fermented raw milk was also monitored. The C1 and C1/23 cultures significantly (P<0.05) inhibited the growth of both pathogens. When inoculated at the beginning of the fermentation, both E. coli 3339 and S. enteritidis 949575 counts were significantly (P<0.05) reduced by about two log cycles in C1 and C1/23 cultured milk. However, in naturally fermented milk and the DL cultured milk, both E. coli 3339 and S. enteritidis 949575 grew and reached high populations of about 9 and 8.8 log cfu ml(-1), respectively, after 18 h. When E. coli 3339 was inoculated into previously fermented milk, the viable counts were significantly (P<0.05) reduced in the presence of C1 and C1/23 from 7 log cfu ml(-1) to 3 log cfu ml(-1) after 48 h. S. enteritidis 949575 could not be recovered from these cultures after 48 h. The addition of the yeast did not enhance or diminish the inhibitory capacity of the LAB cultures. The pathogens survived in high numbers when inoculated into pre-fermented NFM and the commercial DL- (CH-N 22) cultured milk. The C1 strain, therefore, offered the best protection against the pathogens. Its inhibitory effect was mainly related to fast acid production.     

Effect of growth on the thermal resistance and survival of Salmonella Tennessee and Oranienburg in peanut butter, measured by a new thin-layer thermal death time device

In published data the thermal destruction of Salmonella species in peanut butter deviates from pseudo-first-order kinetics. The reasons for such deviation are unknown. This study examined both the method used to measure the thermal destruction rate and the method of growth of the microorganisms to explain variations in destruction kinetics. Growth on a solid matrix results in a different physiological state that may provide greater resistance to adverse environments. In this study, Salmonella Tennessee and Oranienburg were grown for 24 h at 37°C under aerobic conditions in broth and agar media to represent planktonic and sessile cell growth, respectively. Peanut butter was held at 25°C and tested for Salmonella levels immediately after inoculation and at various time intervals up to 2 weeks. Thermal resistance was measured at 85°C by use of a newly developed thin-layer metal sample holder. Although thermal heat transfer through the metal device resulted in longer tau values than those obtained with plastic bags (32.5 ± 0.9 versus 12.4 ± 1.9 s), the bags have a relative variability of about 15 % compared with about 3 % in the plates, allowing improved uniformity of sample treatment. The two serovars tested in the thin-layer device showed similar overall thermal resistance levels in peanut butter regardless of growth in sessile or planktonic states. However, thermal destruction curves from sessile cultures exhibited greater linearity than those obtained from planktonic cells (P = 0.0198 and 0.0047 for Salmonella Oranienburg and Salmonella Tennessee, respectively). In addition, both Salmonella serovars showed significantly higher survival in peanut butter at 25°C when originally grown on solid media (P = 0.001) with a <1-log loss over 2 weeks as opposed to a 1- to 2-log loss when grown in liquid culture. Consequently, the use of cells grown on solid media may more accurately assess the survival of Salmonella at different temperatures in a low-water-activity environment such as peanut butter.     

Effect of compatible solutes on the respiratory activity and growth of Escherichia coli K-12 under NaCl stress

The respiratory activity of Escherichia coli K-12 was inhibited by high NaCl concentrations. The addition of compatible solutes such as proline and ectoine led to the recovery of the respiration of E. coli K-12 inhibited by 1 M NaCl to a similar extent as did the addition of glycine betaine. Glucose, an exogenous substrate for the stimulation of respiratory activity, was not taken up by the cells in the presence of 1 M NaCl, but active uptake of glucose was observed following the addition of compatible solutes. As a result, we obtained a good correlation between respiratory activities and glucose uptake rates, suggesting that the glucose uptake activity inhibited by high NaCl concentrations was facilitated by these solutes. The addition of proline did not lead to cell proliferation in the minimal medium containing 1 M NaCl, although the cells took up proline quite efficiently under high osmolarity. On the other hand, cell growth occurred after a lag time in the medium containing glycine betaine or ectoine in place of proline. Similar actions of the compatible solutes mentioned above were observed for E. coli ATCC 9637.