Loss of D-alanine during sublethal heating of Staphylococcus aureus S6 and magnesium binding during repair.

Staphylococcus aureus S6 sublethally heated at 52 degrees C for 15 min to 0-1 M-potassium phosphate buffer pH 7-2, lost neither the ribitol teichoic acid of the wall nor the glycerol teichoic acid of the membrane. Hurst et al. (1974) showed that this heating caused 40% loss of the cellular Mg, and we now report the loss of 65% of the ester-bound D-alanine of teichoic acid. Repair from sublethal heat injury, measured by the return of salt tolerance, occurs in a simple no-growth medium provided that the cell concentration is less than 5 x 10(8)/ml. During repair, D-alanine is rapidly synthesized. Fully-repaired cells contain four times more D-alanine than do freshly-injured cells. Magnesium is present in the medium at only 3 x 10(-6) M, yet the cellular Mg concentration returns to normal within 1 h of incubation, even in the presence of EDTA. The results suggest that repair occurs in two stages. Soon after injury, in the absence of the competitive effect of D-alanine, Mg is strongly bound to teichoic acid. In repaired or uninjured cells Mg is less strongly bound. The implications of these findings are discussed in relation to the cation-binding function of teichoic acid.     

Methods for decreasing interstitial immunoglobulin in tissue slices and cryostat sections

To determine whether lymphoid antigens and cellular morphology can be preserved after long-distance transport in buffer or cell culture medium, we stained cryostat sections prepared from human tonsil samples that had been kept at 4 degrees C or 20 degrees C for 24, 48 or 72 h. B-Cell antigens, T-cell antigens, and Ia antigens were well preserved after storage up to 72 h in buffer or medium at 4 degrees C. Interstitial immunoglobulin (Ig) was decreased following all incubation procedures. We then investigated methods to diminish interstitial Ig in cryostat sections, since it would be inconvenient to keep 2-3 mm tissue slices in buffer or medium prior to freezing and subsequent Ig staining. Cryostat sections were air dried or briefly fixed in acetone prior to washing in buffer or medium at 4 degrees C, 20 degrees C or 37 degrees C for 1, 2 or 24 h. Then sections were air dried or washed prior to acetone fixation and immunostaining. A method for washing cryostat sections was developed which diminished interstitial Ig without compromising the quality of immunostaining or cellular detail. These methods are especially useful for studying samples of lymphoid tissue in which the presence of large quantities of interstitial Ig obscures the detection of monotypic Ig staining patterns.     

The influence of cyclic heating and cooling on Escherichia coli survival

Repeated heating and cooling in lethal (2-52 degrees C) and nonlethal (2-37 degrees C) temperature ranges resulted in cell death of Escherichia coli B/r and E. coli B(S-1) suspended in 0.01 M phosphate buffer, pH 7.0 at varying osmotic pressure, but not in cow's milk. The lethal effect increased with the rate of heating and with increasing suspension media tonicity; it may be caused by the temperature destabilization of cellular osmotic homeostasis.     

Competition between ligands of glycosyltransferases and horseradish peroxidase for binding sites on intracellular and plasma membranes of HeLa cells. Application of a micro-method for the semi-quantitation of surface-bound HRP

A micro-method for the semi-quantitation of surface-bound horseradish peroxidase (HRP) was developed and was applied to study the competition between ligands of glycosyltransferases and HRP for binding sites on the surface of HeLa cells. Dried coverslip cultures of HeLa cells, fixed in methanol, were placed on 0.3 ml of the incubation medium on parafilm and were incubated for 45 min at 37 degrees C. The incubation medium contained HRP, lysozyme and Ca2+ in HEPES buffer, pH 7.2. After washing, the cells were incubated for 60 min at 37 degrees C in HEPES buffer containing 20 mM Ca2+. After this treatment, the plasma membranes showed a strong cytochemical reaction for HRP. Most of the HRP was released into buffer solution during a 5 h incubation at 37 degrees C in the absence of Ca2+, and was measured by spectrophotometry. The addition of 20 mM Ca2+ to the buffer solution prevented the release of most of the HRP from the plasma membranes thus showing that the binding of HRP required Ca2+. Ligands of glycosyltransferases were added to the incubation medium with HRP. The amount of HRP released from the cells decreased in relation to the competing potency and concentration of these ligands. The method was applied to estimate the concentration of some ligands of galactosyltransferase and sialyltransferase that caused a 50% decrease in the release of previously-bound HRP. CMP-neuraminic acid and gangliosides showed a higher competing potency to the surface binding of HRP than UDP-galactose and chitotriose. The spectrophotometric analysis was correlated (on duplicate samples) with cytochemical observations.(ABSTRACT TRUNCATED AT 250 WORDS)     

Release of outer membrane fragments from wild-type Escherichia coli and from several E. coli lipopolysaccharide mutants by EDTA and heat shock treatments.

EDTA-induced outer membrane losses from whole cells of wild-type Escherichia coli (O111:B4) and several lipopolysaccharide (LPS) mutants derived from E. coli K-12 D21 were analyzed. EDTA treatment induced losses of LPS (up to 40%), outer membrane proteins OmpA, OmpF/C, and lipoprotein, periplasmic proteins, and phosphatidylethanolamine. The extent of these releases was strain specific. Successively more EDTA was necessary to induce these losses from strains containing LPS with increasing polysaccharide chain length. An additional heat shock immediately following the EDTA treatment had no effect on LPS release, but it decreased the release of outer membrane proteins and reduced the leakage of periplasmic proteins, suggesting that the temporary increase in outer membrane "permeability" caused by Ca2+-EDTA treatment was rapidly reversed by the redistribution of outer membrane components, a process which is favored by a mild heat shock. The fact that the material released from E. coli C600 showed a constant ratio of lipoprotein, OmpA, and phosphatidylethanolamine at all EDTA concentrations tested suggests that the material is lost as specific outer membrane patches. The envelope alterations caused by EDTA did not result in cell lysis.     

Effects of Pluronic F-68 on Tetrahymena cells: protection against chemical and physical stress and prolongation of survival under toxic conditions

The effects of the non-ionic surfactant Pluronic F-68 (0.01% w/v) on Tetrahymena cells have been studied. A marked protection against chemical and physical stress was observed. The chemical stress effects were studied in cells suspended in buffer (starvation) or in buffers with added ingredients from a chemically defined medium (Ca2+, Mg2+, Na+, K+, trace metal ions). The physical stress was due to mechanical stress or hyperthermia. The data show that Pluronic: (a) prolongs the survival of low concentration cell suspensions during starvation; (b) prevents the cell death caused by low concentrations of Ca2+ (70 microM); (c) prolongs the survival of cells exposed to higher ion concentrations (10 mM Ca2+, or Na+ or K+); (d) postpones the death caused by trace metal ions like Zn2+, Fe3+ and, Cu2+; (e) protects cells from the death caused by shearing forces; and (f) prolongs the survival of cells exposed to hyperthermia (43 degrees C). The cellular survival is increased at reduced temperatures (e.g. 4 degrees C instead of 36 degrees C) and at increased cellular concentrations (e.g. 100 cells ml(-1) instead of 25 or 10 cells ml(-1)). There is no effect of pre-incubation with Pluronic. The protective effect of Pluronic towards Tetrahymena is observed for concentrations in the range from 0.001 to 0.1% w/v.     

Heat injury and repair in Campylobacter jejuni

A procedure for detecting and quantitating heat injury in Campylobacter jejuni was developed. Washed cells of C. jejuni A7455 were heated in potassium phosphate buffer (0.1 M, pH 7.3) at 46 degrees C. Samples were plated on brucella agar supplemented with Na2S2O3, FeSO4 X 7H2O, and sodium pyruvate and on a medium containing brilliant green, bile, Na2S2O3, FeSO4 X 7H2O, and sodium pyruvate. Colonies were counted after 5 days of incubation at 37 degrees C in an atmosphere containing 5% O2, 10% CO2, and 85% N2. After 45 min at 46 degrees C, there was virtually no killing and ca. two log cycles of injury. Cells grown at 42 degrees C were more susceptible to injury than cells grown at 37 degrees C. The addition to brucella agar supplemented with Na2S2O3, FeSO4 X 7H2O, and sodium pyruvate of three different antibiotic mixtures used in the isolation of C. jejuni from foods or clinical specimens did not prevent recovery of heat-injured C. jejuni. Cells lost 260 nm of absorbing materials during heat injury. The addition of 5% NaCl or 40% sucrose to the heating buffer prevented leakage but did not prevent injury. Of the additional salts, sugars, and amino acids tested for protection, only NH4Cl, KCl, and LiCl2 prevented injury. Heat-injured C. jejuni repaired (regained dye and bile tolerance) in brucella broth supplemented with Na2S2O3, FeSO4 X 7H2O, and sodium pyruvate within 4 h. Increasing the NaCl in this medium to 1.25% inhibited repair, and increasing it to 2% was lethal. Heat-injured C. jejuni will repair at 42 degrees C but not at 5 degrees C.     

Heat injury and repair in Campylobacter jejuni.

A procedure for detecting and quantitating heat injury in Campylobacter jejuni was developed. Washed cells of C. jejuni A7455 were heated in potassium phosphate buffer (0.1 M, pH 7.3) at 46 degrees C. Samples were plated on brucella agar supplemented with Na2S2O3, FeSO4 X 7H2O, and sodium pyruvate and on a medium containing brilliant green, bile, Na2S2O3, FeSO4 X 7H2O, and sodium pyruvate. Colonies were counted after 5 days of incubation at 37 degrees C in an atmosphere containing 5% O2, 10% CO2, and 85% N2. After 45 min at 46 degrees C, there was virtually no killing and ca. two log cycles of injury. Cells grown at 42 degrees C were more susceptible to injury than cells grown at 37 degrees C. The addition to brucella agar supplemented with Na2S2O3, FeSO4 X 7H2O, and sodium pyruvate of three different antibiotic mixtures used in the isolation of C. jejuni from foods or clinical specimens did not prevent recovery of heat-injured C. jejuni. Cells lost 260 nm of absorbing materials during heat injury. The addition of 5% NaCl or 40% sucrose to the heating buffer prevented leakage but did not prevent injury. Of the additional salts, sugars, and amino acids tested for protection, only NH4Cl, KCl, and LiCl2 prevented injury. Heat-injured C. jejuni repaired (regained dye and bile tolerance) in brucella broth supplemented with Na2S2O3, FeSO4 X 7H2O, and sodium pyruvate within 4 h. Increasing the NaCl in this medium to 1.25% inhibited repair, and increasing it to 2% was lethal. Heat-injured C. jejuni will repair at 42 degrees C but not at 5 degrees C.     

The nature of changes in the activity of water-soluble enzymes during the action of injurious agents on the muscles. V. A study of the extractability of lactate dehydrogenase from intact and altered muscles

A study was made of lactate dehydrogenase (LDH) extractability from intact and thermally injured muscles of Rana temporaria L. in the 0.15 M KCl solution and in the non-electrolyte medium. A 15 minute incubation of intact muscles and those treated with heat at 38, 42, 44 and 46 degrees C in the 0.15 M KCl solution led to a much higher extraction of LDH than in the non-electrolyte medium. Following heating at 38 degrees C, causing irreversible injury of muscles, the LDH extractability in the non-electrolyte medium is seen to fall, whereas in the 0.15 M KCl solution it remained at the same level as after LDH extraction from intact muscles. The decrease in LDH extractability in non-electrolyte medium from thermally injured muscles may be due to the increase in LDH binding with thermolabile structural components of muscle. One of the components of muscle cell, known to bind LDH, is actomyosin, since it is isolated from muscles together with LDH, which cannot be removed by actomyosin reprecipitation or by increasing the volume of washing solution.     

Sensitivity to bile salts of Shigella flexneri sublethally heat stressed in buffer or broth.

Batch cultures of Shigella flexneri M4243 were grown at 37 degrees C in broth to early stationary phase, washed, and heated at 50 degrees C in 0.1 M phosphate buffer (pH 7.0). Cells were surface plated on a tryptic phytone glucose agar (TPGA), TPGA with 0.15 or 0.85% bile salts no. 3 (TPGA-BS 0.15 or TPGA-BS 0.85), or TPGA with 0.25 or 0.50% sodium deoxycholate (TPGA-DC 0.25 or TPGA-DC 0.50). Cells sampled after no heating produced colony counts on TPGA-BS 0.85 or on TPGA-DC 0.50 that were no more than about 0.5 log lower than for unheated cell samples plated on TPGA. Cells heated at 50 degrees C for 30 min produced colony counts on TPGA-DC 0.50 or on TPGA-BS 0.85 that were about 1.5 logs lower than on TPGA. Cells heated for 30 min and shifted to TPG broth at 37 degrees C to allow resuscitation required about 2 h to regain tolerance to 0.85% BS. However, heated cells resuscitated on solid TPGA at 35 degrees C before being challenged with overlays of TPGA-BS 0.85 or TPGA-DC 0.50 required 6 to 8 h on TPGA to regain tolerance to 0.85% BS or 0.50% DC. To regain tolerance to overlays of 0.15% BS or 0.25% DC, heated cells required resuscitation periods on TPGA of about 2 or 2 to 6 h, respectively. Cells heated in TPG broth and sampled after no heating produced colony counts on TPGA that were about 1.5 logs lower than for unheated cell suspensions, suggesting greater apparent injury when heat stressed in broth than in buffer.(ABSTRACT TRUNCATED AT 250 WORDS)     

Sensitivity to bile salts of Shigella flexneri sublethally heat stressed in buffer or broth

Batch cultures of Shigella flexneri M4243 were grown at 37 degrees C in broth to early stationary phase, washed, and heated at 50 degrees C in 0.1 M phosphate buffer (pH 7.0). Cells were surface plated on a tryptic phytone glucose agar (TPGA), TPGA with 0.15 or 0.85% bile salts no. 3 (TPGA-BS 0.15 or TPGA-BS 0.85), or TPGA with 0.25 or 0.50% sodium deoxycholate (TPGA-DC 0.25 or TPGA-DC 0.50). Cells sampled after no heating produced colony counts on TPGA-BS 0.85 or on TPGA-DC 0.50 that were no more than about 0.5 log lower than for unheated cell samples plated on TPGA. Cells heated at 50 degrees C for 30 min produced colony counts on TPGA-DC 0.50 or on TPGA-BS 0.85 that were about 1.5 logs lower than on TPGA. Cells heated for 30 min and shifted to TPG broth at 37 degrees C to allow resuscitation required about 2 h to regain tolerance to 0.85% BS. However, heated cells resuscitated on solid TPGA at 35 degrees C before being challenged with overlays of TPGA-BS 0.85 or TPGA-DC 0.50 required 6 to 8 h on TPGA to regain tolerance to 0.85% BS or 0.50% DC. To regain tolerance to overlays of 0.15% BS or 0.25% DC, heated cells required resuscitation periods on TPGA of about 2 or 2 to 6 h, respectively. Cells heated in TPG broth and sampled after no heating produced colony counts on TPGA that were about 1.5 logs lower than for unheated cell suspensions, suggesting greater apparent injury when heat stressed in broth than in buffer.(ABSTRACT TRUNCATED AT 250 WORDS)     

Significance of the inactivation of transport in thermal death of Escherichia coli.

Cells of Escherichia coli ML308-225, harvested from the exponential phase, were heated in 50 mM potassium phosphate, and the loss in viability and inability to transport lactose, proline, and alpha-methylglucoside was compared. After cells were heated at 48 degrees C for 15 min, there was a 16% loss in viability and a similarly small reduction in the steady-state accumulation of lactose at 25 degrees C. The initial rates of lactose and proline transport were severely inhibited by heating at either 48 or 50 degrees C, but substantial recovery occurred within 5 to 7 min at 25 degrees C. Heating at 50 degrees C for 15 min caused an 86% loss in viability, but only a 53% decrease in the steady-state accumulation of lactose and only a 24% reduction in the initial rate of alpha-methylglucoside uptake. Twice as much alpha-methylglucoside was accumulated at 50 degrees C as at 25 degrees C. Although alpha-methylglucoside phosphate leaked from the cells at 50 degrees C, the concentration retained within the cells was about 500 times that externally, when only about 14% of the cells were viable. Overall, these results indicate that cells made nonviable by heating at 50 degrees C still have significant membrane integrity.     

Significance of the inactivation of transport in thermal death of Escherichia coli.

Cells of Escherichia coli ML308-225, harvested from the exponential phase, were heated in 50 mM potassium phosphate, and the loss in viability and inability to transport lactose, proline, and alpha-methylglucoside was compared. After cells were heated at 48 degrees C for 15 min, there was a 16% loss in viability and a similarly small reduction in the steady-state accumulation of lactose at 25 degrees C. The initial rates of lactose and proline transport were severely inhibited by heating at either 48 or 50 degrees C, but substantial recovery occurred within 5 to 7 min at 25 degrees C. Heating at 50 degrees C for 15 min caused an 86% loss in viability, but only a 53% decrease in the steady-state accumulation of lactose and only a 24% reduction in the initial rate of alpha-methylglucoside uptake. Twice as much alpha-methylglucoside was accumulated at 50 degrees C as at 25 degrees C. Although alpha-methylglucoside phosphate leaked from the cells at 50 degrees C, the concentration retained within the cells was about 500 times that externally, when only about 14% of the cells were viable. Overall, these results indicate that cells made nonviable by heating at 50 degrees C still have significant membrane integrity.     

Death and injury of Staphytococcus aureus during thermal treatment of milk

Staphylococcus aureus isolated from milk and grown in milk was heated in milk. The phenomena of death as well as injury was investigated in the range of 50 to 75 degrees C. The D60 value (decimal reduction time on salt-free medium) was 0.87 min, the D'60 value (decimal reduction time in salt-containing medium) was 0.62 min. Cultures were injured as soon as heating started. This initial thermal shock increased with increasing temperature. At 50-60 degrees C injury was more rapid than death. At greater than 60 degrees C death became faster than injury and the two processes coincided at 70 degrees C. The Z value was 9.46 degrees C and the Z' value was 9.93 degrees C.     

Effect of culture age, pre-incubation at low temperature and pH on the thermal resistance of Aeromonas hydrophila.

The thermal resistance of Aeromonas hydrophila strain NCTC 8049 was determined within the range 48 degrees-65 degrees C with a thermoresistometer TR-SC and McIlvaine buffer. The effects of culture age, pre-incubation at 7 degrees C and the pH of the heating menstruum were evaluated. The pattern of thermal death was dependent on culture age. Cells heated in the late logarithmic growth phase (15 h at 30 degrees C) were twice as resistant as those in the early stage (5 h at 30 degrees C), and the maximum D-value was obtained after 72 h incubation (5.5 total increase). The age of the cells did not affect z-values significantly. The heat resistance of cells incubated for 48 h at 30 degrees C increased (twice) after holding at 7 degrees C for 72 h. Pre-incubation at low temperature of older cultures (72 h, 30 degrees C) did not influence their D-values. Maximum heat resistance was found at pH 6.0 and minimal at pH 4.0. Decreasing the pH from 6.0 to 4.0 reduced D-values by a factor of 5. Although the strain studied was heat-sensitive (D55 degrees C = 0.17 min; z = 5.11 degrees C), survivor curves of cultures older than 50 h showed a significant tailing. Organisms surviving in the tails were only slightly more resistant than were the original population.     

Injured arterial smooth muscle cells in culture release factors affecting viability and collagen secretion of new cultures

Cultures of arterial smooth muscle cells were exposed to ultraviolet light, dimethylsulphoxide-soluble particles from cigarette smoke (DSP) and hypoxia. Hypoxia produced no lasting toxic effects but the other stimuli did. Serum free medium was conditioned by cells damaged by these stimuli and the effects on new smooth muscle cell cultures were studied. Hypoxia did not induce any transferable effects. Cells damaged by a standard concentration of DSP released factor(s) that reduced cell mass of new cultures by 25% compared to controls; cell death increased 23%, and DNA synthesis fell by 23% but collagen secretion was unchanged in absolute amounts. If correction for the smaller cell mass was performed, collagen secretion increased 46% while DNA synthesis was unchanged. The DSP induction of transferable cell injury was biphasically dose dependent, maximal effect being noted in the intermediate DSP levels. If ultraviolet light was used as stimulus, cell mass of secondary cultures fell by 32% and cell death increased 31%. Correction for the smaller cell mass showed that both DNA synthesis and collagen secretion were increased compared to controls, both by 61%. The transferable activity remained after dialysis but was completely destroyed by heating at 100 degrees C. The results are discussed in relation to the pathogenesis of atherosclerosis, and it is suggested that cell injury might lead to selection of more active cell clones that could contribute to the progression of atherosclerosis.     

Development of a cell wash buffer that minimizes nucleic acid loss from Clostridium perfringens 10543 A

Autolytic activity and nucleic loss from Clostridium perfringens 10543 A was demonstrated during successive cell washes in hypotonic TES buffer. Autolysis increased nearly sixfold and nucleic acid loss nearly twofold when 10 mM EDTA was added to 0.3 M Tris-sucrose buffer. Attempts to minimize both autolysis and nucleic acid loss from C. perfringens during routine washing steps were unsuccessful when the effects of sucrose concentration, pH, CaCl2 addition, or wash temperature were examined independently. However, autolytic activity was eliminated and nucleic acid loss reduced to less than 5% when C. perfringens cells were washed at 4 or 25 degrees C in 1.0 M sucrose, 50 mM Tris--HCl, and 25 mM CaCl2 at pH 5.7.     

Thermal stability and folding of type IV procollagen and effect of peptidyl-prolyl cis-trans-isomerase on the folding of the triple helix

Intact, monomeric type IV procollagen was isolated from the medium of PF-HR9 cells. Its stability was measured by optical rotatory dispersion, differential scanning calorimetry, and trypsin susceptibility of the partially unfolded molecules. At neutral pH, a complex transition between 35 and 42 degrees C and a smaller transition at 48 degrees C are observed by optical rotatory dispersion, using a heating rate of 10 degrees C/h. Reduction of the heating rate to 1.6 degrees C/h resulted in a 1 degree C lowering of the apparent melting temperatures. A similar curve is observed in 10 mM acetic acid, with transitions about 2 degrees C lower. Differential scanning calorimetry revealed transitions at 36.0, 42.1, and 48.0 degrees C at neutral pH, with a total transition enthalpy of 17.1 kJ/mol tripeptide units. In 10 mM acetic acid, transitions at 35.6, 38.9, 41.7, and 50.0 degrees C are observed. The transition enthalpy is 16.4 kJ/mol tripeptide units. The transition enthalpy is similar to values found for interstitial collagens. Results from trypsin digestion experiments are consistent with the stability found by optical methods and calorimetry. The rate and completeness of refolding after melting were measured. In neutral buffer, the initial rate was found to be 0.041 min-1, faster than the refolding rates observed with types pN III and III collagen. Peptidyl prolyl cis-trans-isomerase increased the refolding rate to 0.083 min-1, indicating that cis-trans-isomerization is the rate-limiting step, despite the interruptions in the triple helix. Trypsin digestion experiments indicated that the refolding mechanism is similar in the presence and absence of the enzyme. Refolding was nearly complete in neutral buffer. In 10 mM acetic acid, folding was considerably slower and went to about 74% completion. In both solvents, the refolded material was only slightly less stable than the native material. Electron microscopy of partially refolded samples showed that most refolding started at the COOH terminus, but some was initiated at other sites.     

Effect of osmotic shock on the viability, optical density and permeability of heated Escherichia coli cells

The object of this work was to study the effect of a short incubation in 0.01 M tris buffer, pH 7.0, with a different NaCl content (0-10%) on the viability, optic density and permeability of intact and heated at 52 degrees C Escherichia coli B/r cells. In contrast to the intact cells, the viability of the heated cells depended on osmotic pressure in the medium into which they were transferred after heating. The survival rate was highest when the cells were transferred into an isotonic buffer. In the case of hypotonic and hypertonic media, the survival rate of the cells decreased owing to the death of cells which were responsible for the formation of small colonies under the isotonic conditions. This was accompanied with a more intensive drop in the optic density of bacterial suspensions while their permeability increased (when the cells were transferred into the hypotonic conditions). The role of membranes in the processes of bacterial heat inactivation is discussed on the basis of the results obtained.     

Heat-induced blebbing and vesiculation of the outer membrane of Escherichia coli.

Thermal damage to the outer membrane of Escherichia coli W3110 was studied. When E. coli cells were heated at 55 degrees C in 50 mM Tris-hydrochloride buffer at pH 8.0, surface blebs were formed on the cell envelope, mainly at the septa of dividing cells. Membrane lipids were released from the cells during the heating period, and part of the released lipids formed vesicle-like structures from the membrane. This vesicle fraction had a lipopolysaccharide to phospholipid ratio similar to that of the outer membrane of intact cells, whereas it had a lower content of protein than the isolated outer membrane. After heating bacterial cells at 55 degrees C for 30 min, the resulting leakage from the cells of a periplasmic enzyme, alkaline phosphatase, amounted to 52% of the total activity, whereas no release of a cytoplasmic enzyme, glucose-6-phosphate dehydrogenase, was detected. The results obtained suggest that surface blebs formed by heat treatment almost completely consist of the outer membrane and that the blebs may be gradually released from the cell surface into the heating menstruum to partially form vesicles.