Physiopathology of bedsores

Listeria monocytogenes is a food-borne pathogenic bacterium that can be found in soft cheese. At the beginning of cheese ripening, the pH is about 4.85-4.90. The aim of this work was to study the influence of temperature, preincubation temperature (temperature at which the inoculum was cultivated) and initial bacterial concentration on the survival of L. monocytogenes (strain Scott A) at pH 4.8. It was demonstrated in an earlier study that these factors did influence growth kinetics. Survival studies of L. monocytogenes were done in a laboratory broth simulating cheese composition. Four test temperatures (2, 6, 10 and 14 degrees C) and two preincubation temperatures were studied (30 degrees C or the test temperature). Listeria monocytogenes (strain Scott A) was unable to grow at pH 4.8 under all conditions tested. The time for 10% survival was about 11 and 2 d, at 2 degrees C with preincubation at 2 degrees C and 30 degrees C, respectively; 9 d at 6 degrees C with preincubation at 6 degrees C; 4 d at 6 degrees C with preincubation at 30 degrees C; and 1 d at 14 degrees C with preincubation at 14 degrees C or at 30 degrees C. The results show that survival of L. monocytogenes (strain Scott A) at pH 4.8 is not dependent on initial bacterial concentration but on both the test and preincubation temperatures.     

Limited access to a dietary fat option affects ingestive behavior but not body composition in male rats

Survival, recoverability and sublethal injury of two strains of Listeria monocytogenes, Scott A and an environmental strain KM, on exposure to sea water at 12.8 or 20.8 degrees C was determined using in situ diffusion chambers. Plate counts were used to assess recoverability and injury while 5-cyano-2,3-ditolyl tetrazolium chloride (CTC) reduction was used to determine respiratory activity. T90 values (times for 10-fold decreases in numbers of recoverable cells) on non-selective medium (trypticase soya agar with 0.6% yeast extract) at 12.8 and 20.8 degrees C were 61.7 and 69.2 h for L. monocytogenes Scott A, and 103.0 and 67.0 h for L. monocytogenes KM, respectively. On selective medium (Oxford agar), T90 values at 12.8 and 20.8 degrees C were 60.6 and 56.9 h for L. monocytogenes Scott A, and 83.0 and 65.9 h for L. monocytogenes KM, respectively. With Scott A, the percentage of sublethally injured cells at 12.8 and 20.8 degrees C was 1.7 and 17.7%, respectively, while for KM the values were 19.0 and 1.6%, respectively. The fraction of cells reducing CTC but which were not recoverable on plating progressively increased on exposure to sea water. Listeria monocytogenes KM challenged at 58 degrees C showed an apparent increase in heat resistance after exposure to sea water at 20.8 degrees C for 7 d (D58 = 2.64 min) compared with before exposure (D58 = 1.24). This increase in thermal resistance was not apparent at temperatures greater than 63 degrees C, and analysis of the best-fit regression lines fitted to the thermal data obtained from the two cell populations indicated that their thermal resistance was not significantly different (P > 0.05) over the temperature range tested (58-62 degrees C).     

Effect of polyphosphate and sodium chloride on the growth of Listeria monocytogenes and Staphylococcus aureus in ultra-high temperature milk

With UHT-sterilized milk as a model system, combinations of polyphosphate (.5 and 1.0%) and NaCl (.5 and 4.5%) were studied to determine their effects on the growth kinetics of Listeria monocytogenes Scott A and Staphylococcus aureus 196E. The milk was inoculated with 10(3) to 10(4) cfu/ml of either L. monocytogenes or S. aureus and incubated under aerobic conditions at 12, 19, 28, or 37 degrees C. The addition of polyphosphate did not significantly inhibit the growth of either microbe at the temperatures studied, but the addition of NaCl or a combination of salts significantly inhibited growth. The addition of .5 or 1.0% polyphosphate alone to dairy products is not likely to affect substantially the growth of S. aureus or L. monocytogenes.     

Influence of environmental stress on the kinetics and strength of attachment of Listeria monocytogenes Scott A to Buna-N rubber and stainless steel

Attachment and detachment of Listeria monocytogenes Scott A to Buna-N rubber and stainless steel under varying conditions of temperature and pH were investigated using model systems. Numbers of attached cells increased with increasing attachment temperature (10 to 45 degrees C) and time (up to 120 min) for both test surfaces. Compared to Buna-N rubber, the rate of attachment to stainless steel was markedly more rapid for all temperature and pH conditions studied and could not be calculated. Rate of attachment to Buna-N rubber was found to be significantly lower when cells were attached at 10 degrees C. Growth temperature did not significantly affect rates of adhesion to Buna-N rubber. Altering the medium pH during attachment between 4 and 9 demonstrated that rates of adhesion were slower under alkaline conditions. Growth pH was also found to significantly affect rates of attachment to Buna-N rubber. Detachment of cells adhered to Buna-N rubber was significantly affected by growth temperature but not growth pH. Significant differences in detachment were also found between Buna-N rubber and stainless steel, inferring stronger attachment to Buna-N rubber. Cell surface hydrophobicity was found to be affected by both growth temperature and growth pH. However, changes in hydrophobicity could not be correlated to differences in rates of attachment. Addition of 0.01% trypsin to the attachment medium during cell exposure to either test surface resulted in a 99.9% reduction in the adhered cell population when compared to controls. This would suggest that proteins play a role in the initial attachment process of L. monocytogenes.     

Altered efficacy and selectivity of tyrosine kinase inhibitors of the activated states of protein tyrosine kinases

Listeria monocytogenes is a pathogenic bacterium which has been implicated in several foodborne illnesses. This microorganism grows into biofilms attached to the surfaces in food-processing plants, increasing its resistance to antimicrobial agents. The present work was realized to investigate the attachment of L. monocytogenes isolates to glass surfaces and to find a decontamination procedure to remove these bacteria in biofilms. Three-day biofilms were prepared by growing L. monocytogenes isolates from food plant environments on glass surfaces. Sixteen decontamination treatments at different pHs, temperatures, and times of exposure were tested against L. monocytogenes biofilms. The most efficient treatments were those applied at 63 degrees C. Combinations of decontamination treatments applied at 55 degrees C for 30 min provided different results according to the other factors used. In general, L. monocytogenes biofilms were found to be not very susceptible to high osmolarity (10.5% NaCl), and the interaction of sodium chloride and acid did not seem to have important effects in inactivating these bacteria (from a 1.3-to a 1.9-log-CFU/cm2 reduction). The combination of NaOH (pH 10.5; 100 mM) and acetic acid (pH 5.4; 76.7 mM) applied sequentially at 55 degrees C for even 5 min was shown to be the most effective treatment to remove L. monocytogenes from biofilms (at least a 4.5-to 5.0-log-CFU/cm2 decline).     

Effects of several factors on the heat-shock-induced thermotolerance of Listeria monocytogenes

The influence of the temperature at which Listeria monocytogenes had been grown (4 or 37 degrees C) on the response to heat shocks of different durations at different temperatures was investigated. For cells grown at 4 degrees C, the effect of storage, prior to and after heat shock, on the induced thermotolerance was also studied. Death kinetics of heat-shocked cells is also discussed. For L. monocytogenes grown at 37 degrees C, the greatest response to heat shock was a fourfold increase in thermotolerance. For L. monocytogenes grown at 4 degrees C, the greatest response to heat shock was a sevenfold increase in thermotolerance. The only survival curves of cells to have shoulders were those for cells that had been heat shocked. A 3% concentration of sodium chloride added to the recovery medium made these shoulders disappear and decreased decimal reduction times. The percentage of cells for which thermotolerance increased after a heat shock was smaller the milder the heat shock and the longer the prior storage.     

Effects of above-optimum growth temperature and cell morphology on thermotolerance of Listeria monocytogenes cells suspended in bovine milk

The thermotolerances of two different cell forms of Listeria monocytogenes (serotype 4b) grown at 37 and 42.8 degrees C in commercially pasteurized and laboratory-tyndallized whole milk (WM) were investigated. Test strains, after growth at 37 or 42.8 degreesC, were suspended in WM at concentrations of approximately 1.5 x 10(8) to 3.0 x 10(8) cells/ml and were then heated at 56, 60, and 63 degrees C for various exposure times. Survival was determined by enumeration on tryptone-soya-yeast extract agar and Listeria selective agar, and D values (decimal reduction times) and Z values (numbers of degrees Celsius required to cause a 10-fold change in the D value) were calculated. Higher average recovery and higher D values (i.e., seen as a 2.5- to 3-fold increase in thermotolerance) were obtained when cells were grown at 42.8 degrees C prior to heat treatment. A relationship was observed between thermotolerance and cell morphology of L. monocytogenes. Atypical Listeria cell types (consisting predominantly of long cell chains measuring up to 60 micron in length) associated with rough (R) culture variants were shown to be 1.2-fold more thermotolerant than the typical dispersed cell form associated with normal smooth (S) cultures (P 相似文献   

Gamma-glutamyltransferase as a marker for the pasteurization of raw milk

The degree and rate of inactivation of gamma-glutamyltransferase in raw cow's milk by heating at 50, 60, 70, and 80 degrees C for 1, 2, 3, 5, 10, 15, 20, 25, and 30 min were measured to evaluate the suitability of this enzyme as a marker for the pasteurization of milk. The enzymes alkaline phosphatase and lactate dehydrogenase were also measured under similar conditions for comparison. The patterns of heat inactivation of gamma-glutamyltransferase and alkaline phosphatase were similar, with only a minimal inactivation of the enzymes at 50 degrees C. The rate of inactivation increased as a result of increasing temperatures and time. A complete inactivation of both enzymes was seen at 70 degrees C after 10 min and at 80 degrees C after 1 min. Lactate dehydrogenase showed a higher heat resistance with almost complete inactivation at 70 degrees C for 30 min, and compete inactivation at 80 degrees C for 3 min. No activities of these enzymes were found in commercially pasteurized or heat-treated milk. The levels of gamma-glutamyltransferase in raw milk were between 8 and 10% higher than those of alkaline phosphatase and lactate dehydrogenase, making it more sensitive and accurate as a testing marker. It seems that gamma-glutamyltransferase may serve as a good pasteurization marker. Furthermore, the simplicity of testing and the availability of commercial kits for testing by both wet and dry chemistry make it an attractive choice, especially because dry chemistry procedures overcome the difficulties originating from the turbidity of milk, which interferes with spectrophotometric procedures.     

A proposed nonpathogenic biological indicator for thermal inactivation of Listeria monocytogenes

Listeria innocua M1 was developed as a thermal processing indicator organism for L. monocytogenes by selection of a rifampin- and streptomycin-resistant mutant. zetaD values were 5.6 and 5.8 degrees C, and D (68 degrees C) values were 3.8 and 4.9 s for L. monocytogenes and L. innocua, respectively, in skim milk. The advantages of easy selection, similar heat resistance, and nonpathogenicity make L. innocua M1 appropriate for challenge studies designed to evaluate process lethality with respect to L. monocytogenes.     

Nonthermal pasteurization of liquid foods using high-intensity pulsed electric fields

Processing foods with high-intensity pulsed electric fields (PEF) is a new technology to inactivate microorganisms and enzymes with only a small increase in food temperature. The appearance and quality of fresh foods are not altered by the application of PEF, while microbial inactivation is caused by irreversible pore formation and destruction of the semipermeable barrier of the cell membrane. High-intensity PEF provides an excellent alternative to conventional thermal methods, where the inactivation of the microorganisms implies the loss of valuable nutrients and sensory attributes. This article presents recent advances in the PEF technology, including microbial and enzyme inactivation, generation of pulsed high voltage, processing chambers, and batch and continuous systems, as well as the theory and its application to food pasteurization. PEF technology has the potential to improve economical and efficient use of energy, as well as provide consumers with minimally processed, microbiologically safe, nutritious and freshlike food products.     

Effect of high hydrostatic pressure on Escherichia coli and Pseudomonas fluorescens strains in ovine milk

Ovine milk that had been standardized to 6% fat was inoculated with Escherichia coli 405 CECT and Pseudomonas fluorescens 378 CECT at a rate of 10(6) and 10(7) cfu/ml, respectively, and treated with high hydrostatic pressure. Treatments consisted of combinations of pressure (300, 400, 450, and 500 MPa), temperature (2, 10, 25, and 50 degrees C), and time (5, 10, and 15 min). Inactivation (> 6 log cfu/ml) of both strains was observed at 50 degrees C for all pressures and treatment times. A similar level of inactivation occurred at > or = 450 MPa and 25 degrees C for E. coli and at > or = 400 MPa and 10 degrees C for P. fluorescens. Destruction was lowest at 10 degrees C for E. coli and at 25 degrees C for P. fluorescens. The test strain of E. coli was more baroresistance than was the P. fluorescens strain.     

An experimental study of ototoxicity induced by deferoxamine mesilate

The radiation resistance and ability of Listeria monocytogenes ATCC 7644, 15313, 43256, and 49594 to multiply on irradiated, air-packed, refrigerated raw or cooked turkey breast meat nuggets (ca. 25 g) and ground turkey breast meat was investigated. Gamma-radiation D values for L. monocytogenes were significantly different on raw and cooked nuggets, 0.56 +/- 0.03 kGy and 0.69 +/- 0.03 kGy, respectively; but they were not significantly different (P < or = 0.05) on raw and cooked ground turkey meat. High populations (approximately 10(9) CFU/g) of L. monocytogenes declined during 14 days of storage at 4 degrees C in both irradiated and nonirradiated samples of raw but not of cooked ground turkey breast meat. A moderate inoculum (approximately 10(3) CFU/g) did not survive a radiation dose of 3 kGy. The population increased in cooked but not in raw samples of irradiated ground turkey meat stored at either 2 or 7 degrees C for 21 days. The D value changed significantly from 0.70 +/- 0.04 to 0.60 +/- 0.02 kGy when the product was cooked to an internal temperature of 80 degrees C before irradiation. Growth on either raw or cooked turkey meat did not alter the radiation resistance of L. monocytogenes. Analyses were performed for pH, aw, moisture, and reducing potential of raw and cooked turkey meat and for pH, amino acid profile, thiamine, and riboflavin contents of aqueous extracts of raw and cooked turkey meats without identifying the factor or factors involved in differences in the survival and multiplication of L. monocytogenes on raw and cooked meat.     

Predictive models of the effect of temperature, pH and acetic and lactic acids on the growth of Listeria monocytogenes

The combined effect of temperature (1-20 degrees C), pH (4.5-7.2) and acetic acid (0-10,000 mg/l; model 1) or lactic acid (0-20,000 mg/l; model 2) on growth of Listeria monocytogenes in laboratory media was studied. Growth curves at various combinations of temperature, pH and acid concentration were fitted by the model of Baranyi and Roberts (1994), and specific growth rates derived from the curve fit were modelled. Predictions of growth from the models were compared with data in the literature, and this showed the models to be suitable for use in predicting growth of L. monocytogenes in a range of foods including meat, poultry, fish, egg and milk and dairy products. The two models are compatible, i.e. they give similar predictions for cases when no acid is present.     

Differentiation of Listeria monocytogenes and Listeria innocua by 16S rRNA genes and intraspecies discrimination of Listeria monocytogenes strains by random amplified polymorphic DNA polymorphisms

Differences in the 16S rRNA genes (16S rDNA) which can be used to discriminate Listeria monocytogenes from Listeria innocua have been detected. The 16S rDNA were amplified by polymerase chain reaction with a set of oligonucleotide primers which flank a 1.5-kb fragment. Sequence differences were observed in the V2 region of the 16S rDNA both between L. monocytogenes Scott A and L. innocua and between different L. monocytogenes serotypes. Although L. monocytogenes SLCC2371 had the same V2 region sequence as L. innocua, the two species were different within the V9 region at nucleotides 1259 and 1292, in agreement with previous studies (R.-F. Wang, W.-W. Cao, and M.G. Johnson, Appl. Environ. Microbiol. 57:3666-3670, 1991). Intraspecies discrimination of L. monocytogenes strains was achieved by using the patterns generated by random amplified polymorphic DNA primers. Although some distinction can be made within the L. monocytogenes species by their 16S rDNA sequence, a far greater discrimination within species could be made by generating random amplified polymorphic DNA patterns from chromosomal DNA. By using a number of 10-bp primers, unique patterns for each isolate which in all cases examined differentiate between various L. monocytogenes serotypes, even though they may have the same 16S rRNA sequences, could be generated.     

Bovine mastitis caused by Listeria monocytogenes: kinetics of antibody responses in serum and milk after experimental infection

The kinetics of antibodies in serum and milk directed against proteins from Listeria monocytogenes were studied using 4 lactating cows after infection was experimentally induced in the udder with four strains of serotypes 4b or 1/2a. Antibodies (IgG and IgA) in samples of composite quarter milk and serum of the cow were measured by indirect ELISA. Microtiter plates were coated with proteins obtained from the culture supernatant of L. monocytogenes 4b. After challenge, an IgG response in serum and milk to listerial infections in the udder occurred for all cows, although the response varied among cows. In sera, the IgG titers reached a peak at 9 to 13 wk after challenge and remained elevated until 21 to 33 wk after challenge. In milk, the IgG titer increased significantly 3 wk after the challenge for all cows. A weak and nonpersistent increase in IgA antibodies also occurred. These results indicate that IMI by L. monocytogenes induced an increase of antibodies in milk, which could be detected with an ELISA test using our antigenic preparation. Therefore, this antigenic preparation could be used for the evaluation of a new method of diagnosis for bovine mastitis caused by L. monocytogenes.     

Effectiveness of salt, pH, and diacetyl as inhibitors for Escherichia coli O157:H7 in dairy foods stored at refrigeration temperatures

The behavior of Escherichia coli O157:H7 inoculated in 10% rehydrated nonfat dry milk adjusted to pH levels between 3.8 and 5.4 with lactic acid, salt levels of 0 to 6%, and diacetyl levels of 0, 5, and 10 micrograms/g was determined at 4 and 12 degrees C. Cell populations were determined by surface plating on tryptic soy agar after 7 and 35 days of incubation. Survival was also determined using retail cultured diary products. E. coli O157:H7 did not survive in skim milk at pH 3.8 and was reduced by 3 log cycles at pH 4.1, regardless of salt, diacetyl, and temperature levels. At pH levels above 4.4, survival was observed at lower salt concentrations for up to 35 days at both 12 and 4 degrees C. The organism grew (up to a 2.2-log increase) at pH 5.0 at 2% salt levels after 35 days of storage at 12 degrees C. Diacetyl at a concentration of 10 ppm had no effect on survival and growth. In all but one case, E. coli O157:H7 was inactivated in yogurt, sour cream, and buttermilk at a rate similar to or greater than what was consistent with the acidified skim milk data. Also consistent with the skim milk data, growth occurred in two of the three cottage cheese samples at 12 degrees C after 7 days but not after 35 days or at 4 degrees C, when a 1- to 2-log decline was observed.     

Rationale and design of the Myocardial Ischemia Reduction with Aggressive Cholesterol Lowering (MIRACL) study that evaluates atorvastatin in unstable angina pectoris and in non-Q-wave acute myocardial infarction

Pediococcus sp. is a nonpathogenic heat-resistant spoilage organism that has been used as a test organism in milk pasteurization studies. These characteristics make this bacterium an attractive test organism to study the mode of bacterial thermal inactivation in a food pilot plant. We report here the effect of growth medium on the thermal D value of this organism in skim milk, whole liquid egg, 10% glucose solution, pineapple juice, apple juice, tomato juice, and water at 60 degrees C. Thermal inactivation was done in a submerged coil; D values were calculated from the linear portion of the survival curves by linear regression analysis. The range of D values of stationary-phase cells grown at 28 degrees C in tryptone glucose yeast extract (TGY) or tryptic soy broth (TSB) was 0.14 to 12.05 min in all heating menstrua tested. The TSB-grown cells exhibited the highest thermal resistance with skim milk and 10% glucose solution as the heating menstrua. Survival curves of the TGY-grown cells indicated the presence of a cell population heterogeneous in thermal resistance. The TSB-grown cells exhibited a cell population uniform in thermal resistance and with a lag time for thermal inactivation. When compared to TGY-grown cells, Pediococcus sp. grown in TSB showed a significant (P < 0.05) increase in D values by up to eightfold in all heating menstrua. Results from this study suggested that thermal inactivation of Pediococcus sp. was dependent on the growth medium and on the heating menstruum with respect to both pH and composition.     

Listeria monocytogenes infection of Caco-2 cells: role of growth temperature

The aim of the present study was to evaluate the role of temperature in the virulence of Listeria monocytogenes, a Gram-positive facultative intracellular food-borne pathogen. The capacity of bacteria grown at 37, 25 and 4 degrees C to develop haemolytic activity, to enter the Caco-2 enterocyte-like cell line and to multiply intracellularly was investigated. We demonstrated that L. monocytogenes penetration was not significantly influenced by the growth temperature of cultures and that bacteria grown at low temperature were capable of synthesizing internalin and, during the infection process, of restoring the haemolytic phenotype which is normally lacking in the extracellular environment at 4 and 25 degrees C. It can be concluded that L. monocytogenes, frequently present in numerous environmental sources and also in refrigerated food products, produces at low temperature, the virulence factors necessary to invade intestinal cells.     

Combined effect of gamma radiation and heating on the destruction of Listeria monocytogenes and Salmonella typhimurium in cook-chill roast beef and gravy

The effect of heating alone (60, 65 or 70 degrees C), heating after irradiation (0.8 kGy) and heating after irradiation and storage for 14 days at 2-3 degrees C on the destruction of Listeria monocytogenes and Salmonella typhimurium in artifically inoculated minced cook-chill roast beef and gravy was investigated. Inoculated minced roast beef samples (5 g) were heated in Stomacher bags completely immersed in a water bath at each of the test temperatures. Survivors were enumerated and D and z values were determined for each of the pathogens. Observed thermal D values for two strains of L. monocytogenes at 60, 65 and 70 degrees C in the absence of pre-irradiation were 90.0-97.5 s, 34.0-53.0 s and 22.4-28.0 s, respectively, whereas thermal D values after pre-irradiation were 44.0-46.4 s, 15.3-16.8 s and 5.5-7.8 s at 60, 65 and 70 degrees C, respectively. This reduction in D values provides evidence for radiation-induced heat-sensitisation in L. monocytogenes. There was some evidence of heat-sensitisation of S. typhimurium at 60 degrees C, but not at either 65 or 70 degrees C. The z value also decreased as a consequence of pre-irradiation to a dose of 0.8 kGy (11.0-12.7 degrees C). The radiation-induced heat-sensitivity in L. monocytogenes was found to persist for up to 2 weeks storage at 2-3 degrees C prior to heating. As cook-chill products are intended to be reheated prior to consumption the results of the present study suggest that any L. monocytogenes present in a cook-chill product would be more easily killed during reheating if it were to be treated with a low dose of gamma radiation during manufacture.