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Acid Tolerance (acid + tolerance)
Selected AbstractsACID TOLERANCE OF ESCHERICHIA COLI FOLLOWING COLD SHOCK TREATMENTJOURNAL OF FOOD SAFETY, Issue 2 2003GREG BLANK ABSTRACT The effect of an initial cold shock treatment (2 h at 10C), following an abrupt downshift in temperature from 37 to 10C, on the subsequent growth and survival of Escherichia coli strains O157:H7 and MY20 (Biotype 1) in acidified Trypticase soy broth (TSB) and fruit juices (orange, apple) was investigated. Overall, no difference in growth at 37C was observed between each cold shocked and noncold shocked E. coli strain when cultured in TSB adjusted with either acetic acid (pH 6.0)or malic, citric and tartaric acid (each adjusted to: pH 4.5, 5.0, 5.5, 6.0). However, significant (P ± 0.05) differences in survival were observed between cold shocked and noncold shocked populations in TSB acidified with acetic acid (pH 5.0) or citric, malic and tartaric acid (pH 4.0). For strain MY20, survivor levels for cold shocked cells in TSB acidified with acetic acid citric, malic and tartaric acid at 8C were significantly (P ± 0.05) higher than in noncold shocked populations. Also, at 37C survival levels for cold shocked cells were significantly (P ± 0.05) higher than noncold shocked cells in TSB acidified with either malic or tartaric acid (pH 4.0). For the O157:H7 strain, survivor levels were higher (P ± 0.05) for cold shocked cells when maintained in TSB at 37C regardless of acid type. At 8C, cold shock treatment only increased (P ± 0.05) the survival of the O157:H7 strain in TSB adjusted with acetic acid (pH 6.0). Acid cross protection induced by cold shocking, as evidenced by enhanced survival, was not apparent for either E. coil strain in apple (pH 3.5) or orange juice (pH 3.8) maintained at 8C. [source] Gamma-hydroxybutyric Acid Tolerance and Withdrawal in a Rat ModelACADEMIC EMERGENCY MEDICINE, Issue 7 2003Theodore C. Bania MD Long-term daily use of gamma-hydroxybutyrate (GHB) and related compounds has recently been associated with a withdrawal syndrome. To the best of the authors' knowledge, there are currently no animal models of GHB withdrawal. Objectives: The authors studied and described the effect of chronic dosing of GHB (3,6 days) on tolerance and withdrawal in a rat model. Methods: Rats were administered GHB every three hours via intraperitoneal catheter. Groups of rats (2 per group) were dosed with GHB for either 3 (24 doses), 4 (32 doses), 5 (40 doses), or 6 (48 doses) days. The GHB dose was 0.25 g/kg for doses 1,8, 0.75 g/kg for doses 9,12, 1 g/kg for doses 13,16, 1.25 g/kg for doses 17,24, 1.5 g/kg for doses 25,32, 1.75 g/kg for doses 33,40, and 2 g/kg for doses 41,48. Following the last dose of GHB, the rats were scored using a 16-point ethanol intoxication,withdrawal scale rating spontaneous behaviors, response to handling, grooming, and neurological signs. Lower scores indicate intoxication, while higher scores indicate withdrawal. Scores were recorded at hours 0, 1, 2, 3, 4, 5, 6, 9, 12, and 24. Results:Tolerance: Rats dosed with GHB for more days were less intoxicated one hour after their last GHB dose despite receiving higher doses. Withdrawal: The scores for all rats dosed with GHB increased at hours 4 (p = 0.028), 5 (p = 0.037), 6 (p = 0.007), and 9 (p = 0.024) after the last dose, indicating withdrawal. The scores demonstrated a linear increase dependent upon the number of days of GHB dosing at hours 3 (p < 0.000), 4 (p = 0.004), 5 (p = 0.002), and 12 (p = 0.039) as well as prior to the last dose at hour 0 (p = 0.000). No rats developed seizures. Conclusions: Tolerance and mild withdrawal in rats can be induced by administering intraperitoneal GHB every three hours for 3,6 days. More prolonged dosing and higher doses of GHB may be necessary to induce severe withdrawal. [source] Determination of survival, identity and stress resistance of probiotic bifidobacteria in bio-yoghurtsLETTERS IN APPLIED MICROBIOLOGY, Issue 3 2006V.S. Jayamanne Abstract Aims:, To determine the level of bifidobacteria in bio-yoghurts in the UK, identify the species, and compare the resistance of common Bifidobacterium spp. to acidity and oxidative stress. Methods and Results:, A storage trial of bio-yoghurts was carried out to determine the level and survival of bifidobacteria. The 16S rRNA gene targeted PCR was used to identify the species. Acid tolerance was determined by introducing the organisms to pH-adjusted skimmed milk and enumerating during storage at 4°C. Oxidative stress resistance was determined using the H2O2 disc diffusion assay technique. Nine of 10 bio-yoghurts contained bifidobacteria at levels >106 CFU g,1 at the time of purchase. The viability of the organism decreased during storage and on expiry only five products retained viability >106 CFU g,1 while two others were very close to the target population. Bifidobacterium animalis ssp. lactis showed superior survival abilities and stress tolerance compared with Bifidobacterium longum, Bifidobacterium breve, Bifidobacterium bifidum, Bifidobacterium adolescentis and Bifidobacterium longum biotype infantis. Conclusions:,Bifidobacterium animalis ssp. lactis, the only Bifidobacterium spp. found in bio-yoghurts, had the greatest resistance to acidity and oxidative stress. Significance and Impact of the Study:, The technological properties of B. animalis ssp. lactis make it suitable for inclusion in bio-yoghurts although its putative health benefits need further investigation. [source] Role of two component signaling response regulators in acid tolerance of Streptococcus mutansMOLECULAR ORAL MICROBIOLOGY, Issue 2 2009M. Kawada-Matsuo Introduction:, In bacteria, two-component systems (TCS) involving the products of a histidine kinase gene (hk) and a response regulator gene (rr) play important roles in adaptation to environmental changes. Fourteen hk - rr homologs and one orphan rr homolog were identified in the Streptococcus mutans UA159 genome database. There have been no comprehensive evaluations of the roles of rr homologs in the acid tolerance of S. mutans. Methods:, The TCS genes (tcs) of S. mutans were designated smtcs01,15. Mutants of S. mutans UA159 with deletions of rr and hk-rr were constructed. Acid tolerance was evaluated by comparing the doubling times at pH 7.2 and pH 5.5 between the wild-type and mutant strains. Results:, Excluding smtcs10 and 12, for which viable mutants could not be obtained, a total of 13 rr deletion mutants were constructed. The rr deletions in smtcs03, 05, 08, and 13 resulted in diminished acid tolerance in comparison with UA159. The hk-rr double-mutants exhibited acid sensitivity levels similar to those of the corresponding rr mutants. The results of the present study reveal the involvement of the rr genes of smtcs03 and 05 in acid tolerance. Deletion of hk and/or rr in smtcs03 generated an acid-sensitive phenotype. In contrast, for smtcs05, while deletion of rr resulted in reduced acid tolerance, a single-deletion of hk had no effect on acid tolerance. Conclusions:, We implicated two rr genes in the acid tolerance of S. mutans. In particular, smtcs05 is a novel tcs, the sole rr of which is involved in the acid tolerance of S. mutans. [source] d -Alanyl ester depletion of teichoic acids in Lactobacillus reuteri 100-23 results in impaired colonization of the mouse gastrointestinal tractENVIRONMENTAL MICROBIOLOGY, Issue 7 2007Jens Walter Summary The dlt operon of Gram-positive bacteria encodes proteins required for the incorporation of d -alanine esters into cell wall-associated teichoic acids (TA). d -Alanylation of TA has been shown to be important for acid tolerance, resistance to antimicrobial peptides, adhesion, biofilm formation, and virulence of a variety of pathogenic organisms. The aim of this study was to determine the importance of d -alanylation for colonization of the gastrointestinal tract by Lactobacillus reuteri 100-23. Insertional inactivation of the dltA gene resulted in complete depletion of d -alanine substitution of lipoteichoic acids. The dlt mutant had similar growth characteristics as the wild type under standard in vitro conditions, but formed lower population sizes in the gastrointestinal tract of ex- Lactobacillus -free mice, and was almost eliminated from the habitat in competition experiments with the parental strain. In contrast to the wild type, the dlt mutant was unable to form a biofilm on the forestomach epithelium during gut colonization. Transmission electron microscope observations showed evidence of cell wall damage of mutant bacteria present in the forestomach. The dlt mutant had impaired growth under acidic culture conditions and increased susceptibility to the cationic peptide nisin relative to the wild type. Ex vivo adherence of the dlt mutant to the forestomach epithelium was not impaired. This study showed that d -alanylation is an important cell function of L. reuteri that seems to protect this commensal organism against the hostile conditions prevailing in the murine forestomach. [source] GEOGRAPHIC VARIATION IN ACID STRESS TOLERANCE OF THE MOOR FROG, RANA ARVALIS.EVOLUTION, Issue 2 2003Abstract Spatially varying directional selection together with restricted gene flow among populations is expected to lead to local adaptation. One environmental factor that potentially causes strong directional selection, but is little explored in evolutionary terms, is naturally and anthropogenically induced acidity. We studied local adaptation to acidity in four Swedish populations (two originating from areas that have suffered from severe anthropogenic acidification during the 1900s and two from areas which have remained neutral due to higher buffering capacity) of the moor frog Rana arvalis in a laboratory experiment by investigating whether differences in acid tolerance correspond to population origin. Embryos were raised from fertilization to hatching at three different pH levels (pH 4.0, 4.25 and 7.5), corresponding to levels experienced by these populations in nature, and acid stress tolerance was measured in terms of embryonic survival, hatchling size, and age. Evidence for local adaptation in all of these traits was found, the acid origin embryos having higher survival and less impaired growth performance under acid conditions than the neutral origin embryos. Our estimated rates of divergence (0.007,0.102 haldanes) suggest a rapid adaptation process in response to anthropogenic environmental change, and that the different traits have evolved at relatively similar rates. [source] Probiotic characteristics of lactic acid bacteria isolated from kimchiJOURNAL OF APPLIED MICROBIOLOGY, Issue 1 2010J.-H. Chang Abstract Aims:, The present work was aimed at identifying strains of lactic acid bacteria (LAB) from kimchi, with properties suitable for use as starter cultures in yogurt fermentation. Methods and Results:, A total of 2344 LAB strains were obtained from two different sources, one group consisted of commercial LAB strains from kimchi, and the second group consisted of those strains isolated from various types of kimchi. The LAB strains from both groups were screened for resistance to biological barriers (acid and bile salts), and the four most promising strains were selected. Further analysis revealed that KFRI342 of the four selected strains displayed the greatest ability to reduce the growth of the cancer cells, SNU-C4. The in vivo efficacy of strains in quinone reductase induction assay was evaluated, and the extent of DNA strand breakage in individual cells was investigated using the comet assay. Strain KFRI342 was identified as Lactobacillus acidophilus by 16S rRNA sequence analysis, showed protection against tumour initiation and imparted immunostimulation as well as protection against DNA damage. Conclusions:, Strain KFRI342, which showed probiotic characteristics reducing cancer cell growth, could be a suitable starter culture for yogurt fermentation because of its strong acid production and high acid tolerance. Significance and Impact of the Study:, This is the first report to describe a bacterium, isolated from kimchi, Lact. acidophilus KFRI342 which has the probiotic characteristics and the acid tolerance needed for its use as a starter culture in yogurt fermentation. [source] Interactions of Salmonella enterica with lettuce leavesJOURNAL OF APPLIED MICROBIOLOGY, Issue 6 2009Y. Kroupitski Abstract Aims:, To investigate the interactions of Salmonella enterica with abiotic and plant surfaces and their effect on the tolerance of the pathogen to various stressors. Methods and Results:,Salmonella strains were tested for their ability to form biofilm in various growth media using a polystyrene plate model. Strong biofilm producers were found to attach better to intact Romaine lettuce leaf tissue compared to weak producers. Confocal microscopy and viable count studies revealed preferential attachment of Salmonella to cut-regions of the leaf after 2 h at 25°C, but not for 18 h at 4°C. Storage of intact lettuce pieces contaminated with Salmonella for 9 days at 4°C resulted only in small changes in population size. Exposure of lettuce-associated Salmonella cells to acidic conditions (pH 3·0) revealed increased tolerance of the attached vs planktonic bacteria. Conclusions:, Biofilm formation on polystyrene may provide a suitable model to predict the initial interaction of Salmonella with cut Romaine lettuce leaves. Association of the pathogen with lettuce leaves facilitates its persistence during storage and enhances its acid tolerance. Significance and Impact of the Study:, Understanding the interactions between foodborne pathogens and lettuce might be useful in developing new approaches to prevent fresh produce-associated outbreaks. [source] Cross-talk involving extracellular sensors and extracellular alarmones gives early warning to unstressed Escherichia coli of impending lethal chemical stress and leads to induction of tolerance responsesJOURNAL OF APPLIED MICROBIOLOGY, Issue 5 2001R.J. Rowbury 1. Summary, 678 2. Introduction 2.1. Chemical and biological stress agents affecting enterobacteria, 678 2.2. Sensing of chemical and biological stress stimuli, 678 2.3. Intracellular sensors detect intracellularly-produced chemical stressing agents, 679 2.4. Intracellular sensors and intracellular induction components could delay response induction by extracellular chemical or biological stress agents, 680 2.5. Extracellular sensors and EICs give early warning of stress, 681 2.6. Disadvantages of extracellular components being needed for stress response induction, 682 2.7. Extracellular sensors and EICs allow stressed cells to warn unstressed ones, 682 2.8. A second role for some extracellular stress sensors, 683 3. Responses switched on by extracellular sensors and EICs 3.1. Involvement of EICs and ESCs in acid tolerance induction at pH 5·0 and at other mildly acidic pH values, 683 3.2. Further evidence for the obligate involvement of extracellular sensors and EICs in acid tolerance induction at pH 5·0, 684 3.3. On the nature of the acid pH tolerance-inducing ESC and EIC, 686 3.4. The acid tolerance ECs and their relation to other extracellular response-inducing components, 686 3.5. Extracellular components are needed for other inducible acid tolerance responses, 687 3.6. Involvement of EICs and extracellular sensors in acid tolerance in E. coli O157, 687 3.7. EICs involved in acid tolerance induction are diffusible, 687 4. Acid sensitization at alkaline pH and the role of extracellular sensor and EIC(s), 688 5. Responses affecting tolerance to alkali 5.1. Alkali sensitization at acidic pH, 688 5.2. Induced alkali tolerance at pH 9·0 and role of extracellular components, 688 6. Inducible tolerance to alkylhydroperoxides, 689 7. Are extracellular sensors and extracellular induction components needed for all stress responses?, 689 8. Altered responsiveness of extracellular sensors depending on growth conditions, 691 9. Protection of living cells from chemical stress by dead cultures, 691 10. How can intracellular levels of stress be detected?, 692 11. Are Nikolaev's extracellular ,protectants' and similar components related to EICs?, 693 12. Conclusions, 693 13. References, 694 [source] Effects of recombinase A deficiency on biofilm formation by Streptococcus mutansMOLECULAR ORAL MICROBIOLOGY, Issue 2 2009S. Inagaki Background/aim:, Recombinase A (RecA) is essential for the transformation of both plasmid and chromosomal DNA in Streptococcus pneumoniae and is considered to be related to the SOS-response in Streptococcus mutans. Methods:, In the present study, a RecA-deficient mutant strain (RAD) was constructed by insertional inactivation of the recA gene encoding the RecA protein in strain MT8148 of S. mutans, after which the biological functions of acid tolerance and biofilm formation were investigated. Results:, RAD showed reduced acid tolerance and produced lower density biofilm compared with the wild-type strain. In addition, confocal microscopic observation indicated that the biofilm produced by RAD was composed of cells with significantly lower viability compared with that produced by strain MT8148. Conclusion:, These results suggest that RecA has a relationship with biofilm formation. [source] Role of two component signaling response regulators in acid tolerance of Streptococcus mutansMOLECULAR ORAL MICROBIOLOGY, Issue 2 2009M. Kawada-Matsuo Introduction:, In bacteria, two-component systems (TCS) involving the products of a histidine kinase gene (hk) and a response regulator gene (rr) play important roles in adaptation to environmental changes. Fourteen hk - rr homologs and one orphan rr homolog were identified in the Streptococcus mutans UA159 genome database. There have been no comprehensive evaluations of the roles of rr homologs in the acid tolerance of S. mutans. Methods:, The TCS genes (tcs) of S. mutans were designated smtcs01,15. Mutants of S. mutans UA159 with deletions of rr and hk-rr were constructed. Acid tolerance was evaluated by comparing the doubling times at pH 7.2 and pH 5.5 between the wild-type and mutant strains. Results:, Excluding smtcs10 and 12, for which viable mutants could not be obtained, a total of 13 rr deletion mutants were constructed. The rr deletions in smtcs03, 05, 08, and 13 resulted in diminished acid tolerance in comparison with UA159. The hk-rr double-mutants exhibited acid sensitivity levels similar to those of the corresponding rr mutants. The results of the present study reveal the involvement of the rr genes of smtcs03 and 05 in acid tolerance. Deletion of hk and/or rr in smtcs03 generated an acid-sensitive phenotype. In contrast, for smtcs05, while deletion of rr resulted in reduced acid tolerance, a single-deletion of hk had no effect on acid tolerance. Conclusions:, We implicated two rr genes in the acid tolerance of S. mutans. In particular, smtcs05 is a novel tcs, the sole rr of which is involved in the acid tolerance of S. mutans. [source] Physicochemical responses of Pythium porphyrae (Oomycota), the causative organism of red rot disease in Porphyra to acidificationAQUACULTURE RESEARCH, Issue 15 2009Eun Kyoung Hwang Abstract Physicochemical responses to acidification in Pythium porphyrae, the causative organism of red rot disease in Porphyra, were investigated. The acid tolerance of P. porphyrae mycelia under pH 4 (acidic condition) condition increased significantly compared with that of the mycelia under pH 8 (condition equivalent to seawater) condition. Free amino acid levels in the mycelia decreased 1.3,8.8-fold under pH 4 condition. However, some free amino acids such as the d -cysteinolic acid-like component, phosphoethanolamine, glutamic acid, aminoadipic acid and methionine increased 2.6,21.7-fold under the same condition. Proton flux on the mycelia exposed to pH 8 increased significantly compared with the mycelia exposed to pH 4. The patterns of proteins present (examined by two-dimensional polyacrylamide gel electrophoresis) differed among the pH conditions. These results suggest that P. porphyrae acquires acid tolerance and is able to adapt to the changing pH conditions. This has significant implications for the use of acidic fungicide treatment for prevention of red rot disease on Porphyra farms. [source] Engineering Propionibacterium acidipropionici for enhanced propionic acid tolerance and fermentationBIOTECHNOLOGY & BIOENGINEERING, Issue 4 2009An Zhang Abstract Propionibacterium acidipropionici, a Gram-positive, anaerobic bacterium, has been the most used species for propionic acid production from sugars. In this study, the metabolically engineered mutant ACK-Tet, which has its acetate kinase gene knocked out from the chromosome, was immobilized and adapted in a fibrous bed bioreactor (FBB) to increase its acid tolerance and ability to produce propionic acid at a high final concentration in fed-batch fermentation. After about 3 months adaptation in the FBB, the propionic acid concentration in the fermentation broth reached ,100,g/L, which was much higher than the highest concentration of ,71,g/L previously attained with the wild-type in the FBB. To understand the mechanism and factors contributing to the enhanced acid tolerance, adapted mutant cells were harvested from the FBB and characterized for their morphology, growth inhibition by propionic acid, protein expression profiles as observed in SDS,PAGE, and H+ -ATPase activity, which is related to the proton pumping and cell's ability to control its intracellular pH gradient. The adapted mutant obtained from the FBB showed significantly reduced growth sensitivity to propionic acid inhibition, increased H+ -ATPase expression and activity, and significantly elongated rod morphology. Biotechnol. Bioeng. 2009; 104: 766,773 © 2009 Wiley Periodicals, Inc. [source] | |||||||||||||