The Experts below are selected from a list of 324 Experts worldwide ranked by ideXlab platform
John W. Foster - One of the best experts on this subject based on the ideXlab platform.
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A Low pH-Inducible, PhoPQ-Dependent Acid Tolerance Response Protects Salmonella typhimurium against Inorganic Acid Stress
Journal of bacteriology, 1998Co-Authors: Bradley L. Bearson, Lee Wilson, John W. FosterAbstract:The Acid Tolerance response enables Salmonella typhimurium to survive exposures to potentially lethal Acidic environments. The Acid stress imposed in a typical assay for Acid Tolerance (log-phase cells in minimal glucose medium) was shown to comprise both inorganic (i.e., low pH) and organic Acid components. A gene previously determined to affect Acid Tolerance, atbR, was identified as pgi, the gene encoding phosphoglucoisomerase. Mutations in pgi were shown to increase Acid Tolerance by preventing the synthesis of organic Acids. Protocols designed to separate the stresses of inorganic from organic Acids revealed that the regulators sigma38 (RpoS), Fur, and Ada have major effects on Tolerance to organic Acid stress but only minor effects on inorganic Acid stress. In contrast, the two-component regulatory system PhoP (identified as Acid shock protein ASP29) and PhoQ proved to be important for Tolerance to inorganic [corrected] Acid stress but had little effect against organic Acid stress. PhoP mutants also failed to induce four ASPs, confirming a role for this regulator in Acid Tolerance. Acid shock induction of PhoP appears to occur at the transcriptional level and requires the PhoPQ system. Furthermore, induction by Acid occurs even in the presence of high concentrations of magnesium, the ion known to be sensed by PhoQ. These results suggest that PhoQ can sense both Mg2+ and pH. Since phoP mutants are avirulent, the low pH activation of this system has important implications concerning the pathogenesis of S. typhimurium. The involvement of four regulators, two of which are implicated in virulence, underscores the complexity of the Acid Tolerance stress response and further suggests that features of Acid Tolerance and virulence are interwoven.
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Internal pH crisis, lysine decarboxylase and the Acid Tolerance response of Salmonella typhimurium
Molecular microbiology, 1996Co-Authors: Yong Keun Park, Bradley L. Bearson, Seong Ho Bang, Iel Soo Bang, John W. FosterAbstract:Salmonella typhimurium possesses an adaptive response to Acid that increases survival during exposure to extremely low pH values. The Acid Tolerance response (ATR) includes both log-phase and stationary-phase systems. The log-phase ATR appears to require two components for maximum Acid Tolerance, namely an inducible pH homeostasis system, and a series of Acid-shock proteins. We have discovered one of what appears to be a series of inducible exigency pH homeostasis systems that contribute to Acid Tolerance in extreme Acid environments. The low pH-inducible lysine decarboxylase was shown to contribute significantly to pH homeostasis in environments as low as pH 3.0. Under the conditions tested, both lysine decarboxylase and sigma s-dependent Acid-shock proteins were required for Acid Tolerance but only lysine decarboxylase contributed to pH homeostasis. The cadBA operon encoding lysine decarboxylase and a lysine/cadaverine antiporter were cloned from S. typhimurium and were found to be 79% homologous to the cadBA operon from Escherichia coli. The results suggest that S. typhimurium has a variety of means of fulfilling the pH homeostasis requirement of the ATR in the form of inducible amino Acid decarboxylases.
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Adaptive Acid Tolerance response (ATR) in Aeromonas hydrophila.
Microbiology, 1994Co-Authors: Kevin L. Karem, John W. Foster, Asim K. BejAbstract:Aeromonas hydrophila, a gastrointestinal pathogen of humans, was shown to exhibit a significant adaptive Acid Tolerance response (ATR) capable of protecting cells from severe Acid at a pH of 3.5. The ATR was induced by exposure to a relatively mild pH level of 5.0 for 20 min. Adaptation required protein synthesis since treatment with chloramphenicol during adaptation to pH 5.0 prevented the development of Acid Tolerance. The adaptation to Acid environment was found to be a non-transient phenomenon. Also, iron was not required for Acid adaptation in A. hydrophila. Two-dimensional protein analyses revealed an increased production of 28 proteins and decreased synthesis of 10 following pH shifts from 7.2 to 5.0. The mild pH treatment must act as a signal to A. hydrophila to adapt and survive in Acid environments by producing ‘protective’ proteins. The adaptation and survival of this pathogen in low pH may provide valuable information about its ability to withstand Acid environments in nature and in the human gastrointestinal tract.
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Role of Acid Tolerance response genes in Salmonella typhimurium virulence.
Infection and immunity, 1993Co-Authors: F Garcia-del Portillo, John W. Foster, B. Brett FinlayAbstract:The atp and fur genes are involved in the Acid Tolerance response of Salmonella typhimurium. An atp::Tn10 mutant was avirulent in the mouse typhoid model when assayed by oral and intraperitoneal routes. However, a fur mutant was completely virulent by the intraperitoneal route. No relevant differences in intracellular survival or invasion rates were observed for the two mutants in macrophages and epithelial cells. These data indicate that separate Acid Tolerance response genes may have different roles in S. typhimurium virulence.
Xiaoyang Pang - One of the best experts on this subject based on the ideXlab platform.
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Whole-genome sequencing and genomic-based Acid Tolerance mechanisms of Lactobacillus delbrueckii subsp. bulgaricus LJJ.
Applied microbiology and biotechnology, 2020Co-Authors: Li Weixun, Lan Yang, Wenlong Nan, Shuwen Zhang, Obaroakpo Joy Ujiroghene, Xiaoyang PangAbstract:The probiotic efficacy and fermentative ability of Lactobacillus delbrueckii subsp. bulgaricus (L. bulgaricus), a widely used probiotic, is majorly affected by its Acid Tolerance. Here, we conducted whole-genome sequencing of the high Acid-tolerant L. bulgaricus LJJ stored in the laboratory. Compared with the whole genome of low Acid-tolerant strain L. bulgaricus ATCC11842, the results show that 16 candidate Acid-tolerant genes may be involved in the regulation of the Acid Tolerance of L. bulgaricus LJJ. Association analysis of candidate Acid-tolerant genes and Acid-tolerant traits of different L. bulgaricus strains revealed that the three genes dapA, dapH, and lysC are the main reasons for the strong Acid Tolerance of L. bulgaricus LJJ. The results of real-time quantitative PCR (RT-qPCR) supported this conclusion. KEGG pathway analysis showed that these three Acid-tolerant genes are involved in the synthesis of lysine; the synthesis of lysine may confer L. bulgaricus LJJ strong Acid Tolerance. This study successfully revealed the Acid Tolerance mechanism of L. bulgaricus LJJ and provides a theoretical basis for the subsequent selection of strains with high Acid Tolerance for improved probiotic functions. • Three genes are identified as Acid-tolerant genes, respectively, lysC, dapA, and dapH. • LysC and dapA are the major key genes in the synthesis of lysine. • The synthesis of lysine may confer L. bulgaricus LJJ strong Acid Tolerance.
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Whole-genome sequencing and genomic-based Acid Tolerance mechanisms of Lactobacillus delbrueckii subsp. bulgaricus LJJ
2019Co-Authors: Xiaoyang Pang, Lan Yang, Shuwen Zhang, Obaroakpo Joy Ujiroghene, Cai ZhangAbstract:Abstract Background: The probiotic efficacy and fermentative ability of Lactobacillus delbrueckii subsp. Bulgaricus ( L. d. bulgaricus ), a widely used probiotic, is majorly affected by its Acid Tolerance. In this study, a genome-wide sequence of a highly Acid-tolerant L. d. bulgaricus LJJ was supposed to be determined, and we expect to find out the Acid Tolerance mechanism of L. d. bulgaricus LJJ by comparative genomics. Results: Functional annotation and pathways of differential genes were determined using bioinformatics. The results in our study showed that the three genes dapA , dapH and lysC identified are implicated in the high Acid Tolerance of LJJ strain. Thus, they are potentially important as Acid-tolerant genes of LJJ strain. Conclusions: This study successfully revealed the Acid Tolerance mechanism of LJJ. Based on the previous research of LJJ in our laboratory, the successful analysis of the Acid-tolerant mechanism of L. d. bulgaricus will further lay the foundation for the subsequent breeding of high Acid-tolerant strains and greatly enhance their probiotic functions. Keywords: Lactobacillus delbrueckii subsp. Bulgaricus ; Acid-tolerant mechanism; comparative genomics; dapA ; dapH ; LysC
Gunnel Svensäter - One of the best experts on this subject based on the ideXlab platform.
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Acid Tolerance properties of dental biofilms in vivo.
BMC microbiology, 2017Co-Authors: Anna Senneby, Julia R. Davies, Gunnel Svensäter, Jessica NeilandsAbstract:The ecological plaque hypothesis explains caries development as the result of the enrichment of Acid tolerant bacteria in dental biofilms in response to prolonged periods of low pH. Acid production by an Acid tolerant microflora causes demineralisation of tooth enamel and thus, individuals with a greater proportion of Acid tolerant bacteria would be expected to be more prone to caries development. Biofilm Acid Tolerance could therefore be a possible biomarker for caries prediction. However, little is known about the stability of biofilm Acid Tolerance over time in vivo or the distribution throughout the oral cavity. Therefore the aim of this study was to assess intra-individual differences in biofilm Acid-Tolerance between different tooth surfaces and inter-individual variation as well as stability of Acid Tolerance over time. The majority of the adolescents showed low scores for biofilm Acid Tolerance. In 14 of 20 individuals no differences were seen between the three tooth sites examined. In the remaining six, Acid-Tolerance at the premolar site differed from one of the other sites. At 51 of 60 tooth sites, Acid-Tolerance at baseline was unchanged after 1 month. However, Acid Tolerance values changed over a 1-year period in 50% of the individuals. Biofilm Acid Tolerance showed short-term stability and low variation between different sites in the same individual suggesting that the Acid Tolerance could be a promising biological biomarker candidate for caries prediction. Further evaluation is however needed and prospective clinical trials are called for to evaluate the diagnostic accuracy.
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Fluoride-supplemented milk inhibits Acid Tolerance in root caries biofilms
Caries research, 2012Co-Authors: Jessica Neilands, Lars G. Petersson, David Beighton, Gunnel SvensäterAbstract:In this study we investigated the effect of fluoride on plaque Acid Tolerance. The test group consumed 200 ml of milk supplemented with 5 mg F/l as NaF once a day, the milk control group drank 200 ml of unsupplemented milk, and the no-milk control group did not consume milk in this manner. Plaque samples were taken at baseline and after 15 months. The proportion of Acid-tolerant bacteria in plaque was estimated using LIVE/DEAD® BacLight™ staining after exposure to pH 3.5 for 2 h. The fluoride group showed a statistically significant decrease in plaque Acid Tolerance compared to baseline. This study shows that daily intake of fluoride in milk reduces plaque Acid Tolerance.
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Acid Tolerance of Biofilm Cells of Streptococcus mutans
Applied and environmental microbiology, 2007Co-Authors: Jessica Welin-neilands, Gunnel SvensäterAbstract:Streptococcus mutans, a member of the dental plaque community, has been shown to be involved in the carious process. Cells of S. mutans induce an Acid Tolerance response (ATR) when exposed to sublethal pH values that enhances their survival at a lower pH. Mature biofilm cells are more resistant to Acid stress than planktonic cells. We were interested in studying the Acid Tolerance and ATR-inducing ability of newly adhered biofilm cells of S. mutans. All experiments were carried out using flow-cell systems, with Acid Tolerance tested by exposing 3-h biofilm cells to pH 3.0 for 2 h and counting the number of survivors by plating on blood agar. Acid adaptability experiments were conducted by exposing biofilm cells to pH 5.5 for 3 h and then lowering the pH to 3.5 for 30 min. The viability of the cells was assessed by staining the cells with LIVE/DEAD BacLight viability stain. Three-hour biofilm cells of three different strains of S. mutans were between 820- and 70,000-fold more Acid tolerant than corresponding planktonic cells. These strains also induced an ATR that enhanced the viability at pH 3.5. The presence of fluoride (0.5 M) inhibited the induction of an ATR, with 77% fewer viable cells at pH 3.5 as a consequence. Our data suggest that adhesion to a surface is an important step in the development of Acid Tolerance in biofilm cells and that different strains of S. mutans possess different degrees of Acid Tolerance and ability to induce an ATR.
Dennis G. Cvitkovitch - One of the best experts on this subject based on the ideXlab platform.
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Acid Tolerance mechanisms utilized by streptococcus mutans
Future Microbiology, 2010Co-Authors: Robert Matsui, Dennis G. CvitkovitchAbstract:Since its discovery in 1924 by J Clarke, Streptococcus mutans has been the focus of rigorous research efforts due to its involvement in caries initiation and progression. Its ability to ferment a range of dietary carbohydrates can rapidly drop the external environmental pH, thereby making dental plaque inhabitable to many competing species and can ultimately lead to tooth decay. Acid production by this oral pathogen would prove suicidal if not for its remarkable ability to withstand the Acid onslaught by utilizing a wide variety of highly evolved Acid-Tolerance mechanisms. The elucidation of these mechanisms will be discussed, serving as the focus of this review.
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Characterization of a Glutamate Transporter Operon, glnQHMP, in Streptococcus mutans and Its Role in Acid Tolerance
Journal of bacteriology, 2009Co-Authors: Kirsten Krastel, Dilani B. Senadheera, Richard W. Mair, Jennifer S. Downey, Steven D. Goodman, Dennis G. CvitkovitchAbstract:Glutamate contributes to the Acid Tolerance response (ATR) of many Gram-negative and Gram-positive bacteria, but its role in the ATR of the oral bacterium Streptococcus mutans is unknown. This study describes the discovery and characterization of a glutamate transporter operon designated glnQHMP (Smu.1519 to Smu.1522) and investigates its potential role in Acid Tolerance. Deletion of glnQHMP resulted in a 95% reduction in transport of radiolabeled glutamate compared to the wild-type UA159 strain. The addition of glutamate to metabolizing UA159 cells resulted in an increased production of Acidic end products, whereas the glnQHMP mutant produced less lactic Acid than UA159, suggesting a link between glutamate metabolism and Acid production and possible Acid Tolerance. To investigate this possibility, we conducted a microarray analysis with glutamate and under pH 5.5 and pH 7.5 conditions which showed that expression of the glnQHMP operon was downregulated by both glutamate and mild Acid. We also measured the growth kinetics of UA159 and its glnQHMP-negative derivative at pH 5.5 and found that the mutant doubled at a much slower rate than the parent strain but survived at pH 3.5 significantly better than the wild type. Taken together, these findings support the involvement of the glutamate transporter operon glnQHMP in the Acid Tolerance response in S. mutans.
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Acid Tolerance response and survival by oral bacteria
Oral microbiology and immunology, 1997Co-Authors: G. Svensater, U.-b. Larsson, E. C. G. Greif, Dennis G. Cvitkovitch, I. R. HamiltonAbstract:Using 21 species of oral bacteria, representing six Acidogenic genera, we undertook to determine whether the pH-limiting exponential growth is related to the ability of the organisms to generate an Acid-Tolerance response that results in enhanced survival at low pH. The lower pH limit of exponential growth varied by more than two units with that of Neisseria A182 at pH 6.34; growth of Lactobacillus casei RB1014 stopped at pH 3.81, with species of Actinomyces, Enterococcus, Prevotella and Streptococcus falling between these limits. The working hypothesis was that the organisms with the higher pH limits for growth are unable to respond to Acidic environments in order to survive, whereas the more Aciduric organisms would possess or acquire Acid Tolerance. Adaptation to Acid Tolerance was tested by determining whether the prior exposure of exponential-phase cells to a low, sub-lethal pH would trigger the induction of a mechanism that would enhance survival at a pH killing pH 7.5 control cells. The killing pH varied from pH 4.5 for Prevotella intermedia ATCC 25611 to pH 2.3 for the three Lactobacillus casei strains in the study, with the three Streptococcus mutans strains killed at pH 3.0 for 3 h. The adaptation experiments revealed three groups of organisms: non-Acid-responders, generally representing strains with the highest terminal pH values; weak Acid-responders in the middle of the pH list, generating low numbers of survivors at one or two pH values, and the Aciduric, strong responders generating a high number of survivors at pH values in the range 6.0 to 3.5, but not at pH 7.5. Predominant among the latter group were the S. mutans and Lactobacilli casei strains, with the most significant adaptive response exhibited by S. mutans LT11 and S. mutans Ingbritt, involving a process that required protein synthesis. Time course experiments with the latter organisms indicated that 90-120 min was required after exposure to the triggering pH before the Acid response was fully functional. These results indicate that the sudden exposure of strains of oral streptococci and lactobacilli, as well as Enterococcus faecalis, to pH values between 6.0 and 3.5 results in the induction of an Acid Tolerance response that enhances the survival of these strains at or below pH 3.5.
B. Brett Finlay - One of the best experts on this subject based on the ideXlab platform.
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Role of Acid Tolerance response genes in Salmonella typhimurium virulence.
Infection and immunity, 1993Co-Authors: F Garcia-del Portillo, John W. Foster, B. Brett FinlayAbstract:The atp and fur genes are involved in the Acid Tolerance response of Salmonella typhimurium. An atp::Tn10 mutant was avirulent in the mouse typhoid model when assayed by oral and intraperitoneal routes. However, a fur mutant was completely virulent by the intraperitoneal route. No relevant differences in intracellular survival or invasion rates were observed for the two mutants in macrophages and epithelial cells. These data indicate that separate Acid Tolerance response genes may have different roles in S. typhimurium virulence.
