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da Cruz Nizer WS, Adams ME, Montgomery MC, Allison KN, Beaulieu C, Overhage J. Genetic determinants of increased sodium hypochlorite and ciprofloxacin susceptibility in Pseudomonas aeruginosa PA14 biofilms. BIOFOULING 2024:1-17. [PMID: 39189148 DOI: 10.1080/08927014.2024.2395378] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/08/2023] [Revised: 06/12/2024] [Accepted: 08/15/2024] [Indexed: 08/28/2024]
Abstract
Reactive chlorine species (RCS) like sodium hypochlorite (NaOCl) are potent oxidizing agents and widely used biocides in surface disinfection, water treatment, and biofilm elimination. Moreover, RCS are also produced by the human immune system to kill invading pathogens. However, bacteria have developed mechanisms to survive the damage caused by RCS. Using the comprehensive Pseudomonas aeruginosa PA14 transposon mutant library in a genetic screen, we identified a total of 28 P. aeruginosa PA14 mutants whose biofilms showed increased susceptibility to NaOCl in comparison to PA14 WT biofilms. Of these, ten PA14 mutants with a disrupted apaH, PA0793, acsA, PA1506, PA1547, PA3728, yajC, queA, PA3869, or PA14_32840 gene presented a 4-fold increase in NaOCl susceptibility compared to wild-type biofilms. While none of these mutants showed a defect in biofilm formation or attenuated susceptibility of biofilms toward the oxidant hydrogen peroxide (H2O2), all but PA14_32840 also exhibited a 2-4-fold increase in susceptibility toward the antibiotic ciprofloxacin. Further analyses revealed attenuated levels of intracellular ROS and catalase activity only for the apaH and PA1547 mutant, providing insights into the oxidative stress response in P. aeruginosa biofilms. The findings of this paper highlight the complexity of biofilm resistance and the intricate interplay between different mechanisms to survive oxidative stress. Understanding resistance strategies adopted by biofilms is crucial for developing more effective ways to fight resistant bacteria, ultimately contributing to better management of bacterial growth and resistance in clinical and environmental settings.
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Affiliation(s)
| | | | | | | | - Carole Beaulieu
- Department of Health Sciences, Carleton University, Ottawa, Canada
| | - Joerg Overhage
- Department of Health Sciences, Carleton University, Ottawa, Canada
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El-Athman F, Zehlike L, Kämpfe A, Junek R, Selinka HC, Mahringer D, Grunert A. Pool water disinfection by ozone-bromine treatment: Assessing the disinfectant efficacy and the occurrence and in vitro toxicity of brominated disinfection by-products. WATER RESEARCH 2021; 204:117648. [PMID: 34543973 DOI: 10.1016/j.watres.2021.117648] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/29/2021] [Revised: 08/31/2021] [Accepted: 09/03/2021] [Indexed: 06/13/2023]
Abstract
Pool water is continuously circulated and reused after an extensive treatment including disinfection by chlorination, ozonation or UV treatment. In Germany, these methods are regulated by DIN standard 19643. Recently, the DIN standard has been extended by a new disinfection method using hypobromous acid as disinfectant formed by introducing ozone into water with naturally or artificially high bromide content during water treatment. In this study, we tested the disinfection efficacy of the ozone-bromine treatment in comparison to hypochlorous acid in a flow-through test rig using the bacterial indicator strains Escherichia coli, Enterococcus faecium, Pseudomonas aeruginosa, and Staphylococcus aureus and the viral indicators phage MS2 and phage PRD1. Furthermore, the formation of disinfection by-products and their potential toxic effects were investigated in eight pool water samples using different disinfection methods including the ozone-bromine treatment. Our results show that the efficacy of hypobromous acid, depending on its concentration and the tested organism, is comparable to that of hypochlorous acid. Hypobromous acid was effective against five of six tested indicator organisms. However, using Pseudomonas aeruginosa and drinking water as test water, both tested disinfectants (0.6 mg L-1 as Cl2 hypobromous acid as well as 0.3 mg L-1 as Cl2 hypochlorous acid) did not achieve a reduction of four log10 levels within 30 s, as required by DIN 19643. The formation of brominated disinfection by-products depends primarily on the bromide concentration of the filling water, with the treatment method having a smaller effect. The eight pool water samples did not show critical values in vitro for acute cytotoxicity or genotoxicity in the applied assays. In real pool water samples, the acute toxicological potential was not higher than for conventional disinfection methods. However, for a final assessment of toxicity, all single substance toxicities of known DBPs present in pool water treated by the ozone-bromine treatment have to be analyzed additionally.
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Affiliation(s)
- Fatima El-Athman
- German Environment Agency (UBA), Section Water Treatment, Schichauweg 58, Berlin 12307, Germany.
| | - Lisa Zehlike
- German Environment Agency (UBA), Section Water Treatment, Schichauweg 58, Berlin 12307, Germany
| | - Alexander Kämpfe
- German Environment Agency (UBA), Section Swimming Pool Water Hygiene, Chemical Analysis, Heinrich-Heine-Str. 12, Bad Elster 08645, Germany
| | - Ralf Junek
- German Environment Agency (UBA), Section Toxicology of Drinking Water and Swimming Pool Water, Heinrich-Heine-Str. 12, Bad Elster 08645, Germany
| | - Hans-Christoph Selinka
- German Environment Agency (UBA), Section Microbiological Risks, Corrensplatz 1, Berlin 14195, Germany
| | - Daniel Mahringer
- German Environment Agency (UBA), Section Water Treatment, Schichauweg 58, Berlin 12307, Germany
| | - Andreas Grunert
- German Environment Agency (UBA), Section Water Treatment, Schichauweg 58, Berlin 12307, Germany.
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3
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Mashruwala AA, Boyd JM. The Staphylococcus aureus SrrAB Regulatory System Modulates Hydrogen Peroxide Resistance Factors, Which Imparts Protection to Aconitase during Aerobic Growth. PLoS One 2017; 12:e0170283. [PMID: 28099473 PMCID: PMC5242492 DOI: 10.1371/journal.pone.0170283] [Citation(s) in RCA: 36] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2016] [Accepted: 01/03/2017] [Indexed: 01/09/2023] Open
Abstract
The SrrAB two-component regulatory system (TCRS) positively influences the transcription of genes involved in aerobic respiration in response to changes in respiratory flux. Hydrogen peroxide (H2O2) can arise as a byproduct of spontaneous interactions between dioxygen and components of respiratory pathways. H2O2 damages cellular factors including protein associated iron-sulfur cluster prosthetic groups. We found that a Staphylococcus aureus strain lacking the SrrAB two-component regulatory system (TCRS) is sensitive to H2O2 intoxication. We tested the hypothesis that SrrAB manages the mutually inclusive expression of genes required for aerobic respiration and H2O2 resistance. Consistent with our hypothesis, a ΔsrrAB strain had decreased transcription of genes encoding for H2O2 resistance factors (kat, ahpC, dps). SrrAB was not required for the inducing the transcription of these genes in cells challenged with H2O2. Purified SrrA bound to the promoter region for dps suggesting that SrrA directly influences dps transcription. The H2O2 sensitivity of the ΔsrrAB strain was alleviated by iron chelation or deletion of the gene encoding for the peroxide regulon repressor (PerR). The positive influence of SrrAB upon H2O2 metabolism bestowed protection upon the solvent accessible iron-sulfur (FeS) cluster of aconitase from H2O2 poisoning. SrrAB also positively influenced transcription of scdA (ytfE), which encodes for a FeS cluster repair protein. Finally, we found that SrrAB positively influences H2O2 resistance only during periods of high dioxygen-dependent respiratory activity. SrrAB did not influence H2O2 resistance when cellular respiration was diminished as a result of decreased dioxygen availability, and negatively influenced it in the absence of respiration (fermentative growth). We propose a model whereby SrrAB-dependent regulatory patterns facilitate the adaptation of cells to changes in dioxygen concentrations, and thereby aids in the prevention of H2O2 intoxication during respiratory growth upon dixoygen.
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Affiliation(s)
- Ameya A. Mashruwala
- Department of Biochemistry and Microbiology, Rutgers University, New Brunswick, New Jersey, United States of America
| | - Jeffrey M. Boyd
- Department of Biochemistry and Microbiology, Rutgers University, New Brunswick, New Jersey, United States of America
- * E-mail:
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Beavers WN, Skaar EP. Neutrophil-generated oxidative stress and protein damage in Staphylococcus aureus. Pathog Dis 2016; 74:ftw060. [PMID: 27354296 DOI: 10.1093/femspd/ftw060] [Citation(s) in RCA: 83] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/08/2016] [Indexed: 01/06/2023] Open
Abstract
Staphylococcus aureus is a ubiquitous, versatile and dangerous pathogen. It colonizes over 30% of the human population, and is one of the leading causes of death by an infectious agent. During S. aureus colonization and invasion, leukocytes are recruited to the site of infection. To combat S. aureus, leukocytes generate an arsenal of reactive species including superoxide, hydrogen peroxide, nitric oxide and hypohalous acids that modify and inactivate cellular macromolecules, resulting in growth defects or death. When S. aureus colonization cannot be cleared by the immune system, antibiotic treatment is necessary and can be effective. Yet, this organism quickly gains resistance to each new antibiotic it encounters. Therefore, it is in the interest of human health to acquire a deeper understanding of how S. aureus evades killing by the immune system. Advances in this field will have implications for the design of future S. aureus treatments that complement and assist the host immune response. In that regard, this review focuses on how S. aureus avoids host-generated oxidative stress, and discusses the mechanisms used by S. aureus to survive oxidative damage including antioxidants, direct repair of damaged proteins, sensing oxidant stress and transcriptional changes. This review will elucidate areas for studies to identify and validate future antimicrobial targets.
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Affiliation(s)
- William N Beavers
- Department of Pathology, Microbiology and Immunology, U.S. Department of Veteran Affairs, Vanderbilt Institute of Chemical Biology, Vanderbilt University School of Medicine, 1161 21st Avenue South, Medical Center North, Nashville, TN 37232, USA
| | - Eric P Skaar
- Department of Pathology, Microbiology and Immunology, U.S. Department of Veteran Affairs, Vanderbilt Institute of Chemical Biology, Vanderbilt University School of Medicine, 1161 21st Avenue South, Medical Center North, Nashville, TN 37232, USA Tennessee Valley Healthcare System, U.S. Department of Veteran Affairs, Vanderbilt Institute of Chemical Biology, Vanderbilt University School of Medicine, 1161 21st Avenue South, Nashville, TN 37232, USA
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Staphylococcus aureus transcriptomic response to inhibition by H2O2-producing Lactococcus garvieae. Food Microbiol 2015; 51:163-70. [PMID: 26187841 DOI: 10.1016/j.fm.2015.05.014] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2014] [Revised: 05/26/2015] [Accepted: 05/28/2015] [Indexed: 12/19/2022]
Abstract
Growth of the foodborne pathogen Staphylococcus aureus can be inhibited in milk and in cheese by the hydrogen peroxide-producing Lactococcus garvieae N201 dairy strain. Transcriptomic responses of two S. aureus strains, the S. aureus SA15 dairy strain and the MW2 human pathogenic strain, to this growth inhibition were investigated in Brain-Heart Infusion broth under a high or a low aeration level. We demonstrated that S. aureus MW2 had a higher resistance to L. garvieae inhibition under the high aeration level: this correlated to a higher survival under hydrogen peroxide exposure. Conversely, the two strains were similarly inhibited under the low aeration level. Expression of S. aureus genes involved in response to H2O2 or other stresses as well as in cell division was generally repressed by L. garvieae. However, differential expressions between the two S. aureus strains were observed, especially under the high aeration level. Additionally, expression of virulence-related genes (enterotoxins, regulatory genes) was modulated by L. garvieae depending on the aeration level and on the S. aureus strain. This study led to new insights into potential molecular mechanisms of S. aureus inhibition by Lactic Acid Bacteria via H2O2 production.
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Vázquez-Sánchez D, Cabo M, Rodríguez-Herrera J. Single and Sequential Application of Electrolyzed Water with Benzalkonium Chloride or Peracetic Acid for Removal of S
taphylococcus Aureus
Biofilms. J Food Saf 2014. [DOI: 10.1111/jfs.12114] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- D. Vázquez-Sánchez
- Seafood Microbiology and Technology Section; Spanish National Research Council (CSIC); Marine Research Institute (IIM); Eduardo Cabello 6 36208 Vigo Spain
| | - M.L. Cabo
- Seafood Microbiology and Technology Section; Spanish National Research Council (CSIC); Marine Research Institute (IIM); Eduardo Cabello 6 36208 Vigo Spain
| | - J.J. Rodríguez-Herrera
- Seafood Microbiology and Technology Section; Spanish National Research Council (CSIC); Marine Research Institute (IIM); Eduardo Cabello 6 36208 Vigo Spain
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Abstract
Hypochlorous acid (HOCl), the active ingredient of household bleach, is the most common disinfectant in medical, industrial, and domestic use and plays an important role in microbial killing in the innate immune system. Given the critical importance of the antimicrobial properties of chlorine to public health, it is surprising how little is known about the ways in which bacteria sense and respond to reactive chlorine species (RCS). Although the literature on bacterial responses to reactive oxygen species (ROS) is enormous, work addressing bacterial responses to RCS has begun only recently. Transcriptomic and proteomic studies now provide new insights into how bacteria mount defenses against this important class of antimicrobial compounds. In this review, we summarize the current knowledge, emphasizing the overlaps between RCS stress responses and other more well-characterized bacterial defense systems, and identify outstanding questions that represent productive avenues for future research.
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Affiliation(s)
- Michael J Gray
- Department of Molecular, Cellular and Developmental Biology, University of Michigan, Ann Arbor, Michigan 48109-1048; , ,
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Higuchi M, Celino FT, Shimizu-Yamaguchi S, Miura C, Miura T. Taurine plays an important role in the protection of spermatogonia from oxidative stress. Amino Acids 2012; 43:2359-69. [PMID: 22619065 DOI: 10.1007/s00726-012-1316-9] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2011] [Accepted: 04/25/2012] [Indexed: 12/13/2022]
Abstract
It has been demonstrated that taurine has various physiological functions in the body. We demonstrated that taurine is abundant in the serum, liver, muscle and testis of the Japanese eel (Anguilla japonica). In the eel testis, taurine is found mainly in spermatogonia and is weakly expressed also in the Sertoli cells. We have further found in the eel testis that taurine is actively accumulated via the sodium/chloride-dependent taurine transporter (TauT; SLC6A6), which is expressed in germ cells. In our current study, the effects of taurine on the anti-oxidant response were examined. Taurine was found to promote the total superoxide dismutase (SOD) activity in the testis. Moreover, our results indicate that taurine does not affect the mRNA levels of copper-zinc (Cu/Zn) SOD or manganese SOD, but promotes the translation of Cu/Zn SOD. Overall, our present data suggest that taurine may modulate Cu/Zn SOD at the translational level and thereby may play an important role in the protection of germ cells from oxidative stress.
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Affiliation(s)
- Masato Higuchi
- Research Group for Reproductive Physiology, South Ehime Fisheries Research Center, Ehime University, Ainan, Ehime, Japan
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Characterization of a Staphylococcus aureus surface virulence factor that promotes resistance to oxidative killing and infectious endocarditis. Infect Immun 2010; 79:342-52. [PMID: 20937760 DOI: 10.1128/iai.00736-10] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Staphylococcus aureus is a prominent human pathogen and a leading cause of community- and hospital-acquired bacterial infections worldwide. Herein, we describe the identification and characterization of the S. aureus 67.6-kDa hypothetical protein, named for the surface factor promoting resistance to oxidative killing (SOK) in this study. Sequence analysis showed that the SOK gene is conserved in all sequenced S. aureus strains and homologous to the myosin cross-reactive antigen of Streptococcus pyogenes. Immunoblotting and immunofluorescence analysis showed that SOK was copurified with membrane fractions and was exposed on the surface of S. aureus Newman and RN4220. Comparative analysis of wild-type S. aureus and an isogenic deletion strain indicated that SOK contributes to both resistance to killing by human neutrophils and to oxidative stress. In addition, the S. aureus sok deletion strain showed dramatically reduced aortic valve vegetation and bacterial cell number in a rabbit endocarditis model. These results, plus the suspected role of the streptococcal homologue in certain diseases such as acute rheumatic fever, suggest that SOK plays an important role in cardiovascular and other staphylococcal infections.
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Wesche AM, Gurtler JB, Marks BP, Ryser ET. Stress, sublethal injury, resuscitation, and virulence of bacterial foodborne pathogens. J Food Prot 2009; 72:1121-38. [PMID: 19517746 DOI: 10.4315/0362-028x-72.5.1121] [Citation(s) in RCA: 296] [Impact Index Per Article: 19.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Environmental stress and food preservation methods (e.g., heating, chilling, acidity, and alkalinity) are known to induce adaptive responses within the bacterial cell. Microorganisms that survive a given stress often gain resistance to that stress or other stresses via cross-protection. The physiological state of a bacterium is an important consideration when studying its response to food preservation techniques. This article reviews the various definitions of injury and stress, sublethal injury of bacteria, stresses that cause this injury, stress adaptation, cellular repair and response mechanisms, the role of reactive oxygen species in bacterial injury and resuscitation, and the potential for cross-protection and enhanced virulence as a result of various stress conditions.
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Affiliation(s)
- Alissa M Wesche
- Department of Food Science and Human Nutrition, Michigan State University, East Lansing, Michigan 48824, USA
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11
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Palazzolo-Ballance AM, Reniere ML, Braughton KR, Sturdevant DE, Otto M, Kreiswirth BN, Skaar EP, DeLeo FR. Neutrophil microbicides induce a pathogen survival response in community-associated methicillin-resistant Staphylococcus aureus. THE JOURNAL OF IMMUNOLOGY 2008; 180:500-9. [PMID: 18097052 DOI: 10.4049/jimmunol.180.1.500] [Citation(s) in RCA: 111] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
In recent years, there has been a dramatic increase in the incidence of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) infections. MW2 (pulsed-field type USA400), the prototype CA-MRSA strain, is highly virulent and has enhanced ability to evade killing by neutrophils. Although progress has been made, the molecular basis for enhanced virulence of CA-MRSA remains incompletely defined. To that end, we studied resistance of MW2 to key microbicides of human neutrophils. Hydrogen peroxide (H2O2), hypochlorous acid, and azurophilic granule proteins had significant bacteriostatic but limited staphylocidal activity toward MW2 under the conditions tested. An MW2-specific microarray revealed common changes in S. aureus gene expression following exposure to each microbicide, such as up-regulation of transcripts involved in gene regulation (e.g., saeRS and kdpDE) and stress response. Azurophilic granule proteins elicited the greatest number of changes in MW2 transcripts, including up-regulation of mRNAs encoding multiple toxins and hemolysins (e.g., hlgA, hlgB, hlgC, hla, lukS-PV, lukF-PV, sec4, and set17-26). Notably, H2O2 triggered up-regulation of transcripts related to heme/iron uptake (e.g., isdA, isdB, and isdCDEFsrtBisdG), and an isogenic isdAB-negative strain of MW2 had increased susceptibility to H2O2 (p<0.001) and human neutrophils (p<0.05) compared with the wild-type parental strain. These findings reveal a S. aureus survival response wherein Iron-regulated surface determinant (Isd) proteins are important for resistance to innate host defense. Collectively, the data provide an enhanced view of the mechanisms used by S. aureus to circumvent destruction by the innate immune system.
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Affiliation(s)
- Amy M Palazzolo-Ballance
- Laboratory of Human Bacterial Pathogenesis, Research Technologies Section, Genomics Unit, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, MT 59840, USA
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12
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Abstract
Peroxiredoxins constitute an important component of the bacterial defense against toxic peroxides. These enzymes use reactive cysteine thiols to reduce peroxides with electrons ultimately derived from reduced pyridine dinucleotides. Studies examining the regulation and physiological roles of AhpC, Tpx, Ohr and OsmC reveal the multilayered nature of bacterial peroxide defense. AhpC is localized in the cytoplasm and has a wide substrate range that includes H2O2, organic peroxides and peroxynitrite. This enzyme functions in both the control of endogenous peroxides, as well as in the inducible defense response to exogenous peroxides or general stresses. Ohr, OsmC and Tpx are organic peroxide specific. Tpx is localized to the periplasm and can be involved in either constitutive peroxide defense or participate in oxidative stress inducible responses depending on the organism. Ohr is an organic peroxide specific defense system that is under the control of the organic peroxide sensing repressor OhrR. In some organisms Ohr homologs are regulated in response to general stress. Clear evidence indicates that AhpC, Tpx and Ohr are involved in virulence. The role of OsmC is less clear. Regulation of OsmC expression is not oxidative stress inducible, but is controlled by multiple general stress responsive regulators.
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Affiliation(s)
- James M Dubbs
- Laboratory of Biotechnology, Chulabhorn Research Institute, Lak Si, Bangkok 10210, Thailand
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13
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Chang MW, Toghrol F, Bentley WE. Toxicogenomic response to chlorination includes induction of major virulence genes in Staphylococcus aureus. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2007; 41:7570-7575. [PMID: 18044543 DOI: 10.1021/es070929k] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
Despite the widespread use of chlorination for microbial control in aqueous environments, cellular response mechanisms of human pathogens, such as Staphylococcus aureus, against chlorination remain unknown. In this work, genome-wide transcriptional analysis was performed to elucidate cellular response of S. aureusto hypochlorous acid, an active antimicrobial product of chlorination in aqueous solution. Our results suggest that hypochlorous acid repressed transcription of genes involved in cell wall synthesis, membrane transport, protein synthesis, and primary metabolism, while amino acid synthesis genes were induced. Furthermore, hypochlorous acid induced transcription of genes encoding major virulence factors of S. aureus, such as exotoxins, hemolysins, leukocidins, coagulases, and surface adhesion proteins, which all play essential roles in staphylococcal virulence. This work implies that chlorination may stimulate production of virulence factors, which provides new insight into host-pathogen interactions and effects of chlorine application for microbial control.
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Affiliation(s)
- Matthew Wook Chang
- School of Chemical and Biomedical Engineering, Nanyang Technological University, Singapore
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14
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Helbling DE, Vanbriesen JM. Free chlorine demand and cell survival of microbial suspensions. WATER RESEARCH 2007; 41:4424-34. [PMID: 17624396 DOI: 10.1016/j.watres.2007.06.006] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/19/2006] [Revised: 03/21/2007] [Accepted: 06/04/2007] [Indexed: 05/02/2023]
Abstract
The utility of chlorine residual and chlorine demand as a surrogate for microbial contamination in the water distribution system was evaluated. The chlorine demanded by and cell survival of pure culture suspensions of Escherichia coli, Staphylococcus epidermidis, and Mycobacterium aurum were quantified in solutions with initial free chlorine concentrations of 0.20, 0.40, and 0.80 mg/L. The chlorine demand increased with initial concentration of cells and free chlorine for all species. At equivalent initial cell concentrations, chlorine demand was greatest for M. aurum, followed by S. epidermidis and E. coli. The chlorine contact time required for a 3-log inactivation of E. coli, S. epidermidis, and M. aurum was calculated as 0.032+/-0.009, 0.221+/-0.080, and 42.9+/-2.71 mg min/L, respectively. The ultimate chlorine demand and cell survival were directly proportional. No chlorine demand was observed at cell concentrations less than 10(5)CFU/mL for E. coli or 10(4)CFU/mL for S. epidermidis. M. aurum demanded chlorine at all initial cell concentrations including 10(3)CFU/mL, which was the detection limit of the cell quantification assay. Chlorine demand was determined to be a suitable surrogate indicator of the organisms studied and its utility may be enhanced in locations of the water distribution system that maintain a higher free chlorine residual.
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Affiliation(s)
- Damian E Helbling
- Department of Civil and Environmental Engineering, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA 15213, USA.
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