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Bivona D, Bonomo C, Colombini L, Bonacci PG, Privitera GF, Caruso G, Caraci F, Santoro F, Musso N, Bongiorno D, Iannelli F, Stefani S. Generation and Characterization of Stable Small Colony Variants of USA300 Staphylococcus aureus in RAW 264.7 Murine Macrophages. Antibiotics (Basel) 2024; 13:264. [PMID: 38534699 DOI: 10.3390/antibiotics13030264] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2024] [Revised: 03/08/2024] [Accepted: 03/13/2024] [Indexed: 03/28/2024] Open
Abstract
Intracellular survival and immune evasion are typical features of staphylococcal infections. USA300 is a major clone of methicillin-resistant S. aureus (MRSA), a community- and hospital-acquired pathogen capable of disseminating throughout the body and evading the immune system. Carnosine is an endogenous dipeptide characterized by antioxidant and anti-inflammatory properties acting on the peripheral (macrophages) and tissue-resident (microglia) immune system. In this work, RAW 264.7 murine macrophages were infected with the USA300 ATCC BAA-1556 S. aureus strain and treated with 20 mM carnosine and/or 32 mg/L erythromycin. Stable small colony variant (SCV) formation on blood agar medium was obtained after 48 h of combined treatment. Whole genome sequencing of the BAA-1556 strain and its stable derivative SCVs when combining Illumina and nanopore technologies revealed three single nucleotide differences, including a nonsense mutation in the shikimate kinase gene aroK. Gene expression analysis showed a significant up-regulation of the uhpt and sdrE genes in the stable SCVs compared with the wild-type, likely involved in adaptation to the intracellular milieu.
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Affiliation(s)
- Dalida Bivona
- Medical Molecular Microbiology and Antibiotic Resistance Laboratory (MMARLab), Department of Biomedical and Biotechnological Sciences (BIOMETEC), University of Catania, 95123 Catania, Italy
| | - Carmelo Bonomo
- Medical Molecular Microbiology and Antibiotic Resistance Laboratory (MMARLab), Department of Biomedical and Biotechnological Sciences (BIOMETEC), University of Catania, 95123 Catania, Italy
| | - Lorenzo Colombini
- Laboratory of Molecular Microbiology and Biotechnology, Department of Medical Biotechnologies, University of Siena, 53100 Siena, Italy
| | - Paolo G Bonacci
- Medical Molecular Microbiology and Antibiotic Resistance Laboratory (MMARLab), Department of Biomedical and Biotechnological Sciences (BIOMETEC), University of Catania, 95123 Catania, Italy
| | - Grete F Privitera
- Department of Clinical and Experimental Medicine, University of Catania, 95123 Catania, Italy
| | - Giuseppe Caruso
- Department of Drug and Health Sciences, University of Catania, 95125 Catania, Italy
- Oasi Research Institute-IRCCS, 94018 Troina, Italy
| | - Filippo Caraci
- Department of Drug and Health Sciences, University of Catania, 95125 Catania, Italy
- Oasi Research Institute-IRCCS, 94018 Troina, Italy
| | - Francesco Santoro
- Laboratory of Molecular Microbiology and Biotechnology, Department of Medical Biotechnologies, University of Siena, 53100 Siena, Italy
| | - Nicolò Musso
- Biochemical Section, Department of Biomedical and Biotechnological Sciences (BIOMETEC), University of Catania, 95123 Catania, Italy
| | - Dafne Bongiorno
- Medical Molecular Microbiology and Antibiotic Resistance Laboratory (MMARLab), Department of Biomedical and Biotechnological Sciences (BIOMETEC), University of Catania, 95123 Catania, Italy
| | - Francesco Iannelli
- Laboratory of Molecular Microbiology and Biotechnology, Department of Medical Biotechnologies, University of Siena, 53100 Siena, Italy
| | - Stefania Stefani
- Medical Molecular Microbiology and Antibiotic Resistance Laboratory (MMARLab), Department of Biomedical and Biotechnological Sciences (BIOMETEC), University of Catania, 95123 Catania, Italy
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Millán-Pacheco C, Rios-Soto L, Corral-Rodríguez N, Sierra-Campos E, Valdez-Solana M, Téllez-Valencia A, Avitia-Domínguez C. Discovery of Potential Noncovalent Inhibitors of Dehydroquinate Dehydratase from Methicillin-Resistant Staphylococcus aureus through Computational-Driven Drug Design. Pharmaceuticals (Basel) 2023; 16:1148. [PMID: 37631063 PMCID: PMC10458038 DOI: 10.3390/ph16081148] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2023] [Revised: 08/10/2023] [Accepted: 08/10/2023] [Indexed: 08/27/2023] Open
Abstract
Bacteria resistance to antibiotics is a concerning global health problem; in this context, methicillin-resistant Staphylococcus aureus (MRSA) is considered as a high priority by the World Health Organization. Furthermore, patients with a positive result for COVID-19 received early antibiotic treatment, a fact that potentially encourages the increase in antibiotic resistance. Therefore, there is an urgency to develop new drugs with molecular mechanisms different from those of the actual treatments. In this context, enzymes from the shikimate pathway, a route absent in humans, such as dehydroquinate dehydratase (DHQD), are considered good targets. In this work, a computer-aided drug design strategy, which involved exhaustive virtual screening and molecular dynamics simulations with MM-PBSA analysis, as well as an in silico ADMETox characterization, was performed to find potential noncovalent inhibitors of DHQD from MRSA (SaDHQD). After filtering the 997 million compounds from the ZINC database, 6700 compounds were submitted to an exhaustive virtual screening protocol. From these data, four molecules were selected and characterized (ZINC000005753647 (1), ZINC000001720488 (2), ZINC000082049768 (3), and ZINC000644149506 (4)). The results indicate that the four potential inhibitors interacted with residues important for substrate binding and catalysis, with an estimated binding free energy like that of the enzyme's substrate. Their ADMETox-predicted properties suggest that all of them support the structural characteristics to be considered good candidates. Therefore, the four compounds reported here are excellent option to be considered for future in vitro studies to design new SaDHQD noncovalent inhibitors and contribute to the search for new drugs against MRSA.
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Affiliation(s)
- César Millán-Pacheco
- Facultad de Farmacia, Universidad Autónoma del Estado de Morelos, Cuernavaca, Morelos 62209, Mexico;
| | - Lluvia Rios-Soto
- Facultad de Medicina y Nutrición, Universidad Juárez del Estado de Durango, Av. Universidad y Fanny Anitua S/N, Durango 34000, Mexico; (L.R.-S.); (N.C.-R.)
| | - Noé Corral-Rodríguez
- Facultad de Medicina y Nutrición, Universidad Juárez del Estado de Durango, Av. Universidad y Fanny Anitua S/N, Durango 34000, Mexico; (L.R.-S.); (N.C.-R.)
| | - Erick Sierra-Campos
- Facultad de Ciencias Químicas, Universidad Juárez del Estado de Durango Campus Gómez Palacio, Avenida Artículo 123 S/N, Fracc. Filadelfia, Gómez Palacio 35010, Mexico; (E.S.-C.); (M.V.-S.)
| | - Mónica Valdez-Solana
- Facultad de Ciencias Químicas, Universidad Juárez del Estado de Durango Campus Gómez Palacio, Avenida Artículo 123 S/N, Fracc. Filadelfia, Gómez Palacio 35010, Mexico; (E.S.-C.); (M.V.-S.)
| | - Alfredo Téllez-Valencia
- Facultad de Medicina y Nutrición, Universidad Juárez del Estado de Durango, Av. Universidad y Fanny Anitua S/N, Durango 34000, Mexico; (L.R.-S.); (N.C.-R.)
| | - Claudia Avitia-Domínguez
- Facultad de Medicina y Nutrición, Universidad Juárez del Estado de Durango, Av. Universidad y Fanny Anitua S/N, Durango 34000, Mexico; (L.R.-S.); (N.C.-R.)
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Mashayamombe M, Carda-Diéguez M, Mira A, Fitridge R, Zilm PS, Kidd SP. Subpopulations in Strains of Staphylococcus aureus Provide Antibiotic Tolerance. Antibiotics (Basel) 2023; 12:antibiotics12020406. [PMID: 36830316 PMCID: PMC9952555 DOI: 10.3390/antibiotics12020406] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2023] [Revised: 02/12/2023] [Accepted: 02/15/2023] [Indexed: 02/22/2023] Open
Abstract
The ability of Staphylococcus aureus to colonise different niches across the human body is linked to an adaptable metabolic capability, as well as its ability to persist within specific tissues despite adverse conditions. In many cases, as S. aureus proliferates within an anatomical niche, there is an associated pathology. The immune response, together with medical interventions such as antibiotics, often removes the S. aureus cells that are causing this disease. However, a common issue in S. aureus infections is a relapse of disease. Within infected tissue, S. aureus exists as a population of cells, and it adopts a diversity of cell types. In evolutionary biology, the concept of "bet-hedging" has established that even in positive conditions, there are members that arise within a population that would be present as non-beneficial, but if those conditions change, these traits could allow survival. For S. aureus, some of these cells within an infection have a reduced fitness, are not rapidly proliferating or are the cause of an active host response and disease, but these do remain even after the disease seems to have been cleared. This is true for persistence against immune responses but also as a continual presence in spite of antibiotic treatment. We propose that the constant arousal of suboptimal populations at any timepoint is a key strategy for S. aureus long-term infection and survival. Thus, understanding the molecular basis for this feature could be instrumental to combat persistent infections.
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Affiliation(s)
- Matipaishe Mashayamombe
- Department of Vascular Surgery, Royal Adelaide Hospital, Adelaide, SA 5000, Australia
- Discipline of Surgery, Adelaide Medical School, The University of Adelaide, Adelaide, SA 5000, Australia
- Basil Hetzel Institute for Translational Research, The Queen Elizabeth Hospital, Adelaide, SA 5000, Australia
| | - Miguel Carda-Diéguez
- Department of Health and Genomics, Center for Advanced Research in Public Health, FISABIO Institute, 46020 Valencia, Spain
| | - Alex Mira
- Department of Health and Genomics, Center for Advanced Research in Public Health, FISABIO Institute, 46020 Valencia, Spain
- School of Health and Welfare, Jönköping University, 551 11 Jönköping, Sweden
| | - Robert Fitridge
- Department of Vascular Surgery, Royal Adelaide Hospital, Adelaide, SA 5000, Australia
- Discipline of Surgery, Adelaide Medical School, The University of Adelaide, Adelaide, SA 5000, Australia
- Basil Hetzel Institute for Translational Research, The Queen Elizabeth Hospital, Adelaide, SA 5000, Australia
| | - Peter S. Zilm
- Adelaide Dental School, The University of Adelaide, Adelaide, SA 5000, Australia
| | - Stephen P. Kidd
- Department of Molecular and Biomedical Sciences, School of Biological Sciences, The University of Adelaide, Adelaide, SA 5005, Australia
- Research Centre for Infectious Disease, The University of Adelaide, Adelaide, SA 5005, Australia
- Australian Centre for Antimicrobial Resistance Ecology (ACARE), The University of Adelaide, Adelaide, SA 5005, Australia
- Correspondence:
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Rodríguez Á, Maneiro M, Lence E, Otero JM, van Raaij MJ, Thompson P, Hawkins AR, González-Bello C. Quinate-based ligands for irreversible inactivation of the bacterial virulence factor DHQ1 enzyme-A molecular insight. Front Mol Biosci 2023; 10:1111598. [PMID: 36762206 PMCID: PMC9902378 DOI: 10.3389/fmolb.2023.1111598] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2022] [Accepted: 01/10/2023] [Indexed: 01/26/2023] Open
Abstract
Irreversible inhibition of the enzyme type I dehydroquinase (DHQ1), a promising target for anti-virulence drug development, has been explored by enhancing the electrophilicity of specific positions of the ligand towards covalent lysine modification. For ligand design, we made use of the advantages offered by the intrinsic acid-base properties of the amino substituents introduced in the quinate scaffold, namely compounds 6-7 (R configuration at C3), to generate a potential leaving group, as well as the recognition pattern of the enzyme. The reactivity of the C2-C3 bond (Re face) in the scaffold was also explored using compound 8. The results of the present study show that replacement of the C3 hydroxy group of (-)-quinic acid by a hydroxyamino substituent (compound 6) provides a time-dependent irreversible inhibitor, while compound 7, in which the latter functionality was substituted by an amino group, and the introduction of an oxirane ring at C2-C3 bond, compound 8, do not allow covalent modification of the enzyme. These outcomes were supported by resolution of the crystal structures of DHQ1 from Staphylococcus aureus (Sa-DHQ1) and Salmonella typhi (St-DHQ1) chemically modified by 6 at a resolution of 1.65 and 1.90 Å, respectively, and of St-DHQ1 in the complex with 8 (1.55 Å). The combination of these structural studies with extensive molecular dynamics simulation studies allowed us to understand the molecular basis of the type of inhibition observed. This study is a good example of the importance of achieving the correct geometry between the reactive center of the ligand (electrophile) and the enzyme nucleophile (lysine residue) to allow selective covalent modification. The outcomes obtained with the hydroxyamino derivative 6 also open up new possibilities in the design of irreversible inhibitors based on the use of amino substituents.
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Affiliation(s)
- Ángela Rodríguez
- Centro Singular de Investigación en Química Biolóxica e Materiais Moleculares (CiQUS), Departamento de Química Orgánica, Universidade de Santiago de Compostela, Santiago de Compostela, Spain
| | - María Maneiro
- Centro Singular de Investigación en Química Biolóxica e Materiais Moleculares (CiQUS), Departamento de Química Orgánica, Universidade de Santiago de Compostela, Santiago de Compostela, Spain
| | - Emilio Lence
- Centro Singular de Investigación en Química Biolóxica e Materiais Moleculares (CiQUS), Departamento de Química Orgánica, Universidade de Santiago de Compostela, Santiago de Compostela, Spain
| | - José M. Otero
- Centro Singular de Investigación en Química Biolóxica e Materiais Moleculares (CiQUS), Departamento de Química Orgánica, Universidade de Santiago de Compostela, Santiago de Compostela, Spain
| | - Mark J. van Raaij
- Departamento de Estructura de Macromoléculas, Centro Nacional de Biotecnología (CSIC), Madrid, Spain
| | - Paul Thompson
- Newcastle University Biosciences Institute, The Medical School, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Alastair R. Hawkins
- Newcastle University Biosciences Institute, The Medical School, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Concepción González-Bello
- Centro Singular de Investigación en Química Biolóxica e Materiais Moleculares (CiQUS), Departamento de Química Orgánica, Universidade de Santiago de Compostela, Santiago de Compostela, Spain,*Correspondence: Concepción González-Bello,
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Acute Infection with a Tobramycin-Induced Small Colony Variant of Staphylococcus aureus Causes Increased Inflammation in the Cystic Fibrosis Rat Lung. Infect Immun 2022; 90:e0023722. [PMID: 36165627 PMCID: PMC9671023 DOI: 10.1128/iai.00237-22] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Cystic fibrosis (CF) disease is characterized by lifelong infections with pathogens such as Staphylococcus aureus, leading to eventual respiratory failure. Small colony variants (SCVs) of S. aureus have been linked to worse clinical outcomes for people with CF. Current studies of SCV pathology in vivo are limited, and it remains unclear whether SCVs directly impact patient outcomes or are a result of late-stage CF disease. To investigate this, we generated a stable menadione-auxotrophic SCV strain by serially passaging a CF isolate of S. aureus with tobramycin, an aminoglycoside antibiotic commonly administered for coinfecting Pseudomonas aeruginosa. This SCV was tobramycin resistant and showed increased tolerance to the anti-staphylococcal combination therapy sulfamethoxazole-trimethoprim. To better understand the dynamics of SCV infections in vivo, we infected CF rats with this strain compared with its normal colony variant (NCV). Analysis of bacterial burden at 3 days postinfection indicated that NCVs and SCVs persisted equally well in the lungs, but SCV infections ultimately led to increased weight loss and neutrophilic inflammation. Additionally, cellular and histopathological analyses showed that in CF rats, SCV infections yielded a lower macrophage response. Overall, these findings indicate that SCV infections may directly contribute to lung disease progression in people with CF.
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Functional mgrA Influences Genetic Changes within a Staphylococcus aureus Cell Population over Time. J Bacteriol 2022; 204:e0013822. [PMID: 36154359 DOI: 10.1128/jb.00138-22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Prolonged survival in the host-bacteria microenvironment drives the selection of alternative cell types in Staphylococcus aureus, permitting quasi-dormant sub-populations to develop. These facilitate antibiotic tolerance, long-term growth, and relapse of infection. Small Colony Variants (SCV) are an important cell type associated with persistent infection but are difficult to study in vitro due to the instability of the phenotype and reversion to the normal cell type. We have previously reported that under conditions of growth in continuous culture over a prolonged culture time, SCVs dominated a heterogenous population of cell types and these SCVs harbored a mutation in the DNA binding domain of the gene for the transcription factor, mgrA. To investigate this specific cell type further, S. aureus WCH-SK2-ΔmgrA itself was assessed with continuous culture. Compared to the wild type, the mgrA mutant strain required fewer generations to select for SCVs. There was an increased rate of mutagenesis within the ΔmgrA strain compared to the wild type, which we postulate is the mechanism explaining the increased emergence of SCV selection. The mgrA derived SCVs had impeded metabolism, altered MIC to specific antibiotics and an increased biofilm formation compared to non-SCV strain. Whole genomic sequencing detected single nucleotide polymorphisms (SNP) in phosphoglucosamine mutase glmM and tyrosine recombinase xerC. In addition, several genomic rearrangements were detected which affected genes involved in important functions such as antibiotic and toxic metal resistance and pathogenicity. Thus, we propose a direct link between mgrA and the SCV phenotype. IMPORTANCE Within a bacterial population, a stochastically generated heterogeneity of phenotypes allows continual survival against current and future stressors. The generation of a sub-population of quasi-dormant Small Colony Variants (SCV) in Staphylococcus aureus is such a mechanism, allowing for persistent or relapse of infection despite initial intervention seemingly clearing the infection. The use of continuous culture under clinically relevant conditions has allowed us to introduce time to the growth system and selects SCV within the population. This study provides valuable insights into the generation of SCV which are not addressed in standard laboratory generated models and reveals new pathways for understanding persistent S. aureus infection which can potentially be targeted in future treatments of persistent S. aureus infection.
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Zhou S, Rao Y, Li J, Huang Q, Rao X. Staphylococcus aureus small-colony variants: Formation, infection, and treatment. Microbiol Res 2022; 260:127040. [DOI: 10.1016/j.micres.2022.127040] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2021] [Revised: 04/10/2022] [Accepted: 04/11/2022] [Indexed: 10/18/2022]
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Lee J, Zilm PS, Kidd SP. Novel Research Models for Staphylococcus aureus Small Colony Variants (SCV) Development: Co-pathogenesis and Growth Rate. Front Microbiol 2020; 11:321. [PMID: 32184775 PMCID: PMC7058586 DOI: 10.3389/fmicb.2020.00321] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2019] [Accepted: 02/13/2020] [Indexed: 01/08/2023] Open
Abstract
Staphylococcus aureus remains a great burden on the healthcare system. Despite prescribed treatments often seemingly to be successful, S. aureus can survive and cause a relapsing infection which cannot be cleared. These infections are in part due to quasi-dormant sub-population which is tolerant to antibiotics and able to evade the host immune response. These include Small Colony Variants (SCVs). Because SCVs readily revert to non-SCV cell types under laboratory conditions, the characterization of SCVs has been problematic. This mini-review covers the phenotypic and genetic changes in stable SCVs including the selection of SCVs by and interactions with other bacterial species.
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Affiliation(s)
- James Lee
- Department of Molecular and Biomedical Science, The University of Adelaide, Adelaide, SA, Australia.,Research Centre for Infectious Diseases, Adelaide, SA, Australia.,Australian Centre for Antimicrobial Resistance Ecology, Adelaide, SA, Australia
| | - Peter S Zilm
- Faculty of Health and Medical Sciences, The University of Adelaide, Adelaide, SA, Australia
| | - Stephen P Kidd
- Department of Molecular and Biomedical Science, The University of Adelaide, Adelaide, SA, Australia.,Research Centre for Infectious Diseases, Adelaide, SA, Australia.,Australian Centre for Antimicrobial Resistance Ecology, Adelaide, SA, Australia
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Abstract
Respiratory mutants, both naturally occurring and genetically constructed, have taught us about the importance of metabolism in influencing virulence factor production, persistence, and antibiotic resistance. As we learn more about small colony variants, we find that Staphylococcus aureus has many pathways to produce small colony variants, although the respiratory variants are the best described clinically and in the laboratory.
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Torres NJ, Hartson SD, Rogers J, Gustafson JE. Proteomic and Metabolomic Analyses of a Tea-Tree Oil-Selected Staphylococcus aureus Small Colony Variant. Antibiotics (Basel) 2019; 8:antibiotics8040248. [PMID: 31816949 PMCID: PMC6963719 DOI: 10.3390/antibiotics8040248] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2019] [Revised: 11/25/2019] [Accepted: 11/27/2019] [Indexed: 11/16/2022] Open
Abstract
Tea tree oil (TTO) is hypothesized to kill bacteria by indiscriminately denaturing membrane and protein structures. A Staphylococcus aureus small colony variant (SCV) selected with TTO (SH1000-TTORS-1) demonstrated slowed growth, reduced susceptibility to TTO, a diminutive cell size, and a thinned cell wall. Utilizing a proteomics and metabolomics approach, we have now revealed that the TTO-selected SCV mutant demonstrated defective fatty acid synthesis, an alteration in the expression of genes and metabolites associated with central metabolism, the induction of a general stress response, and a reduction of proteins critical for active growth and translation. SH1000-TTORS-1 also demonstrated an increase in amino acid accumulation and a decrease in sugar content. The reduction in glycolytic pathway proteins and sugar levels indicated that carbon flow through glycolysis and gluconeogenesis is reduced in SH1000-TTORS-1. The increase in amino acid accumulation coincides with the reduced production of translation-specific proteins and the induction of proteins associated with the stringent response. The decrease in sugar content likely deactivates catabolite repression and the increased amino acid pool observed in SH1000-TTORS-1 represents a potential energy and carbon source which could maintain carbon flow though the tricarboxylic acid (TCA) cycle. It is noteworthy that processes that contribute to the production of the TTO targets (proteins and membrane) are reduced in SH1000-TTORS-1. This is one of a few studies describing a mechanism that bacteria utilize to withstand the action of an antiseptic which is thought to inactivate multiple cellular targets.
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Schleimer N, Kaspar U, Ballhausen B, Fotiadis SA, Streu JM, Kriegeskorte A, Proctor RA, Becker K. Adaption of an Episomal Antisense Silencing Approach for Investigation of the Phenotype Switch of Staphylococcus aureus Small-Colony Variants. Front Microbiol 2019; 10:2044. [PMID: 31551979 PMCID: PMC6738336 DOI: 10.3389/fmicb.2019.02044] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2019] [Accepted: 08/20/2019] [Indexed: 11/13/2022] Open
Abstract
Staphylococcus aureus small-colony variants (SCVs) are associated with chronic, persistent, and relapsing courses of infection and are characterized by slow growth combined with other phenotypic and molecular traits. Although certain mechanisms have been described, the genetic basis of clinical SCVs remains often unknown. Hence, we adapted an episomal tool for rapid identification and investigation of putative SCV phenotype-associated genes via antisense gene silencing based on previously described Tnl0-encoded tet-regulatory elements. Targeting the SCV phenotype-inducing enoyl-acyl-carrier-protein reductase gene (fabI), plasmid pSN1-AS‘fabI’ was generated leading to antisense silencing, which was proven by pronounced growth retardation in liquid cultures, phenotype switch on solid medium, and 200-fold increase of antisense ‘fabI’ expression. A crucial role of TetR repression in effective regulation of the system was demonstrated. Based on the use of anhydrotetracycline as effector, an easy-to-handle one-plasmid setup was set that may be applicable to different S. aureus backgrounds and cell culture studies. However, selection of the appropriate antisense fragment of the target gene remains a critical factor for effectiveness of silencing. This inducible gene expression system may help to identify SCV phenotype-inducing genes, which is prerequisite for the development of new antistaphylococcal agents and future alternative strategies to improve treatment of therapy-refractory SCV-related infections by iatrogenically induced phenotypic switch. Moreover, it can be used as controllable phenotype switcher to examine important aspects of SCV biology in cell culture as well as in vivo.
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Affiliation(s)
- Nina Schleimer
- Institute of Medical Microbiology, University Hospital Münster, Münster, Germany
| | - Ursula Kaspar
- Institute of Medical Microbiology, University Hospital Münster, Münster, Germany
| | - Britta Ballhausen
- Institute of Medical Microbiology, University Hospital Münster, Münster, Germany
| | - Sarah A Fotiadis
- Institute of Medical Microbiology, University Hospital Münster, Münster, Germany
| | - Jessica M Streu
- Institute of Medical Microbiology, University Hospital Münster, Münster, Germany
| | - André Kriegeskorte
- Institute of Medical Microbiology, University Hospital Münster, Münster, Germany
| | - Richard A Proctor
- Departments of Medical Microbiology/Immunology and Medicine, School of Medicine and Public Health, University of Wisconsin, Madison, WI, United States
| | - Karsten Becker
- Institute of Medical Microbiology, University Hospital Münster, Münster, Germany
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Zhang P, Wright JA, Tymon A, Nair SP. Bicarbonate induces high-level resistance to the human antimicrobial peptide LL-37 in Staphylococcus aureus small colony variants. J Antimicrob Chemother 2019; 73:615-619. [PMID: 29211886 PMCID: PMC5890704 DOI: 10.1093/jac/dkx433] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2017] [Accepted: 10/25/2017] [Indexed: 01/29/2023] Open
Abstract
Objectives Staphylococcus aureus small colony variants (SCVs) cause persistent infections and are resistant to cationic antibiotics. Antimicrobial peptides (AMPs) have been suggested as promising alternatives for treating antibiotic-resistant bacteria. We investigated the capacity of the human cationic AMP LL-37 to kill SCVs in the presence of physiological concentrations of bicarbonate, which are reported to alter bacterial membrane permeability and change resistance of bacteria to AMPs. Methods MBCs of LL-37 for S. aureus SCVs with mutations in different genes in the presence and absence of bicarbonate were determined. Results In the absence of bicarbonate, SCVs of S. aureus strains LS-1 and 8325-4 had the same level of resistance to LL-37 as the parental strain (8 mg/L). In the presence of bicarbonate, hemB, menD and aroD SCVs of LS-1 had high-level resistance to LL-37 (≥128 mg/L) compared with the parental strain (16 mg/L). However, only the aroD SCV of strain 8324-5 showed high-level resistance. 8325-4 harbours mutations in two genes, tcaR and rsbU, which are involved in antimicrobial sensing and the stress response, respectively. When rsbU was repaired in 8325-4 it displayed high-level resistance to LL-37 in the presence of bicarbonate. This phenotype was lost when tcaR was also repaired, demonstrating that RsbU and TcaR are involved in LL-37 resistance in the presence of bicarbonate Conclusions S. aureus SCVs would be resistant to high concentrations of LL-37 in niches where there are physiological concentrations of bicarbonate and therefore this AMP may not be effective in combating SCVs.
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Affiliation(s)
- Ping Zhang
- Department of Microbial Diseases, UCL Eastman Dental Institute, 256 Gray's Inn Road, London WC1X 8LD, UK
| | - John A Wright
- Immunology Catalyst, GSK, Stevenage, Hertfordshire, UK
| | - Anna Tymon
- Department of Microbial Diseases, UCL Eastman Dental Institute, 256 Gray's Inn Road, London WC1X 8LD, UK
| | - Sean P Nair
- Department of Microbial Diseases, UCL Eastman Dental Institute, 256 Gray's Inn Road, London WC1X 8LD, UK
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Schleimer N, Kaspar U, Drescher M, Seggewiß J, von Eiff C, Proctor RA, Peters G, Kriegeskorte A, Becker K. The Energy-Coupling Factor Transporter Module EcfAA'T, a Novel Candidate for the Genetic Basis of Fatty Acid-Auxotrophic Small-Colony Variants of Staphylococcus aureus. Front Microbiol 2018; 9:1863. [PMID: 30154773 PMCID: PMC6102330 DOI: 10.3389/fmicb.2018.01863] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2018] [Accepted: 07/25/2018] [Indexed: 11/29/2022] Open
Abstract
Staphylococcal small-colony variants (SCVs) are invasive and persistent due to their ability to thrive intracellularly and to evade the host immune response. Thus, the course of infections due to this phenotype is often chronic, relapsing, and therapy-refractory. In order to improve treatment of patients suffering from SCV-associated infections, it is of major interest to understand triggers for the development of this phenotype, in particular for strains naturally occurring in clinical settings. Within this study, we comprehensively characterized two different Staphylococcus aureus triplets each consisting of isogenic strains comprising (i) clinically derived SCV phenotypes with auxotrophy for unsaturated fatty acids, (ii) the corresponding wild-types (WTs), and (iii) spontaneous in vitro revertants displaying the normal phenotype (REVs). Comparison of whole genomes revealed that clinical SCV isolates were closely related to their corresponding WTs and REVs showing only seven to eight alterations per genome triplet. However, both SCVs carried a mutation within the energy-coupling factor (ECF) transporter-encoding ecf module (EcfAA’T) resulting in truncated genes. In both cases, these mutations were shown to be naturally restored in the respective REVs. Since ECF transporters are supposed to be essential for optimal bacterial growth, their dysfunction might constitute another mechanism for the formation of naturally occurring SCVs. Another three triplets analyzed revealed neither mutations in the EcfAA’T nor in other FASII-related genes underlining the high diversity of mechanisms leading to the fatty acid-dependent phenotype. This is the first report on the ECF transporter as genetic basis of fatty acid–auxotrophic staphylococcal SCVs.
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Affiliation(s)
- Nina Schleimer
- Institute of Medical Microbiology, University Hospital Münster, Münster, Germany
| | - Ursula Kaspar
- Institute of Medical Microbiology, University Hospital Münster, Münster, Germany
| | - Mike Drescher
- Institute of Medical Microbiology, University Hospital Münster, Münster, Germany
| | - Jochen Seggewiß
- Institute of Human Genetics, University Hospital Münster, Münster, Germany
| | - Christof von Eiff
- Institute of Medical Microbiology, University Hospital Münster, Münster, Germany
| | - Richard A Proctor
- Departments of Medical Microbiology/Immunology and Medicine, University of Wisconsin School of Medicine and Public Health, Madison, WI, United States
| | - Georg Peters
- Institute of Medical Microbiology, University Hospital Münster, Münster, Germany
| | - André Kriegeskorte
- Institute of Medical Microbiology, University Hospital Münster, Münster, Germany
| | - Karsten Becker
- Institute of Medical Microbiology, University Hospital Münster, Münster, Germany
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Suwantarat N, Rubin M, Bryan L, Tekle T, Boyle MP, Carroll KC, Jennings MT. Frequency of small-colony variants and antimicrobial susceptibility of methicillin-resistant Staphylococcus aureus in cystic fibrosis patients. Diagn Microbiol Infect Dis 2017; 90:296-299. [PMID: 29343421 DOI: 10.1016/j.diagmicrobio.2017.11.012] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2017] [Revised: 11/09/2017] [Accepted: 11/19/2017] [Indexed: 01/15/2023]
Abstract
BACKGROUND Small-colony variants (SCVs) are a distinct phenotype of Staphylococcus aureus, known for their role in chronic, difficult to treat infections, including cystic fibrosis (CF) lung disease. The goal of this study was to characterize SCV MRSA infection in an adult and pediatric CF population and to identify antibiotic susceptibility patterns unique to SCV MRSA. METHODS We recovered methicillin-resistant S. aureus (MRSA) from respiratory culture samples from CF patients at the Johns Hopkins Hospital during a 6month study period. RESULTS Of 1161 samples, 200 isolates (17%) were identified as MRSA, and 37 isolates from 28 patients were identified as SCV MRSA. A higher proportion of MRSA was found among SCV isolates (37/66, 56%) compared to normal colony variant (NCV) isolates (163/417, 39%), p=0.02. All SCV MRSA isolates from individual patients were susceptible to vancomycin and ceftaroline, but they demonstrated higher rates of antibiotic resistance to trimethoprim/sulfamethoxazole, moxifloxacin, and erythromycin, compared to NCV MRSA isolates. Additionally, individuals with SCV MRSA had lower lung function, higher rates of persistent MRSA infection, and higher rates of previous antibiotic use, compared to individuals with NCV MRSA. CONCLUSIONS A significant proportion of MRSA isolates recovered from patients with CF have the SCV morphology. Compared to individuals with NCV MRSA, those with SCV MRSA have higher rates of persistent MRSA infection and lower lung function. SCV MRSA isolates were more resistant than NCV, but they are highly susceptible to vancomycin, linezolid and ceftaroline.
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Affiliation(s)
- Nuntra Suwantarat
- Division of Medical Microbiology, Department of Pathology, The Johns Hopkins University School of Medicine, Baltimore, MD, USA; Chulabhorn International College of Medicine, Thammasat University, PathumThani, Thailand
| | - Mayer Rubin
- Division of Medical Microbiology, Department of Pathology, The Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Latetia Bryan
- Division of Medical Microbiology, Department of Pathology, The Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Tsigereda Tekle
- Division of Medical Microbiology, Department of Pathology, The Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Michael P Boyle
- The Cystic Fibrosis Foundation, Bethesda, MD, USA; Division of Pulmonary and Critical Care Medicine, Department of Medicine, The Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Karen C Carroll
- Division of Medical Microbiology, Department of Pathology, The Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Mark T Jennings
- Division of Pulmonary and Critical Care Medicine, Department of Medicine, The Johns Hopkins University School of Medicine, Baltimore, MD, USA.
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