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Watts SC, Judd LM, Carzino R, Ranganathan S, Holt KE. Genomic Diversity and Antimicrobial Resistance of Haemophilus Colonizing the Airways of Young Children with Cystic Fibrosis. mSystems 2021; 6:e0017821. [PMID: 34463568 DOI: 10.1128/msystems.00178-21] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2021] [Accepted: 08/04/2021] [Indexed: 11/20/2022] Open
Abstract
Respiratory infection during childhood is a key risk factor in early cystic fibrosis (CF) lung disease progression. Haemophilus influenzae and Haemophilus parainfluenzae are routinely isolated from the lungs of children with CF; however, little is known about the frequency and characteristics of Haemophilus colonization in this context. Here, we describe the detection, antimicrobial resistance (AMR), and genome sequencing of H. influenzae and H. parainfluenzae isolated from airway samples of 147 participants aged ≤12 years enrolled in the Australian Respiratory Early Surveillance Team for Cystic Fibrosis (AREST CF) program, Melbourne, Australia. The frequency of colonization per visit was 4.6% for H. influenzae and 32.1% for H. parainfluenzae, 80.3% of participants had H. influenzae and/or H. parainfluenzae detected on at least one visit, and using genomic data, we estimate 15.6% of participants had persistent colonization with the same strain for at least two consecutive visits. Isolates were genetically diverse and AMR was common, with 52% of H. influenzae and 82% of H. parainfluenzae displaying resistance to at least one drug. The genetic basis for AMR could be identified in most cases; putative novel determinants include a new plasmid encoding blaTEM-1 (ampicillin resistance), a new inhibitor-resistant blaTEM allele (augmentin resistance), and previously unreported mutations in chromosomally carried genes (pbp3, ampicillin resistance; folA/folP, cotrimoxazole resistance; rpoB, rifampicin resistance). Acquired AMR genes were more common in H. parainfluenzae than H. influenzae (51% versus 21%, P = 0.0107) and were mostly associated with the ICEHin mobile element carrying blaTEM-1, resulting in more ampicillin resistance in H. parainfluenzae (73% versus 30%, P = 0.0004). Genomic data identified six potential instances of Haemophilus transmission between participants, of which three involved participants who shared clinic visit days. IMPORTANCE Cystic fibrosis (CF) lung disease begins during infancy, and acute respiratory infections increase the risk of early disease development and progression. Microbes involved in advanced stages of CF are well characterized, but less is known about early respiratory colonizers. We report the population dynamics and genomic determinants of AMR in two early colonizer species, namely, Haemophilus influenzae and Haemophilus parainfluenzae, collected from a pediatric CF cohort. This investigation also reveals that H. parainfluenzae has a high frequency of AMR carried on mobile elements that may act as a potential reservoir for the emergence and spread of AMR to H. influenzae, which has greater clinical significance as a respiratory pathogen in children. This study provides insight into the evolution of AMR and the colonization of H. influenzae and H. parainfluenzae in a pediatric CF cohort, which will help inform future treatment.
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Affiliation(s)
- Stephen C Watts
- Department of Biochemistry and Molecular Biology, Bio21 Molecular Science and Biotechnology Institute, University of Melbournegrid.1008.9, Melbourne, Victoria, Australia
- Department of Infectious Diseases, Central Clinical School, Monash Universitygrid.1002.3, Melbourne, Victoria, Australia
| | - Louise M Judd
- Department of Infectious Diseases, Central Clinical School, Monash Universitygrid.1002.3, Melbourne, Victoria, Australia
| | - Rosemary Carzino
- Infection and Immunity, Murdoch Children's Research Institute, Melbourne, Victoria, Australia
| | - Sarath Ranganathan
- Infection and Immunity, Murdoch Children's Research Institute, Melbourne, Victoria, Australia
- Department of Paediatrics, University of Melbournegrid.1008.9, Melbourne, Victoria, Australia
| | - Kathryn E Holt
- Department of Biochemistry and Molecular Biology, Bio21 Molecular Science and Biotechnology Institute, University of Melbournegrid.1008.9, Melbourne, Victoria, Australia
- Department of Infectious Diseases, Central Clinical School, Monash Universitygrid.1002.3, Melbourne, Victoria, Australia
- London School of Hygiene & Tropical Medicine, London, United Kingdom
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2
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Riboldi GP, Zigweid R, Myler PJ, Mayclin SJ, Couñago RM, Staker BL. Identification of P218 as a potent inhibitor of Mycobacterium ulcerans DHFR. RSC Med Chem 2021; 12:103-109. [PMID: 34046602 PMCID: PMC8130613 DOI: 10.1039/d0md00303d] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2020] [Accepted: 10/07/2020] [Indexed: 11/21/2022] Open
Abstract
Mycobacterium ulcerans is the causative agent of Buruli ulcer, a debilitating chronic disease that mainly affects the skin. Current treatments for Buruli ulcer are efficacious, but rely on the use of antibiotics with severe side effects. The enzyme dihydrofolate reductase (DHFR) plays a critical role in the de novo biosynthesis of folate species and is a validated target for several antimicrobials. Here we describe the biochemical and structural characterization of M. ulcerans DHFR and identified P218, a safe antifolate compound in clinical evaluation for malaria, as a potent inhibitor of this enzyme. We expect our results to advance M. ulcerans DHFR as a target for future structure-based drug discovery campaigns.
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Affiliation(s)
- Gustavo P Riboldi
- Centro de Química Medicinal (CQMED), Centro de Biologia Molecular e Engenharia Genética (CBMEG), Universidade Estadual de Campinas (UNICAMP) Campinas SP 13083-875 Brazil
- Structural Genomics Consortium, Departamento de Genética e Evolução, Instituto de Biologia, UNICAMP Campinas SP 13083-886 Brazil
| | - Rachael Zigweid
- Center for Infectious Disease Research, Seattle Children's Research Institute Seattle Washington 98109 USA
| | - Peter J Myler
- Center for Infectious Disease Research, Seattle Children's Research Institute Seattle Washington 98109 USA
- Department of Pediatrics, University of Washington Seattle Washington 91895 USA
| | - Stephen J Mayclin
- Seattle Structural Genomics Center for Infectious Disease (SSGCID) Seattle Washington 98109 USA
- UCB Bainbridge Island Washington 98110 USA
| | - Rafael M Couñago
- Centro de Química Medicinal (CQMED), Centro de Biologia Molecular e Engenharia Genética (CBMEG), Universidade Estadual de Campinas (UNICAMP) Campinas SP 13083-875 Brazil
- Structural Genomics Consortium, Departamento de Genética e Evolução, Instituto de Biologia, UNICAMP Campinas SP 13083-886 Brazil
| | - Bart L Staker
- Center for Infectious Disease Research, Seattle Children's Research Institute Seattle Washington 98109 USA
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3
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Role of Horizontal Gene Transfer in the Development of Multidrug Resistance in Haemophilus influenzae. mSphere 2020; 5:5/1/e00969-19. [PMID: 31996416 PMCID: PMC6992377 DOI: 10.1128/msphere.00969-19] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Haemophilus influenzae colonizes the respiratory tract in humans and causes both invasive and noninvasive infections. As a threat to treatment, resistance against critically important antibiotics is on the rise in H. influenzae. Identifying mechanisms for horizontal acquisition of resistance genes is important to understand how multidrug resistance develops. The present study explores the antimicrobial resistance genes and their context in beta-lactam-resistant H. influenzae with coresistance to up to four non-beta-lactam groups. The results reveal that this organism is capable of acquiring resistance to a wide range of commonly used antibiotics through conjugative transfer of mobile genetic elements and transformation of chromosomal genes, resulting in mosaic genes with a broader resistance spectrum. Strains with chromosomally mediated resistance to extended-spectrum cephalosporins, co-trimoxazole, and quinolones combined with mobile genetic elements carrying genes mediating resistance to ampicillin, tetracyclines, and chloramphenicol have been reported, and further dissemination of such strains represents a particular concern. Haemophilus influenzae colonizes the respiratory tract in humans and causes both invasive and noninvasive infections. Resistance to extended-spectrum cephalosporins in H. influenzae is rare in Europe. In this study, we defined acquired resistance gene loci and ftsI mutations in multidrug-resistant (MDR) and/or PBP3-mediated beta-lactam-resistant (rPBP3) H. influenzae strains, intending to understand the mode of spread of antibiotic resistance determinants in this species. Horizontal transfer of mobile genetic elements and transformation with resistance-conferring ftsI alleles were contributory. We found one small plasmid and three novel integrative conjugative elements (ICEs) which carry different combinations of resistance genes. Demonstration of transfer and/or ICE circular forms showed that the ICEs are functional. Two extensively MDR genetically unrelated H. influenzae strains (F and G) from the same geographical region shared an identical novel MDR ICE (Tn6686) harboring blaTEM-1, catA2-like, and tet(B). The first Nordic case of MDR H. influenzae septicemia, strain 0, originating from the same geographical area as these strains, had a similar resistance pattern but contained another ICE [Tn6687 with blaTEM-1, catP and tet(B)] with an overall structure quite similar to that of Tn6686. Comparison of the complete ftsI genes among rPBP3 strains revealed that the entire gene or certain regions of it are identical in genetically unrelated strains, indicating horizontal gene transfer. Our findings illustrate that H. influenzae is capable of acquiring resistance against a wide range of commonly used antibiotics through horizontal gene transfer, in terms of conjugative transfer of ICEs and transformation of chromosomal genes. IMPORTANCEHaemophilus influenzae colonizes the respiratory tract in humans and causes both invasive and noninvasive infections. As a threat to treatment, resistance against critically important antibiotics is on the rise in H. influenzae. Identifying mechanisms for horizontal acquisition of resistance genes is important to understand how multidrug resistance develops. The present study explores the antimicrobial resistance genes and their context in beta-lactam-resistant H. influenzae with coresistance to up to four non-beta-lactam groups. The results reveal that this organism is capable of acquiring resistance to a wide range of commonly used antibiotics through conjugative transfer of mobile genetic elements and transformation of chromosomal genes, resulting in mosaic genes with a broader resistance spectrum. Strains with chromosomally mediated resistance to extended-spectrum cephalosporins, co-trimoxazole, and quinolones combined with mobile genetic elements carrying genes mediating resistance to ampicillin, tetracyclines, and chloramphenicol have been reported, and further dissemination of such strains represents a particular concern.
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4
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Sierra Y, Tubau F, González-Díaz A, Carrera-Salinas A, Moleres J, Bajanca-Lavado P, Garmendia J, Domínguez MÁ, Ardanuy C, Martí S. Assessment of trimethoprim-sulfamethoxazole susceptibility testing methods for fastidious Haemophilus spp. Clin Microbiol Infect 2019; 26:944.e1-944.e7. [PMID: 31811916 DOI: 10.1016/j.cmi.2019.11.022] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2019] [Revised: 11/20/2019] [Accepted: 11/21/2019] [Indexed: 11/19/2022]
Abstract
OBJECTIVES To compare the determinants of trimethoprim-sulfamethoxazole resistance with established susceptibility values for fastidious Haemophilus spp., to provide recommendations for optimal trimethoprim-sulfamethoxazole measurement. METHODS We collected 50 strains each of Haemophilus influenzae and Haemophilus parainfluenzae at Bellvitge University Hospital. Trimethoprim-sulfamethoxazole susceptibility was tested by microdilution, E-test and disc diffusion using both Mueller-Hinton fastidious (MH-F) medium and Haemophilus test medium (HTM) following EUCAST and CLSI criteria, respectively. Mutations in folA, folP and additional determinants of resistance were identified in whole-genome-sequenced isolates. RESULTS Strains presented generally higher rates of trimethoprim-sulfamethoxazole resistance when grown on HTM than on MH-F, independent of the methodology used (average MIC 2.6-fold higher in H. influenzae and 1.2-fold higher in H. parainfluenzae). The main resistance-related determinants were as follows: I95L and F154S/V in folA; 3- and 15-bp insertions and substitutions in folP; acquisition of sul genes; and FolA overproduction potentially linked to mutations in -35 and -10 promoter motifs. Of note, 2 of 19 H. influenzae strains (10.5%) and 9 of 33 H. parainfluenzae strains (27.3%) with mutations and assigned as resistant by microdilution were inaccurately considered susceptible by disc diffusion. This misinterpretation was resolved by raising the clinical resistance breakpoint of the EUCAST guidelines to ≤30 mm. CONCLUSIONS Given the routine use of disc diffusion, a significant number of strains could potentially be miscategorized as susceptible to trimethoprim-sulfamethoxazole despite having resistance-related mutations. A simple modification to the current clinical resistance breakpoint given by the EUCAST guideline for MH-F ensures correct interpretation and correlation with the reference standard method of microdilution.
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Affiliation(s)
- Y Sierra
- Microbiology Department, Hospital Universitari de Bellvitge, IDIBELL-UB, Barcelona, Spain
| | - F Tubau
- Microbiology Department, Hospital Universitari de Bellvitge, IDIBELL-UB, Barcelona, Spain; Research Network for Respiratory Diseases (CIBERES), ISCIII, Madrid, Spain
| | - A González-Díaz
- Microbiology Department, Hospital Universitari de Bellvitge, IDIBELL-UB, Barcelona, Spain; Research Network for Respiratory Diseases (CIBERES), ISCIII, Madrid, Spain
| | - A Carrera-Salinas
- Microbiology Department, Hospital Universitari de Bellvitge, IDIBELL-UB, Barcelona, Spain
| | - J Moleres
- Instituto de Agrobiotecnología, CSIC-Gobierno, Navarra, Spain
| | - P Bajanca-Lavado
- Haemophilus Influenzae Reference Laboratory, Department of Infectious Diseases, National Institute of Health, Lisbon, Portugal
| | - J Garmendia
- Research Network for Respiratory Diseases (CIBERES), ISCIII, Madrid, Spain; Instituto de Agrobiotecnología, CSIC-Gobierno, Navarra, Spain
| | - M Ángeles Domínguez
- Microbiology Department, Hospital Universitari de Bellvitge, IDIBELL-UB, Barcelona, Spain; Spanish Network for Research in Infectious Diseases (REIPI), ISCIII, Madrid, Spain; Department of Pathology and Experimental Therapeutics, Faculty of Medicine, University of Barcelona, Barcelona, Spain
| | - C Ardanuy
- Microbiology Department, Hospital Universitari de Bellvitge, IDIBELL-UB, Barcelona, Spain; Research Network for Respiratory Diseases (CIBERES), ISCIII, Madrid, Spain; Department of Pathology and Experimental Therapeutics, Faculty of Medicine, University of Barcelona, Barcelona, Spain.
| | - S Martí
- Microbiology Department, Hospital Universitari de Bellvitge, IDIBELL-UB, Barcelona, Spain; Research Network for Respiratory Diseases (CIBERES), ISCIII, Madrid, Spain.
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5
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Trimethoprim and other nonclassical antifolates an excellent template for searching modifications of dihydrofolate reductase enzyme inhibitors. J Antibiot (Tokyo) 2019; 73:5-27. [PMID: 31578455 PMCID: PMC7102388 DOI: 10.1038/s41429-019-0240-6] [Citation(s) in RCA: 70] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2019] [Revised: 08/07/2019] [Accepted: 08/22/2019] [Indexed: 12/17/2022]
Abstract
The development of new mechanisms of resistance among pathogens, the occurrence and transmission of genes responsible for antibiotic insensitivity, as well as cancer diseases have been a serious clinical problem around the world for over 50 years. Therefore, intense searching of new leading structures and active substances, which may be used as new drugs, especially against strain resistant to all available therapeutics, is very important. Dihydrofolate reductase (DHFR) has attracted a lot of attention as a molecular target for bacterial resistance over several decades, resulting in a number of useful agents. Trimethoprim (TMP), (2,4-diamino-5-(3′,4′,5′-trimethoxybenzyl)pyrimidine) is the well-known dihydrofolate reductase inhibitor and one of the standard antibiotics used in urinary tract infections (UTIs). This review highlights advances in design, synthesis, and biological evaluations in structural modifications of TMP as DHFR inhibitors. In addition, this report presents the differences in the active site of human and pathogen DHFR. Moreover, an excellent review of DHFR inhibition and their relevance to antimicrobial and parasitic chemotherapy was presented.
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6
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Kordus SL, Baughn AD. Revitalizing antifolates through understanding mechanisms that govern susceptibility and resistance. MEDCHEMCOMM 2019; 10:880-895. [PMID: 31303985 PMCID: PMC6595967 DOI: 10.1039/c9md00078j] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/05/2019] [Accepted: 05/07/2019] [Indexed: 12/12/2022]
Abstract
In prokaryotes and eukaryotes, folate (vitamin B9) is an essential metabolic cofactor required for all actively growing cells. Specifically, folate serves as a one-carbon carrier in the synthesis of amino acids (such as methionine, serine, and glycine), N-formylmethionyl-tRNA, coenzyme A, purines and thymidine. Many microbes are unable to acquire folates from their environment and rely on de novo folate biosynthesis. In contrast, mammals lack the de novo folate biosynthesis pathway and must obtain folate from commensal microbiota or the environment using proton-coupled folate transporters. The essentiality and dichotomy between mammalian and bacterial folate biosynthesis and utilization pathways make it an ideal drug target for the development of antimicrobial agents and cancer chemotherapeutics. In this minireview, we discuss general aspects of folate biosynthesis and the underlying mechanisms that govern susceptibility and resistance of organisms to antifolate drugs.
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Affiliation(s)
- Shannon Lynn Kordus
- Department of Microbiology and Immunology , University of Minnesota , Minneapolis , MN , USA .
| | - Anthony David Baughn
- Department of Microbiology and Immunology , University of Minnesota , Minneapolis , MN , USA .
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7
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González-Díaz A, Tubau F, Pinto M, Sierra Y, Cubero M, Càmara J, Ayats J, Bajanca-Lavado P, Ardanuy C, Marti S. Identification of polysaccharide capsules among extensively drug-resistant genitourinary Haemophilus parainfluenzae isolates. Sci Rep 2019; 9:4481. [PMID: 30872664 PMCID: PMC6418240 DOI: 10.1038/s41598-019-40812-2] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2018] [Accepted: 02/21/2019] [Indexed: 12/18/2022] Open
Abstract
The human commensal Haemophilus parainfluenzae is emerging as an opportunistic multidrug-resistant pathogen. The objectives of this work were to characterise a new capsular operon of extensively drug-resistant (XDR) H. parainfluenzae clinical isolates and study their resistance mechanisms using whole-genome sequencing. All strains were resistant to: ß-lactams, via amino acid changes in PBP3 (S385T, I442F, V511A, N526K and V562I); quinolones, by alterations in GyrA (S84F and D88Y) and ParC (S84F and S138T); chloramphenicol, through the presence of catS; macrolides, via the presence of mel and mef(E)-carrying MEGA element; and tetracycline, through the presence of tet(M) and/or tet(B). Phylogenetic analysis revealed high genomic diversity when compared to the H. parainfluenzae genomes available on the NCBI, the isolates from this study being closely related to the Swiss XDR AE-2096513. A full capsular operon showing homology to that of H. influenzae was identified, in accordance with the observation of a capsular structure by TEM. This study describes for the first time a capsular operon in H. parainfluenzae, a major determinant of pathogenicity that may contribute to increased virulence in XDR clinical isolates. Moreover, phylogenetic analysis suggests the possible spread of an XDR-encapsulated strain in Europe.
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Affiliation(s)
- Aida González-Díaz
- Microbiology Department, Hospital Universitari de Bellvitge, Universitat de Barcelona-IDIBELL, Barcelona, Spain.,CIBER de Enfermedades Respiratorias (CIBERes), Instituto de Salud Carlos III, Madrid, Spain
| | - Fe Tubau
- Microbiology Department, Hospital Universitari de Bellvitge, Universitat de Barcelona-IDIBELL, Barcelona, Spain.,CIBER de Enfermedades Respiratorias (CIBERes), Instituto de Salud Carlos III, Madrid, Spain
| | - Miguel Pinto
- Bioinformatics Unit, Department of Infectious Diseases, National Institute of Health, Lisbon, Portugal
| | - Yanik Sierra
- Microbiology Department, Hospital Universitari de Bellvitge, Universitat de Barcelona-IDIBELL, Barcelona, Spain
| | - Meritxell Cubero
- Microbiology Department, Hospital Universitari de Bellvitge, Universitat de Barcelona-IDIBELL, Barcelona, Spain.,CIBER de Enfermedades Respiratorias (CIBERes), Instituto de Salud Carlos III, Madrid, Spain
| | - Jordi Càmara
- Microbiology Department, Hospital Universitari de Bellvitge, Universitat de Barcelona-IDIBELL, Barcelona, Spain.,CIBER de Enfermedades Respiratorias (CIBERes), Instituto de Salud Carlos III, Madrid, Spain
| | - Josefina Ayats
- Microbiology Department, Hospital Universitari de Bellvitge, Universitat de Barcelona-IDIBELL, Barcelona, Spain.,CIBER de Enfermedades Respiratorias (CIBERes), Instituto de Salud Carlos III, Madrid, Spain
| | - Paula Bajanca-Lavado
- Haemophilus influenzae Reference Laboratory, Department of Infectious Diseases, National Institute of Health, Lisbon, Portugal
| | - Carmen Ardanuy
- Microbiology Department, Hospital Universitari de Bellvitge, Universitat de Barcelona-IDIBELL, Barcelona, Spain. .,CIBER de Enfermedades Respiratorias (CIBERes), Instituto de Salud Carlos III, Madrid, Spain.
| | - Sara Marti
- Microbiology Department, Hospital Universitari de Bellvitge, Universitat de Barcelona-IDIBELL, Barcelona, Spain. .,CIBER de Enfermedades Respiratorias (CIBERes), Instituto de Salud Carlos III, Madrid, Spain.
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Abstract
Members of the highly heterogeneous family Pasteurellaceae cause a wide variety of diseases in humans and animals. Antimicrobial agents are the most powerful tools to control such infections. However, the acquisition of resistance genes, as well as the development of resistance-mediating mutations, significantly reduces the efficacy of the antimicrobial agents. This article gives a brief description of the role of selected members of the family Pasteurellaceae in animal infections and of the most recent data on the susceptibility status of such members. Moreover, a review of the current knowledge of the genetic basis of resistance to antimicrobial agents is included, with particular reference to resistance to tetracyclines, β-lactam antibiotics, aminoglycosides/aminocyclitols, folate pathway inhibitors, macrolides, lincosamides, phenicols, and quinolones. This article focusses on the genera of veterinary importance for which sufficient data on antimicrobial susceptibility and the detection of resistance genes are currently available (Pasteurella, Mannheimia, Actinobacillus, Haemophilus, and Histophilus). Additionally, the role of plasmids, transposons, and integrative and conjugative elements in the spread of the resistance genes within and beyond the aforementioned genera is highlighted to provide insight into horizontal dissemination, coselection, and persistence of antimicrobial resistance genes. The article discusses the acquisition of diverse resistance genes by the selected Pasteurellaceae members from other Gram-negative or maybe even Gram-positive bacteria. Although the susceptibility status of these members still looks rather favorable, monitoring of their antimicrobial susceptibility is required for early detection of changes in the susceptibility status and the newly acquired/developed resistance mechanisms.
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Abstract
During the past decades resistance to virtually all antimicrobial agents has been observed in bacteria of animal origin. This chapter describes in detail the mechanisms so far encountered for the various classes of antimicrobial agents. The main mechanisms include enzymatic inactivation by either disintegration or chemical modification of antimicrobial agents, reduced intracellular accumulation by either decreased influx or increased efflux of antimicrobial agents, and modifications at the cellular target sites (i.e., mutational changes, chemical modification, protection, or even replacement of the target sites). Often several mechanisms interact to enhance bacterial resistance to antimicrobial agents. This is a completely revised version of the corresponding chapter in the book Antimicrobial Resistance in Bacteria of Animal Origin published in 2006. New sections have been added for oxazolidinones, polypeptides, mupirocin, ansamycins, fosfomycin, fusidic acid, and streptomycins, and the chapters for the remaining classes of antimicrobial agents have been completely updated to cover the advances in knowledge gained since 2006.
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Korsak D, Krawczyk-Balska A. Identification of the Molecular Mechanism of Trimethoprim Resistance inListeria monocytogenes. Foodborne Pathog Dis 2017; 14:696-700. [PMID: 28910155 DOI: 10.1089/fpd.2017.2323] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Affiliation(s)
- Dorota Korsak
- Department of Applied Microbiology, Faculty of Biology, Institute of Microbiology, University of Warsaw, Warsaw, Poland
| | - Agata Krawczyk-Balska
- Department of Applied Microbiology, Faculty of Biology, Institute of Microbiology, University of Warsaw, Warsaw, Poland
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11
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Rodríguez-Arce I, Martí S, Euba B, Fernández-Calvet A, Moleres J, López-López N, Barberán M, Ramos-Vivas J, Tubau F, Losa C, Ardanuy C, Leiva J, Yuste JE, Garmendia J. Inactivation of the Thymidylate Synthase thyA in Non-typeable Haemophilus influenzae Modulates Antibiotic Resistance and Has a Strong Impact on Its Interplay with the Host Airways. Front Cell Infect Microbiol 2017; 7:266. [PMID: 28676846 PMCID: PMC5476696 DOI: 10.3389/fcimb.2017.00266] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2016] [Accepted: 06/02/2017] [Indexed: 12/29/2022] Open
Abstract
Antibacterial treatment with cotrimoxazol (TxS), a combination of trimethoprim and sulfamethoxazole, generates resistance by, among others, acquisition of thymidine auxotrophy associated with mutations in the thymidylate synthase gene thyA, which can modify the biology of infection. The opportunistic pathogen non-typeable Haemophilus influenzae (NTHi) is frequently encountered in the lower airways of chronic obstructive pulmonary disease (COPD) patients, and associated with acute exacerbation of COPD symptoms. Increasing resistance of NTHi to TxS limits its suitability as initial antibacterial against COPD exacerbation, although its relationship with thymidine auxotrophy is unknown. In this study, the analysis of 2,542 NTHi isolates recovered at Bellvitge University Hospital (Spain) in the period 2010–2014 revealed 119 strains forming slow-growing colonies on the thymidine low concentration medium Mueller Hinton Fastidious, including one strain isolated from a COPD patient undergoing TxS therapy that was a reversible thymidine auxotroph. To assess the impact of thymidine auxotrophy in the NTHi-host interplay during respiratory infection, thyA mutants were generated in both the clinical isolate NTHi375 and the reference strain RdKW20. Inactivation of the thyA gene increased TxS resistance, but also promoted morphological changes consistent with elongation and impaired bacterial division, which altered H. influenzae self-aggregation, phosphorylcholine level, C3b deposition, and airway epithelial infection patterns. Availability of external thymidine contributed to overcome such auxotrophy and TxS effect, potentially facilitated by the nucleoside transporter nupC. Although, thyA inactivation resulted in bacterial attenuation in a lung infection mouse model, it also rendered a lower clearance upon a TxS challenge in vivo. Thus, our results show that thymidine auxotrophy modulates both the NTHi host airway interplay and antibiotic resistance, which should be considered at the clinical setting for the consequences of TxS administration.
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Affiliation(s)
- Irene Rodríguez-Arce
- Instituto de Agrobiotecnología, Consejo Superior de Investigaciones Científicas-Universidad Pública Navarra-GobiernoNavarra, Spain
| | - Sara Martí
- Centro de Investigación Biomédica en Red de Enfermedades RespiratoriasMadrid, Spain.,Departamento Microbiología, Hospital Universitari Bellvitge, University of Barcelona, Institut d'Investigació Biomédica de BellvitgeBarcelona, Spain
| | - Begoña Euba
- Instituto de Agrobiotecnología, Consejo Superior de Investigaciones Científicas-Universidad Pública Navarra-GobiernoNavarra, Spain.,Centro de Investigación Biomédica en Red de Enfermedades RespiratoriasMadrid, Spain
| | - Ariadna Fernández-Calvet
- Instituto de Agrobiotecnología, Consejo Superior de Investigaciones Científicas-Universidad Pública Navarra-GobiernoNavarra, Spain
| | - Javier Moleres
- Instituto de Agrobiotecnología, Consejo Superior de Investigaciones Científicas-Universidad Pública Navarra-GobiernoNavarra, Spain
| | - Nahikari López-López
- Instituto de Agrobiotecnología, Consejo Superior de Investigaciones Científicas-Universidad Pública Navarra-GobiernoNavarra, Spain
| | | | - José Ramos-Vivas
- Servicio Microbiología, Hospital Universitario Marqués de Valdecilla and Instituto de Investigación Marqués de ValdecillaSantander, Spain.,Red Española de Investigación en Patología Infecciosa, Instituto de Salud Carlos IIIMadrid, Spain
| | - Fe Tubau
- Centro de Investigación Biomédica en Red de Enfermedades RespiratoriasMadrid, Spain.,Departamento Microbiología, Hospital Universitari Bellvitge, University of Barcelona, Institut d'Investigació Biomédica de BellvitgeBarcelona, Spain
| | - Carmen Losa
- Servicio de Microbiología, Clínica Universidad de NavarraNavarra, Spain
| | - Carmen Ardanuy
- Centro de Investigación Biomédica en Red de Enfermedades RespiratoriasMadrid, Spain.,Departamento Microbiología, Hospital Universitari Bellvitge, University of Barcelona, Institut d'Investigació Biomédica de BellvitgeBarcelona, Spain
| | - José Leiva
- Servicio de Microbiología, Clínica Universidad de NavarraNavarra, Spain
| | - José E Yuste
- Centro de Investigación Biomédica en Red de Enfermedades RespiratoriasMadrid, Spain.,Centro Nacional de Microbiología, Instituto de Salud Carlos IIIMadrid, Spain
| | - Junkal Garmendia
- Instituto de Agrobiotecnología, Consejo Superior de Investigaciones Científicas-Universidad Pública Navarra-GobiernoNavarra, Spain.,Centro de Investigación Biomédica en Red de Enfermedades RespiratoriasMadrid, Spain
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12
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Bossé JT, Li Y, Walker S, Atherton T, Fernandez Crespo R, Williamson SM, Rogers J, Chaudhuri RR, Weinert LA, Oshota O, Holden MTG, Maskell DJ, Tucker AW, Wren BW, Rycroft AN, Langford PR. Identification of dfrA14 in two distinct plasmids conferring trimethoprim resistance in Actinobacillus pleuropneumoniae. J Antimicrob Chemother 2015; 70:2217-22. [PMID: 25957382 PMCID: PMC4500777 DOI: 10.1093/jac/dkv121] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2014] [Accepted: 04/05/2015] [Indexed: 11/30/2022] Open
Abstract
Objectives The objective of this study was to determine the distribution and genetic basis of trimethoprim resistance in Actinobacillus pleuropneumoniae isolates from pigs in England. Methods Clinical isolates collected between 1998 and 2011 were tested for resistance to trimethoprim and sulphonamide. The genetic basis of trimethoprim resistance was determined by shotgun WGS analysis and the subsequent isolation and sequencing of plasmids. Results A total of 16 (out of 106) A. pleuropneumoniae isolates were resistant to both trimethoprim (MIC >32 mg/L) and sulfisoxazole (MIC ≥256 mg/L), and a further 32 were resistant only to sulfisoxazole (MIC ≥256 mg/L). Genome sequence data for the trimethoprim-resistant isolates revealed the presence of the dfrA14 dihydrofolate reductase gene. The distribution of plasmid sequences in multiple contigs suggested the presence of two distinct dfrA14-containing plasmids in different isolates, which was confirmed by plasmid isolation and sequencing. Both plasmids encoded mobilization genes, the sulphonamide resistance gene sul2, as well as dfrA14 inserted into strA, a streptomycin-resistance-associated gene, although the gene order differed between the two plasmids. One of the plasmids further encoded the strB streptomycin-resistance-associated gene. Conclusions This is the first description of mobilizable plasmids conferring trimethoprim resistance in A. pleuropneumoniae and, to our knowledge, the first report of dfrA14 in any member of the Pasteurellaceae. The identification of dfrA14 conferring trimethoprim resistance in A. pleuropneumoniae isolates will facilitate PCR screens for resistance to this important antimicrobial.
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Affiliation(s)
- Janine T Bossé
- Section of Paediatrics, Department of Medicine, Imperial College London, St Mary's Campus, London W2 1PG, UK
| | - Yanwen Li
- Section of Paediatrics, Department of Medicine, Imperial College London, St Mary's Campus, London W2 1PG, UK
| | - Stephanie Walker
- Section of Paediatrics, Department of Medicine, Imperial College London, St Mary's Campus, London W2 1PG, UK
| | - Tom Atherton
- Section of Paediatrics, Department of Medicine, Imperial College London, St Mary's Campus, London W2 1PG, UK
| | - Roberto Fernandez Crespo
- Section of Paediatrics, Department of Medicine, Imperial College London, St Mary's Campus, London W2 1PG, UK
| | - Susanna M Williamson
- Animal and Plant Health Agency (APHA) Bury St Edmunds, Rougham Hill, Bury St Edmunds, Suffolk IP33 2RX, UK
| | - Jon Rogers
- Animal and Plant Health Agency (APHA) Bury St Edmunds, Rougham Hill, Bury St Edmunds, Suffolk IP33 2RX, UK
| | - Roy R Chaudhuri
- Department of Veterinary Medicine, University of Cambridge, Madingley Road, Cambridge CB3 0ES, UK
| | - Lucy A Weinert
- Department of Veterinary Medicine, University of Cambridge, Madingley Road, Cambridge CB3 0ES, UK
| | - Olusegun Oshota
- Department of Veterinary Medicine, University of Cambridge, Madingley Road, Cambridge CB3 0ES, UK
| | - Matt T G Holden
- The Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge CB10 1SA, UK
| | - Duncan J Maskell
- Department of Veterinary Medicine, University of Cambridge, Madingley Road, Cambridge CB3 0ES, UK
| | - Alexander W Tucker
- Department of Veterinary Medicine, University of Cambridge, Madingley Road, Cambridge CB3 0ES, UK
| | - Brendan W Wren
- Faculty of Infectious and Tropical Diseases, London School of Hygiene & Tropical Medicine, Keppel Street, London WC1E 7HT, UK
| | - Andrew N Rycroft
- Department of Pathology and Pathogen Biology, The Royal Veterinary College, Hawkshead Campus, Hatfield, Hertfordshire AL9 7TA, UK
| | - Paul R Langford
- Section of Paediatrics, Department of Medicine, Imperial College London, St Mary's Campus, London W2 1PG, UK
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13
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Wilén M, Buwembo W, Sendagire H, Kironde F, Swedberg G. Cotrimoxazole resistance of Streptococcus pneumoniae and commensal streptococci from Kampala, Uganda. ACTA ACUST UNITED AC 2009; 41:113-21. [PMID: 19140088 DOI: 10.1080/00365540802651889] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
Trimethoprim sulfamethoxazole (cotrimoxazole, CTX) is used frequently as part of standard medical care for people living with HIV/AIDS in Africa. The mechanisms of resistance to sulfonamides and trimethoprim in commensal streptococci from Uganda were determined and compared to S. pneumoniae. Commensal streptococci showing high-level resistance to cotrimoxazole were cultured and analysed for species identity and polymorphisms in the genes coding for dihydropteroate synthase (DHPS) and dihydrofolate reductase (DHFR). Seven isolates of S. pneumoniae from blood and cerebrospinal fluid (CSF) were similarly examined. There was considerable polymorphism in both DHPS and DHFR. In DHFR, the mutations E20D and I100L were present in all sequenced isolates. Other mutations such as L135F, and different substitutions in D92, were frequent. The most common DHPS variants had 2 serine residues added after amino acid 60, or arginine and proline added after amino acid 59. In addition, 3 new insertions/substitutions were found. There were no obvious differences between the mutation patterns in S. pneumoniae and commensal streptococci, suggesting that the chromosomal mutations have been spread by transformational interchanges of DNA among related organisms.
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Affiliation(s)
- Maria Wilén
- Department of Medical Biochemistry and Microbiology, Uppsala University, Sweden
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14
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Brueggemann AB. Antibiotic resistance mechanisms among pediatric respiratory and enteric pathogens: A current update. Pediatr Infect Dis J 2006; 25:969-73. [PMID: 17006308 DOI: 10.1097/01.inf.0000239365.60595.d5] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
Antibiotic resistance is a continually increasing problem that has, to a greater or lesser extent, affected virtually every area of the world. The scientific literature is abundant with papers related to antibiotics and antibiotic resistance. Many excellent papers and reviews have been published during the past few years, and the literature base continues to expand at rapid speed. This review is meant to provide a recent update on antibiotic resistance among respiratory and enteric pathogens, with a focus on infections in children. Not a small task, but this paper is not meant to be exhaustive. Rather, the intention is to highlight the key antibiotics and antibiotic resistance mechanisms that are currently the most relevant to pediatrics. The most recently published literature is used wherever possible, and the reader is encouraged to explore specific topics of interest further by reviewing the referenced literature.
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15
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Navarro-Martínez MD, Navarro-Perán E, Cabezas-Herrera J, Ruiz-Gómez J, García-Cánovas F, Rodríguez-López JN. Antifolate activity of epigallocatechin gallate against Stenotrophomonas maltophilia. Antimicrob Agents Chemother 2005; 49:2914-20. [PMID: 15980368 PMCID: PMC1168674 DOI: 10.1128/aac.49.7.2914-2920.2005] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The catechin epigallocatechin gallate, one of the main constituents of green tea, showed strong antibiotic activity against 18 isolates of Stenotrophomonas maltophilia (MIC range, 4 to 256 microg/ml). In elucidating its mechanism of action, we have shown that epigallocatechin gallate is an efficient inhibitor of S. maltophilia dihydrofolate reductase, a strategic enzyme that is considered an attractive target for the development of antibacterial agents. The inhibition of S. maltophilia dihydrofolate reductase by this tea compound was studied and compared with the mechanism of a nonclassical antifolate compound, trimethoprim. Investigation of dihydrofolate reductase was undertaken with both a trimethoprim-susceptible S. maltophilia isolate and an isolate with a high level of resistance. The enzymes were purified using ammonium sulfate precipitation, gel filtration, and methotrexate affinity chromatography. The two isolates showed similar levels of dihydrofolate reductase expression and similar substrate kinetics. However, the dihydrofolate reductase from the trimethoprim-resistant isolate demonstrated decreased susceptibility to inhibition by trimethoprim and epigallocatechin gallate. As with other antifolates, the action of epigallocatechin gallate was synergistic with that of sulfamethoxazole, a drug that blocks folic acid metabolism in bacteria, and the inhibition of bacterial growth was attenuated by including leucovorin in the growth medium. We conclude that the mechanism of action of epigallocatechin gallate on S. maltophilia is related to its antifolate activity.
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Affiliation(s)
- María Dolores Navarro-Martínez
- Grupo de Investigación de Enzimología, Departamento de Bioquímica y Biología Molecular A, Facultad de Biología, Universidad de Murcia, E-30100 Espinardo, Murcia, Spain
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16
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Jones ME, Karlowsky JA, Blosser-Middleton R, Critchley I, Thornsberry C, Sahm DF. Relationship between antibiotic resistance in Streptococcus pneumoniae and that in Haemophilus influenzae: evidence for common selective pressure. Antimicrob Agents Chemother 2002; 46:3106-7. [PMID: 12183285 PMCID: PMC127418 DOI: 10.1128/aac.46.9.3106-3107.2002] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
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17
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Enne VI, King A, Livermore DM, Hall LMC. Sulfonamide resistance in Haemophilus influenzae mediated by acquisition of sul2 or a short insertion in chromosomal folP. Antimicrob Agents Chemother 2002; 46:1934-9. [PMID: 12019111 PMCID: PMC127234 DOI: 10.1128/aac.46.6.1934-1939.2002] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Determinants of sulfonamide resistance were investigated in clinical isolates of Haemophilus influenzae from the United Kingdom and Kenya. The mechanism of sulfonamide resistance in H. influenzae has not previously been reported. Eight isolates requiring at least 1,024 microg of sulfamethoxazole per ml for inhibition carried the sul2 gene, a common mediator of acquired sulfonamide resistance in enteric bacteria. In other isolates with similarly high levels of resistance, the chromosomal gene encoding dihydropteroate synthase, folP, was found to carry an insertion of 15 bp together with other missense mutations relative to folP of H. influenzae strain Rd RM118 (MIC, 8 microg/ml); the folP sequence was identical in all seven such isolates investigated, although they represented three different strains by restriction pattern analysis. The 15-bp insertion was absent in isolates inhibited by sulfamethoxazole at 2 to 64 microg/ml (although these exhibited considerable divergence in folP sequence) and in highly resistant isolates carrying sul2. Transformation with a 599-bp fragment of folP containing the insertion but no other differences conferred high-level resistance on a recipient strain, confirming the role of the insertion. Other amino acid substitutions in dihydropteroate synthase may modulate the level of sulfonamide inhibition in susceptible isolates and those with more moderate levels of resistance. The two mechanisms of resistance, mediated by sul2 and modified folP, were detected in isolates from both the United Kingdom and Kenya.
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Affiliation(s)
- Virve I Enne
- Department of Medical Microbiology, Barts and The London School of Medicine and Dentistry, Queen Mary, University of London, United Kingdom
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18
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Huovinen P. Resistance to trimethoprim-sulfamethoxazole. Clin Infect Dis 2001; 32:1608-14. [PMID: 11340533 DOI: 10.1086/320532] [Citation(s) in RCA: 248] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2000] [Revised: 01/25/2001] [Indexed: 11/03/2022] Open
Abstract
Sulfonamides have a glorious history. In 1935, they were the first class of true antimicrobial agents with life-saving potency. Today, 66 years later, increased bacterial resistance to sulfonamides and to trimethoprim (TMP), a synthetic antimicrobial agent that is 30 years younger than sulfonamides, has limited their use to only a few indications. In the treatment and prophylaxis of patients with urinary tract infections, trimethoprim-sulfamethoxazole (TMP-SMZ) or TMP alone is still considered the first-line drug of choice, although increased bacterial resistance to these agents has been linked with treatment failure. TMP-SMZ has a possible role as a second- or third-line treatment for patients who have respiratory tract infections. In the developing world, where this inexpensive drug is widely used as first-line treatment, bacterial resistance has caused problems, especially with regard to the treatment of patients with severe respiratory tract infections. Use of TMP-SMZ as prophylaxis for Pneumocystis carinii infection has rapidly increased the multidrug resistance of bacterial pathogens found in human immunodeficiency virus-infected patients. Today, detailed and reliable knowledge on the resistance of bacterial pathogens to both TMP-SMZ and TMP is an essential requirement for the safe and effective use of these drugs in all clinical settings.
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Affiliation(s)
- P Huovinen
- Antimicrobial Research Laboratory, National Public Health Institute, Turku, Finland.
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Ouellette M, Leblanc E, Kündig C, Papadopoulou B. Antifolate resistance mechanisms from bacteria to cancer cells with emphasis on parasites. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 1999; 456:99-113. [PMID: 10549365 DOI: 10.1007/978-1-4615-4897-3_6] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Affiliation(s)
- M Ouellette
- Département de Microbiologie, Université Laval, Québec, Canada
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20
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Adrian PV, Klugman KP. Mutations in the dihydrofolate reductase gene of trimethoprim-resistant isolates of Streptococcus pneumoniae. Antimicrob Agents Chemother 1997; 41:2406-13. [PMID: 9371341 PMCID: PMC164136 DOI: 10.1128/aac.41.11.2406] [Citation(s) in RCA: 80] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Streptococcus pneumoniae isolates resistant to several antimicrobial agent classes including trimethoprim-sulfamethoxazole have been reported with increasing frequency throughout the world. The MICs of trimethoprim, sulfamethoxazole, and trimethoprim-sulfamethoxazole (1:19) for 259 clinical isolates from South Africa were determined, and 166 of these 259 (64%) isolates were resistant to trimethoprim-sulfamethoxazole (MICs > or =20 mg/liter). Trimethoprim resistance was found to be more strongly correlated with trimethoprim-sulfamethoxazole resistance (correlation coefficient, 0.744) than was sulfamethoxazole resistance (correlation coefficient, 0.441). The dihydrofolate reductase genes from 11 trimethoprim-resistant (MICs, 64 to 512 microg/ml) clinical isolates of Streptococcus pneumoniae were amplified by PCR, and the nucleotide sequences were determined. Two main groups of mutations to the dihydrofolate reductase gene were found. Both groups shared six amino acid changes (Glu20-Asp, Pro70-Ser, Gln81-His, Asp92-Ala, Ile100-Leu, and Leu135-Phe). The first group included two extra changes (Lys60-Gln and Pro111-Ser), and the second group was characterized by six additional amino acid changes (Glu14-Asp, Ile74-Leu, Gln91-His, Glu94-Asp, Phe147-Ser, and Ala149-Thr). Chromosomal DNA from resistant isolates and cloned PCR products of the genes encoding resistant dihydrofolate reductases were capable of transforming a susceptible strain of S. pneumoniae to trimethoprim resistance. The inhibitor profiles of recombinant dihydrofolate reductase from resistant and susceptible isolates revealed that the dihydrofolate reductase from trimethoprim-resistant isolates was 50-fold more resistant (50% inhibitory doses [ID50s], 3.9 to 7.3 microM) than that from susceptible strains (ID50s, 0.15 microM). Site-directed mutagenesis experiments revealed that one mutation, Ile100-Leu, resulted in a 50-fold increase in the ID50 of trimethoprim. The resistant dihydrofolate reductases were characterized by highly conserved redundant changes in the nucleotide sequence, suggesting that the genes encoding resistant dihydrofolate reductases may have evolved as a result of inter- or intraspecies recombination by transformation.
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Affiliation(s)
- P V Adrian
- Pneumococcal Diseases Research Unit of South African Institute for Medical Research, University of the Witwatersrand, and Medical Research Council, Johannesburg.
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