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      Capsular Type, Sequence Type and Microbial Resistance Factors Impact on DNase Activity of Streptococcus agalactiae Strains from Human and Bovine Origin

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          Abstract

          Extracellular deoxyribonucleases (DNases) contribute to the spread of pathogenic bacteria through the evasion from host innate immunity. Our main objective was to evaluate the production of extracellular DNases by human and bovine Streptococcus agalactiae clinical strains and perform a correlation of genetic lineages and DNase activity with capsular type, genetic determinants, clinical origin (colonization and infection), and host (human or bovine). DNase activity was evaluated by qualitative and quantitative assays for a collection of 406 human ( n = 285) and bovine ( n = 121) strains. All (121/121) bovine were isolated from mastitis and revealed to be DNase (+), indicating a putative pathogenic role in this clinical scenario. From the human S. agalactiae strains, 86% (245/285) showed DNase activity, among which all strains belonging to capsular types, namely, Ia, Ib, III-2, and IV. All CC17 strains ( n = 58) and 56/96 (58.3%) of the CC19 displayed DNase activity. DNase (–) strains belonged to the CC19 group. However, the subcharacterization of CC19 S. agalactiae strains through multiple-locus variable number tandem repeat analysis (MLVA), antibiotic resistance, mobile elements, and surface proteins did not provide any distinction among DNase producers and non-producers.

          The production of DNases by all human CC17 strains, about two-fifths of human CC19, and all bovine strains, suggest an important contribution of DNases to hypervirulence.

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          Extracellular deoxyribonuclease made by group A Streptococcus assists pathogenesis by enhancing evasion of the innate immune response.

          R. E. Long, Robert Gardner, Adeline Whitney … (2005)
          Many pathogenic bacteria produce extracellular DNase, but the benefit of this enzymatic activity is not understood. For example, all strains of the human bacterial pathogen group A Streptococcus (GAS) produce at least one extracellular DNase, and most strains make several distinct enzymes. Despite six decades of study, it is not known whether production of DNase by GAS enhances virulence. To test the hypothesis that extracellular DNase is required for normal progression of GAS infection, we generated seven isogenic mutant strains in which the three chromosomal- and prophage-encoded DNases made by a contemporary serotype M1 GAS strain were inactivated. Compared to the wild-type parental strain, the isogenic triple-mutant strain was significantly less virulent in two mouse models of invasive infection. The triple-mutant strain was cleared from the skin injection site significantly faster than the wild-type strain. Preferential clearance of the mutant strain was related to the differential extracellular killing of the mutant and wild-type strains, possibly through degradation of neutrophil extracellular traps, innate immune structures composed of chromatin and granule proteins. The triple-mutant strain was also significantly compromised in its ability to cause experimental pharyngeal disease in cynomolgus macaques. Comparative analysis of the seven DNase mutant strains strongly suggested that the prophage-encoded SdaD2 enzyme is the major DNase that contributes to virulence in this clone. We conclude that extracellular DNase activity made by GAS contributes to disease progression, thereby resolving a long-standing question in bacterial pathogenesis research.
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            Nuclease expression by Staphylococcus aureus facilitates escape from neutrophil extracellular traps.

            Marc Monestier, Maren von Köckritz-Blickwede, Alexander Horswill … (2009)
            Neutrophils are key effectors of the host innate immune response against bacterial infection. Staphylococcus aureus is a preeminent human pathogen, with an ability to produce systemic infections even in previously healthy individuals, thereby reflecting a resistance to effective neutrophil clearance. The recent discovery of neutrophil extracellular traps (NETs) has opened a novel dimension in our understanding of how these specialized leukocytes kill pathogens. NETs consist of a nuclear DNA backbone associated with antimicrobial peptides, histones and proteases that provide a matrix to entrap and kill various microbes. Here, we used targeted mutagenesis to examine a potential role of S. aureus nuclease in NET degradation and virulence in a murine respiratory tract infection model. In vitro assays using fluorescence microscopy showed the isogenic nuclease-deficient (nuc-deficient) mutant to be significantly impaired in its ability to degrade NETs compared with the wild-type parent strain USA 300 LAC. Consequently, the nuc-deficient mutant strain was significantly more susceptible to extracellular killing by activated neutrophils. Moreover, S. aureus nuclease production was associated with delayed bacterial clearance in the lung and increased mortality after intranasal infection. In conclusion, this study shows that S. aureus nuclease promotes resistance against NET-mediated antimicrobial activity of neutrophils and contributes to disease pathogenesis in vivo. Copyright © 2010 S. Karger AG, Basel.
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              Multilocus sequence types associated with neonatal group B streptococcal sepsis and meningitis in Canada.

              Abigail H. Davies, Erica A. Lehotzky, Philip A. Lewis … (2009)
              Group B streptococci (GBS), a leading cause of neonatal sepsis and meningitis, are transferred to neonates from colonized mothers during childbirth. Prior studies using multilocus sequence typing (MLST) have found specific GBS clones (e.g., sequence type 17 [ST-17]) to be associated with neonatal disease in several geographic locations. Few population-based studies, however, have been conducted to determine the frequency of disease caused by specific GBS clones. MLST was used to assess the genetic diversity of 192 GBS strains from neonates and young children identified by population-based surveillance in Alberta, Canada, from 1993 to 2002. Comparisons were made to 232 GBS strains collected from colonized pregnant women, and all strains were characterized for one of nine capsule (cps) genotypes. A total of 47 STs were identified, and more than 80% of GBS strains were represented by 7 STs that have been shown to predominate in other populations. ST-17 and ST-19 were more prevalent in strains causing early onset disease (EOD) and late onset disease (LOD) than from pregnant women, whereas STs 1, 12, and 23 were more common in pregnant women. In addition, ST-17 strains and close relatives more frequently caused meningitis than sepsis and LOD versus EOD in this population of neonates. Further research is required to better understand why strains belonging to the ST-17 phylogenetic lineage are more likely to cause both LOD and meningitis and may provide clues into the pathogenesis of these conditions.
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                Author and article information

                Journal
                Journal ID (nlm-ta): Eur J Microbiol Immunol (Bp)
                Journal ID (iso-abbrev): Eur J Microbiol Immunol (Bp)
                Journal ID (publisher-id): EUJMI
                Title: European Journal of Microbiology & Immunology
                Publisher: Akadémiai Kiadó (Budapest )
                ISSN (Print): 2062-509X
                ISSN (Electronic): 2062-8633
                Publication date (Electronic): 11 December 2018
                Publication date Collection: 23 December 2018
                Volume: 8
                Issue: 4
                Pages: 149-154
                Affiliations
                [1 ] Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa , Departamento de Ciências da Vida, UCIBIO
                [2 ] Department of Infectious Diseases, National Institute of Health , Lisbon
                [3 ] Institute of Medical Microbiology and Hygiene, Ulm University
                Author notes
                * Author for correspondence: National Institute of Health, Avenida Padre Cruz, 1649-016 Lisbon; E-mail: m.jose.borrego@ 123456insa.min-saude.pt ; Tel: +351 217519241; Fax: +351 217526400

                †In memory of Ilda Santos-Sanches, 1958–2017

                Article
                DOI: 10.1556/1886.2018.00026
                PMC ID: 6348702
                SO-VID: 839cbde6-3a7e-4148-9d5c-b25c4e8cb35d
                Copyright © © 2018, The Author(s)
                License:

                This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International License ( https://creativecommons.org/licenses/by-nc/4.0/), which permits unrestricted use, distribution, and reproduction in any medium for non-commercial purposes, provided the original author and source are credited, a link to the CC License is provided, and changes - if any - are indicated.

                History
                Date received : 18 September 2018
                Date accepted : 13 October 2018
                Page count
                Figures: 3, Tables: 4, Equations: 0, References: 27, Pages: 9
                Categories
                Subject: Original Research Paper

                Keywords: bovine and human strains,cc17,cc19,dnase activity assays,extracellular dnases,streptococcus agalactiae
                Data availability:
                Keywords: bovine and human strains, cc17, cc19, dnase activity assays, extracellular dnases, streptococcus agalactiae

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