Cytosolic Replication of Group A <italic toggle="yes">Streptococcus</italic> in Human Macrophages

ABSTRACT As key components of innate immune defense, macrophages are essential in controlling bacterial pathogens, including group A Streptococcus (GAS). Despite this, only a limited number of studies have analyzed the recovery of GAS from within human neutrophils and macrophages. Here, we determine...

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Autores principales:	Alan M. O’Neill, Teresa L. M. Thurston, David W. Holden
Formato:	article
Lenguaje:	EN
Publicado:	American Society for Microbiology 2016
Materias:	Microbiology QR1-502
Acceso en línea:	https://doaj.org/article/ffab9758c9e641c7be7569313cf1184d
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spelling	oai:doaj.org-article:ffab9758c9e641c7be7569313cf1184d2021-11-15T15:41:42ZCytosolic Replication of Group A <italic toggle="yes">Streptococcus</italic> in Human Macrophages10.1128/mBio.00020-162150-7511https://doaj.org/article/ffab9758c9e641c7be7569313cf1184d2016-05-01T00:00:00Zhttps://journals.asm.org/doi/10.1128/mBio.00020-16https://doaj.org/toc/2150-7511ABSTRACT As key components of innate immune defense, macrophages are essential in controlling bacterial pathogens, including group A Streptococcus (GAS). Despite this, only a limited number of studies have analyzed the recovery of GAS from within human neutrophils and macrophages. Here, we determined the intracellular fate of GAS in human macrophages by using several quantitative approaches. In both U937 and primary human macrophages, the appearance over time of long GAS chains revealed that despite GAS-mediated cytotoxicity, replication occurred in viable, propidium iodide-negative macrophages. Whereas the major virulence factor M1 did not contribute to bacterial growth, a GAS mutant strain deficient in streptolysin O (SLO) was impaired for intracellular replication. SLO promoted bacterial escape from the GAS-containing vacuole (GCV) into the macrophage cytosol. Up to half of the cytosolic GAS colocalized with ubiquitin and p62, suggesting that the bacteria were targeted by the autophagy machinery. Despite this, live imaging of U937 macrophages revealed proficient replication of GAS after GCV rupture, indicating that escape from the GCV is important for growth of GAS in macrophages. Our results reveal that GAS can replicate within viable human macrophages, with SLO promoting GCV escape and cytosolic growth, despite the recruitment of autophagy receptors to bacteria. IMPORTANCE Classically regarded as an extracellular pathogen, GAS can persist within human epithelial cells, as well as neutrophils and macrophages. Some studies suggest that GAS can modulate its intracellular vacuole to promote survival and perhaps replicate in macrophages. However, an in-depth single-cell analysis of the dynamics of survival and replication is lacking. We used macrophage-like cell lines and primary macrophages to measure the intracellular growth of GAS at both the population and single-cell levels. While CFU counts revealed no increase in overall bacterial growth, quantitative fluorescence microscopy, flow cytometry, and time-lapse imaging revealed bacterial replication in a proportion of infected macrophages. This study emphasizes the importance of single-cell analysis especially when studying the intracellular fate of a pathogen that is cytotoxic and displays heterogeneity in terms of intracellular killing and growth. To our knowledge, this study provides the first direct visualization of GAS replication inside human cells.Alan M. O’NeillTeresa L. M. ThurstonDavid W. HoldenAmerican Society for MicrobiologyarticleMicrobiologyQR1-502ENmBio, Vol 7, Iss 2 (2016)
institution	DOAJ
collection	DOAJ
language	EN
topic	Microbiology QR1-502
spellingShingle	Microbiology QR1-502 Alan M. O’Neill Teresa L. M. Thurston David W. Holden Cytosolic Replication of Group A <italic toggle="yes">Streptococcus</italic> in Human Macrophages
description	ABSTRACT As key components of innate immune defense, macrophages are essential in controlling bacterial pathogens, including group A Streptococcus (GAS). Despite this, only a limited number of studies have analyzed the recovery of GAS from within human neutrophils and macrophages. Here, we determined the intracellular fate of GAS in human macrophages by using several quantitative approaches. In both U937 and primary human macrophages, the appearance over time of long GAS chains revealed that despite GAS-mediated cytotoxicity, replication occurred in viable, propidium iodide-negative macrophages. Whereas the major virulence factor M1 did not contribute to bacterial growth, a GAS mutant strain deficient in streptolysin O (SLO) was impaired for intracellular replication. SLO promoted bacterial escape from the GAS-containing vacuole (GCV) into the macrophage cytosol. Up to half of the cytosolic GAS colocalized with ubiquitin and p62, suggesting that the bacteria were targeted by the autophagy machinery. Despite this, live imaging of U937 macrophages revealed proficient replication of GAS after GCV rupture, indicating that escape from the GCV is important for growth of GAS in macrophages. Our results reveal that GAS can replicate within viable human macrophages, with SLO promoting GCV escape and cytosolic growth, despite the recruitment of autophagy receptors to bacteria. IMPORTANCE Classically regarded as an extracellular pathogen, GAS can persist within human epithelial cells, as well as neutrophils and macrophages. Some studies suggest that GAS can modulate its intracellular vacuole to promote survival and perhaps replicate in macrophages. However, an in-depth single-cell analysis of the dynamics of survival and replication is lacking. We used macrophage-like cell lines and primary macrophages to measure the intracellular growth of GAS at both the population and single-cell levels. While CFU counts revealed no increase in overall bacterial growth, quantitative fluorescence microscopy, flow cytometry, and time-lapse imaging revealed bacterial replication in a proportion of infected macrophages. This study emphasizes the importance of single-cell analysis especially when studying the intracellular fate of a pathogen that is cytotoxic and displays heterogeneity in terms of intracellular killing and growth. To our knowledge, this study provides the first direct visualization of GAS replication inside human cells.
format	article
author	Alan M. O’Neill Teresa L. M. Thurston David W. Holden
author_facet	Alan M. O’Neill Teresa L. M. Thurston David W. Holden
author_sort	Alan M. O’Neill
title	Cytosolic Replication of Group A <italic toggle="yes">Streptococcus</italic> in Human Macrophages
title_short	Cytosolic Replication of Group A <italic toggle="yes">Streptococcus</italic> in Human Macrophages
title_full	Cytosolic Replication of Group A <italic toggle="yes">Streptococcus</italic> in Human Macrophages
title_fullStr	Cytosolic Replication of Group A <italic toggle="yes">Streptococcus</italic> in Human Macrophages
title_full_unstemmed	Cytosolic Replication of Group A <italic toggle="yes">Streptococcus</italic> in Human Macrophages
title_sort	cytosolic replication of group a <italic toggle="yes">streptococcus</italic> in human macrophages
publisher	American Society for Microbiology
publishDate	2016
url	https://doaj.org/article/ffab9758c9e641c7be7569313cf1184d
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Cytosolic Replication of Group A <italic toggle="yes">Streptococcus</italic> in Human Macrophages

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