Related Experiment Video

Updated: Jun 19, 2026

Implementation of a Permeable Membrane Insert-based Infection System to Study the Effects of Secreted Bacterial Toxins on Mammalian Host Cells
09:25

Implementation of a Permeable Membrane Insert-based Infection System to Study the Effects of Secreted Bacterial Toxins on Mammalian Host Cells

Published on: August 19, 2016

STUDIES ON THE HEMOLYTIC STREPTOCOCCUS OF HUMAN ORIGIN : I. OBSERVATIONS ON THE VIRULENT, ATTENUATED, AND AVIRULENT

H K Ward1, C Lyons

  • 1Department of Bacteriology and Immunology of The Harvard Medical School, Boston.

The Journal of Experimental Medicine
|October 30, 2009
PubMed

Insights

Four hemolytic streptococcus variants (F, M, attenuated M, C) were identified. Virulence in human blood correlates with resistance to phagocytosis, distinguishing pathogenic strains from avirulent ones.

Area of Science:

  • Microbiology
  • Immunology
  • Bacteriology

Background:

  • Hemolytic streptococcus presents common human variants.
  • Understanding streptococcal virulence factors is crucial for infection control.

Purpose of the Study:

  • To describe and differentiate four common variants of hemolytic streptococcus.
  • To establish a reliable test for human virulence based on phagocytosis resistance.

Main Methods:

  • Isolation and characterization of streptococcal variants from human infections and laboratory cultures.
  • Assessment of phagocytosis resistance in human blood as a virulence indicator.
  • Correlation of observed variants with existing literature.

Main Results:

  • Four variants (F, M, attenuated M, C) were identified, with F and M isolated from bloodstream infections.
  • Only the M variant demonstrated primary virulence in mice.
  • Resistance to phagocytosis in human blood was a reliable indicator of human virulence.
  • The attenuated M variant, despite having a capsule, did not resist phagocytosis, while the C variant lacked a capsule and was readily phagocytosed.

Conclusions:

  • Phagocytosis resistance in human blood serves as a key test for hemolytic streptococcus virulence.
  • The identified variants (F, M, attenuated M, C) provide a framework for understanding streptococcal pathogenicity.
  • Findings contribute to the broader understanding of bacterial virulence mechanisms and host-pathogen interactions.

More Related Videos

Staphylococcus aureus Growth using Human Hemoglobin as an Iron Source06:37

Staphylococcus aureus Growth using Human Hemoglobin as an Iron Source

Published on: February 7, 2013

A Murine Model of Group B Streptococcus Vaginal Colonization10:19

A Murine Model of Group B Streptococcus Vaginal Colonization

Published on: November 16, 2016

Related Concept Videos

Determinants of Bacterial Pathogenicity and Virulence01:20

Determinants of Bacterial Pathogenicity and Virulence

Pathogenic bacteria employ a variety of strategies to establish infections, including the secretion of extracellular enzymes that act as potent virulence factors. These enzymes facilitate bacterial colonization of host tissues and help evade immune surveillance. By targeting structural components of host tissues and interfering with immune mechanisms, these enzymes play a pivotal role in disease progression.Extracellular Enzymes Facilitating Tissue Invasion: Several bacterial pathogens secrete...
Special Staining Techniques01:13

Special Staining Techniques

Specialized staining techniques play a vital role in microbiology by enabling the visualization of specific bacterial structures that remain undetectable with standard microscopy methods. These techniques not only enhance the structural visualization of bacterial cells but also provide critical insights into their pathogenicity and classification. Additionally, they support diagnostic and research endeavors in microbiology by identifying key bacterial features.Capsule Staining for Virulence...
Regulation of Bacterial Virulence01:28

Regulation of Bacterial Virulence

Pathogenic bacteria employ a range of regulatory mechanisms to modulate the expression of virulence genes in response to environmental and host-derived signals. These mechanisms ensure that virulence factors are expressed only under favorable conditions, thereby optimizing infection and survival strategies.Mechanisms of Virulence RegulationKey regulatory strategies include:Two-Component Systems: These consist of a membrane-bound sensor kinase and a cytoplasmic response regulator. Environmental...
Bacteriophages of the Human Virome01:23

Bacteriophages of the Human Virome

Bacteriophages are found throughout the human body. They may even outnumber eukaryotic viruses, forming an important and dynamic component of the human virome. Indeed, phages represent the most abundant viral entities, with densities in the gut reaching up to 10⁹ particles per gram of fecal matter, and many belonging to orders such as Caudovirales and Microviridae, while a substantial proportion remains unclassified as viral “dark matter.”Lysogeny and Genetic ExchangeIn the gut, bacteriophages...
Streptococcal Pharyngitis01:27

Streptococcal Pharyngitis

Streptococcal pharyngitis, commonly known as “strep throat,” is an acute infection of the oropharyngeal tissues caused by the Gram‑positive Group A Streptococcus (Streptococcus pyogenes). Transmission occurs primarily through respiratory droplets expelled during coughing, sneezing, or talking.Mechanisms of Host Entry and Immune EvasionUpon entering the host, S. pyogenes adheres to the mucosal epithelial cells of the pharynx via surface proteins, notably lipoteichoic acid and the antiphagocytic...
Blood Transfusion and Agglutination02:45

Blood Transfusion and Agglutination

Blood transfusion is a therapeutic measure to restore the blood volume after extensive blood loss due to an accident or a medical procedure. Blood transfusion involves drawing a certain amount of blood from a suitable donor and infusing it into the recipient.
History
The history of blood transfusion dates back to the 17th century, when early attempts were made in animals. In 1818 James Blundell, a British doctor, performed the first successful human blood transfusion. Later in 1900, Karl...