Gram Positive Bacteria: Streptococcus spp.

Gram Positive Bacteria: Streptococcus spp.

• Streptococcus bacteria are Gram-positive cocci, typically found in chains or pairs.
• Streptococcus species can be differentiated by their hemolytic activity on blood agar.
• Beta-hemolysis, which is complete red blood cell hemolysis, is diagnostic for Streptococcus pyogenes (Group A Streptococcus).
• Alpha-hemolysis (partial hemolysis) is characteristic of the viridans group streptococci.
• The viridans group includes Streptococcus anginosus, Streptococcus mitis, Streptococcus sanguinis, Streptococcus salivarius, Streptococcus mutans, Streptococcus gordonii, and Streptococcus oralis.
• Streptococcus mutans is associated with dental caries.

Streptolysin

• Streptolysins are toxins produced by certain Streptococcus bacteria, particularly Streptococcus pyogenes.
• Streptolysin O (SLO) is oxygen-sensitive and causes hemolysis under anaerobic conditions.
• Streptolysin S (SLS) is oxygen-stable and causes hemolysis under aerobic conditions.
• Both streptolysins contribute to the bacteria's ability to lyse red blood cells and evade the immune system.

Lancefield Grouping

• Streptococci are classified into serological groups (A-H, K-V) based on the presence of group-specific wall polysaccharides known as Lancefield antigens.
• Streptococcus pyogenes is the only bacterium within the Lancefield Group A classification.

Virulence Factors of Streptococcus pyogenes

• M Protein: A surface protein that inhibits phagocytosis by preventing complement deposition and opsonization.
• Hyaluronic Acid Capsule: Mimics human hyaluronic acid, allowing evasion of the immune system by hiding from phagocytes.
• Streptolysins (S and O): Hemolysins that lyse cells, including red blood cells, white blood cells, and platelets, contributing to tissue damage and inflammation.
• Streptococcal Pyrogenic Exotoxins (SPEs): Superantigens that can cause streptococcal toxic shock syndrome (STSS) and scarlet fever.
• Streptokinase: Converts plasminogen to plasmin, which breaks down fibrin clots.

Necrotizing Fasciitis

• Necrotizing fasciitis, commonly known as “flesh eating disease", is a serious condition caused by Streptococcus pyogenes.
• It can also be caused by a combination of bacteria including Staphylococcus aureus and Clostridium perfringens.

Firmicutes: Nonsporulating Bacillales and Clostridiales

• Key genera: Listeria, Sarcina, Clostridium
• Listeria:
  • Found widely in soils, an opportunistic pathogen that causes foodborne illness.
  • Gram-positive, catalase-positive, rod-shaped, facultatively aerobic chemoorganotrophs.
  • Acid-, salt-, and cold-tolerant.
  • Listeria monocytogenes causes listeriosis, a serious infection that can be fatal, especially in pregnant women, newborns, and individuals with weakened immune systems.
• Sarcina:
  • Catalase-negative.
  • Obligate anaerobe, exceptionally acid tolerant, often found in the stomach.
  • Sarcina ventriculi is associated with pyloric ulceration.
• Clostridium:
  • Includes important pathogens like Clostridium difficile, Clostridium botulinum, Clostridium tetani, and Clostridium perfringens.

This quiz focuses on the characteristics and differentiation of Streptococcus bacteria, highlighting their hemolytic activity and specific species. Learn about beta-hemolysis, alpha-hemolysis, and the role of streptolysins in pathogenicity.