Gram positive bacteria

Cards (19)

  • Gram Positives
    • Thick peptidoglycan wall (90%), many sheets of peptidoglycan stacked on top of each other
    Contains surface antigens including teichoic acids and lipoteichoic acids
  • Cocci shapes
    • Coccus (single-celled)
    Diplococci (occur in pairs)
    Tetrad (group of 4 in same plane)
    Sarcina (cube-like shape)
    Streptococci (chain-like)
    Staphylococci (grape-like cluster)
  • Micrococcus
    Obligate Aerobe
    Catalase positive
    Tolerates salt and drying fairly well
    Often pigmented
    Can be part of the normal skin flora (e.g. Micrococcus luteus)
    Can cause infections in the immunocompromised
  • Staphylococcus
    Facultative anaerobe
    Catalase positive
    Tolerates salt and drying fairly well
    Often pigmented (S. aureus: gold/yellow)
    Commonly found on humans and animals (e.g. S. epidermidis)
  • Infections caused by Staphylococci
    • Acne, boils, pimples, impetigo
    Pneumonia
    Meningitis
    Many of these diseases are suppurative (pus-forming)
    Common in normal flora and upper respiratory tract
    Serious infections occur when resistance is low
  • Staphylococcus aureus and virulence
    Can produce extracellular toxins or enzymes
    Coagulase coagulates fibrin to cause clots (Exoenzyme)
    Leukocidin causes cell destruction and pus formation (Exotoxin)
    Can produce enterotoxins (associated with foodborne illnesses)
  • Toxic Shock Syndrome (TSS)
    Extremely serious outcome of a S. aureus infection – rare but life threatening
    High fever, rash, vomiting, diarrhoea and occasionally leads to death
    Associated with tampon use, but rare
    Can occur in men and women following surgery
    Massive inflammatory response, which leads to associated symptoms
  • Staphylococcus aureus and Food Poisoning
    S. aureus can produce staphylococcal enterotoxins:
    Superantigens which lead to massive immune response
    Lead to increased permeability of the intestine
    Severe, short-lived diarrhoea and vomiting
  • Methicillin Resistant S. aureus (MRSA)

    Hospital 'superbug'
    Associated with the overuse (and incorrect use) of antibiotics
    Selection of resistant strains
    Often seen in patients with lowered resistance
    Others can be carriers
    Drug therapy a problem – vancomycin?
  • Streptococcus sp.
    Facultative anaerobe and catalase negative
    Non-motile with fastidious nutritional requirements
    Often part of the normal flora of skin and mucosal membranes
    Some strains are aggressive pathogens, whereas others are opportunistic pathogens
  • Streptococcal Diseases: S. pyogenes
    • Streptococcal pharyngitis (strep throat)
    Impetigo
    Scarlet fever
    Necrotising fasciitis
    Rheumatic fever
    Frequent isolate of the URT
    Acute bacterial infection
  • Streptococcal Pharyngitis: S. pyogenes
    Severe sore throat
    Enlarged tonsils
    Tonsillar exudate
    Tender cervical lymph nodes
    Mild fever
    General malaise
  • Scarlet Fever: S. pyogenes
    Some strains of S. pyogenes carry a lysogenic bacteriophage encoding an exotoxin
    This exotoxin is responsible for most of the symptoms of scarlet fever:
    Pink/red rash
    Damage to blood vessels
    fever
  • Streptococcal Impetigo: S. pyogenes
    Causes infection of superficial layers of the skin
    Two types:
    Bullous – large, painless, fluid-filled blisters
    Non-bullous – more contagious, sores which quickly rupture to leave yellow/brown crust
    Also caused by S. aureus
  • Necrotising fasciitis: S. pyogenes
    Can also be caused by S. aureus
    'Flesh-eating' bacteria
    Exotoxins A and B recruit T-cells to infected tissues
    1. cells secrete cytokines which activate effector cells
    Leads to massive inflammation, tissue destruction and death in up to 30% of cases
  • Streptococcus pneumoniae
    Causes lung infections
    Capsule capable of resisting phagocytosis
    Cells invade alveolar tissue of lower respiratory tract leading to strong inflammatory response
    Can lead to bacteraemia
    Pneumococcal pneumonia
    30% mortality in untreated cases
    1. 10% mortality with antimicrobial treatment
    Vaccine for at risk groups to protect against most common pathogenic strain
  • Listeria monocytogenes
    Gram-positive coccobacilli
    Require full aerobic or microaerobic conditions for growth
    Major foodborne illness
    Ready to each foods such as some cheeses and pâtés
    Survives in refrigerators (psychrophile)
    Mild illness to fatal meningitis
    Listeriosis a serious problem in pregnancy
  • Gram positive organisms can cause a wide range of infections of varying severity
  • Individual Gram positive species can cause a wide-range of diseases: e.g. S. aureus can cause TSS, Impetigo, food poisoning etc)