Fungal skin infection

• Tinea pedis is the most common fungal infection, affecting up to 70% of adults at some point.
• Diagnosis of S.pyogenes infections

  1. Specimens: infected wound – pus, necrotising fasciitis – blood

  2. Laboratory tests: Gram stain – Gram positive cocci in chains, Culture – Small, pin-point colonies with beta haemolysis on blood agar, Identification – Lancefield grouping by latex agglutination test
• 10% of healthy children are colonized by S.pyogenes (throat), They are transient flora of the skin, Common cause of community acquired infections
• Treatment for S.pyogenes infections

  • Penicillin
  • Erythromycin
• Organisms causing skin infections

  • Aetiology
  • Pathogenesis
  • Clinical features
  • Immunological response
  • Laboratory diagnosis
  • Treatment
  • Epidemiology
  • Prevention and Control
• Opportunistic pathogens can cause infections if they get into an unusual site or if the host’s immunity is low
• Normal flora of the Skin

  • Coagulase negative staphylococci
  • Staphylococcus aureus – carriage
  • Streptococcus pyogenes - carriage
  • Corynebacteria
  • Micrococci
  • Propionobacteria
  • Candida sp
• Staphylococcus aureus is carried by 40% of the population
• GRAM POSITIVE COCCI


  • Staphylococcus
  • Streptococcus
• Coagulase positive staphylococci


  • Staphylococcus aureus
• Coagulase negative staphylococci


  • Staphylococcus epidermidis
  • Staphylococcus saprophyticus
  • Staphylococcus capitis
  • Staphylococcus haemolyticus
  • S hominis
• S.aureus - Aetiology


  • Skin and soft tissue infections
  • Deep infections
  • Food poisoning
  • Toxic shock syndrome
  • Scalded skin syndrome
  • Hospital acquired infection (wound/surgical site/pneumonia/UTI)
  • Folliculitis
  • Carbuncle
  • Impetigo
  • Cellulitis
  • Wound infection
  • Toxic shock syndrome
  • Staphylococcal scalded skin syndrome
• S.aureus - Pathogenesis


  • Source: Humans. Patients with infections and Carriers (nose, skin, throat) S.aureus is shed from the skin and mucous membranes of carriers. Carriers may also get infections from colonising S.aureus. (endogenous infection)
  • Route of Transmission: S.aureus is resistant to drying. Found in dust, clothing, bedding. Also on the hands of patients and carriers. Generally transmitted by direct contact with hands or indirect contact with dust or fomites.
  • Virulence factors: Heat stable enterotoxin – Food poisoning, TSST- Causes cytokine release resulting in toxic shock, Cytolytic toxins – kills leucocytes and Macrophages, Exfoliative toxins - SSSS, ProteinA binds to Fc region of Igs – protects organism from humoral response, Penicillinase producing Staph
• S.aureus - Pathology


  • Pyogenic infections
  • Skin and soft tissue infections
  • Deep infections
  • Exotoxin mediated infections
• S.aureus is a pathogen that causes skin infections
• Objectives


  • Identify the pathology underlying the common skin infections
  • Outline the laboratory diagnosis of these infections
  • Outline the management of these infections
  • Identify the important epidemiological features of these infections
  • Describe the prevention and control of these infections including any currently available vaccines
• S.aureus


  • Pathology: Pyogenic infections, Skin and soft tissue infections, Deep infections, Exotoxin mediated infections, Food poisoning, Toxic shock syndrome, Scalded skin syndrome
• Diagnosis of S.aureus


  1. Specimens: pus

  2. Specimens: blood culture

  3. Laboratory tests: Gram stain – Gram positive cocci in grape-like clusters, Culture – Large, golden-yellow colonies with beta haemolysis on blood agar, S.aureus is coagulase positive, Coagulase test, Free coagulase – Tube Coagulase Test, Free Coagulase – Slide Coagulase test
• S.aureus


  • Management: Cloxacillin, Vancomycin for MRSA (Methicillin resistant S.aureus), Drain pus collections if any, Wound cleaning
• S.aureus


  • Epidemiology: 40% of healthy adults are colonized (anterior nares, throat, skin) – lead to endogenous infections, Common cause of community acquired infection
• S.aureus


  • Prevention & Control: Protocols to eradicate the carrier state, However they often get re-colonised
• Coagulase negative staphylococci


  • Includes S.epidermidis and S. saprophyticus, Normal commensals of the skin, Opportunistic pathogens
• S.epidermidis


  • Aetiology: Infects medical devices in hospital (hospital acquired infection), Intravenous catheters, Shunts, Prosthetic valves and joints, Peritonitis in dialysis patients, Pathogenesis: Commensal of the skin and mucous membranes, Route of transmission – Endogenous infections, Virulence factors – Adhere to medical devices (catheters, Shunts) by ‘slime’ & protects organisms from clearance and allows colonisations, Treatment & Prevention: Often resistant to penicillins and methicilin, Vancomycin resistance is also observed, Remove unwanted catheters and shunts, Follow good surgical practice, Washing hands regularly
• S.saprophyticus


  • Aetiology: Common cause of urinary tract infection in women, Normal flora of the lower urinary tract, Diagnosis: Gram stain – Gram positive cocci in grape-like clusters, Culture – Large, white colonies without beta haemolysis on blood agar in general
• Coagulase negative Streptococci


  • Includes Streptococci and Steptococci, Gram stain – Gram positive cocci in chains, Culture – Pinpoint colonies. May be β haemolytic, α haemolytic or non-haemolytic
• Streptococcus


  • Beta haemolytic streptococci: Streptococcus pyogenes (Group A), Streptococcus agalactiae (Group B), Enterococci (Group D), Alpha haemolyic streptococci: Streptococcus pneumoniae, Viridans group of streptococci, Lancefield groups A-H, K-V, Serotypes, Streptococcus pyogenes (Group A)
• S.pyogenes


  • Aetiology: Pharyngitis, tonsillitis, Otitis media, sinusitis, Wound infections, Cellulitis, impetigo, erysipelas, Necrotising fasciitis, Streptococcal TSS, Scarlet fever - Fever/ rash/strawberry tongue, Rheumatic fever (1-5 weeks after pharyngitis
• Objectives


  • Name and describe the main pathogens that cause skin infections, List the other main infections that each of these organisms cause, Describe the pathogenesis (source, mode of transmission, portal of entry and virulence factors) of these infections
• Virulence factors of S.pyogenes infections

  • Hyaluronic acid capsule is antiphagocytic
  • M proteins breaks C3b and escape opsonization
  • C5a peptidase destroy C5a and reduce chemotaxis
  • Streptolysin S and O are cytolytic that destroy leucocytes
  • Enzymes that help in invasion of tissues: Hyaluronidase, streptokinase, DNAses
• Pathogenesis of S.pyogenes infections

  1. Source: Humans. Patients with infections and Carriers (throat)

  2. Route of Transmission: Droplets are inhaled into the respiratory tract. It can spread from infected skin by direct contact or through fomites to cause skin infections
• Rheumatic fever


  • Immunological complication following a streptococcal sore throat. Affects the heart
• Acute glomerulonephritis


  • Immunological complication following a streptococcal sore throat or skin infection. Affects the kidney
• Immunopathology of S.pyogenes infections

  1. Rheumatic fever is caused by autoantibodies shared between M protein and Heart muscle

  2. AGN is due to IC deposition
• Diagnosis of S.pyogenes infections

  1. Specimens: infected wound – pus, necrotising fasciitis – blood

  2. Laboratory tests: Gram stain – Gram positive cocci in chains, Culture – Small, pin-point colonies with beta hemolysis on blood agar, Identification – Lancefield grouping by latex agglutination test
• Pathology of S.pyogenes infections

  Streptococcus pyogenes infection results in acute inflammation, Acute pyogenic infections
• Laboratory diagnosis of S.pyogenes infections

  Gram stain – Gram positive cocci in chains, Culture – Small, pin-point colonies with beta hemolysis on blood agar, Identification – Lancefield grouping by latex agglutination test
• Treatment of S.pyogenes infections

  Penicillin, Erythromycin
• Epidemiological features of S.pyogenes infections

  • 10% of healthy children are colonized (throat), They are transient flora of the skin, Common cause of community acquired infections
• Epidemiology of S.pyogenes infections

  10% of healthy children are colonized (throat), They are transient flora of the skin, Common cause of community acquired infections