Bacteria

• Staphylococcus


  Gram positive, spherical cells arranged in grape-like clusters, normally grow on skin and mucous membrane, non-motile, non spore-forming
• Staphylococcus


  • Facultative anaerobes, active fermenters, produce pigment hence colonies appears white to deep yellow, Easily acquire antibiotic resistance, Catalase producers (Streptococci are catalase negative)
• Virulence Factors of Staphylococcus


  • Cell wall
  • Protein A – antiphagocytic
  • Fibronectin-binding protein (PnBP) – promote binding
  • Cytolytic exotoxins – hemolysin
  • Superantigen exotoxins – enhances T lymphocyte response
  • Enterotoxins
  • Toxic shock syndrome toxin
  • Exfoliative toxin – causes scalded skin syndrome
• Other Virulence Factors of Staphylococcus

  • Coagulase - Clots plasma
  • Catalase - Converts hydrogen peroxide into water and oxygen; vs. catalase negative Streptococci
  • Others: hyaluronidase or spreading factor, staphylokinase (fibrinolysis), lipases, nucleases
• Types of skin lesions

  • Macules – flat lesions characterized by change in color of the affected area
  • Papules – raised lesion, solid in consistency, less than 5 mm diameter
  • Plaques – flat with elevated surface, more than 5 mm diameter
  • Nodules – rounded raised lesions, more than 5 mm diameter
  • Urticaria (wheals and hives) – annular or ring-like papules or plaques with pinkish color
  • Vesicles – circumscribed fluid-filled lesions, less than 5 mm diameter
  • Bullae - circumscribed fluid-filled lesions, more than 5 mm diameter
  • Pustules – circumscribed, exudate-filled lesions
  • Purpura – skin lesions due to bleeding into the skin
  • Ulcer – crater-like lesion that may involve the deeper layers of the epidermis and dermis
  • Eschar – necrotic ulcer covered with a blackened scab or crust

  
• Petechiae


  Purpura less than 3 mm diameter
• Ecchymosis


  Purpura more than 3 mm diameter
• Pathology of Staphylococcus aureus


  • Localized skin infections
  • Toxic shock syndrome
  • Staphylococcal gastroenteritis
• Localized skin infections of Staphylococcus aureus


  • Small, superficial abscess involving hair follicles, sweat or sebaceous gland – STY
  • Subcutaneous abscess around foreign body, splinters – FURUNCLES, BOILS
  • Deep, multiloculated skin infection that can lead to bacteremia and require debridement – CARBUNCLE
  • Localized, superficial, spreading crusty skin lesion - IMPETIGO
  • Staphylococcal scalded skin syndrome/ Ritter's disease - in newborns and children
• Localized skin infections can metastasize due to trauma and can lead to osteomyelitis, arthritis, acute endocarditis, septicemia, pneumonia
• Toxic shock syndrome


  Common in menstruating women with tampons, Symptoms: Fever, vomiting, diarrhea, hypotension, rash, multiple organ system involvement
• Staphylococcal gastroenteritis


  Symptoms: nausea, vomiting, diarrhea, no fever, Short incubation period – 30 mins to 8 hrs
• Coagulase negative Staphylococcus


  • Staphylococcus epidermidis - causes infection on prosthetic devices
  • Staphylococcus saprophyticus - causes urinary tract infections
• Epidemiology of Staphylococcus


  • Ubiquitous, Mode of transmission: droplets, lesion drainage, Control: cleanliness, hygiene and aseptic management of lesions, aerosols, ultraviolet irradiation, antiseptics
• Streptococcus


  • Gram positive
  • Spherical/ cocci in pairs or in chains
  • Normal flora
  • Facultative anaerobes
  • Capsulated
  • Has pili
  • Non-motile
  • Non-spore forming
• Hemolytic properties of Streptococcus


  • α hemolytic – cause chemical change in hemoglobin of RBC – green pigment of colony
  • β hemolytic – cause lysis of RBC, clear ring around the colony
  • γ Hemolytic – no color or lysis of RBC
• Lancefield groupings of Streptococcus

  • Grp A through U
  • C carbohydrate on cell wall, linked in their peptidoglycan
  • β-hemolytic strep – Type A and B
• Pathogenesis of Streptococcus


  • Capsule
  • Cell wall - resists phagocytosis and promotes adherence
  • Fimbriae – M protein
  • Group A-specific C-carbohydrate
  • Protein F
  • Extracellular products
• Extracellular products of Streptococcus

  • Streptococcal pyrogenic exotoxins (SPEs)
  • Cytolytic toxins and other exoenzymes
  • Streptolysin O – oxygen labile hemolysin causing release of lysosomes; basis of ASO test in rheumatic fever
  • Streptolysin S – lyses RBC, WBC and platelets
  • Streptokinase – fibrinolysin
  • Streptodornase – degrade DNA
  • C5a peptidase – inteferes mobilization of WBC
  • Hyaluronidase – hydrolyzes hyaluronic acid
• Streptococcus pyogenes


  • Most virulent of Streptococcus
  • Grp A Strep, beta hemolytic
  • Can be normal inhabitants of the nasopharynx (and skin) especially in children
  • Low inoculum is sufficient to cause an infection
• Diseases caused by Streptococcus pyogenes


  • Pharyngitis or pharyngotonsilitis
  • Strep throat
  • Scarlet fever – sun-burn like rash on neck, trunk and extremities
  • Rheumatic fever
  • Glumerulonephritis
  • Impetigo/pyoderma
  • Erysipelas (St. Anthony's fire)
  • Puerperal sepsis
  • Cellulitis
  • Necrotizing fasciitis
• Streptococcus pneumoniae or Pneumococcus


  • G(+) cocci in pairs or short chains, lancet-shaped
  • Encapsulated
  • Alpha hemolytic
  • Also called "diplococcus pneumoniae"
  • May be present in the nasopharynx of healthy individuals
• Virulence factors of Streptococcus pneumoniae


  • Capsule
  • Autolysin – in bacterial cell wall
  • Pneumolysin – attack cell membrane causing lysis
• Clinical syndromes of Streptococcus pneumoniae


  • Bacterial pneumonia
  • Otitis media
  • Bacteremia
  • Meningitis
• Streptococcus pneumoniae account for 60-80% of all bacterial pneumonias
• Streptococcus viridans group


  Part of the N flora of the mouth
• Streptococcus mutans


  • Causes dental caries
  • Produces lactic acid which breaks down enamel
  • Dental plaques
  • Dental caries – tooth decay
  • Dental calculus – hardened plaques
• Streptococcus produce disease only when established parts in the where they do not normally occur
• Transmission of Streptococcus is via droplets
• Prevention and control measures for Streptococcus


  • Detection and early antimicrobial therapy
  • Antistreptococcal chemoprophylaxis in persons who have suffered from rheumatic fever
  • Eradication of Group A Streptococci from carriers
  • Dust control, ventilation, air filtration, ultraviolet light and aerosol
  • Drug prophylaxis in a mother with positive cultures
• Spore-forming Gram-Positive Bacilli


  Bacillus and Clostridium Species

  
• Bacillus and Clostridium Species

  • Gram positive
  • Spore-forming
  • Ubiquitous
  • Form spores which allows them to survive for many years
  • Bacillus - aerobes
  • Clostridium - obligate anaerobes

  
• Bacillus species


  • Aerobic, Gram positive rods occurring in chains
  • Saprophytic
  • Square ends ("cut-glass" appearance)

  
• Bacillus anthracis


  • Bamboo fishing rod appearance or Medusa head
  • Individual or in pairs or long serpentine chain
  • Aerobic
  • Sporeformer
  • Encapsulated

  
• Bacillus anthracis


  • Inhalation anthrax
  • Gastrointestinal anthrax
  • Skin anthrax

  
• Bacillus anthracis pathogenesis


  • It is a primarily a disease of sheep, cattle and horses
  • May infect human via entry to the skin, inhalation or ingestion of the spores
  • Spore germinate into vegetative cells and spread via the lymphatics and bloodstream

  
• Bacillus anthracis virulence factors


  • Protective antigen
  • Edema factor
  • Toxic factor

  
• Bacillus anthracis diagnostic tests


  • Immunofluorescence staining technique
  • In BAM, the organisms produce non-hemolytic gray colonies

  
• Bacillus anthracis prevention and control


  • Disposal of animal carcasses by burning or by deep burial
  • Decontamination of animal products
  • Protective clothing and gloves for handling infected materials
  • Active immunization of domestic animals
• Bacillus anthracis treatment


  • Penicillin
  • Tetracycline
  • Erythromycin
  • Clindamycin