seminar 1 staphylococcus, streptococcus

Page 2: Staphylococcus Aureus

• Name: Golden Staff of Moses

• Genus Features:

  • Gram-positive

  • Cocci shape in clusters

  • Catalase positive

  • Small yellow colonies on blood agar

  • Beta-hemolytic

  • Coagulase positive

  • Ferments mannitol on mannitol salt agar

• Reservoir:

  • Normal flora of nasal mucosa (25% of population carriers)

  • Skin

• Transmission:

  • Hands, sneezing, surgical wounds

  • Contaminated foods (e.g., custard pastries, potato salad, canned meats)

• Predisposing Factors for Infection:

  • Surgery/wounds

  • Foreign bodies (e.g., tampons, surgical packing, sutures)

  • Severe neutropenia, IV drug abuse, chronic granulomatous disease, cystic fibrosis

• Disease and Pathogenesis:

  • Protein A inhibits phagocytosis

  • Diseases:

    • Gastroenteritis (food poisoning):

      • Toxin preformed in food; symptoms appear 2-6 hours after ingestion

      • Symptoms: nausea, abdominal pain, vomiting, diarrhea

    • Acute Infective Endocarditis:

      • Often from IV drug abuse; right-sided heart infection

      • Symptoms: fever, malaise, leukocytosis, heart murmur

    • Toxic Shock Syndrome:

      • Symptoms: fever, hypotension, scarlatiniform rash (desquamation)

      • TSST-1 superantigen causes cytokine storm

    • Osteomyelitis:

      • Bone pain, fever, redness; lytic bone lesions

    • Pneumonia:

      • Not leading cause; occurs in individuals with viral illnesses

      • Symptoms: productive pneumonia, salmon-colored sputum

    • Abscesses and Mastitis:

      • Symptoms: tenderness, redness, swelling

    • Impetigo, Scalded Skin Syndrome:

      • Symptoms: diffuse epidermal peeling

    • Surgical Infections:

      • Fever, cellulitis, abscesses

• Treatment:

  • Gastroenteritis is self-limiting

  • Penicillin (Nafcillin/Oxacillin as DOC due to resistance)

  • MRSA: vancomycin

  • VRSA/VISA: quinupristin/dalfopristin

Page 4: Staphylococcus Epidermidis and Saprophyticus

• Genus Features:

  • Gram-positive

  • Catalase positive, coagulase negative

  • Gamma-hemolysis/no hemolysis

• Staphylococcus Epidermidis:

  • Novobiocin-sensitive

  • Biofilm producer

  • Reservoir: Skin flora—can contaminate blood cultures

  • Disease Presentations:

    • Endocarditis (artificial heart valves)

    • Catheter infections

    • Prosthetic device infections

  • Treatment: Vancomycin

• Staphylococcus Saprophyticus:

  • Novobiocin-resistant

  • Disease Presentation: UTIs in newly sexually active females

Page 6: Streptococcus Pyogenes (Group A)

• Name: The Pie Genies’ Bakery

• General Features:

  • Gram-positive cocci in chains

  • Catalase negative, beta-hemolytic

  • Encapsulated with hyaluronic acid capsule

  • Bacitracin sensitive, PYR positive

• Reservoir: Human throat, skin

• Transmission: Direct contact, respiratory droplets

• Pathogenesis:

  • Hyaluronic acid is non-immunogenic

  • M-protein is antiphagocytic

  • Streptolysin O immunogenic; Streptolysin S not

  • Spreading factors:

    • Streptokinase and streptococcal DNAse

• Diseases:

  • Pyoderma/Impetigo

  • Pharyngitis/Strep Throat

  • Cellulitis/Erysipelas

  • Scarlet Fever

  • Toxic Shock-Like Syndrome

  • Rheumatic Fever

  • Acute Glomerulonephritis

• Laboratory Diagnosis:

  • Rapid strep test (ELISA-based)

  • Culture all negatives

• Treatment: Penicillin (macrolides for allergies)

• Prevention: Prophylactic antibiotics post-acute RF

Page 8: Streptococcus Agalactiae (Group B)

• Name: A Galactic Baby

• General Features:

  • Gram-positive, catalase negative

  • Beta-hemolytic, bacitracin resistant

  • Hydrolyzes hippurate, encapsulated

  • CAMP test positive

• Reservoir: Human vagina and GI tract (15-20% of women)

• Transmission: Newborns infected during birth

• Diseases:

  • Neonatal septicemia, meningitis, pneumonia

• Treatment: Ampicillin with aminoglycoside or cephalosporin

• Prevention: Prophylaxis during delivery in at-risk women.