Mod 6

• All cocci are Gram-positive except NVB!
• Natural habitants of the skin and mucus membranes in humans


  • Can be ubiquitous in the environment
• Among the gram-positive cocci, the most important human pathogens

  • Staphylococcus aureus
  • Streptococcus pyogenes
  • Streptococcus agalactiae
  • Streptococcus pneumoniae
  • Enterococcus faecalis and E. faecium

  
• Other genera in the Staphylococcaceae family

  • Macrococcus (animal commensals)
  • Gemella
  • Salinicoccus (halophile:river)

  
• Staphylococcus

  Greek words: staphule (bunches of grapes) and kokkos (berries)

  
• Staphylococcus

  • Catalase-producing / Catalase (+)
  • Aerobic or facultative anaerobic
  • Nonmotile, non-spore-forming glucose fermenters
  • Normal inhabitants of the skin, mucous membranes, and intestines
• S. saccharolyticus

  Obligate anaerobe
• Catalase reaction

  H2O2 + Catalase= copious bubbles
• Carbohydrate fermentation

  1. Acid or acid with gas are produced

  2. Acid lowers the pH of the test medium, which is detected by the color change of the pH indicator

  3. Color change only occurs when a sufficient amount of acid is produced, as bacteria may utilize the peptone producing alkaline by-products
• Staphylococcus aureus

  • Most virulent species of staphylococci
  • Halophilic
  • Causes infection when it enters a normally sterile site

  
• Cultural Characteristics of Staphylococcus aureus


  • BAP: β hemolytic; round, smooth, opaque and butyrous(Butterlike); gray to deep golden yellow
  • MSA: yellow colonies

  
• Mannitol salt agar (MSA)


  Selective and differential medium used in the isolation of staphylococci<|>Contains 7.5% sodium chloride and thus selects for bacteria that can tolerate high salt concentrations
• Coagulase test


  Precipitation of fibrinogen on the staphylococcal cell, causing the cells to clump when a bacterial suspension is mixed with plasma
• Staphylococcus aureus

  • Mannitol fermenter
  • Resistant to polymyxin B (for Gram- antibiotics)
  • Susceptible to lysostaphin (antibacterial enzyme that cleaves peptidoglycan)
  • Positive DNAse test

  
• Clinical Manifestations of S. aureus

  • Skin infections (folliculitis, boils/furuncles, carbuncle, impetigo, mastitis, and infection of surgical wounds)
  • Septic arthritis in prepubertal children
  • Bacteremia in hospitalized patients (may cause endocarditis)
  • Spinal epidural abscess and suppurative intracranial phlebitis
  • Toxin-mediated diseases (e.g. scalded skin syndrome and toxic shock syndrome)
  • Food poisoning, UTI, osteomyelitis
• Characteristics of Blisters caused by S. aureus

  • Itchy & easy to pop
  • Filled with yellow or honey-colored fluid
  • Oozing and crusting over
• Impetigo, one of the most common skin infections among kids, usually produces blisters or sores on the face, neck, hands, and diaper area
• Impetigo is generally caused by Staphylococcus aureus or Streptococcus pyogenes
• Pathogenic Determinants of S. aureus

  • Protein A
  • Coagulase- principal virulence factor
  • Staphylokinase
  • Exfoliatin
  • Lipase
  • Hyaluronidase
  • Cytotoxins (Alpha, Beta, Delta, Gamma)
  • Leukocidin (Panton- Valentine Leukocidin)
  • Hemolysin
  • Enterotoxins A–E
  • Toxic shock syndrome toxin (TSST-1)
• Protein A

  Bound to the cytoplasmic membrane of the organism, and has a high affinity for the Fc receptor on IgG molecules as well as complement, directly bind immunoglobulins, thereby decreasing the immune-mediated clearance of organisms from the site of infection, inhibits phagocytosis & involved in coagglutination
• Coagulase


  Converts fibrinogen to fibrin; coats PMN with fibrin to inhibit phagocytosis
• Staphylokinase


  Enables infection once fibrin clot is dissolved
• Exfoliatin


  Responsible for Scalded Skin Syndrome (SSS) aka Ritter-Lyell disease
• Lipase


  Hydrolyze lipids in plasma and skin; responsible for skin infections
• Hyaluronidase


  Spreading factor: dissolves hyaluronic acid in connective tissues
• Cytotoxins

  Alpha toxin, Beta toxin, Delta toxin, Gamma toxin (in association with the Panton- Valentine Leukocidin)
• Panton- Valentine Leukocidin (PVL)


  Lyse WBC and macrophages, found in CA-MRSA
• Hemolysin


  Lyse RBCs, causes anemia and makes iron available for bacteria
• Enterotoxins A–E


  Food poisoning (preformed toxin) occurs 1-6 hours after ingestion
• Toxic shock syndrome toxin (TSST-1)

  Aka Enterotoxin F, Disease In women who use tampons
• Methicillin-resistant S. aureus (MRSA)


  • S. aureus strain resistant to antibiotics such as Methicillin, Nafcillin, And Oxacillin
  • Acquired after prolonged stay in the hospital, close contact with carriers, broad-spectrum antibiotics
  • In the community, mostly skin infections
  • In healthcare settings usually more severe and life-threatening (bloodstream infections, surgical site infections, or pneumonia)
• Chromogenic test for MRSA

  Changes in the color of MRSA colonies within 24-48 hours using CHROM agar against colorless colonies of non-MRSA

  
• Appearance and color of the MRSA colonies in chromogenic media

  • HiCrome agar: bluish green
  • CHROMagar: mauve to pink

  
• Coagulase-Negative Staphylococci (CoNS)

  • Novobiocin resistant: S. saprophyticus, S. cohnii, S. kloosii, S. xylosus
  • Novobiocin susceptible: S. epidermidis, S. capitis, S. haemolyticus, S. hominis subsp. hominis, S. lugdunensis, S. saccharolyticus, S. warneri
• Staphylococcus epidermidis

  • Very similar to S. aureus in microscopic morphology
  • Catalase (+); Non-mannitol fermenter
  • Coagulase test (-)
  • DNAse (-)
  • Susceptible to novobiocin

  
• Staphylococcus epidermidis

  Resistant flora of the skin/mucous membrane (cause infection in compromised hosts)<|>Blood culture contaminant<|>Opportunistic pathogen<|>Distinct predilection for foreign bodies (artificial heart valves, CNS shunts, IV catheters)

  
• Staphylococcus saprophyticus

  • Very similar to S. aureus in microscopic morphology
  • Resistance to novobiocin and nalidixic acid
  • Negative Phosphatase reaction (meaning NO alkaline phosphatase present)

  
• Staphylococcus saprophyticus

  Normal flora of skin and urethra<|>Common cause of UTI in young sexually active women<|>2nd most common cause of UTI in young women<|>Low urine colony count is considered significant (<100,00 Urine CFU/mL)

  
• Mannitol fermentation on agar

  • Yellow colonies of S. aureus
  • White colonies of S. epidermidis
• Micrococcus


  Family Micrococcaceae, including Micrococcus, Arthrobacteria, and Kocuria<|>Occur worldwide and are ubiquitous (found everywhere)<|>Indigenous skin biota, often recovered with staphylococci<|>Rarely infectious