3

• catalase enzyme


  breaks down hydrogen peroxide into water and oxygen, bubbles (protects from oxidative burst from phagocytic cell)
• catalase reaction test


  staphylococci = positive, streptococci = negative
• CoNS


  generally low virulence pathogens that don't cause disease, most normal skin flora
• coagulase test 


  for staphylococci, test for production of coagulase enzyme (positive only in s.aureus) which coagulates plasma otherwise spread across tube
• when will CoNS cause disease

  skin barrier breached by invasive devices or in infants
• 2 CoNS example


  s.epidermidis and s.saprophyticus
• how many people carry s.aureus and where

  20-40% population, groin, nostrils and armpits
• s.aureus infection


  localised or disseminated infection, pyogenic (pus forming - abscess) infections in most organs
• coagulase toxin (s.aureus)


  walls off infection while lytic toxins destroy tissue
• quorum sensing 


  chemical communication between bacteria that depends on the surrounding environmental conditions, including bacterial density (more = more talk)
• QS influences bacterial behaviour, allowing bacteria to collaborate in response to environmental conditions
• how QS system works in s.aureus

  though accessory gene regulator (agr), contributes to pathogenicity in several infection types (transition from colonisation to disease, will it become a pathogen or commensal) - subcutaneous abscesses, endocarditis
• what type of circuit is the agr sensing system

  auto activating
• progression of s.aureus infection

  folliculitis - furucles - carbunicles - impetigo (spreading skin infection)
• severe forms s.aureus 


  localised infections - lung access, brain access
• toxin producing strain s.aureus cause non pyogenic disease

  1. staphylococcal scalded skin syndrome (SSSS)
  2. staphylococcal toxic shock syndrom (STSS)
  3. staphylococcal food poisoning
• superantigens 


  bypass normal antigen presentation by directly cross linking TCR and MCH2 causing polyclonal activation of broad range of TCRs, no specificity in reaction(binds outside presenting cleft)
• SSSS


  caused by an enterotoxin (a super antigen) the gene acquired a bacteriophage via transduction, causes layers of skin to peel off
• enterotoxin 


  harms digestive system
• beta hemolysis


  blood is dissolved, agar transparent (enzyme breaks down RBC)
• alpha hemolysis


  partial haemolysis od agar
• gamma hemolysis 


  no hemolysis
• B haemolytic strep classification

  according to antigenic differences in cell wall carbs (Lancefield system A-H, K-V)
• 2 lancefield groups significance

  group A (step A) = streptococcus pyogenes

  group B = streptococcus agalactiae
• a - haemolytic streptococci 


  common commensal of upper respiratory, gut, genital tract
• 2 groups of a haemolytic streptococci


  1 - streptococcus pneumonia 2 - viridans group of strep (includes strep mutants group)
• streptococcus pneumoniae


  gram positive diplococcus, leading bacterial cause of pneumonia, also cause meningitis
• streptococcus pneumoniae capsule


  more than 94 types, pathogenic factor
• streptococcus pneumoniae vaccine


  protection to specific capsular type (serotype), common vaccine targets 13
• S.pneumoniae carriage


  nasopharyngeal carriage needed for transmission of bacteria and precedes invasive disease, carriage common in children (usually through mucus membranes)
• evolution of s.mutans


  acquired gtf gene via horizontal gene transfer from lactic acid bacilli, selected for this because could catabolise sugar
• polysaccharide vaccines problem


  based on bacterial capsules, they don't induce strong or persistent immune response in young children, only stimulate B cells not T cells. B cells just die, don't produce memory B cells
• conjugate vaccines


  polysaccharide linked to a carrier protein molecule
• why are conjugate vaccines better

  induce memory responses and reduce nasopharyngeal carriage of bacteria (impact transmission), stimulates B and T cells and produce memory B cells/antibodies
• primary infection sites of strep A infection (pyogenes)

  throat (pharyngitis and tonsillitis) or skin (impetigo or cellulitis)
• complications of strep A throat infection

  abscess
• complications of strep A skin infection

  necrotizing fascitis (rapid tissue breakdown)
• non suppurative complications strep A infection (pyogenes)

  throat - acute rheumatic fever (can lead to heart disease)

  skin - renal disease
• acute rheumatic fever syndrome (following strep A)

  arthritis, rash (raised boarder), carditis (damage to heart vales), involuntary movements
• who gets acute rheumatic fever

  associated with poor living conditions, aboriginal children, people in poverty