Bacteria Classification

Bacteria Classification

1. METHODS

   • GRAM +IVE
     • CATALASE TEST
       • catalase +ive
         • Staphylococcus
           • COAGULASE TEST
             • clots plasma
             • coagulase +ive
               • S. aureus
             • coagulase -ive
               • normal colonisers (harmful if get into blood)
           • most serious infections
           • clumps
       • catalase -ive
         • Streptococcus
           • HAEMOLYTIC TEST
             • Non-haemolytic: no Hb breakdown
               • Enterococcus faecalis
               • "non-haemolytic"
             • a-haemolytic: partial breakdown -> green zone
               • S. pneumoniae
               • "green hemolysis"
             • b-haemolytic: complete breakdown -> clear zone
               • S. pyrogenes
               • "complete heamolysis"
       • hydrogen peroxide -> water + O2
         • bubbles!
     • ACID-FAST STAIN
       • Mycobacteria
         • gram stain -> abnormal gram +ive -> requires further testing
         • Mycolic acid in membranes -> poor absorption then high retention
       • Stain with conc dyes at high temp. Not stained with acid wash -> "acid-fast" bacterium
         • i.e. resist dilute acid decolourisation
       • Ziehl-Neelsen Stain
         • carbol fuchsin stain -> wash -> counter stain with methylene blue
           • Acid fast: retain first stain -> id as red stains against blue backround
   • GRAM -IVE
     • CAPSULE?
       • Neissaria
         • N. gonorrhoeae: no
         • N. meningiditis: yes
     • MORPHOLOGY
       • diplococcus
         • Neissaria
       • cocco-bacilli
         • Moraxella
       • curved rod
         • Vibrio cholerae
     • NUTRITIONAL REQUIREMENTS (fastidious)
       • Legionella
       • Haemophilus influenzae
       • Bacteroides
     • LACTOSE FERMENTATION?
       • Lactose fermenters
         • Enterbacteriacaea
         • E. coli
         • Klebsiella
         • acid -> lower pH -> red colonies
       • Non-lactose fermenters
         • Salmonellas
         • Shigellas
         • Proteae
         • Use peptone (not lac) -> ammonia -> raises pH -> colourless colonies
       • GRAM -IVE BACILLI (rod shape)
       • MacConkey agar
   • DNA BASED
     • PCR
       • amplification
       • rDNA sequencing
     • Speed up diagnosis
     • Identify atypical bacteria - difficult to identify with culture based methods

2. STRUCTURE

   • GENERAL
     • Surface structures
       • Cell wall
         • peptidoglycan
         • absent in Mycoplasma -> no definite shape
       • Plasma membrane
       • Periplasmic space
         • between membrane/outer membrane or membrane/wall
         • store degradative enzymes
     • Internal structures
       • Nucleoid
       • Ribosomes
       • Storage granules
         • nutrients in form of lipids, glycogen, phosphates, or sulphur or nitrogen
       • Endospore
         • Clostridium botulinum
     • Appendages
       • Flagella
         • chemotaxis
         • flagellin subunit proteins
         • propella action
       • Pili (fimbrae)
         • sexual conjugation
         • biofilms (adhesion to host epithelium)
         • self assembly
       • Axial Filaments
         • in spirochetes
         • similar function to flagella
         • run lengthwise of body
         • snake-like motion
   • GRAM +IVE
     • Pep cell wall: THICK
     • Outer membrane: ABSENT
     • Periplasmic space: LITTLE/NONE
     • Capsule: mostly ABSENT
     • lipoteichoic acids
       • adhesins
     • hyaluronic acid capsule
       • camouflage
   • GRAM -IVE
     • Pep cell wall: THIN
     • Outer membrane: PRESENT
     • Periplasmic space: PRESENT
     • Capsule: can be PRESENT
     • Lipopolysaccharide
       • superantigen, PAMP

3. GRAM STAIN

   • stain with CRYSTAL VIOLET dye
     • Counter stain with FUCHSIN / SAFRANIN
       • crystal violet retained by peptidoglycan
         • Gram +ive will retain purple colour

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