Week 6

Today's Topics:
○ Bacterial Taxonomy

Lecture Topic:
○ 2 major functions: identification and classification
○ Basic unit: species
○ Species are grouped into a genus
○ Genera are grouped into a family
○ Families are grouped into an order.

○ Identification needs a pure culture.
○ Procedure:
§ Examine morphology of culture
§ Examine morphology of cells (eg methylene blue stain) - note: use lowercase for morphology, to distinguish from genera.
□ Single sphere - cocci
□ Pairs - diplococci
□ Chains - streptococci
□ Cluster - staphylococci
□ Single rod - bacilli
□ Curved rod (comma) - vibrio
□ Wavy rod (fixed) - spirillum
□ Wavy rod (flexible) - spirochæte
□ Determine composition & structure of cell wall - gram stain and/or acid fast stain
□ Acid fast species are gram+, but do not take gram stain well due to lipids in cell wall. Good for identifying tb and leprosy, which can be distinguished by differing acid resistance.
□ There are also stains that will differentially stain features such as flagella, spores, etc.
§ Biochemical tests, eg:
□ Sugar tests - can species use a particular carbohydrate?
¨ Liquid culture containing only one carbon source - individual CHO
¨ pH indicator for eg lactic acid
¨ Inverted tube (durham tube) to collect gas (eg CO2)
□ Gelatin tube
¨ Stab innoculation
¨ some organisms metabolise gelatin
¨ Different growth patterns
□ Nitrate reduction (to nitrite or nitrogen)
§ You can then select from:
§ Physiological tests
□ Factors such as
□ optimum temperature eg:
¨ Mycobacterium tuberculosis prefers 37C
¨ M. avium prefers 42C
¨ M. marinium prefers 25C
□ pH
§ Pathological tests:
□ Which organisms does it affect?
¨ Staphylococcus epidermidis - rarely pathogenic
¨ S. aureus - can cause several diseases
¨ (don't actually need for these two - se is white, sa is golden)
§ Immunological tests, eg for species of Salmonella
□ Test for reaction with specific antibodies.
○ Standard system:eg:
§ Escherichia coli
§ Genus: Escherichia
§ Species: coli.
§ Conventions:
□ written in italics or underlined.
□ Genus has initial capital.
□ Genus may be abbreviated to initial, or shorter version where this will not cause confusion.
□ Several species from one genus may be referred to as, eg Escherichia spp.
§ Current bacterial classification: Bergey's Manual of Systematic Bacteriology, 2nd ed (2001)
□ http://www.cme.msu.edu/bergeys
□ Volume 1: Archaea
¨ Eg Halobacterium spp., Thermococcus spp.
□ Volume 2: Proteobacteria (gram negative)
¨ Eg enteric bacteria & Pseudomonas spp.
¨ P. florescens - fluorescent
¨ P. aeruginosa - cause some effects of cystic fibrosis
□ Volume 3: Low G+C Gram Positive bacteria
¨ Eg lactic acid bacteria (such as Lactobacillus spp.), Bacillus spp., Clostridium spp., Streptococcus spp.
¨ B. subtilis
¨ C. sporogenes
□ Volume 4: High G+C Gram Positive bacteria
¨ Eg Mycobacterium Spp., Streptomyces spp.
¨ Streptomyces spp. Are good sources of antibiotics.
□ Volume 5: Everything else
¨ Eg spirochaetes, Bacteriodes spp.