Bacterial Identification, growth, gene exchange & Isolation Flashcards
4 main environmental factors on bacterial growth
- Temp
- pH
- Availability of water
- Air/Oxygen
Nutrients & microbial growth
- As nutrient conc. increases, bacterial growth rate increases exponentially until eventually reach a plateau
- growth can’t increase further because transport mechanisms for nutrient uptake is saturated
Temperature & microbial growth
-3 types of organisms
- Thermophiles - like it hot
- Mesophiles - include moth pathogens (optimum = 37)
- Psychrophiles - grow at low temps
*slow increase in growth rate w/ temp, then sudden drop off as temp denatures enzymes & melts membrane proteins
pH and microbial growth
- All bacteria need aqueous phase, therefore pH will always be important
- many have optima around pH 7.0
Salts/Osmotic pressure & Microbial growth
e.g. of halophile
-Halphiles - i.e. Staph aureus can tolerate saline solutions
Gaseous environment & microbial growth
-5 types & examples of organisms
- Obligate aerobes - little or no fermentation (as lack enzymes)
- e.g. Pseudomonas sp., mycobacterium tuberculosis
- Facultative anaerobes - can grow w/out air, but shift to aerobic respiration in presence of air
- e.g. Enterobacteriaceae
- Aerotolerant anaerobes: survive in air but don’t shift to aerobic respiration
- e.g. streptococcus
- Microaerophilic: prefer reduced oxygen tensions (and extra CO2) such as found in respiratory systems
- e.g. Brucella sp.
- Obligate Anaerobes: cannot tolerate oxygen - lacks enzymes to deal w/ very oxidative molecule that reacts rapidly (aerobes have enzymes to deal with it)
- e.g. Clostridia sp.
Features of Culture media
Need to supply;
- Energy
- carbon source
- nitrogen source
- inorganic radicals
- Some require accessory growth factors (i.e. vitamins)
Types of media to grow pathogens (4)
Basal media: Contains meat extracts; support most micro-organisms
-e.g. nutrient agar/broth
Enriched media: basal media + supplements
-e.g. blood, serum
Solid media: Used for isolation of single cells: these cells grow into discrete colonies
-agar (long chain polysaccharide from algae)
Liquid Media: used for subsequent growth of pure cultures (e.g. peptone water = meat digest + salt + water)
Selective Media
-To enhance isolation/growth of specific bacterial species can use selective media (agar) or enrichment media (broth)
Selective media: agar
-used to select for growth of part. groups of bacteria - contain inhibitors to certain organisms
e.g. Maccokey agar, brilliant green agar (Salmonella), Mannitol salt agar (staphs), Edwards media (for Streps)
Enrichment Media: Browths
-contains factors that favour growth of desired organism
e.g. selenite broth for salmonella
3 reasons we would need to identify bacteria
- Know what we are working with
- Describe roles in the environment
- Diagnose and treat diseases
Techniques for identifying bacteria
- colony morphology
- growth on different media
- Biochemical tests - can test metabolic pathways
- protein analysis
- different staining
- serological methods
- phage typing (bacterial viruses - highly specific on what they infect)
- nucleotide analysis
Shapes of cells (3)
- Coccus (round)
- Rod
- Spiral
API 20E test strip
- Rapid identification of Enterobacteriaceae and other Gram -tive bacteria)
- different substrates in vials - inoculate w/ bacteria and incubate overnight
- indicates whether bacteria has grown or not
Genotype vs Phenotype
Genotype: genetic potential of an individual
Phenotype: Observed characteristics - not all genes are expressed
Mutation: 2 types
- Mutation: cause inheritable change in the genes
1. Spontaneous mutation: due to v. rapid transcription in bacterial cells - random errors occur
i) Point mutation (change in one base)
ii) Frame shift mutation (either deletion or insertion)
2. Induced mutations: due to mutagens such as UV light, gamma irradiation, alkylating agents. Can either have;- no effect
- deleterious effect
- advantageous effect
