MICROBIAL GROWTH

1
MICROBIAL GROWTH Microbes are ubiquitous.
Survival of a species in a given area is
dependent upon whether the needs of the
microorganism are met. Environmental
factors Nutritional requirements Temperature
Oxygen Water pH
2
MICROBIAL NUTRITION Autotrophs vs.
Heterotrophs Nutritional needs Carbon - CO2 to
organics Nitrogen - N2 to NH4 to organic
N Phosphorus - phosphate Sulfur Trace
elements - Mg, Fe, K, etc. Growth factors
- vitamins Growth medium Defined Complex
3
TEMPERATURE Range 0º to 100º (individual
range much smaller) Range minimum ? maximum
(optimum) Classification psychrophiles
0-15º mesophiles 15-45º thermophiles
45º vant Hoff Rule 10º rise doubles the rate
4
OXYGEN Obligate aerobes - oxygen
mandatory Obligate anaerobes - oxygen
toxic Facultative anaerobes Microaerophiles -
low oxygen levels required Aerotolerant -
anaerobic metabolism, oxygen not toxic
5
OXYGEN TOXICITY Product of oxygen use hydrogen
peroxide H2O2 superoxide O2- Catalase
or Peroxidase H2O2 ? H2O and O2 Superoxide
dismutase 2 O2- 2 H ? H2O O2 Obligate
anaerobes lack catalase and/or superoxide
dismutase Anaerobes need reducing
environment to remove O2
6
WATER Water availability Aw pure water
1.0 Solute reduces Aw Osmosis Hypotonic
0.1 M 0.5 M Isotonic Hypert
onic Osmotic pressure - force to prevent
osmosis Osmophile - requires high solute
environment Osmotolerant - prefers lower solute,
but can survive Halophile - requires high salt
environment Halotolerant - prefers lower
solute, but can survive
7
pH Range 1 - 11 most pH 5 -
9 Acidophiles pH 1 - 4 Alkalophiles pH 9 -
11 Buffer mixture of a weak acid and its salt
or weak base and its salt, which retards pH
change
8
BACTERIAL GROWTH Binary fission Measuring
growth viable cell counts turbidity Mathemat
ics of growth 2n 1 ? 2 ? 4 ? 8 ? 16 ?
32 Generation time time between divisions
9
BACTERIAL GROWTH CURVE Lag phase Log
phase Stationary phase Death phase
10
Mathematics of growth Generation time - time
between cell divisions g 0.301 t____
log Nt - log N0 N0 number at time
zero Nt number at time t g generation
time
11
CONTROL OF MICROBIAL GROWTH Asepsis - keep
pathogens out Sterilization - kill all
organisms Disinfection - reduce
pathogens Antiseptic - agent to kill pathogens
on skin Disinfectant - reduce/kill pathogens on
surfaces Bacteriostasis - inhibit bacterial
growth Sanitization - reduce pathogens on
surfaces
12
PHYSICAL CONTROL METHODS Temperature - moist
heat, dry heat Boiling - 10 min for cells,
hours for spores Autoclave - 10-15 min for
spores Pasteurization - 63ºC for 30 min
72ºC for 15 sec 140ºC for 3 sec Dry heat
- 160-180ºC for 2-3 hr Refrigeration Freezing
13
PHYSICAL CONTROL METHODS Filtration Desiccation
Radiation x-rays - artificially
generated gamma rays - radioactive decay UV
14
CHEMICAL CONTROL METHODS Ideal
agent Effective against many types of
organisms Effective at low concentration Non-t
oxic to humans Stable Cheap Selecting an
agent What organism? What object?
15
CHEMICAL CONTROL METHODS Antiseptics
Disinfectants Phenol related
compounds Phenol coefficient Chlorhexidine
Halogens I2 iodophor Cl2 hypochlorite Tinc
ture of iodine Alcohols Heavy metals -
silver, mercury Surfactants detergents
quarternary nitrogen compounds
16
CHEMICAL CONTROL METHODS Antibiotics Natural
vs. Synthetic Therapeutic dose vs. Toxic
dose Targets Cell wall penicillin,
vancomycin, cephalosporins Protein synthesis
streptomycin, chloromycetin tetracycline Nucl
eic acid synthesis rifamycin, acyclovir,
naldixic acid, AZT Metabolism blockers
sulfa drugs, isoniazid
17
CHEMICAL CONTROL METHODS Antibiotic
resistance Mutation of antibiotic target
site Enzymes to degrade antibiotic Transport
systems to pump out of the cell Plasmids and
resistance