Unit 5

Psychrophiles

optimal growth at 15C, colder temps

Mesophiles

optimal growth temp of 37C because live on human body

Thermophiles

optimal growth temp within food danger zone of 60-130C * food safety

Hyperthermophiles

optimal growth at high temps (geyser + hyperthermal vent)

Psychrotrophs

Mesophilic organisms that are capable of growing at low temps but thrive in warmer conditions

bacteriostatic

stasis w/o active binary fission (typical when bacteria is in 10C fridge)

neutrophile

pH 6.5-7.5

Acidophiles

optimal pH is less than 4 → utilize food spoilage prevention (pickled), Helicobacter pylori (stomach ulcer) → coat itself with enzyme urease → creates ammonia (alkaline area) to increase pH 

Osmotic pressure

high concentration of salt or sugar → cause osmosis → shrink bacterium (plasmolysis) *cell wall unaffected

extreme/obligate halophiles

require high concentration of salt for growth

Organic Growth Factors

usually vitamin or essential amino acid or purines and pyrimidines needed *encourage bacterial growth and must be obtained directly from environment

obligate aerobe

must have O2 to live *have both superoxide dismutase and catalase enzymes

facultative anaerobe

if O2 is present they will utilize it for cellular respiration but can also exist w/o O2 *dense growth at surface but minimal growth throughout

Obligate anaerobe

can’t use O2 (toxic) —> don’t have 2 enzymes to neutralize free radicals (in gut and sewer pipes)

microaerophiles

O2 concentration must be less than atmospheric, tolerate a little O2 but too much overwhelms their enzyme capabilities *growth just below red line of oxygen

aerotolerant anaerobes

O2 not toxic but can’t utilize it for cellular respiration *can exist w/o O2

Inoculum

introduction of microbes into a medium (plate/slant/broth)

sterile

no living microbes

culture

microbes (population) growing on a culture medium

culture medium

nutrients prepared for microbial growth —> criteria: nutrients, space, correct pH, initially sterile, suitable O2 *incubate at correct temp

Enrichment Culture

trying to encourage bacterial growth, provide certain nutrients + environmental conditions that we know a specific bacteria will grow in 

microaerophiles

grow best when O2 < atmospheric *candle jar

capnophiles

prefer CO2 concentration higher than atmospheric *candle jar or CO2 generating packet

generation time

time it takes for bacteria to double its population

counting methods

spread plate method and pour plate method

serial dilutions

want to be able to count between 30 and 300 colonies

indirect method

*faster, look at whether light can penetrate solution of bacteria and comparing it with a control/standard —> determine # bacteria in sample, use spectrum photometer to determine turbidity

look for metabolic activity

tells if bacteria is viable, look at waste product presence —> producing lot of hydrogen sulfide gas? —> decent population if yes

dry down bacteria

need a lot of bacteria, dry bacteria in oven, weigh the bacteria and estimate # of bacteria

Direct microscopic count

A small, known volume of a sample is placed on a counting slide, cells are then visually counted in specific grid areas.