Exam 2 - Lecture 8 Flashcards
what are some things microbes can do to endure periods without nutrients?
- form endospores
- enter a dormant, metabolically inactive state
- synthesize starvation response proteins
- make biofilms
when microbes grow in free floating in liquid, it is called ___________ growth.
planktonic growth
when microbes grow attached to surfaces in communities, it is called a:
biofilm
what holds the bacteria together in a biofilm?
extracellular polymeric substances (EPS)
what kinds of molecules can be found in a biofilm matrix?
- polysaccharides
- proteins
- DNA
true or false: biofilms are not uniform.
true
is it more likely for there to be more than one species in a biofilm or just one?
more than one
what causes differences in the metabolic activity of microbes in a biofilm?
heterogenous exposition of bacteria to different environmental conditions in different parts of the biofilm
true of false: biofilm bacteria are fairly easy to kill.
false; they are extremely difficult to kill.
what makes biofilm bacteria hard to kill?
- the matrix protects them from harmful agents (UV, antibiotics, antimicrobials)
- altered physiologies make them less sensitive
how do bacteria communicate in/out of the biofilm?
in a density-dependent manner called quorum sensing
as they grow, what do bacteria in a biofilm start producing?
autoinducers that diffuses out of the cell that alters gene expression when it diffuses back inside because it did some quorum sensing
what are the two major types of autoinducer cells?
- N-acyl-homoserine lactones (AHLs, Gram-negative)
- autoinducer peptides (AIPs, Gram-positive)
culture media can be prepared as ________ or _________
solid or liquid
how is media classified?
- chemical constituents from which they are made
- physical nature
- function
what are the two major types of media?
- chemically defined (or synthetic)
- complex
what are some media components?
- peptones: protein hydrolysates (fragments) prepared by partial partial digestion of various protein sources
- extracts: aqueous extracts, usually beef or yeast
- agar: polysaccharide (extracted from algae) use to solidify liquid media. most microorganisms can’t degrade it
what are four types of functional media?
- supportive (general use) media that supports the growth of many microorganisms, example: TSA
- enriched media that is supplemented by blood or other special nutrients, examples: blood agar, chocolate agar
- selective media: favors the growth of some microbes and inhibits the growth of others
- differential media: distinguishes between groups of microbes based on their biological characteristics
what does MacConket agar select for?
Gram-negative bacteria
what is the purpose of plate streaking?
to isolate single colonies
a population of cells arising from a single cell is called a:
colony
what is the statistically significant range for number of colonies on a plate?
30-300
what are the characteristics, such as size and shape, of a colony called?
the colonial morphology
what are the four phases a bacterial growth curve?
- lag phase
- exponential phase
- stationary phase
- death phase
what is taking place in the lag phase?
- cells are adapting to their new environment/media
- cells are synthesizing new components
- lag phase isn’t always the same length
what characterizes the exponential phase?
- aka the log phase
- rate of growth an division during this time is constant
- high metabolism and nutrient availability
- population is most uniform in terms of chemical and physical properties during this phase
what characterizes the stationary phase?
- nutrients are depleted
- metabolic byproducts build up
- population growth slows and eventually stops
- reproduction stops
- number of viable/living cells stays constant
what does entry into the stationary phase activate in the bacteria?
survival strategies (morphological changes like endospore formation, dismantling of ribosomes, decrease in size, nucleoid condensation, protoplast shrinkage, yeah)
when you do and spread and pour plate technique for counting colonies, are the CFUs that you are counting alive?
yes, this method only counts living cells. then you multiply by the dilution factor
what is the disadvantage of counting chambers?
you can’t distinguish between living and dead cells
what is turbidity?
the cloudiness or haziness of a fluid caused by suspended particles
what is a turbidometric measurement?
a measurement of turbidity or scattering of light
what wavelength is used in optical density measurements?
600 nm
a high absorbance means there is a (high or low) number of cells being detected.
high
