lecture 1.8 Flashcards
(19 cards)
Planctonic=
free floating in culture medium
Biofilm/Sessile=
communities of single or multiple species growing on surfaces
Oligotrophic growth=
growth on/ a requirement for a complex mixture of nutrients that are preset at low concentrations
Describe the characteristics of a biofilm
complex, slime enclosed communities called a biofilm
Biofilms are ubiquitous in nature in water
Can be formed on any conditioned surface
heterogeneity is differences in metabolic activity and locations of microbes
exchanges take place metabolically: DNA uptake and communication
Whats the problem with biofilms in health?
When formed on medical devices, such as implants, often lead to illness
Sometimes difficult to cure with antibiotics – there may be persisters that are more resistant to antibiotics
Sloughing off of organisms can result in contamination of water phase above the biofilm such as in a drinking water system
quorum sensing=
density-dependent manner in which biofilms communicate
How do biofilms uptake DNA?
DNA uptake occurs, bacteriocins are released
bacteriocins are chemical that kill (cannibalize?) bacteria of the same species as the ones making the bacteriocins
bacteriocin producing strains carry a resistance factor against the bacteriocin
How does Quorum Sensing work?
Acylhomoserine lactone (AHL) --molecule produced by many gram-negative organisms diffuses across plasma membrane once inside the cell, induces expression of target genes regulating a variety of functions
What are the different ways in which culture media can be classified
chemical constituents from which they are made
physical nature
function
peptones=
protein hydrolysates prepared by partial digestion of various protein sources
Extracts=
aqueous extracts, usually of beef or yeast
Agar=
sulfated polysaccharide used to solidify liquid media; most microorganisms cannot degrade it
What are the advantages of a complex media?
can support rapid growth (because the bacteria don’t have to make lots of biosynthetic precursors
What are the disadvantages of a complex media?
we don’t know and can’t control composition
What are the different types of media?
Supportive or general purpose media
Enriched media (e.g. blood agar/ media supplemented by blood or other special nutrients)
Selective
Differential
How does selective media work?
MacConkey agar
contain bile salts that are toxic to gram-positives
selects for gram-negative bacteria
How does blood agar differentiate?
hemolytic versus nonhemolytic bacteria
How does MacConkey agar differentiate?
lactose fermenters versus nonfermenters: Lac+ (e.g. E. coli) are red on MacConkey, Lac- (e.g. Salmonella) are white
What percent of bacteria observed can be cultured in lab media and why?
approx 1%
Medium used is too rich or too poor
Medium does not contain a necessary supplement
O2 tension, temperature not right
Organism requires some other species to feed it
Who knows?
