Flashcards in lecture 1.8 Deck (19):
free floating in culture medium
communities of single or multiple species growing on surfaces
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
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
protein hydrolysates prepared by partial digestion of various protein sources
aqueous extracts, usually of beef or yeast
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)
How does selective media work?
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