6.3.2 Bacteria Physiology Flashcards
How do bacteria replicate?
binary fission
rods split in shorter axis, cocci can split in any direction
What is generation / doubling time?
time from completion of septum formation to septum formation (from 1 cell to 2 cells at the same stage)
20 min for E. coli
16h for Mycobacterium bovis
for diagnostics usually those with short doubling time are used
Outline the process of bacteria replication
DNA replicates
Cell elongates
Cell pinches in the middle
Daughter cells separate
Outline the phases of bacterial growth (bacterial growth curve)
Lag - constant number, they get used to new environment
Log / exponential - phase of divisions
Stationary - they use up space and nutrients, don’t divide more
Decline - some cells get old and lyse
What are endospores?
dormant, highly resistant bodies
survive adverse environmental conditions
only Clostridium spp. and Bacillus spp. (both gram + rods) can form them
What is sporulation?
sporulation - spore formation
What is germination?
germination - reverting back to the ‘vegetative cycle’
What are two types of culture media for bacteria? (structure)
How usually prepared?
agar - solid
broth - liquid
powder added to sterile water, sterilised and poured to the containers (Petri dishes or special bottles)
What are 4 functional types of culture media?
Complete - grows almost all culturable bacteria e.g. blood agar
Selective - selects against some bacteria species e.g. MacConkey (no gram +), Mannitol Salt (no gram - )
Differential - different appearance of bacterial species e.g. MacConkey
Enrichment - enhances growth of a particular bacterial species e.g. selenite broth (salmonella), salt broth (staphylococci)
MacConkey agar properties
Selective - most gram +ve cannot grow (due to bile salts and crystal violets)
Differential - ph indicator (red pH < 6.8) (colourless pH > 6.8)
How to assess bacteria culture growth?
we’re looking to see visible bacteria cells
in agar single colonies - groups of cells that used to be a single cell
in broth visible cloudiness
Why is it important to obtain single colonies on agar?
when we have to identify particular types of bacteria
(when there are different types on one agar)
What is a bacterial colony?
a group of clones derived from one bacteria
What are the possible incubation conditions?
temperature, pH
Temp - 37ºc normally
pH - neutral normally
How to test oxygen requirements of bacteria?
bacteria dispersed into semi-solid media open to the environment
strict aerobes will only grow in presence of oxygen
obligate anaerobe will grow only without oxygen
facultative anaerobe can grow in both presence and absence of oxygen
microaerophil likes about 5% O2
