practical information Flashcards
What factors affect microbiota composition?
Genetics, age, gender, antibiotics, environment, diet, occupation, birth mode, siblings.
Why is E. coli a useful water safety indicator?
Found only in intestines, short-lived outside → indicates faecal contamination.
What is the CFU/mL in unwashed lettuce if 13 colonies seen at 10⁻⁵ dilution, 100 µL plated?
13 × 100,000 = 1,300,000 (dilution)
× 100 (to get per mL) = 1.3 × 10⁸ CFU/mL
What is the CFU/mL in washed lettuce if 9 colonies at 10⁻⁵, 100 µL plated?
9 × 100,000 × 100 = 9 × 10⁷ CFU/mL
What size filter removes both vegetative cells and spores?
0.2 µm — effective for most bacteria.
Why might spores pass through a 0.8 µm filter?
They’re small, tough, and more resistant than vegetative cells.
which survives heat better: spores or vegetative cells?
Spores – survive even autoclaving if not long enough.
what is beta haemolysis
complete lysis of red blood cells, visible around colonies that are grown on blood agar plates
several bacterial species release virulence factors called hemolysis to do this
benefit = enhancement of acquiring iron from environment
macconkey agar
Selective medium for Enterobacteriaceae
Differential medium for fermentation of
lactose
The fermentation of lactose in the medium decreases
the pH changing the indicator to pink
chromID agar
Chromogenic (colour producing) agars
rely on the ability of a microbe to break
down or use a specific chromogenic
substrate in the medium
ChromID C. difficile agar contains a
chromogenic substrate. After esculin in
the agar is hydrolysed by a glucosidase
enzyme from the bacteria, glucose and
esculetin react with ferric citrate to give
black colonies indicating C. difficile is
present.
mannitol salt agar
salt tolerant colonies present and phenol red indicator in agar change to yellow which indicates fermentation of mannitol and production of acidic products - colonies are small circular and colourless
Using antibodies to diagnose Streptococcus pyogenes infection
The purpose of this experiment is to demonstrate an immunological method applied to the diagnosis of a bacterial infection.
An important aspect is that whilst the two assays utilise agglutination and
whilst the readout looks identical, the CRP assay is used to detect antigen whilst the
ASO assay is used to detect antibody.
