Lesson 1: Bacterial structure, growth, enumeration and identification Flashcards
Gram positive bacteria
- More peptidoglycan than -ve, contains technoic acid and has no liposaccharides and less proteins
Gram negative bacteria
- Cell envelope can produce symptoms of disease (endotoxins)
- Rod shaped (bacilli) or spherical (cocci)
- Has a complex structure
- Outer membrane compromised of lipopolysaccharides
- Contains more proteins and lipid than +ve
Features of the cytoplasmic membrane
- Semi-permeable (only low Mr pass)
- Contains vomit pumps
- Many proteins and enzymes for bacterial survival
- Target to many antibiotics
Ribosomes
70s ribosomes made up of ribosomal protein and ribosomal RNA.
Flagellum
Bacterium mobility
Pilli (fimbrae)
Fine hair like filaments that are sneaker than flagella
Types of function for pilli
Adherence- attatchment
Antigenic- Chemotaxis
Genetic exchange- virulence: toxins
How does binary fission happen?
- Increase of cell mass
- Duplication of genome
- Cell membrane and cell wall separation
How is bacterial growth measured and what does the growth diagram tell us?
It is measured in change in population rather than mass or size, the diagram shows us lag phase, growth phase, stationary phase and death phase.
What is formula used to tell us the total population at the end of a giving period (starting with 1 cell)
b = 1x2^n
n is number of generations
Chemical requirements for growth
- Energy source
- Source of electrons
- Carbon source
- Nitrogen source
- Oxygen, sulphur and phosphorous
- Ions
Physical requirements for growth
Optimum:
- Temperature (depends on type of bacterium)
- pH 6.5-7.5
Preventing growth using pH
- extreme pH prevent microbial growth
- neutral pH: bacterial spoilage
- pH>8: rare spoilage (soap based emulsion)
- low pH: spoilage by moulds and yeast e.g fruit juice flavoured syrups
Water Activity
Water activity of aqueous formulations can be lowered to decrease microbial growth
What do sterile pharmaceutical products need to be ?
- sterile on dosage form and other preparations labelled sterile
- needs to comply with test for sterility
Non sterile pharmaceutical products
- prep for topical use, use in resp tract, oral and rectal administration + containing raw materials
- herbal remedies
Enumeration/Colony count
Single bacterium in OG culture is plated to give rise to a viable colony counted in cfu
What are some plate count methods?
- pour plate
- spread plate
Where can contamination or bacterial growth happen?
- Cosmetics
- Emulsion
- Trans-parenteral nutrition bag
Why is rRNA important in classification?
It’s present in all living celss and its sequence forms basis pf phylogeny (study of evolution of organisms)
Traditional methods of bacterial identification
- Cultivation- growth requirement
- Cultivation- selective agar
-Biochemical profiling - Serological testing
Advantages of tradiitonal bacterial identification methods
- No specialised equipment
- Can be done by most laboratories
- Minimal training
Disadvantage of traditional bacterial identification methods
- 24-72 h for results
Advantage of newer bacterial identification methods
- Faster -6hrs
- Some have low running costs (e.g
MALDI-TOF MS) - More samples required so more accurate
Disadvantage of newer bacterial identification methods
- Specialised equipment required (£)
What happens is gram positive bacteria in gram staining tests?
They remain blue because of its low lipid content (which lipid is needed for retention of iodine crystal violet complex)
What happens to gram negative bacteria in staining tests?
It turns colourless because of its high lipid concentration in cell wall outer layers which facilitates release of iodine crystal violet complex leaving cell colourless.
Staph aur structure
Gram positive, facultative anaerobe, catalase-positive cocci
E.coli structure
Gram negative enetric rod, faculative anaerobe, pink in MAC agar
Pseudonomoas
Gram negative rod
What is a facultative anaerobe?
makes ATP by aerobic respiration if oxygen is present, but is capable of switching to fermentation if oxygen is absent.
