Microbiology

Eduqas Biology Alevel component 1.4

Different shapes of Bacteria

Cocus= round

Spirillum= spiral

Bacillus= rod shaped

What are bacteria cell walls made of

largely peptidoglycan- a mixed polymer of hexose sugars and amino acids

How does cross-linking help with the cell wall

adds strength, flexibility, supports cells contents and protects cell of lysis

Features of gram positive bacteria

• thick peptidoglycan layer walls, meaning it can retain the crystal violet stain

• Retains crystal violet/ iodine complex stain,

• counterstain with safranin has no effect

• more susceptible to antibiotics and lysozymes

Features of gram negative bacteria

• thinner walls of peptidoglycan

• does NOT retain crystal violed/iodine complex and colour will be washed away by alcohol

• safranin counterstain stains it red

• layers of lipopolysaccherides which means they are

• not effected by lysozyme and resistant to peniciln

Why does gram negative bacteria not retain crystal violet stainm

outer lipopolysaccharide layer lost with the alcohol wash so crystal violet stain no longer there so can take up safranin stain

How to gram stain

-heat fix the bacteria

-stain with crystal violent

-seal stain with iodine

-decolourise with alcohol (if negative the stain will wash away)

-counter stain with safranin

Obligate aerobes

microorganisms that Need oxygen for metabolism/ to grow

Obligate anaerobes

microorganisms that require an absence of oxygen to grow/metabolise

Facultative anaerobes

Microorganisms that prefer to grow/ metabnolise in oxygen but can anaerobically

Genetic variance in bacteria

-random mutations that can be passed on to daughter cells by vertical transmission or other bacteria by horizontal transmission

Growing bacteria- nutrition

-require a carbon compound, usually glucose as an energy source

-a nitrogen source for amino acids

-growth factors like vitamins and mineral salts

Growing bacteria- Temperature

25-45° is favourable for most.

27° for mammalian pathogens

Growing bacteria- pH

-most favour slightly alkaline (7.4)

-ph of medium may change during growth

Bacterial growth chart

Growth chart- lag phase

Little growth but cells take yo water and carry out protein synthesis and produce enzymes

Growth chart- exponential phase

Population increases rapidly

growth chart- starionary phase

Dying at the same rate they are being produced

Growth chart- death phase

More are dying then being produced

Aseptic technique

-bunsen burner on a roaring flame for a convection current

-sterilise equipment by passing over flame

-keep lids in hands

-flame neck of agar bottle

-lids of petri dishes should not be taken fully off

-bit off tape NOT fully tape

-incubated upside down at 25degrees

culturing bacteria-serial dilutions

-take 1cm cubed of solution and add it to 9cm of water, MIX

-take 1 cm of this solution and add it to 9cm of water, MIX

-keep going until a spear cultured sample has a countable number of colonies

10^-1, 10^-2, 10^-3 ect

What is the equation for finding the original count of bacteria after a serial dilution?

number of colonies or cells x dilution factor= number of original cells

total cell count

counts living and dead

viable cell count

counts living bacterial

turbidimetry

the size of a population in a liquid culture can be measured by looking at the cloudyness using a colorimeter.- total cell count

What is the problem wiht assuming one colony is one cell

doesnt account for cells possibly clumping, meaning the estimate of cells is lower