2. Identification of bacterial cells Flashcards
name two culture collections across the world
American type culture collection (ATCC)
national collection of type cultures (NCTC) -> public health england
what does NCIMB stand for
national collection of industrial, food and marine bacteria
how many classes of bacteria are there
4
which class of bacteria: 1. can cause severe disease?
class 3
which class of bacteria: 2. is safe to use (non-pathogenic)
class 1
which class of bacteria: 3. is incurable
class 4
how many strains of class 4 bacteria are there
none
name a class 4 virus
ebola
what are class 2 bacteria
cause mild, treatable disease, can be worked with in the lab
how does Gram staining work
crystal violet applied to samples, if Gram-positive, crystal violet will bind tightly to peptidoglycan and following an ethanol wash, be stained purple. (positively purple)
if not, following ethanol wash, and counter staining with safranin, will stain pink
(negative pink)
we can identify shapes based on morphology, name some shapes
cocci (circle)
rods
spiral
corkscrew
how do we measure oxygen tolerance
inoculate broths with bacterium, note location of growth
where will obligate aerobe’s grow in broth medium, what does this show?
at the top
- preference for oxygen
where will obligate anaerobe’s grow in broth medium, what does this show?
growth at the bottom
- no tolerance for oxygen
where will aerotolerant anaerobe grow in broth medium, what does this show?
bacterium distributed throughout, tolerance for presence and absence of oxygen
how can we identify the presence of endospores
malachite green stains bacteria black and endospores appear white
what type of cells are endospores found in
Gram positive bacteria only
where do endospores form under, what does this mean?
unfavourable conditions
they are highly resilient to heat, drying, radiation and chemicals
how do you remove endospores
a strict course of antibiotics taken for months to eradicate further infections
describe the structure of endospores (2)
- contain calcium dipicolinate
2. have special proteins to protect their DNA.
how can cell motility be measured
place a sterile needle containing the bacterium colony into sloppy agar. this medium contains a dye which stains cells red.
non-motile bacterium will remain in one place, motile bacterium will move around the medium.
what does catalase convert
toxic hydrogen peroxide into water and oxygen
how do you perform the catalase test, what would a positive result show?
- adding a bacterial culture to a bubble of hydrogen peroxide
- if catalase is present, bubbles of oxygen will be produced
what does kovac’s reagent test for
the presence of cytochrome C and oxidase
what is a positive oxidase test result
change in colouration from white to purple
what can a melt curve show to help us classify bacteria
- melting temperature is relative to nucleotide composition
- higher guanine-cytosine concentration = higher melting temperature = more energy required to separate the strands
how can we test whether a bacterium uses lactose
placing bacterium in a growth medium containing only lactose as the sugar source , we can then measure growth
how can we detect growth in lactose medium
when there is growth, the pH changes and oxygen is produced, the solution turns from red to yellow
what infection is known to produce black insoluble hydrogen sulphide
salmonella
what is hydrogen sulphide produced from
fe2+ and S2-
how do media kits work for identifying clinical isolates
test kit contains various dehydrated tests
you add the bacterium to each test strip and incubate for 24 hrs
then measure colour change
each change is assigned a number value which using the website helps inform what microbe you have
how do macConkey agar plates help to distinguish bacteria
contains a pH indicator,
lactose fermenting bacteria produce pink colonies,
non-lactose fermenting bacteria will produce yellow colonies
how do chromagar plates help to distinguish bacteria
medium contains artificial substrates that when hydrolysed by yeast produce specific colourations
e.g. candida tropicalis = blue
what do beta haemolysis zones show, what bacteria does this
show where RBCs have been digested,
e.g. streptococcus
what medium enhances N. gonorrhoeae growth
thaymer-martin medium
Name 2 selective media
Thaymer-Martin (gonorrhoea)
Mac Conkey agar
How is macconkey agar selective
Contains bile salts = prevents Gram-positive growth
Name two differential media
Blood agar
Chromagenic
Chromagar is both a nutrient and differential media, why?
Funghal produce enzymes that react with different compounds in the medium, producing colonies of different colours
What is Ziehl- Neesen another name for
Acid fast technique
How does ziehl-neesen work
Uses fluorescence or stain to highlight microorganisms
What is Ziehl- neesen used for
Cryptosporidium
What’s is an advantage of Ziehl- neesen
Rapid results, cheap, targeted to the pathogen
Give an example of a coloured colony produced on chromager
Candida tropicalis = blue colonies
Describe chocolate agar, give an example of the colonies produced
Differential media - Identification of colony colour
Contains lysed RBCs
Neisseria gonorrhoea = white colonies
Haemophililus = colourless
How is blood agar differential
3 different types of haemolysis can be seen on this plate
- alpha, beta, gamma (no haemolysis)
Give an example of a pathogen thAt conducts beta haemolysis
Streptococcus pyogenes
