Microbiology

Question 1

initial step in identifying bacteria

Answer 1

gram stain

Question 2

benefits of quick stain

Answer 2

quick and easy

Question 3

results of gram stain

Answer 3

positive - purple

negative - red

Question 4

example of gram -ve

Answer 4

E coli

Question 5

example of gram +ve

Answer 5

staphylococcus aureus

Question 6

gram stain protocol

Answer 6

pick up colony using sterile plastic loop and make suspension on slide with drop of PBS water
dry with hairdryer
place slide on staining rack
add crystal violet to cover slide and leave for 1min
rinse with tap water
cover with alcohol - decolourise soln - leave 10s
immediately rinse with tap water
cover with safranin leave for 1min
gently rinse with tap water
blot excess liquid with tissue
inspect

Question 7

what can be seen ny microscopy

Answer 7

the shape of the bacteria (rod/coccus)
size
grouping arrangements

Question 8

shape of coccus

Answer 8

spherical

Question 9

grouping arrangements

Answer 9

clusters or chains or single bacteria

Question 10

what is shown from a MacConkey agar plate

Answer 10

lactose fermenter - red

lactose non-fermenter - yellow/colourless

Question 11

purpose of blood agar plates

Answer 11

pathogens produce haemolysins - substances that destroy/lyse RBC in blood containing media - haemolysis
agar plates used to show the different types

Question 12

alpha haemolysis

Answer 12

very small zone

colonies appear green

Question 13

beta haemolysis

Answer 13

large clear zone haemolysis around the colonies

Question 14

gamma haemolysis

Answer 14

no haemolysis

Question 15

purpose of oxidase test

Answer 15

determine if organism produces cytochrome C oxidase

oxidase +ve bacteria are aerobic and use O2 as an electron receptor in respiration

Question 16

test strip of oxidase test

Answer 16

contains tetra methyl-p-phenylenediamine (TMPD)
redox indicator - chemical that changes colour depending on the oxidation state of the molecule) and acts as artificial electron acceptor
colourless when reduced and dark blue/purple when oxidised

Question 17

method for oxidase test

Answer 17

use strips
rub paper pad on the strips onto bacterial colonies on the agar plate
watch for colour change

Question 18

catalase test

Answer 18

hydrogen peroxide toxic end product of aerobic breakdown of sugars
catalase break H2O2 into O2(g) and H2O

Question 19

method for catalase test

Answer 19

pick loopful of bacteria and place with H2O2

bubbles = catalase +ve

Question 20

coagulase test

Answer 20

check for presence of coagulase - clumping factor which reacts with fibrinogen = clots
used to distinguish different types of staphylococcus

Question 21

method for coagulase test

Answer 21

shake test reagent from kit
add 1 drop test reagent to test circle
using plastic loop pick up bacterial colonies - mix with reagent in test circle
if there is clotting - bacteria are coagulase +ve
= staphylococcus aureus