Labs

Question 1

Gram stain

Answer 1

Crystal violet - 1min
Gram's iodine - 1min
Decolourise
Safranin - 1min 
Examine at 1000x magnification under oil immersion

Question 2

E.coli features

Answer 2

Gram-negative rod shaped, green sheen on EMB agar, facultative anaerobe, lactose fermenter

Question 3

Staphylococcus. aureus

Answer 3

gram positive coccus, catalase positive, coagulase positive

Question 4

Candida albicans

Answer 4

fungi, diploid, yeast or hyphae, pseduohyphae

Question 5

Moxarella catarrhalis

Answer 5

gram negative, coccus, diplococcus, bean shaped

Question 6

Moulds stained with?

Answer 6

Lactophenol

Question 7

Ziehl-Nielsen stain

Answer 7

Carbol fuchsin - 5min
Wash
Acid fast cells appear pink due to mycolic acid

Question 8

Inhibiting factor for most microbes

Answer 8

Lack of water

Question 9

Autoclaving

Answer 9

Using heat and pressure to sterilise

Question 10

Alpha haemolytic

Answer 10

Green

Question 11

Beta haemolytic

Answer 11

Transparent

Question 12

Gamma haemolytic

Answer 12

Red

Question 13

Novobiocin sensitivity test

Answer 13

Used after coagulase negative
Sensitive = S.epidermidis
Resistant = S.saprophyticus

Question 14

Optochin senstivity

Answer 14

Use after alpha haemolysis
Sensitive = S.pneumoniae
Resistant = ‘viridans’ streptococcus

Question 15

Bacitracin sensitivity

Answer 15

Use after beta haemolysis
Sensitive = S.pyogenes
Resistant = Group B,C,G streptococcus
confirm these tests with grouping test

Question 16

Bile Esculin agar

Answer 16

Use after gamma haemolysis
Growth = enterococcus species
No growth = further tests
Black = positive
White/yellow = negative

Question 17

Endospores: surviving heat

Answer 17

Diplocholinic acid with Ca2+ form complex in endospores allowing core to dehydrate by absorbing water making it heat resistant. Found in Bacillus subtillus. Complex can also insert itself between base pairs making it more stable

Question 18

Identifying Pseudomonas sp

Answer 18

Oxidase positive
Straight rod
Grows on nutrient agar with green/blue pigment
Grows on MAC without fermentation so white colonies
Grows well on Pseudomonas Chromagar with a blue halo

Question 19

Identifying E.coli

Answer 19

Negative oxidase test
Grows with lactose fermentation on MAC agar (pink)
Grows on EMB agar with metallic green sheen

Question 20

Identifying Klebsiella and Enterobacter species

Answer 20

Negative oxidase test
Grows with lactose fermentation on MAC agar (pink)
Grows on EMB agar with pink colonies

Question 21

Identifying Serratia species

Answer 21

Red on nutrient agar plate
Negative oxidase test
Grows without lactose fermentation on MAC agar (white)
Grows with black/brown colour on BE agar

Question 22

Identifying Shigella species

Answer 22

Negative oxidase test
Grows without lactose fermentation on MAC agar (white)
Red colonies of XLD agar

Question 23

Identifying Salmonella species

Answer 23

Negative oxidase test
Grows without lactose fermentation on MAC agar (white)
Colonies with dark center on XLD agar

Question 24

Identifying proteus species

Answer 24

Oxidase negative
Grows without lactose fermentation on MAC agar (white)
Swarming (no distinct colonies of nutrient agar)