Water microbiology Part 2

Question 1

Heterotrophic plate count is formerly known as?

Answer 1

Standard plate count

Question 2

A procedure for estimating the number of LIVE heterotrophic bacteria

Answer 2

Heterotrophic plate count

Question 3

What is the unit for heterotrophic plate count?

Answer 3

Colony forming Units (CFU)

Question 4

Causes no heat shock
Colonies are ON the agar (Easy transfer and distinguish)

Answer 4

Spread Plate method

Question 5

What is the amount of sample for Spread plate method?

Answer 5

0.1 - 0.5 mL

Question 6

Simple to perform
Colonies are small and compact
Less tendency to encroach

Slow grower and difficult to transfer
Thermostatically controlled water bath (Heat shock)

Answer 6

Pour plate

Question 7

What is the amount of sample can be use in pour plate?

Answer 7

0.1 - 2mL

Question 8

No heat shock

Expensive (Filter and vacuum pump)
Small display area
Possible damage to cells due to vacuum

Answer 8

Membrane filtration technique

Question 9

What is the amount of sample for Membrane filtration technique?

Answer 9

100mL

Question 10

Size of pore in filtration?

Answer 10

0.2 or 0.4 mm

Question 11

Procedure for HPC spread plate?

Answer 11

1. Label Plates
2. Mixed the bottle (Invert)
3. aseptic
4. Transfer by using serological pipette (0.1mL)
5. Place it on the middle
6. Spread using glass spreader or metal spreader
   6.1. Aseptic by putting it on ethanol and flame it
7. Spread it evenly
8. w8 15 mins to dry out
9. invert it for incubation

Question 12

Procedure for HPC pour plate

Answer 12

1. Label
2. Mix water sample
3. Aseptic the bottle
4. Transfer 1 mL on empty petri dish
5. Add molten plate count agar
6. Swirl it to mix and let the cover open

Question 13

What is the temp for molten agar?

Answer 13

44 -46C

Question 14

For pour plate what is the first thing to do?

Answer 14

Prepare dilution water

Question 15

What is the water used in dilution water?

Answer 15

Buffered water / Peptone water

Question 16

How to prepare Stock phosphate buffer solution?

Answer 16

Dissolve 34g potassium dihydrogen phosphate in 500mL reagent grade water (Deionized water)

pH 7.2 +- 0.5 with 1N sodium hydroxide

Dilute to 1L with reagent grade water

Question 17

2nd steps on creating dilution water?

Answer 17

1.25 mL Phosphate buffer solution
+
5.0 mL of Magnesium chloride (81.1g / L)
+
Dilute it till 1L using reagent grade water

Question 18

How to prepare peptone water?

Answer 18

10% solution = 10g / 100mL
0.1% solution = 1g / 1000mL

Final pH: 6.8

Question 19

How many minutes can bacteria die that is suspended in a dilution water?

Answer 19

30 mins at room temp

Question 20

2nd step in preparing pour plate?

Answer 20

Prepare molten plate count agar?

Question 21

What is the pH required for molten plate count agar?

Answer 21

7.0+- 0.2

Question 22

Temp for maintaining the molten plate count agar?

Answer 22

44 and 46C

Question 23

How many hours should Molten plate agar be used?

Answer 23

Not longer than 3 hours

Question 24

Size of Standard sterile glass?

Answer 24

65cm^2

Question 25

Size of pre-sterilized disposable plastic petri dishes?

Answer 25

57 cm^2

Question 26

Amount of PCA to be poured in a petri dish?

Answer 26

10-12 mL

Question 27

Incubation for Pour plate?

Answer 27

35+- 0.5 for 48 hours with humidity

Question 28

Average colonies to count?

Answer 28

30-300

Question 29

What is the appearance of colonies in pour plate?

Answer 29

Small banana shape colonies

Question 30

What is the reporting for "No colonies"?

Answer 30

<1.0 CFU/mL

Question 31

What is the reporting for "Less than 300 colonies per plate"?

Answer 31

_Count_est. CFU/mL (39 est. CFU/mL)

Question 32

How to report "If colonies exceed 300, and if there are fewer than 10 colonies/cm^2"?

Answer 32

Glass plate - Count in 13 squares in colony counter - Add - Multiply it by 5 Plastic plate - Count in 19 squares - Add - Multiple it by 3 _Count_est. CFU/mL (39 est. CFU/mL)

Question 33

How to report "If colonies exceed 300, and if there are greater than 100 colonies/cm^2"?

Answer 33

Glass plate - Reported as >6500 CFU/mL Plastic plate - Reported as >5700 CFU/mL

Question 34

What is the value that is satisfactory enough to drink?

Answer 34

<500

Question 35

What happens if the value for CFU is >500?

Answer 35

Unsatisfactory