Microbiology: Lab Exercise 12-Counting Bacteria In Milk Using Pour-Plate Method

Front 1

Flash Pasteurization method

Back 1

Flash Pasteurization method - (HTST)

(1) HIGH Temperature/Short-Time method
(2) 161 degrees F/ 15 seconds

see CH 27 pg 820

Front 2

Vat Pasteurization Method

Back 2

Vat Pasteurization Method -

(1) LOW temperature
(2) holding method (longer time)
(3) 145 degrees F/ 30 MIN

Front 3

Pour-plate method

Back 3

Pour-plate method -

(1) Serially diluted samples of milk are mixed w/sterile agar
(2) Pour into sterile petri dishes
(3) Incubate in order to view & count bacterial colonies in agar

Front 4

How do you estimate the viable number of bacteria present in the original sample.

Back 4

Estimating viable # of bacteria:

"# OF COLONIES (on an agar plate)" x "DILUTION FACTOR of the sample"

EXAMPLE:
# of Colonies:(1/4 of petri dish =18)
or 18 x 4 = 72

Dilution Factor: 10 ^4 (10,000)

Viable Bacteria = 72 x 10^4

Front 5

Explain why just counting the # of bacteria (in milk) is NOT ENOUGH for judging the safety of the product?

Back 5

Problems that can be overlooked:

(1) low bacterial count DOES NOT mean bacteria are not PATHOGENIC
(2) ANAEROBIC bacteria may NOT be counted
(3) Bacterial clusters may form a SINGLE COLONY

Front 6

If you observe very few colonies or too few colonies in a petri dish why does this happen?

Back 6

Errors in calculation:

(1) INACCURACY in pipetting- volume of milk may be inaccurate
(2) CONTAMINATION- by using same pipettes in serial dilution

Front 7

Give methods that can be followed while milking cows and storing milk to control the microbial growth in the milk

Back 7

To kill microbes:

(1) Flash pasteurization method
(2) Vat pasteurization method

Front 8

Give at least (3) pathogenic bacteria that could be found in the milk. What diseases do these bacteria cause?

Back 8

Pathogenic bacteria in Milk:

(1) Listeria monocytogenes
CAUSES: Listerosis

(2) Yersinia Enterocolitica
CAUSES: Gastroenteritis

(3) Campylobacter Jejuni
CAUSES:Campylobacteriosis

Front 9

Listeria monocytogenes

Back 9

Listeria monocytogenes (Gram +)

CAUSES: Listerosis

GROWTH CONDITIONS:
(1) Can resist extreme temp. Heat/Freezing

SYMPTOMS
(1) Flu-like symptoms
(2) persistent fever
(3) vomiting
(4) diarrhea
(5) nausea.

Front 10

Yersinia Enterocolitica

Back 10

Yersinia Enterocolitica

CAUSES: Gastroenteritis

SYMPTOMS:
(1) similar to APPENDICITIS
(2) vomiting
(3) diarrhea
(4) abdominal pain
(5) fever

Front 11

Campylobacter Jejuni

Back 11

Campylobacter Jejuni (Gram -)

CAUSES:Campylobacteriosis

CONDITIONS:
(1) Needs small amts of O2 to grow

SYMPTOMS:
(1) Bacterial diarrhea
(2) abdominal pain
(3) headache
(4) muscle pain
(5) nausea
(6) fever