Micro December 2018

1

Prior to inoculation of pasteurized whole milk, butter and pasteurized carrot juice, the

inoculating broth cultures were heat stressed in a water bath for 10 ± 1 min at 50 ± 1°C. The 2

degree of injury of each culture was estimated by plating an aliquot of diluted culture onto VRB 3

agar tryptic soy agar (TSA) for coliform determination, and VRB with MUG and TSA for E. coli . 4

The agar plates were incubated at 35 ± 1°C for 24 ± 2 h and the colonies enumerated. The 5

6

degree of injury was estimated as:

n

1(

100 )

x

select

−

n

7 8

nonselect

Where n select = number of colonies on selective agar and n nonselect = number of colonies on non- 9

10

selective agar. Results of the heat are listed in Table 11.

11

The stainless steel and sealed concrete were evaluated after artificial contamination. Each

test portion area (4” x 4”) was evenly inoculated with 250 µL of mixed coliform and E. coli 12

culture diluted in 0.1% Peptone Water and allowed to dry for 16–24 h at 20–25 o C. Prior to 13

sampling, 10 mL of Letheen broth was added to each dry sampling sponge. Both environmental 14

matrices were sampled using horizontal and vertical sweeping motions. Sampling sponges were 15

held for a minimum of 2 h at 20–25 o C prior to analysis. To determine the inoculation level for 16

the environmental surfaces, aliquots of each inoculating organism was plated in duplicate onto 17

18

TSA and then enumerated.

19

20

3M Petrifilm Rapid E. coli/Coliform Count Plate Count Method

21

17