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Evaluation of Easygel Card (now renamed to R-Card®) for detection of Aerobic Bacteria Counts

By Dr. Fu-Chih Hsu and Rebecca Wong  (Date: 2-4-2015)

Scientific Methods Inc.

I. Materials and Methods

Samples:         Garlic granulated (Tone’s Brand)

                        Honey ham (Carl Buddig, packaged)

                        Smoked sweet ham (Cherrywood, pre-sliced in the store)

                        Cocktail shrimp (cooked shrimp)

                        Ranch dressing (Kraft)

                        Ice cream (Prairie Farms)       

All samples were purchased local supermarket (Martine’s)

           

Sample preparation: 28 g of samples with 225 mL of phosphate buffered saline (PBS) in a stomacher bag with a pre-filter were stomached for 15 sec using a Pulsifer (Microgen Bioproducts Ltd, UK).  The supernatant was then poured from the bag containing pre-filter  to remove large debris.  A serial 10-fold dilution was prepared using sterile PBS.   One mL of sample was added onto Easygel Card™, or Petrifilm™.  Pour plate method was used for aerobic plate count agar (APC) and Easygel™ Total Count.  All samples were incubated at 35⁰C for 24 to 48 hr.  All samples were tested in two trails and duplicate plates.

 II. Results

The results from Table 1 indicate that Easygel Card™ total count is comparable to any medium tested.  In ranch dressing, Easygel Card™ total count had the highest counts.  Moreover, most results could be obtained at 24 hr incubation for all food samples tested by Easygel Card™ total count because of obvious red colonies.  Easygel and APC require at least 40 hr incubation for smoked ham, cooked shrimp, and ice cream samples because the counts at 24 and 48 hr are significant lower.  Many colonies on both plates are too tiny to count at 24 hr incubation.   Overall, the

 

Table 1. Total bacterial counts by 4 different media in various food samples

 Food

APC (cfu/g)

Easygel (cfu/g)

Easygel Card (cfu/g)

3M (cfu/g)

Garlic powder

1.40 ± 3.0 x 105

1.27 ± 4.1 x 105

1.10 ± 4.2 x 105

9.50  ± 2.1 x 104

Honey ham

   35 ± 7

   90 ± 14

   30 ± 28

    25 ± 21

Smoked ham

3.60 ± 0.7 x 103

2.95 ± 1.2 x 103

2.85 ±1.1 x 103

1.10  ± 0.3 x 103

Cooked shrimp

3.00 ± 2.1 x 104

3.67 ± 2.3 x 104

2.93 ± 1.8 x 104

2.20  ± 1.2 x 104

Ice cream

2.28 ± 4.2 x 104

1.49 ± 3.9 x 104

2.34 ± 2.8 x 104

1.99 ± 0.5 x 104

Ranch dressing

5.20 ± 0.8 x 102

6.20 ± 3.3 x 102

9.80 ± 6.3 x 102

6.40 ± 2.8 x 102

Counts by Petrifilm™ Total Count were lowest among food tested with the exception of ranch dressing.   It is interest that pre-sliced ham was 2 log more that packaged ham.  However, more studies are needed to confirm this observation.

Pictures 1 to 4 show colonies of Easygel Card™ and Petrifilm™ Total Count on garlic powder, ham, ranch dressing and cooked shrimp. 

Picture 1.  Colonies from garlic powder in Easygel Card™ and Petrifilm™ Total Count after 20 hr incubation. 

Picture 2.  Colonies from smoked ham in Easygel Card™ and Petrifilm™ Total Count after 40 hr incubation. 

Picture 3.  Colonies from ranch dressing in Easygel Card™ and Petrifilm™ Total Count after 20 hr incubation. 

Picture 4.  Colonies from cooked shrimp in Easygel Card™ and Petrifilm™ Total Count after 40 hr incubation. 

Picture 5.  Colonies from ice cream in Easygel Card™ and Petrifilm™ Total Count after 20 and 40 hr incubation (above: 20 hr; below:40hr)

From the pictures, colonies from Easygel Card™ are bigger than the colonies on Petrifilm™ Total Count, especially in ice cream sample.   It is impossible to have an accurate count in  Petrifilm™ Total Count without magnification.  

III. Conclusion

The overall results from 6 samples including a dry product (garlic powder), meat (honey and smoked ham), seafood (cooked shrimp), dressing and diary product (ice cream)  by Easygel

Card™ Total Count are as good as the traditional method, aerobic plate count agar, and are better than Petrifilm™ Total Count.  Moreover, it is more convenient to use Easygel Card™ Total Count because no additional stamp is required unlike Petrifilm™ Total Count.  Total count can be obtained at 24 hr incubation for most food samples by Easygel Card™ Total Count, but it still requires additional 20 hr incubation for certain types of food, such as cooked shrimp and ice cream.  This study has demonstrated that it is feasible to detect aerobic bacteria counts from various types of food by Easygel Card™ Total Count.  A more complete study is necessary to validate Easygel Card™ Total Count for an approval by AOAC.

   

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