Microbiological Quality of Self Serve Salad Bars

July - September 1998

Report prepared by Geoff Millard

Objective

This survey was designed to determine the microbiological status of Self-Serve Salads available in the ACT.

Background

Self-Serve Salads are widely available in the ACT. Previous surveys conducted between January June 1995 and October - December 1996 highlighted some problems with handling, storage and cross contamination. A comparison with the previous surveys has been made where possible.

Standards

The Australia New Zealand Food Authority (ANZFA) does not have microbiological standards for Self-Serve Salad Bars but other organisations have prepared and used "inhouse" microbiological guidelines for this product including South Australia (SA) Health Commission, Choice and Western Australia State Health Laboratory. The Health Protection Service (HPS) decided to use the Western Australia State Health Laboratory guidelines (WA) for this survey (See Appendix 1 for details).

Survey

Between July and September 1998, the ACT Government Analytical Laboratory (ACTGAL) collected 76 Self-Serve Salad (SSS) samples from 17 different establishments. Samples were purchased as consumer items over the counter by ACTGAL staff and analysed by the Microbiology Unit. The samples covered the range of available Self-Serve Salads from food-halls and supermarkets. All of the samples were assessed for overall hygiene quality by Standard Plate Count (SPC), Escherichia coli (E. coli) count and coagulase-positive Staphylococcus (Coag+Staph) count. The specific food pathogens tested for were Bacillus cereus (B. cereus), Listeria monocytogenes (L. monocytogenes) and Salmonella sp. The survey collected a number of different SSS samples from each outlet and each outlet was only tested once.

Results

Standard Plate Count (SPC)

Graph 1

The median SPC value was 185,000 cfu/g. Forty-six (63.9%) samples had an SPC less than 1,000,000,cfu/g, nineteen (26.4%) had an SPC between 1,000,000 and 10,000,000 cfu/g, seven samples had an SPC greater than 10,000,000 cfu/g. There were no samples with an SPC greater than 100,000,000 cfu/g. SPC counts for 4 samples could not be determined as more than 25% of the surface area of the plate was covered in spreading organisms.

Escherichia coli

E. coli was detected in eleven (14.5%) of samples with the range and median of positive samples tabulated in Table 2.

Table 2

 

Test Organism

% positive

Range cfu/g

Median of the positive samples cfu/g

E. coli

14.5% 
(11 samples)

2 - 540

27

 

Coagulase Positive Staphylococcus

Coagulase-positive Staphylococcus was detected in three (3.9%) samples with the range and median of positive samples tabulated in Table 3.

Table 3

 

Test Organism

% positive

Range cfu/g

Median of the positive samples cfu/g

Coagulase-positive Staphylococcus

3.9% (3 samples)

50 - 4500

100

 

Bacillus cereus

Bacillus cereus was isolated from three (3.9%) samples with the range and median of positive samples tabulated in Table 4.

Table 4

 

Test Organism

% positive

Range cfu/g

Median of the positive samples cfu/g

Bacillus cereus

3.9% (3 samples)

3100 - 35000

9700

 

Salmonella

Salmonella was not isolated from any of the 76 samples tested for this organism.

Listeria monocytogenes

Listeria monocytogenes was isolated from seven (9.2%) of the 76 samples. Four positive samples were collected from the same outlet on the same day while the other 3 samples were random.

Discussion

Percentage compliance for the 1998 survey, utilising the WA guidelines is given in Table 5.

Table 5

 

Test Criteria

Satisfactory

 

Fairly satisfactory

Unsatisfactory

 

Unacceptable

SPC <1000000 cfu/g

63.9%

36.1%

E. coli cfu/g

90.8%

3.9%

5.3%

0%

Salmonella absent in 25 grams

100%

0%

L. monocytogenes absent in 25 grams*

90.8%

9.2%

Coagulase positive staphylococcus cfu/g

97.4%

1.3%

1.3%

0%

 

*While the WA Listeria monocytogenes guideline includes counts for the Fairly satisfactory, Unsatisfactory and Unacceptable categories, ACTGAL only determined the presence/absence for pathogen and did not perform counts. Therefore, this criterion can only be assessed as either satisfactory or unsatisfactory.

Comparison of all survey results.

The following table represents a comparison of results for surveys conducted in 1995, 1996 and 1998. The test criteria are based on the WA guidelines for a satisfactory result.

Table 6

 

 

Survey Date and % Satisfactory

Test Criteria

1995

1996

1998

SPC <1,000,000 cfu/g

Not performed

50

63.9

E. coli <10 cfu/g

81.3

90.8

92.1

Salmonella absent in 25g

100

100

100

Listeria monocytogenes absent in 25g

100

100

90.8

Coag+staph <100 cfu/g

95.3

98.2

96.1

 

The following trends can be seen from Table 6.

  • SPC results have improved from 1996 to 1998,
  • E. coli has steadily improved from 1995 to 1998,
  • Salmonella sp has maintained its satisfactory status,
  • Coagulase positive Staphylococcus results improved from 1995 to 1996 and declined marginally in 1998. Considering the low number of positive samples the differences between the years is probably not that significant,
  • The Listeria monocytogenes results declined significantly from the 1996 level, even though over 50% of the positive samples were collected on the same day from the same store.

Conclusion

This survey has identified that while Self-Serve Salads in the ACT have generally improved, the rise in the incidence of salad samples containing L. monocytogenes is of significant public health concern.

Bibliography

West Australia State Health Laboratory Service, Microbiological Quality of Ready to Eat Foods April 1999.

APPENDIX 1

West Australia State Health Laboratory Service guidelines for Microbiological Quality of Ready to eat foods.

Western Australia State Health Laboratory Guidelines Table 1

 

Test Criteria

Satisfactory

Fairly satisfactory

Unsatisfactory

Unacceptable

 

Unlikely to cause disease

Unlikely to cause disease, Indicate possible hygiene problems with food handling preparation.

May cause disease in some people. Food not manufactured hygienically.

Likely to cause disease in most people

 

Action: Nil

Action: If these results are produced regularly, examine hygiene and handling practices.

Action Investigate production practices.

Action Withdraw any food still on sale. Follow up with any known contacts. Investigate production practices

Bacillus cereus

<100/g

Between 100 and 1000/g

Between 1000 and 10,000/g

>10,000/g

Campylobacter sp

Not detected in 25g

-

-

Present in 25 g

Vibrio parahaemolyticus

Not detected in 25g

-

<1000 in 25/g

>1000 in 25 g

Coagulase positive Staphylococci

<100/g

Between 100 and 1000/g

Between 1,000 and 10,000/g

>10,000/g

Clostridium perfringens

<100/g

Between 100 and 1000/g

Between 1,000 and 10,000/g

>10,000/g

Listeria monocytogenes*

Not detected in 25g

Less than 10/g

Between 10 and 100/g

>100/g

Salmonella sp

Not detected in 25g

-

-

Present in 25g

E. coli count

<10/g

Between 10 and 70/g

>70/g

Contains verotoxigenic E. coli

 

*Special Note 1. These results are for the product at point of sale.

Special Note 5: Microorganisms are not always evenly distributed in food. Therefore, even if the food falls into the Fairly Satisfactory category it may be the source of infection.

Note: As a general guide, a SPC of less than 1,000,000 and a Total coliform count of less than 100 are considered satisfactory.

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Microbiological Quality of Self Serve Salad Bars.