Food Survey Reports 2001-2002

Microbiological quality of kebabs

July 2002 November 2002

Report prepared by Simon Rockliff and Sheba Khan

Objective

  • To determine the microbiological status of kebabs in the ACT to ensure their safety.
  • Determine the current range of food handling practices in the kebab industry and to establish whether or not pathogens can be transmitted via kebab meat.

Background

Kebabs are a traditional Middle Eastern meat dish made by stacking layers of meat such as chicken, beef or lamb, which is seasoned, marinated and sliced or minced, onto a vertical skewer to form a cone or cylinder shape. The skewer rotates in front of a vertical heat source and as the outer layer of meat is cooked, it is carved off in slices. The meat is then served in flat bread together with salads and dips.

Kebabs are a very popular type of convenience take away food. The preparation and cooking practices of kebabs have the potential to allow the consumption of undercooked meat that may harbour pathogenic bacteria.

Following a number of cases of illness that had circumstantial links to the consumption of kebabs1, a survey was conducted to assess the microbiological safety and quality of cooked kebab meat (chicken, lamb and beef) from vertical spits. Environmental Health Officers randomly selected and sampled businesses selling meat cooked on a vertical rotating spit.

Survey

This survey was conducted between the 03 July 2002 and 27 November 2002. During this period samples from a range of ACT retail outlets were collected randomly by Environmental Health Officers (EHO) and processed by the Microbiology Unit of ACTGAL.

Standards

Kebabs have been categorised as a ready-to-eat food. The Food Standard Australia New Zealand (FSANZ) Draft Guidelines for the Microbiological Examination (RTE) Foods are shown in Table 1 are applicable to this food.

Table 1 Microbiological Examination (RTE) Foods

 

Table  Microbiological Examination (RTE) Foods
cfu/g = colony forming units per gram of material analysed.
# Pathogenic strains of E. coli should be absent.
* Foods with a long shelf life stored under refrigeration should have no L. monocytogenes detected in 25g.
** The detection of L. monocytogenes in ready-to-eat foods prepared specifically for “at risk” population groups (the elderly, immuno-compromised and infants) should also be considered as potentially hazardous.

Results

A total of 82 samples of whole kebabs were tested for the organisms listed in Table 1. Samples consisted of 36 chicken, 20 lamb, 22 beef and 4 vegetarian Kebabs. Results of the survey are tabulated in Table 2 below.

Table 2 Results of the survey

 

Table  Results of the survey
NA= Not applicable.
*expressed as colony forming units per gram.

Escherichia coli
82.3% of the samples showed a satisfactory microbiological quality. E. coli was detected in 14 of the 79 samples tested. 15.2% of samples were marginal and 2.5% were categorised as unsatisfactory. The positive results isolated ranged from 7-460 colony forming units/gram (cfu/g). The vegetarian kebab had the maximum 460 cfu/g E. coli present. No re-samples were requested for the results, which fell into either the marginal or the unsatisfactory category.

The presence of E. coli is undesirable because it is indicative of poor hygiene conditions, which have lead to contamination or inadequate heat treatment. Ideally E. coli should not be detected and as such a level of <3 cfu/g has been given as the satisfactory criteria for this organism. Levels exceeding 100 cfu/g are unacceptable and indicate a level of contamination, which may have introduced pathogens or that pathogens, if present in the kebabs prior to processing, may have survived.

Coagulase positive Staphylococci
Coagulase positive Staphylococci were detected in only 8 (10.1%) of the tested samples. 89.9% of the samples were free of coagulase positive staphylococci indicating good microbiological quality. The highest coagulase positive Staphylococci contamination was found to be 450 cfu/g. This particular sample was also contaminated with E. coli. None of the samples, which tested positive for coagulase positive Staphylococci, exceeded 1000 cfu/g and thus were found to be compliant with the Guidelines. No resample was requested for the results falling in the “marginal” category. Contamination of kebabs with coagulase-positive Staphylococci is largely as a result of human contact. Contamination should be minimised through good food handling practices and growth of the organism prevented through adequate temperature controls.

Salmonella spp.
No Salmonella was isolated from any of the kebab samples in this study. The results indicate that 100% of the samples were satisfactory and of good microbiological quality.

Listeria monocytogenes
Listeria monocytogenes was isolated from 10 (12.2%) samples categorising these as marginal. 87.8% of the samples tested were satisfactory. Three of the samples positive for Listeria monocytogenes were also positive for E. coli. These results indicate that this sample may have been cross-contaminated due to unhygienic conditions. According to the FSANZ Guidelines, no Listeria monocytogenes should be detected in the sample to pass the satisfactory criterion. Re-samples were requested for all samples in which Listeria monocytogenes was isolated. Only one sample was received and re-sampled. A semi-quantitatively analysis of the re-sample was undertaken with L. monocytogenes isolated at a range of 1-10 organisms per gram.

Higher levels of L. monocytogenes (>100 cfu/g) definitely indicate a failure with food handling controls and based on current epidemiological evidence are considered a public health risk.

Clostridium perfringens
No Clostridium perfringens was isolated from any of the kebab samples in this study. 100% of the samples indicated good microbiological quality.

Figure 2 below, shows the microbiological quality of kebabs tested in this survey.

Figure 2 Microbiological quality of kebabs

Figure microbiological quality of kebabs

Discussion

Overall the standard of microbiological quality of kebabs is good. None of the 82 samples tested contained Salmonella spp. or Clostridium perfringens. Only 2 samples were unsatisfactory as they contained 100 cfu/g of E. coli. Results outside of acceptable microbiological limits are indicative of poor hygiene or food handling practices. Listeria monocytogenes was detected in 10 samples categorising them as marginal. 12 samples containing E. coli were also marginal in their microbiological quality. Marginal results are borderline in that they are within limits of acceptable microbiological quality but may indicate possible hygiene problems in the preparation of food.

The way the kebab rotating spit is designed where the meat cooks from the outside to the inside, even when the surface temperature may be above 75C, means the internal temperature of the meat could potentially be in the danger zone of 5-60C. This temperature zone could provide an ideal temperature for the pathogenic bacteria to multiply. Even if the surface temperature is high enough to destroy food poisoning bacteria, the meat can still be cross-contaminated during slicing by fluids draining from the inside of the vertical raw meat skewer.

Results of this survey indicate that there is evidence that inadequate cooking temperatures/ times and/ or cross contamination of kebabs was occurring due to improper or unhygienic handling of the food. Use of a second cook step to further cook the sliced meat prior to serving would help destroy bacteria that could have survived the initial cooking step.

Re-samples

Health Protection Services (HPS) Sampling Working Group needs to evaluate its re-sampling protocol for future surveys. Re-sampling should be requested when a sample fails to meet the acceptable microbiological standard. Presently re-samples are requested only when Listeria monocytogenes or Salmonella spp. is isolated. Re-samples need to be also requested for other microbiological bacteria isolated at Unsatisfactory levels.

Conclusion

Overall, the microbiological quality of kebabs sold in the ACT is good. However poor processing hygiene can give unsatisfactory or marginal results, which are not compliant to the FSANZ Guidelines. For the premises that gave unsatisfactory results further sampling and investigation should be undertaken to determine whether food handling controls and hygiene practices are adequate.

Recommendation

  • That a future survey be conducted to confirm the proper handling / processing of the product is occurring.
  • Retailers are educated in proper handling practises as per FSANZ Foods Safety Standards.
  • Investigate the option of introducing a second heat treatment step to ensure product is adequately cooked.
  • Undertake re-sampling and investigation of premises with unsatisfactory results.

Bibliography

1 Report on Microbiological Survey of Kebabs – Food Safety Victoria 2002
2 Guidelines for the Microbiological Examination of Ready-to-eat-Foods (December 2001)

References

1. CDI 2002 Vol 27 June 2003
2. CDI 2002 Vol 26 Sept 2002

Microbiological quality of seafoods

November 2001 - April 2002

Report prepared by Simon Rockliff

Objectives

  • To maintain surveillance of seafood products in the ACT to ensure their safety and continued compliance to current Standards.
  • Where possible compare survey results with previous survey data.

 

Background

A previous survey had been conducted on Microbial Quality of Marinara Mix in 1996/7. This survey was designed to determine the overall quality of seafood available in the ACT from a number of samples collected across a four-month period. Various standards exist for different categories of seafood and this aspect is discussed below.

Standards

The Food Standards Australia New Zealand (FSANZ) Food Standards Code (FSC) includes microbiological standards for certain types of seafood. At the August Health Protection Service (HPS) Food Sampling Working Group (WG) meeting it became evident that the 2001 2002 Food Survey testing regime is based on the new joint Food Standards of Australia and New Zealand (jFSCANZ).

During the phase in period of the jFSCANZ code, either the current FSANZ or jFSCANZ codes can apply to a food item. The appropriate testing Standard is determined by the manufacturing standard under which the food was produced. The label determines this, as the new jFSCANZ requires % compositional labelling while the current FSANZ FSC requires food ingredients to be listed in order of total composition.

Unfortunately the food labels were destroyed when half the Health Protection building in Holder was destroyed by the 18 January bush fires. It is therefore not possible to determine if the food was prepared under the old FSANZ FSC or new (jFSCANZ). For the purposes of this report it was decided that it would be practical if the new (jFSCANZ) levels were used to determine the compliance of the sample results. The acceptable levels for each organism and sample category are shown in Table 2.

The following tables set out the testing requirements for the current FSANZ FSC and new jFSCANZ for the seafood survey.

Table 1 Comparison of Testing Criteria

 

Table  Comparison of Testing Criteria
#This is extra testing performed by ACTGAL, which is not included in ANZ Food Standards Code.
Cfu/g = colony forming units per gram of material analysed.

Those samples that did not fall into these categories were analysed according to the Draft ANZFA Guidelines for Ready-to-eat food.

Table 2 Testing Criteria and levels

 

Table  Testing Criteria and levels

Survey

This survey was conducted between the 7th of November 2001 and the 3rd of April 2002. During this period a total of 91 samples were collected by Environmental Health Officers (EHO) and processed by the Microbiology Unit of ACTGAL. The following range of seafood samples were collected from a range of retail outlets and covered a number of product manufacturers and types available on the ACT market. Testing for Vibrio parahaemolyticus was not undertaken.

The survey was responsible for covering a diverse range of food Standard Categories. The categories are identified as follows:

Mollusc - A total of 18 samples were collected and analysed including Oysters, Mussels, Scallops, Pipies and Vongolis.

Crustacea - This category can be further split into Raw and Cooked Crustacea. In all, the survey tested 23 Crustacea included prawns of various sizes, various crabs, lobster and Balmain Bugs.

Fin Fish – Consisted of 10 samples of finfish including Salmon, Tuna, Herring, Kipper and Oste.

Marinara Mix – A total of 10 samples of seafood mixes were collected and analysed.

Smoked seafood products – 24 smoked seafood products were collected and analysed. They included Cod, Salmon, Kipper, Trout, Mackerel and mussels.

Other –There were a total of 6 items in this category. They consisted of Tuna and Shallots Dip and Sushi.

Figure 1 Number of Samples Collected for Each Category

 

Figure  Number of Samples Collected for Each Category

Results

Mollusc
The molluscs were tested for the presence of Listeria Monocytogenes and numbers of E. coli per gram of sample tested. Neither Listeria monocytogenes nor E. coli was isolated from the 18 mollusc samples tested.

Crustacea
Samples collected were analysed for Standard Plate Count (SPC), E. coli, Listeria monocytogenes, coagulase positive Staphylococci and Salmonella. The pH of the samples was also determined Table 3 gives the Overall isolation rates for the 23 samples.

Table 3 Overall isolation rates

 

Overall isolation rates for the  samples
*expressed as colony forming units per gram.

pH of the product ranged from 6.64 to 9.97 with an average of 7.05.

The Crustacea SPC data was further analysed and is represented in Graph 1 shown below. Twenty-two of the 23 samples were tested to determine their SPC result. It was difficult to determine the cooked status of the product from the product description entered into the data base so the results were combined and the raw Crustacea level used to determine the level of unsatisfactory results. Graph 1 indicates that 5 (23.8%) of the samples exceeded the Raw Crustacea SPC Standard of 5 x 106 cfu/gm.

Graph 1 Further evaluation of SPC data

 

Graph  Further evaluation of SPC data

Fin Fish
Samples collected were analysed for Listeria monocytogenes, coagulase positive Staphylococci, Salmonella and pH. Table 4 gives the Overall isolation rates for the 10 samples.

Table 4 Overall isolation rates

 

Table  gives the Overall isolation rates for the  samples.
*expressed as colony forming units per gram.

pH of the product ranged from 6.65 to 7.00 with an average of 6.81

Marinara Mix
Samples collected were analysed for E. coli, Listeria monocytogenes, coagulase positive Staphylococci, Salmonella and pH. Table 5 gives the Overall isolation rates for the 10 samples.

Table 5 Overall isolation rates

 

Table  gives the Overall isolation rates for the  samples
*expressed as colony forming units per gram.

pH of the product ranged from 6.9 to 7.00 with an average of 6.99.
A sample of Gourmet seafood Salad was positive for Listeria Monocytogenes. A re-sample of this product was not collected.

Smoked seafood products
Samples collected were analysed for Listeria monocytogenes, coagulase positive Staphylococci, Salmonella and pH. Table 6 gives the Overall isolation rates for the 24 samples.

Smoked seafood products
Samples collected were analysed for Listeria monocytogenes, coagulase positive Staphylococci, Salmonella and pH. Table 6 gives the Overall isolation rates for the 24 samples.

Table 6 Overall isolation rates

 

Table  gives the Overall isolation rates for the  samples.
*expressed as colony forming units per gram.

pH of the product ranged from 6.83 to 7.00 with an average of 6.91. The 3 samples positive for Listeria monocytogenes were 2 smoked salmon and one smoked cod product. All products are sourced from outside the ACT. The products are unlikely to undergo further processing prior to consumption. The detection of L. monocytogenes in the smoked salmon and cod fillets resulted in the analysis of re-sampled fillets, the bulk product from which the fillets were prepared and the tongs used to handle the products. The investigation found that L. monocytogenes could be isolated from the cod and salmon fillets, the bulk salmon and the tongs used to handle the salmon.
 

Extensive cleaning of the premises and improved handling procedures had resolved the matter within 3 weeks. No attempt was made to determine the level of L. monocytogenes within the product. It was decided that future re-samples of foods for L. monocytogenes would be tested semi-quantitatively to determine the level of the pathogen in the foods.

Other
Samples collected were analysed for Listeria monocytogenes, coagulase positive Staphylococci, Salmonella and pH. Table 7 gives the Overall isolation rates for the 6 samples.

Table 7 Overall isolation rates

 

Table  gives the Overall isolation rates for the  samples.
*expressed as colony forming units (CFU) per gram.

pH of the product ranged from 6.6 to 6.84 with an average of 6.99.

The 4 samples positive for Listeria monocytogenes were a brand of Tuna and Shallots dip. After the first sample was found to be positive 3 other samples were tested and also found to be positive. The EHO’s contacted the manufacturer and NSW Health concerning this matter.

Discussion

It is pleasing to see that E. coli, Salmonella and Coagulase positive Staphylococci were not isolated in any samples tested during this survey.

It is pleasing to see that E. coli, Salmonella and Coagulase positive Staphylococci were not isolated in any samples tested during this survey.

Listeria monocytogenes was isolated from 1 Marinara Mix, 4 Smoked Seafood Products and 4 other samples i.e. Tuna and Shallots Dip. The investigation into the L. monocytogenes indicated that the most likely reason for the presence of the organism in the product was poor handling and allowing cross contamination to occur.

Conclusion

The quality of seafood sold in the ACT is generally good, however there appears to be a problem with Listeria monocytogenes in some samples. While some re-samples were collected they were not collected for all products. Strategies need to be put into place that will ensure that all products positive for pathogens are retested to determine the level of the pathogen and its spread within the food product.

Recommendation

Bibliography

1 Report on Microbial Quality of Marinara Mix in 1996/7.
2 Food Standards Australia And New Zealand FSANZ Draft Ready to Eat Guidelines.
3 Food Standards Australia And New Zealand FSANZ - Food Standards Code.

Microbiological quality of cheese

April 2002 - June 2002

Report prepared by Sheba Khan and Simon Rockliff

Objectives

  • To maintain surveillance of cheese products in the ACT to ensure there safety and continued compliance to current Food Standards Australia New Zealand (FSANZ) Food Standards Codes.
  • Compared analysis results with data obtained from previous survey conducted in April June 1998

Background

The Health Protection Service (HPS) continued its pro-active surveillance of these high-risk products. As identified in previous Health Protection reports, cheese are considered a potentially hazardous product as they are:

  • normally intended to be eaten as purchased, ie without further processing,
  • raw milk cannot be guaranteed to be free from pathogenic bacteria.
  • if the milk has not been pasteurised it is difficult to ensure the safety of the cheese no matter how good the control of hygiene during production.

Cross-contamination of the product due to unhygienic conditions:

  • handling different varieties of cheese;
  • from other foods on sale, especially raw foods;
  • from shelves, racks, trolleys or other storage or handling equipment;
  • cheese handling areas, or from the general environment;
  • by pests;
  • from customers.

Contaminated cheese has been responsible for outbreaks of food poisoning by several types of bacteria and sporadic cases of illness associated with contaminated cheese has also been reported. Experience shows that there have probably been many others which were undetected or unreported. Some of these bacteria can cause severe illness with long-term consequences and death. For example, Listeria monocytogenes can cause meningitis and septicaemia with up to 30% mortality. L. monocytogenes is of particular concern to pregnant women as it has the potential to cause spontaneous abortion and stillbirth. Gastroenteritis due to Salmonella spp. can lead to long-term illness such as reactive arthritis. Infection with Salmonella paratyphi B may lead to septicaemia (enteric fever). Verocytotoxigenic Escherichia coli O157: H7 causes enteritis and may also cause haemolytic uremic syndrome (HUS) and kidney damage, particularly in young children and others with a weaken immune system.

Australia New Zealand Food Authority (ANSFA) introduced specific requirements into the Australian Food Standards Code concerning the manufacture and sale of cheese. This included strict control on manufacturing processes (to minimise possible contamination) and more stringent labelling requirements.

Standards

The Food Standards Australia New Zealand (FSANZ) Food Standards Code (FSC) includes microbiological standards for certain types of cheese. At the August Health Protection Service (HPS) Food Sampling Working Group meeting it became evident that the 2001 2002 Food Survey testing regime was based on the new joint Food Standards of Australia and New Zealand (jFSCANZ).

During the phase in period of the legislation either the current FSANZ FSC or jFSCANZ Standards can apply to a food item. The applicable testing criteria is determined by the labelling Standard under which the food was produced i.e. the new jFSCANZ requires percentage compositional labelling while the current FSANZ FSC requires food ingredients to be listed in order of total composition.

The Health Protection Service Sampling Working Group (HPSSWG) decided that it would be wise to test food products against both standards, as they are both current. The Microbiology Unit organised for the retention of the food labels to determine which version of the standard applies to out of specification food.

Unfortunately the food labels were destroyed when half the Health Protection building in Holder was destroyed by the 18 January bush fires. It is therefore not possible to determine if the food was prepared under the old FSANZ FSC or new (jFSCANZ). For the purposes of this report it was decided that it would be practical if the new (jFSCANZ) levels were used to determine the compliance of the sample results. The Food Standards Australia New Zealand Food Standards Code (FSANZ) includes microbiological standards for cheese (Standard 1.6.1). The acceptable levels for each organism and sample category are shown in Table 1.

 

Table 1
Food Organism Acceptable Level (cfu/g)
All Cheese E. coli /g 10
  Coagulase positive Staphylococcus /g 102
Soft and semi soft cheese (moisture content >50%) with pH>5.0 Listeria monocytogenes /25g 0
  Salmonella /25g 0
All raw milk cheese (cheese made from milk not pasteurised or thermised) Listeria monocytogenes /25g 0
  Salmonella /25g 0
Raw milk unripened cheese (moisture content >50%) with pH>5.0 Campylobacter /25g 0
  Salmonella /25g 0
cfu/g = colony forming units per gram of material analysed.

Survey

This survey was conducted between the 17 April 2002 and 26 June 2002. During this period a total of 130 samples were collected by Environmental Health Officers (EHO) and processed by the Microbiology Unit of ACTGAL. The cheese samples were collected from a range of retail outlets and covered a number of product manufacturers and types available on the ACT market.

Results

Table 2
Organism No. of samples positive (%) Range of positive results*
E. coli (n=128) 6.38 9 - 93
Salmonella spp. (n=128) 0 0
Listeria monocytogenes (n=130) 2.1 N/A
N/A= Not applicable.
*expressed as colony forming units per gram.
Note: average pH of all samples was calculated to be 6.79

E. coli
E. coli was detected in 3 (6.38%) samples. This included bulk Ricotta and one sample of the soft cheese Valcancay. The positive results ranged from 9 – 93 cfu/g of sample. According to the Code if the microbiological level exceeded 100 cfu/g in one or more samples, it would result in the sample lot being rejected. As only single samples were collected, and the products were not resampled using the ANZFA FSC sampling plan, the products were considered to have complied with the Code.

E. coli was not isolated from any Gouda or Cheddar cheese samples and these were found to comply with the Code.

Salmonella sp
No Salmonella was isolated from any of the cheese samples in this study.

Campylobacter
No Raw unripened cheeses with a moisture content >50% and a pH>5.0 were collected, so no tests for Thermophilic Campylobacter were conducted.

Listeria monocytogenes
Listeria monocytogenes was isolated from 1(2.1%) sample. This included a Ricotta cheese sample (E. coli was also isolated). Results indicate that this sample may have been cross-contaminated due to unhygienic conditions.

Discussion

Salmonella does not appear to be a significant contaminant of cheese since it was not isolated in this survey or the past survey conducted April-June 1998.

E. coli was isolated in 6.38% (3 samples, 2 Ricotta and 1 Valcancay cheese) of the total samples tested. The previous report (April-June 1998) also detected this pathogen in 5.5% of the samples with bulk Ricotta cheese being identified as one of the food types where this pathogen was isolated. Unfortunately the positive E. coli samples were not re-sampled.

Listeria monocytogenes was isolated from 1 (2.1%) cheese sample only as compared to the previous report where the isolation rate was 9.7%. An investigation into the L. monocytogenes result which included the analysis of re-samples indicated that the most likely reason for the presence of both E. coli and L. monocytogenes in the product was poor handling and unhygienic conditions that allowed cross-contamination to occur. The re-samples were found to be negative for L. monocytogenes and not tested for E. coli.

Conclusion

The quality of cheese and cheese products sold in the ACT is generally good. This survey identified a low level of microbiological contamination of certain cheese products (particularly Ricotta cheese, which has a short shelf life). The results indicate an improvement in the isolation of E. coli and L. monocytogenes from these products. Minor problems seem to be occurring with the handling of the cheese products particularly Ricotta cheese. More education of the staff and management of retail premises within the ACT may be necessary in order to decrease the incidences of cross contamination.

Recommodations

  • That a future survey be conducted to confirm the proper handling of the product is occurring.
  • Those retailers are educated in proper handling practises as per the FSANZ Food Safety Standard

Bibliography

  • 1. Report on Cheese and Cheese Products Survey April-June 1998. (HPS)
  • 2. FSANZ Food Standards Code (current as at 28 January 2003)
    • Standard 1.6.1 – Microbiological Limits for Food
    • Standard 2.5.4 – Cheese

Microbiological quality of ready to eat foods

July 2001 June 2002

Report prepared by Simon Rockliff and Sheba Khan

Objective

  • Determine the bacteriological status of ready-to-eat food products available on the ACT market.
  • Determine the compliance of these products relative to the Food Standard Australia New Zealand (FSANZ) Draft Guidelines for the Microbiological Examination of RTE Foods.
  • Compare results from surveys conducted over past few years to trend the microbiological status of this food category.

Background

Ready-to-eat (RTE) food is food that is ordinarily consumed in the same state as that in which it is sold or distributed and does not include nuts in the shell and whole, raw fruits and vegetables that are intended for hulling, peeling or washing by the consumers.

Sandwiches, rolls, stir-fries, baked goods as well as various other RTE foods are widely available in approximately 450 ACT establishments. Due to the diverse nature of these foods and popularity it was considered prudent to perform ongoing surveys on these products in conjunction with the Environmental Health Auditing Program for establishments that produce these high-risk foods. The previous studies on RTE foods (2000-2001) (2001-2002) highlighted some problems with handling, storage and cross-contamination. This is a report on the third years results with a comparison to the previous two years results.

Standards

Samples collected for surveillance and monitoring purposes are often multi-component products for which there are no microbiological standards or guidelines. Interpreting the significance of the types and levels of microorganisms reported when these foods are tested may therefore be difficult. The Food Standard Australia New Zealand (FSANZ) Draft Guidelines for the Microbiological Examination of RTE Foods identify four categories of microbiological quality ranging from satisfactory to potentially hazardous. Table 1 below shows the recommended guidelines. This reflects both the high level of microbiological quality that is achievable for RTE foods in Australia and New Zealand and indicates the level of contamination that is considered to be a significant risk to public health.

Table 1 Recommended guidelines

 

Table  Microbiological Quality (CFU per gram)

NOTE:

** Pathogenic strains of E. coli should be absent.
# Foods with a long shelf life stored under refrigeration should have no L. monocytogenes detected in 25g.

« The detection of L. monocytogenes in ready-to-eat-foods prepared specifically for “at risk” population groups (the elderly, immuno-compromised and infants) should also be considered as potentially hazardous.

* see below “Standard Plate Counts” for definition of level..

SET +ve : Staphylococcus enterotoxin positive.

N/A – SPC testing not applicable. This applies to foods such as fresh fruits and vegetables (including salad vegetables), fermented foods and foods incorporating these (such as sandwiches and filled rolls).
 

Standard Plate Count (SPC)

The Standard Plate Count (SPC), also referred to as the Aerobic Plate Count or the Total Viable Count, is one of the most common tests applied to indicate the microbiological quality of food. This total count of viable microbes reflects the handling/ storage history of the food. Total counts may be taken to indicate the type of sanitary control exercised in the production, transport, and storage of the food. The significance of SPCs, however, varies markedly according to the type of food product and the processing it has received. When the SPC testing is applied on a regular basis it can be a useful means of observing trends by comparing SPC results over time.
Three levels of SPC are listed in Table 1 based on food type and the processing/ handling the food has undergone.

Level 1 – applies to ready-to-eat foods in which all components of the food have been cooked in the manufacturing process/preparation of the final food product and, as such, microbial counts should be low.

Level 2 – applies to ready-to-eat foods, which contain some components, which have been cooked and then further handled (stored, sliced or mixed) prior to preparation of the final food or where no cooking process has been used.

Level 3 – SPCs not applicable. This applies to foods such as fresh fruits and vegetables (including salad vegetables), fermented foods and foods incorporating these (such as sandwiches and filled rolls). It would be expected that these foods would have an inherent high plate count because of the normal microbial flora present.

Note: An examination of the microbiological quality of a food should not be based on SPCs alone. The significance of high (unsatisfactory) SPCs cannot truly be made without identifying the microorganisms that predominate or without other microbiological testing.

Survey

This survey was conducted between the 02 July 2001 and 18 July 2002. During this period 193 samples from 69 ACT retail outlets were collected randomly by Environmental Health Officers (EHO) and processed by the Microbiology Unit of ACTGAL. The samples were collected in such a manner as to cover a wide range of the available RTE food types including salads, pies, quiches, sandwiches, noodles, pasta, meats and desserts. The SPC, E.coli, coagulase positive Staphylococci analyses assessed samples for overall hygiene quality. The pH of all samples was determined. Where the foods contained meat / rice, other food pathogens such as Salmonella spp., Listeria monocytogenes and Bacillus cereus were tested. The survey collected multiple samples from single outlets and outlets were only tested once.

Results / Discussion

Standard Plate Counts (SPC)

A total of 198 samples were tested for SPC. The results for all samples ranged between <50 and 3,200,000,000 colony forming units /g (cfu/g). A total of 89 of these RTE food samples were assessed as having to comply with the Level 1 criterion (see Table 1 above. Of these 18 (20.2%) samples gave unsatisfactory results, 11(12.4%) gave marginal results and 60 (67.4%) gave satisfactory results.

A total of 72 samples were assessed as having to comply with the Level 2 criterion. The results ranged between <50 and 2,300,000,000 cfu/g. Of these 13 (18.0%) samples that were tested gave unsatisfactory results, 11(15.3%) gave marginal results and 48 (66.6%) gave satisfactory results.

37 samples were assessed as Level 3. There are no set limits for the Level 3 criterion. The results ranged from as low as 200 to as high as 28,000,000 cfu/g. This is to be expected as these foods (mostly raw fruits and vegetables or fermented foods) would have an inherent high plate count because of the normal microbial flora present.

Fugure 1 Standard Plate counts estimated in Ready-to-eat Foods

 

Standard Plate counts estimated in Ready-to-eat Foods

Figure 1 above shows the results for the four categories of microbiological quality for the RTE foods based on the SPC. Majority of the results were satisfactory and no further action is required for those samples/ premises.

The marginal results are borderline in that they are within the limits of acceptable microbiological quality but may indicate possible hygiene problems in the preparation of the food. Re-sampling maybe appropriate.

The unsatisfactory results are outside of the acceptable microbiological limits and are indicative of poor hygiene or food handling practices. One outlet in particular had unsatisfactory results for all test levels. Further sampling of the foods from this and other premises may be required and an investigation undertaken to determine whether food handling controls and hygiene practices are adequate. No unsatisfactory samples were re-sampled.

Figure 2 Microbiological Quality of Ready-to-eat Foods

 

Fig  Microbiological Quality of Ready-to-eat Foods

Escherichia coli
236 samples were tested for E. coli. Figure 2 above represents the results for the four microbiological categories included in the guidelines. The presence of E. coli in RTE foods is undesirable because it indicates that the food has been prepared under poor hygienic conditions. Ideally E. coli should not be detected and as such a level of <3 cfu per gram (the limit of the Most Probable Number test) has been given as the satisfactory criterion for this organism. 97.4%) of the samples had <3 cfu/g E.coli and met the satisfactory criterion. Levels exceeding 100 per gram are unacceptable and indicate a level of contamination which may have introduced pathogens or that pathogens, if present in the food prior to processing, may have survived processing.1 A total of 6 samples were positive for E. coli. The results ranged from 43 - >1100 cfu/g. One (0.4%) sample was marginal whereas 5 (2.1 %) samples were unsatisfactory.

Re-samples were requested for all 5 unsatisfactory samples and tested for E. coli only. E. coli was not isolated from any of the re-samples.

Coagulase positive Staphylococci
236 RTE samples were tested for coagulase positive Staphylococci. 97.8% of the samples were satisfactory. 3 (1.3%) samples gave unsatisfactory results and 2 (0.86%) were assessed as being marginal. The positive results for coagulase positive Staphylococci ranged from 100-600. Unsatisfactory levels of coagulase positive Staphylococci indicate that time/temperature abuse of a food is likely to have occurred following improper handling during food preparation.

Contamination of ready-to-eat foods with coagulase positive Staphylococci is largely as a result of human contact. Contamination should be minimised through good food handling practices and growth of the organism prevented through adequate temperature controls. No re-samples were requested or tested for coagulase positive Staphylococcus.

Salmonella spp.
No Salmonella spp. was detected in 25-gram amounts of any of the 233 samples tested. 100% of the samples were satisfactory. RTE foods should be free of Salmonella as consumption of food containing this pathogen may result in food borne illness.

Listeria monocytogenes
214 samples were analysed for Listeria monocytogenes. 93.4%) of the samples were satisfactory whereas 14 (6.5%) samples were marginal. The detection of Listeria monocytogenes in RTE foods at high levels (102 cfu per gram) indicates a failure with food handling controls and is considered a public health risk. Foods in which all components have been cooked in the final food preparation, or have received some other listericidal treatment, should be free of Listeria monocytogenes. The detection of L. monocytogenes in such foods indicates the food was inadequately cooked or the food was contaminated post preparation.

A total of 10 re-samples were requested for foods positive for Listeria monocytogenes. 5 re-samples were received. Re-samples were tested semi-quantitatively and no Listeria monocytogenes was detected. All results for the re-samples met the satisfactory criterion.

Bacillus cereus
52 samples were tested for B. cereus. 98.1% of samples tested were satisfactory. Only one sample (1.9%) gave an unsatisfactory result. 2500 cfu/g of B. cereus was isolated from this sample. Re-sampling of this premise gave a satisfactory result. An unsatisfactory level of B. cereus in cooked foods generally occurs as a result of inadequate temperature control. Cooked foods should be held at or above 60°C or at below 5°C to prevent growth.

Environmental Health Audit Findings
Evaluation of the bacteriological results and the Environmental Health shop audit findings was not possible as the audit records were destroyed when the Health Protection Service building was partially destroyed in the January 2003 bushfires.

Comparision to previous survey (2000 - 2001)

Standard Plate Counts
67.4% of samples passed the “satisfactory” criterion for Level 1 as compared to the previous survey where 88.7% samples passed. Also the highest count reached 3.2 x 109 cfu/g compared to last year where the highest count was only 1.7 x 107 cfu/g. 66.7% of the samples satisfied the Level 2 criterion whereas in the previous year 86.6% of the samples were satisfactory.

Table 2 Comparison of the Microbiological Quality Surveys between 2000-01 and 2001-02

 

Table  Comparison of the Microbiological Quality Surveys between - and -

Approximately 97% of the samples tested for E. coli in the present and the previous study passed the satisfactory criterion. Around 97% of the total samples tested for coagulase positive Staphylococci were also satisfactory for both surveys. In the 2001/2 survey Salmonella spp. was not isolated in any of the samples whereas one sample had Salmonella spp. isolated in the previous year. 93.4% of the samples tested for Listeria monocytogenes were classified as “satisfactory” in this study. The previous study had 98.9% of the samples as “satisfactory”.

98.1% of the samples tested for Bacillus cereus were satisfactory in this study as compared to 94.4% from last year. In the present study no samples were tested for Clostridium perfringens.

Resamples

Health Protection Services (HPS) Food Sampling Working Group needs to further improve the re-sampling protocol for future surveys. Re-sampling should be requested when a sample fails to meet the acceptable microbiological guideline.

Conclusion

In general the microbiological quality of the Ready-to-eat Foods sold in the ACT is good, however some premises are inadequately handling / processing the food product they produce. More education of the staff and management of retail premises within the ACT may be necessary in order to decrease the incidences of unsatisfactory levels of pathogens in food product.

Recommendation

  • That the Ready-to-eat Survey continues for the future to confirm the continued quality of the product and co-relation with audit findings.
  • That the HPS Sampling Working Group improves compliance with current re-sampling guidelines.
  • Continue to undertake re-sampling and investigation of premises with unsatisfactory results.

Bibliography

1 Guidelines for the microbiological examination of ready-to-eat foods ANZFA Dec 2001
2 Report on Microbiological Quality of Ready-to-Eat Foods 2000-2001