Food Survey Reports 2002-2003
- Incidence of salmonella in ACT aquariums
- Quality of fried rice
- Microbiological quality of long life refrigerated products
- Microbiological quality of ready-to-eat foods
- Quality of sushi
October December 2003
To determine the incidence of Salmonella species in ACT commercial tropical aquariums.
Determine semi-quantitatively the level of Salmonella in positive tanks.
Approximately six million tropical fish a year are imported into Australia, mainly from Asian countries. Tropical fish are popular pets in Canberra with 18 suppliers advertising in the yellow pages. World Wide a number of studies have established the presence of human pathogen stains of Salmonella in tropical fish tanks and small outbreaks associated with these strains. Salmonella are not known to be pathogenic for tropical fish and the fish can act as reservoirs of Salmonella for many weeks. Salmonella can survive in tank water and in sediments for considerable periods of time. Purchased fish are transported in their tank water, which is then added to the home tank adding to the chance of contaminating the home tank. Currently there is no requirement for imported fish to be certified as Salmonella free.
This survey was conducted between the 8 October and 17 December 2003. During this period a total of 42 samples from 9 different establishments were collected. The samples consisted of 38 tank-waters and 4 gravels. The samples were collected by the Environmental Health Technical Officer and processed by the Microbiology Unit of the ACT Government Analytical Laboratory. Initially 100mL quantities of water or 25 gram samples of gravel were each tested for the presence of Salmonella. When positive samples were detected they were re-sampled and 100, 10 and 1mL volumes tested for the presence of Salmonella.
There are no standards for Salmonella in aquarium waters or gravel.
November 2002 February 2003
Report prepared by Simon Rockliff and Sheba Khan
Incidences of rice-associated food poisoning have been linked to the practice of preparing bulk rice in advance, in anticipation of subsequent need. Fried rice is a leading cause of Bacillus cereus emetic-type food poisoning in Australia. B. cereus is frequently present in uncooked rice, and heat-resistant spores may survive cooking. If cooked rice is subsequently held at room temperature, surviving spores will germinate into vegetative forms. The vegetative forms will multiply, these forms may then produce a heat-stable toxin and this low molecular weight toxin can survive brief heating, such as stir frying.1, 3
In the ACT approximately 27 people a year attend an emergency department for bacterial foodborne intoxication (Personal communication from Dr Drew Richardson The Canberra Hospital (TCH) emergency department. As the TCH only sees just over half of the cases in the ACT the true number is nearer 50.
The purpose of this survey was to establish the microbiological quality of fried rice, sampled at the point of sale from a wide range of takeaway premises in the ACT. The tests E. coli, Coagulase positive Staphylococcus and B. cereus were performed to determine the microbial quantity of fried rice.
Food Standards Australia New Zealand Food (FSANZ) Draft for Ready-To-Eat (RTE) Foods consider Fried Rice as a Ready-to-eat Food and identify four categories of microbiological quality ranging from satisfactory to potentially hazardous for this food category. Table 1 below details the Draft guideline categories. This reflects both the high level of microbiological quality that is achievable for ready-to-eat 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 Draft guideline categories
* Pathogenic strains of E. coli should be absent.
# 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. Fried Rice is a “level 1” product in which all components have been cooked before consumption.
SET +ve: Staphylococcus enterotoxin positive.
This survey was conducted between the 06 Nov 2002 and Feb 2003. Samples were collected only until 18 Dec 2002. Further sampling and testing was suspended due to bushfire damage to the Health Protection building on 18 Jan 2003. ACT Government Analytical Laboratory (ACTGAL) was partially functioning from 17 Feb 2003 with food analysis not commencing until Mar 2003. Since the survey on fried rice was to end on in February 2003, the decision was made to cease this survey where it stood and proceed with the next scheduled survey identified by the Health Protection Service (HPS) Sampling Working Group (WG).
Survey samples were taken randomly from a range of ACT retail outlets by Environmental Health Officers (EHO) and processed by the Microbiology Unit of ACTGAL. The SPC, E. coli and coagulase positive Staphylococci analyses assessed samples for overall hygiene quality. Fried rice samples were also tested for the specific pathogen Bacillus cereus, which has been associated with food poisoning resulting from poorly handled and/or stored product. The survey collected multiple samples from single outlets with all outlets (19 in number) being tested once only.
Results / Discussion
Standard Plate Counts (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 overall microbial quality of the food. Total count of viable microbes may be taken to indicate the type of sanitary control exercised in the production, transport, and storage of the food.
A total of 28 fried rice samples were assessed according to the RTE food guidelines. The results ranged between <50 and 6,500,000 colony forming units/gram (cfu/g) with 3 (10.7%) samples giving unsatisfactory results. 89.3% of the samples tested passed satisfactorily. The unsatisfactory results are outside of the acceptable microbiological limits and are indicative of poor hygiene or food handling practices. No unsatisfactory samples were re-sampled. Results are graphed in Fig 1 below.
Figure 1 Standard Plate Counts of fried rice samples
29 samples were tested for E. coli. Figure 2 below represents the results for the four categories. The presence of E. coli in RTE foods is undesirable because it indicates poor hygienic 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 per gram (the limit of the MPN test) has been given as the satisfactory criteria for this organism. 96.7% of the samples had <3 cfu/g E. coli and thereby met the satisfactory criterion. Levels exceeding 100 cfu 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.1 Only 3.4% (1 out of 29) of the samples were unsatisfactory and failed to comply with the Draft RTE guidelines.
Coagulase positive Staphylococci
29 fried rice samples were tested for coagulase positive Staphylococci. 96.7% of the samples were satisfactory while 3.4% (1 out of 29) of the samples showed unsatisfactory results. In this instance the same sample that had an unsatisfactory E. coli result was also unsatisfactory for coagulase positive Staphylococci. Unsatisfactory levels of coagulase-positive Staphylococci also indicate that time/temperature abuse of a food is likely to have occurred following improper handling during food preparation. Contamination of RTE foods such as fried rice 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.
29 samples were tested for B. cereus. 96.6% of samples tested for were satisfactory. Only one sample (3.4%) gave an unsatisfactory result (potentially hazardous). Levels of ³ 104 cfu per gram are considered potentially hazardous as consumption of foods with this level of contamination may result in foodborne illness. While a resample was requested no clearly identified resample was submitted for analysis. An unsatisfactory level of B. cereus in cooked foods like fried rice 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.
Figure 2 Microbiological quality of Fried Rice samples
This survey indicated that most of the fried rice sampled from various takeaway premises was of acceptable microbiological quality. Overall 10% of the tested samples were classified as unsatisfactory for the Standard Plate count while one surveyed outlet had unsatisfactory results for all tests. Further sampling of the foods from this premise may be required and an investigation should be instigated to determine the source/cause of the problem so that remedial actions can commence.
- 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.
1. Terranova W, Blake PA. Bacillus cereus food poisoning. N England J Med 1978; 298: pp143-4
2. Guidelines for the microbiological examination of ready-to-eat foods ANZFA – December 2001
3 Jenson I and Moir CJ. Bacillus cereus and other Bacillus sp., In Foodborne Microorganisms of Public Health Significance, Sixth Edition, AIFST, 2003
March 2003 June 2003
To establish the prevalence of L. monocytogenes and Salmonella sp in a variety of Packaged Long Shelf Life Refrigerated Foods (PLSLRF)
To test the compliance of these products to Food Standards Australia New Zealand (FSANZ) Draft Guidelines for the Microbiological Examination of Ready-to-Eat Foods
Packaged long shelf life refrigerated foods are becoming more common on ACT delicatessen and supermarket shelves, they include items such as salami, sliced meats, soft cheeses and smoked fish. Many of these food products are sold 'ready-to-eat' and are considered at high risk of bacterial contamination. Of particular concern in this type of product is L. monocytogenes, which is capable of replication at refrigeration temperatures1 and possibly of reaching high numbers in the food. Food Safety Victoria was sufficiently concerned about this problem that they produced a guide for Environmental Health officers for the testing of L. monocytogenes in ready to eat food2. The other major pathogen of concern in this type of product is Salmonella sp as they are also capable of extended survival at refrigeration temperatures and many strains will grow at 7C 3.
A number of these products have been tested previously, as part of Cheese, Smallgoods and Ready to Eat surveys without significant findings. The Health Protection Service Sampling Working Group (HPSSWG) decided that, due to the high-risk nature of the product it would be desirable to conduct a survey dedicated to this product type.
The HPSSWG decided that it would be wise to test these foods against the FSANZ Draft Microbiological Guidelines for Ready-to-Eat Foods as the FSANZ Food Standards Code (FSC) does not include microbiological standards for this type of product
July 2002 - June 2003
Determine the bacteriological status of ready-to-eat food products available on the ACT market.
Determine the compliance of these products to Food Standards Australia New Zealand (FSANZ) Draft Guidelines for the Microbiological Examination of Ready-to-Eat Foods.
- "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 consumers1."
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 and popularity of these foods it was considered prudent to perform ongoing surveys on these products in conjunction with the Environmental Health Section Premises Auditing Program of high-risk food producing establishments. The previous surveys on RTE foods conducted in 2000-2001 and 2001-2002 highlighted some problems with handling, storage and cross-contamination. This is a report on the third year's survey including comparisons with the previous two years results.
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 reported microorganisms for these foods may therefore be difficult. The FSANZ Draft Guidelines for the Microbiological Examination of Ready-to-Eat Foods (the Guidelines) identify four categories of microbiological quality ranging from satisfactory to potentially hazardous. Table 1 below details the recommended guidelines. This Table reflects both the high level of microbiological quality that is achievable for RTE foods in Australia and New Zealand and also indicates the level of contamination that is considered to be a significant risk to public health.
July 2003 - September 2003
Report prepared by Geoff Millard and Simon Rockliff
- To determine the microbiological status of sushi in the ACT to ensure their safety.
- Determine the compliance of these products to the Food Standards Australia New Zealand (FSANZ) Draft Guidelines for the Microbiological Examination of Ready to Eat (RTE) Foods.
Sushi is a traditional Japanese dish made by placing a piece of high quality fish on a roll of cold vinegared rice wrapped in dried seaweed. Variations of the dish are common and often involve filling the rice with small pieces of meat, fish or vegetable.
Sushi is a very popular type of convenience Ready to Eat food. The preparation, use of raw products and cooking practices involved in the production of sushi has the potential to allow contamination. In the Australian Capital Territory (ACT) a number of large scale producers, supply the majority of retail outlets.
Following a number of cases of contaminated sushi detected in a previous food survey, it was decided by the Health Protection Service (HPS) Food Sampling Working Group to conduct a dedicated survey on sushi to assess its microbiological safety and quality.
This survey was conducted between 9 July and 1 October 2003. During this period a total of 55 samples were collected and processed by the Microbiology Unit of the ACT Government Analytical Laboratory (ACTGAL). The sushi samples were collected from 14 different establishments and consisted of 41 different types. The samples consisted of a wide variety of meat sushi including beef, chicken, and pork; fish sushi including salmon, crab and tuna and vegetarian sushi including egg and tofu. As the survey was getting underway the Health Protection Service became aware of an initiative from the Victorian Department of Health to allow sushi to be kept for up to eight hours at 15C as long as the pH of the rice was less than or equal to 4.8. The ACT survey was immediately modified to include a test for pH. Initially the pH was determined for the whole sushi, this was later changed to determining the pH of the rice and fillings separately.
Sushi are categorised as a Ready-to-Eat food. The FSANZ Draft Guidelines for the Microbiological Examination (RTE) Foods as shown in Table 1 are applicable to this food.
47 (85.4%) of the samples showed a satisfactory microbiological quality for E. coli i.e.<3cfu/g. The positive E. coli results ranged from 3-460 cfu/g. 4 (7.3%) samples were marginal with between 3 and 100 cfu E. coli/g while 4 (7.3%) samples were greater than 100 cfu E. coli/g and categorised as unsatisfactory. The vegetarian and chicken sushi had the maximum of 460 cfu E. coli/g.
The presence of E. coli is undesirable because it is indicative of poor hygiene conditions, which have lead to contamination of the product. 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 pathogens if present in the sushi prior to processing, survived.
Coagulase positive Staphylococci
85.4% of the samples had less than 100 Coagulase positive Staphylococci indicating satisfactory microbiological quality. 5 (9.1%) of the samples contained counts between 100 and 1000 cfu/g and were marginal. There were 3 (5.4%) samples with counts in excess of 1000cfu/g and were regarded as unsatisfactory. There were no samples in the potentially hazardous category.
The highest Coagulase positive Staphylococci contamination was found to be 5500 cfu/g. This particular sample was also contaminated with E. coli. Contamination of sushi 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 Salmonella was isolated from any of the sushi samples in this study. The results indicate that 100% of the samples were satisfactory.
The presence of Listeria monocytogenes was detected in 7 (12.7%) samples categorising these as marginal. 87.3% of the samples tested were satisfactory. 5 of the samples positive for Listeria monocytogenes were also positive for Coagulase positive Staphylococci and 1 also for E. coli. These results indicate that this sample may have been cross-contaminated due to unhygienic conditions or practices. According to the Guidelines, no Listeria monocytogenes should be detected in the sample to pass the satisfactory category.
46 (83.6%) of the samples were found to be in the less than 100 cfu/g satisfactory category. There were 6 (10.9%) samples in the 100 1000 cfu/g marginal category; 2 (3.6%) in the 1000 10,000 cfu/g unsatisfactory category and 1 (1.8%) in the potentially hazardous category of greater than 10,000 cfu/g. The potentially hazardous sample was also positive for Listeria monocytogenes.
As sushi rice is made using vinegar the normal pH of the rice is reduced. In Victoria the Technical Review Body of Victorian Department of Health has approved an amendment to the Food Act to allow Sushi products to be held at 15C for up to eight hours if the rice has a pH of 4.8 or less. As previously stated initially the pH was determined for the whole sushi which was later changed to determining the pH of the rice and fillings separately. This arrangement resulted in the pH of 50 sushi samples being taken for both rice and fillings. However, only 35 of the sushi samples had the pH of the rice content only taken and of these only 22 (62.9%) had a pH less than or equal to 4.8. The pH range extended from 4.30 5.85 with one outlier at 6.54. The median value for the rice itself was 4.70 and the fillings was 5.37. There was no obvious correlation between pH and SPC see Graph 1.
The pH of the rice from which L. monocytogenes was isolated ranged from 4.55 to 5.85; E. coli from 4.31 to 5.85; Coagulase positive Staphylococci from 4.72 to 5.85 and B. cereus 4.55 to 5.38.The pH of the satisfactory category sushi samples ranged from 4.43 to 6.54 with marginal category samples ranging from 4.31 to 5.55 and unsatisfactory category samples from 4.65 to 5.85. See above Graphs 2, 3 and 4.
The sushi samples falling into each Guideline category compared to combined pH is given in Table 2.
The majority of the sushi had a combined pH greater than 4.8. The Table 2 results indicate that the mere presence of a low pH in the sushi is not necessarily protective.
The point of sale temperature, of individual sushi samples was available for 45 of the 55 samples. The legal storage temperature for this type of product is equal to or below 5C. The temperature ranged from <5 to 25C with a median of 15C. See Graph 5.
The majority of the marginal, unsatisfactory and potentially hazardous samples had temperatures in excess of 15C.
Table 4 below, shows the microbiological quality of sushi tested in this survey.
A review of the results revealed that the contamination was not evenly spread amongst the sushi samples, 17 of the 55 samples from 7 of the 16 sample batches contained pathogens. 6 samples had only 1 pathogen with 6 samples having 2 pathogens and 5 samples having 3 pathogens. 5 of the E. coli positive samples also contained >100 cfu/g of Coagulase positive Staphylococci. 6 of the 7 Listeria monocytogenes positive samples were also positive for B. cereus with 4 of those also positive for Coagulase positive Staphylococci. Samples from the same establishment varied from sample batch to sample batch. The way the product is prepared, with a degree of skin contact and no final bactericidal control step renders sushi a very high-risk food.
The majority of the sushi had a combined pH greater than 4.8 - Table 2. These results indicate that the mere presence of a low pH in the sushi is not necessarily protective. It also appears that the pH of the rice does not affect the pH of the fillings therefore, if the filling itself can support bacterial growth eg chicken or fish, then pathogens will grow in the sushi filling even with a low rice pH. These findings are similar to those found by the New Zealand Food Safety Authority. For all of the bacterial categories except E. coli and Salmonella, sushi performed poorer in each Guideline category i.e. was more prone to contamination than other Ready to Eat foods. See Tables 4 and 5
Overall the microbiological quality of sushi appears to be poorer than other Ready to Eat foods available in the ACT. This is evident from a comparison between data in Table 4 (Sushi results) and Table 5 (Ready to Eat food minus any sushi results). While none of the 55 samples tested contained Salmonella spp, 4 (7.3 %) samples were unsatisfactory in that they contained 100 cfu/g E. coli. This result does not compare well to other Ready to Eat foods in the unsatisfactory category, which ranged from 0 to 2.1% (Table 5). Similarly 5.5% of Sushi samples were unsatisfactory for Coagulase positive Staphylococci while other Ready to Eat foods ranged from 1 to 2.9% over the past 3 years. 1.8 % of sushi samples were found to be potentially hazardous and 3.6% unsatisfactory for B. cereus compared to 0 and 1.9% respectively (Table 5) for other Ready to Eat foods. Results outside of acceptable microbiological limits are indicative of poor hygiene or food handling practices. Listeria monocytogenes was detected in 7 (12.7%) sushi samples categorising them as marginal while other Ready to Eat foods ranged from 1.1 to 6.5% for this category. 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.
Overall, the microbiological quality of Sushi sold in the ACT is not of the standard of other Ready to Eat foods. The pH of the vinegared rice appears to be variable and does not seem to affect the pH of the fillings. This variable pH combined with generally elevated storage temperature leads to a product that can give marginal or unsatisfactory category results, which are not compliant to the FSANZ RTE Food Guidelines.
- Guidelines for the Microbiological Examination of Ready-to-eat-Foods (December 2001) FSANZ
- Victorian Department of Human Services, Food Safety Template.
- New Zealand email communication.