Microbiological Guidelines for Ready-to-eat Food

(HTML Format) | (PDF Format)


Food safety control aims to safeguard public health and provide assurance on food safety. To this end, microbiological analyses are useful ways to assess the safety and quality of food involved. This paper presents the recommended microbiological guidelines for ready-to-eat food.

Scope of the Guidelines

2. In the Hong Kong Special Administrative Region, the legal powers and instruments for the enforcement of microbiological safety of food are provided for in the Public Health and Municipal Services Ordinance, Cap. 132. Section 54 stipulates that it is an offence to sell food that is unfit for human consumption. General protection for purchasers of food is provided in Section 52 of the Ordinance when the food is not of the nature, substance, quality of the food demanded by the purchaser.

3. For enforcement purposes, microbiological limits are specified which are also used for assessment of microbiological safety and monitoring of food . This set of recommended microbiological guidelines for ready-to-eat food provides operational support for food safety monitoring and control.

Definition and Interpretation

4. Microbiological Guidelines are criteria indicating the microbiological condition of the food concerned so as to reflect its safety and quality. They can be introduced to the food industry to observe voluntarily or stipulated in legislation for compliance.

5. "Ready-to-eat" is defined as the status of the food being ready for immediate consumption at the point of sale. It could be raw or cooked, hot or chilled, and can be consumed without further heat-treatment including re-heating.

6. "Aerobic colony count (ACC)" is a count of viable bacteria based on counting of colonies grown in nutrient agar plate. This is commonly employed to indicate the sanitary quality of foods. The incubation condition of ACC used in this guideline is 30°C for 48 hours.

7. "Indicator organism" refers to the selected surrogate markers. The main objective of using bacteria as indicators is to reflect the hygienic quality of food. E. coli is commonly used as surrogate indicator. Its presence in food generally indicates direct or indirect faecal contamination. Substantial number of E. coli in food suggests a general lack of cleanliness in handling and improper storage.

8. "Specific pathogens" refer to bacteria that may cause food poisoning. Mechanisms involved may be toxins produced in food or intestinal infection. The symptoms of food poisoning vary from nausea and vomiting (e.g. caused by S. aureus), through diarrhoea and dehydration (Salmonella spp. and Campylobacter spp.) to paralysis and death in the rare cases of botulism. The infectious doses vary from less than 10 to more than 106 organisms.

Components of Microbiological Criteria

9. The microbiological limits of this set of guidelines are organized under the following three components:

  1. Aerobic Colony Count;
  2. Indicator Organisms - E. coli count is the only indicator organism included; and
  3. Specific Food Poisoning Pathogens - nine specific bacterial pathogens are included in this set of guidelines.

10. For assessment of hygienic quality, food items are grouped into five categories taking into account the raw ingredients used, and the nature and degree of processing before sale. The categorization is summarized in the Food category table for ACC assessment in the Annex.

Classification of Microbiological Quality

11. The microbiological assessment of ready-to-eat food on the above three components will lead to the classification of the food quality into one of the following four classes.

  1. Class A: the microbiological status of the food sample is satisfactory.
  2. Class B: the microbiological status of the food sample is less than satisfactory but still acceptable for consumption.
  3. Class C: the microbiological status of the food sample is unsatisfactory. This may indicate a sub-optimal hygienic conditions and microbiological safety levels. Licensees of food premises should be advised to investigate and find out the causes and to adopt measures to improve the hygienic conditions. Taking of follow-up samples to verify the improvement may be required.
  4. Class D: the microbiological status of the food sample is unacceptable. The food sample contains unacceptable levels of specific pathogens that is potentially hazardous to the consumer. In addition to giving advice to the licensee of the food premises as stated in (c) above, warning letters as well as other enforcement actions should be considered.

Table of Microbiological Limits

12. Microbiological limits in respect of the above components, and the associated microbiological quality of the food samples concerned are summarized in the following table.

Microbiological Limits for Assessment of Microbiological Quality of Ready-to-Eat Foods

Criterion Microbiological quality
colony-forming unit (cfu) per gram unless specified
Class A
Class B
Class C
Class D
Aerobic colony count (ACC) [30°C/48 hours]
(see table next page)
1 < 103 103 - < 104 ≥ 104 N/A
2 < 104 104 - < 105 ≥ 105 N/A
3 < 105 105 - < 106 ≥ 106 N/A
4 < 106 106 - < 107 ≥ 107 N/A
5 N/A N/A N/A N/A
Indicator organisms (apply to all food categories)
E. coli (total) < 20 20 - < 100 ≥ 100 N/A
Pathogens (apply to all food categories)
Campylobacter spp. Not detected in 25g N/A N/A Present
in 25g
E. coli O157 Not detected in 25g N/A N/A Present
in 25g
L. monocytogenes Not detected in 25g N/A N/A Present
in 25g
Salmonella spp. Not detected in 25g N/A N/A Present
in 25g
V. cholerae Not detected in 25g N/A N/A Present
in 25g
V. parahaemolyticus < 20 20 - < 100 100 - < 103 ≥ 103
S. aureus < 20 20 - < 100 100 - <104 ≥ 104
C. perfringens < 20 20 - < 100 100 - <104 ≥ 104
B. cereus < 103 103 - < 104 104 - < 105 ≥ 105

N/A denotes "Not applicable"

Annex: Food Category Table for Aerobic Colony Count Assessment

Food group Food item Category
Meat Beefburgers and kebabs 1
Dim sum 2
Pate (meat, seafood or vegetable) 3
Poultry (unsliced) 2
Preserved meat 4
Salami and fermented meat products 5
Sausages 2
Smoked meat 5
Siu-mei & lo-mei 3
Sliced meat (ham and tongue) (cold) 4
Sliced meat (beef, haslet, pork, poultry, etc.) (dried) 3
Steak and kidney / meat pies 2
Tripe and other offal 4
Seafood Crustaceans 3
Pickled fish 1
Other fish (cooked) 3
Oysters (raw) 5
Seafood meals 3
Shellfish (cooked) 4
Smoked fish 4
Dessert Cakes, pastries, slices and desserts - with dairy cream 3
Cakes, pastries, slices and desserts - without dairy cream 2
Cheesecake 5
Mousse / dessert 1
Tarts, flans and pies 2
Trifle 3
Savoury Bean curd 5
Cheese-based bakery products 2
Fermented foods 5
Flan / quiche 2
Dips 4
Mayonnaise / dressings 2
Samosa 2
Satay 3
Spring rolls 3
Vegetable Coleslaw / salads (with or without meat) 3
Fruit and vegetables (dried) 3
Fruit and vegetables (fresh) 5
Rice 3
Vegetables and vegetable meals (cooked) 2
Dairy Cheese 5
Yoghurt 5
Ready-to-eat meals Pasta / pizza 2
Meals (others) 2
Sandwiches and filled rolls With salad 4
Without salad 3
Sushi & sashimi Fish fillet and fish roe sashimi / sushi 3
Sashimi other than fish fillet and fish roe 4

The Frozen Confection Regulations and Milk Regulations under Cap 132 provide specification on the microbiological quality of frozen confections and milk and milk beverages. The Milk Regulations also include microbiological limits for milk in its raw state.


Centre for Food Safety
Food and Environmental Hygiene Department