Food Control, Vol. 6, No. 1, 2%36, 1995 pp. Copyright 0 1995 Elsevier Science Ltd

Printed in Great Britain. All rights reserved

0956-7135195 $10.00 + 0.00

Development of industrial procedures to ensure the microbiological safety of food

A.C. Baird-Parker

This paper discusses the concepts applied by the food industry to assure the microbiological safety of food products. It considers the development of these concepts and their relevance to the current needs of the industry. It discusses hazard and risk ranking, testing and measurements, design to a performance standard and the application of HACCP. It also considers, in depth, the use of formal risk assessment schemes based on hazard and exposure measurement and some of the difficulties of applying such schemes to measure microbial risks.

Keywords: microbiological safety; risk assessment; control

INTRODUCTION

Mankind has learnt over many millennia which of nature’s products to eat and which not to eat. As a hunter and gatherer, man learned to distinguish be- tween edible and inedible species, and as a farmer and food producer learned to grow, harvest, process and to store produce so as to provide food from one season to the next. He also discovered the value of drying, freezing, smoking, curing, fermentation and acidifica- tion as means of preserving his food supply as well as adding welcome variety to his diet. At the same time man learnt much about the ravages of food poisoning. Thus St Anthony’s fire (ergotism) destroyed many communities in the middle ages and sausage poisoning (botulism) so concerned the Byzantine Emperor Leo VI (886911 AD) that he banned the consumption of blood sausage (Meyer, 1928). Similarly, many religious taboos related to eating food and the early public health acts were concerned with avoiding illness from food consumption (Bell, 1993). Thus some means of avoidance of food poisoning were developed by com-

Rosewood, 13 Church View, Burton Latimer, Northants NN15 5LG, U.K. Received 7 March 1994; revised 14 April 1994; accepted 15 April 1994

munities long before there was any recognition that microorganisms caused foodborne illness.

The introduction of commercially processed foods in the last century, and notably sterilized canned food in the second half of the century, allowed perishable foods to be distributed and stored for long time periods at ambient temperatures. The rapid spread of such mass- produced convenience foods, and evidence of them causing illness, led to the recognition in the early part of this century of the need to establish a means of assuring safety of food products better than the process of trial and error that mankind had used in the preced- ing 8-10 000 years (Figure I). For instance, in 1918, the USA health authorities set up a Botulism Commission that in 1922 published its findings on the extent of botulism from commercially canned foods (150 cases between 1918-1922 alone), and work carried out by Esty and Meyer (1922) on the heat resistance of Clostridium botufinum spores established the basis of a microbiologically safe process for canned food. The recommendations developed from this work were rapidly accepted by the US canning industry, and later internationally, and are still the basis of the thermal process used for assuring the microbiological safety of low-acid canned foods. Since such pioneering work, industry has increasingly recognized the need to base microbiological safety on sound knowledge of the

Food Control 1995 Volume 6 Number 1 29

Microbiological safety of food: A.C. Baird-Parker

I:

1850 no

THE LEARNING CURV J

Figure 1 Evolution of food safety concepts

microbiological hazards associated with a food and the development of technological means for their control based on the assessment of their microbiological risks.

The aim of this paper is to explore some of the concepts that industry has developed and applied to assure food safety. General procedures for assessing health risks will be considered first, together with their application in the context of the microbiological safety of foods; secondly, the development of specific proce- dures will be addressed.

ASSESSMENT OF MICROBIOLOGICAL SAFETY

The microbiological risks associated with the consump- tion of any food depend on the types and number of microorganisms, or amounts of microbially produced toxin(s), present in a food at the time of consumption and the susceptibility of the person consuming the food to these factors. Thus any microbiological safety re- quirements must, on the one hand, take account of microbiological knowledge concerning the occurrence and fate of potentially hazardous microorganisms with- in a particular product and, on the other, medical knowledge concerning the numbers of microorganisms (or amounts of toxin) able to cause illness.

Formal health risk assessments procedures generally applied to assessing the risks associated with chemicals and other substances in foods mostly apply four analy- tical steps (Kaplan and Garrick, 1981; Hathaway, 1993). These are:

(a) Hazard identification: a qualitative indication that the substance or agent may adversely affect human health.

(b) Hazard assessment: the qualitative and quantita- tive evaluation of the nature of the adverse affects.

(c) Exposure assessment: the qualitative and quan- titative evaluation of the degree of exposure to a substance or agent likely to occur.

(d) Risk characterization (assessment): integration of the above steps into a quantitative estimate (probability) of the adverse affects likely to occur in a given population.

Such formalized assessment procedures have not gener- ally been applied to microbiological hazards associated with foods (for reasons see below), although some attempt to do so is being made by the US National Advisory Committee on Microbiological Criteria for Foods (NACMCF) Subcommittee on Risk Assessment and there is a recent report of applying such procedures to viral contamination of shellfish (Rose, 1993). However, the first two stages of the formal procedure (hazard identification and hazard assessment) are wide- ly used in HACCP, an internationally accepted proce- dure for defining conditions for the production, manu- facture and distribution of microbiologically safe foods (ICMSF, 1988).

Hazard identification

We have reasonably good qualitative knowledge, and some quantitative knowledge, of the occurrence of microbial pathogens in the many components of our diet and the extent to which they cause illness. Such information has been derived from a number of surveys of the microbiology of raw materials and foodstuffs and from epidemiological surveillance of foodborne infec- tions and intoxications (Richmond Committee, 1990; WHO, 1992). However, our knowledge is incomplete, as in most foodborne illness incidents a food source is not identified and, in many cases of illness, food poisoning organisms are not isolated from the ill per- son. Further, for a variety of reasons there is gross under-reporting of food poisoning incidents to the health authorities (Hauschild and Bryan, 1980). It is expected that the use of Sentinel studies, where pa- tients of general practitioners with symptoms of gastro- intestinal illness, are asked to fill in a questionnaire and to submit faecal samples for laboratory examination, will improve our knowledge of causative agents but not necessarily the source of the organisms, or the events that lead to the illness. Studies done recently in The Netherlands revealed striking differences between types of causative organisms and extent of foodborne illness measured by a Sentinel study compared with data gathered by the health authorities (Notermans and van der Giessen, 1993). The UK department of health has recently started a large Sentinel study involving >70 general practitioners in England and Wales which is expected to provide valuable data on food poisoning incidence and causative agents in the UK.

We have much knowledge of the growth, survival and death of foodborne disease-causing microorgan- isms and this can be used to identify potential microbiological hazards in a particular foodstuff (ICMSF, 1980; Doyle, 1989; Varnum and Evans, 1991). The development of databases and associated mathematical models able to predict microbial growth, death and survival rates such as UK MAFF Food Micromodel (McClure et al., in press) and the USDA Eastern Regional Research Centre database and mod- els will further to assist us objectively to identify and quantify microbial hazards; an international database is expected to be available within the next few years.

30 Food Control 1995 Volume 6 Number 1

Microbiological safety of food: A.C. Baird-Parker

Hazard assessment

Hazard assessment, in order to be effective, must be both quantitative and objective. Thus the significance of a microbiological hazard in terms of severity and likely occurrence must be understood, and interpret- able in any hazard assessment. In this regard, micro- biologists have made significant progress in recent years in devising methods for quantitatively and objec- tively assessing microbiological hazards associated with food and identifying strategies for their control. Such hazard assessment procedures have been used to build the hazard analysis critical control point (HACCP) concept (Baumann, 1974) into a system (ICMSF, 1988; Mayes, 1992) whereby microbiological hazards identi- fied in the food production and use chain are assessed objectively in relation to any health concerns likely to be associated with consumption of a food. A similar, but less well developed procedure (longitudinally inte- grated safety assurance; LISA) has been proposed by Mossel (Mossel and Struijck, 1992). HACCP will be discussed in more detail below.

A major problem with microbiological hazard assess- ments is the paucity of quantitative information con- cerning the likely outcome of ingestion of a food contaminated with different levels of pathogenic micro- organisms: ie. will infection occur, and, if so, will this lead to mild, moderate or severe illness? We know that a large number of factors will affect the initiation of infection and disease. These include factors associated with the organism per se and particularly concern viability and how well developed are its virulence factors. These will depend on the particular strain and its history prior to, and during, its association with the food, including its location in a foodstuff and effects of processing, storage and use. There are also the effects of food per se, including whether it is; liquid or solid (including size of particles); part of a snack or a meal; fat and iron content, acidity; other flora; preservative factors; and storage conditions - all of which will effect microbial viability and ability to survive passage through the stomach and to establish itself in the lower intestinal tract. Finally there are the idiosyncratic fac- tors associated with an individual consuming the food including: nutritional and physiological factors; im- munological status; age; status of intestinal tract at the time of consumption; and previous exposure of the individual to infection by the organism. Some of these factors may also affect the outcome of infection and, in particular, severity (D’Aoust, 1989). For instance, in human volunteer studies, subjects responding to re- infection with Gram-negative enteric organisms gener- ally has less severe symptoms than the initial illness, and more organisms were necessary to initiate infection (McCullough and Eisele, 1951; Levine et al., 1979). These aspects of disease initiation were discussed at a recent ILSI(Europe)-sponsored workshop (ILSI, 1994) which came to a number of conclusions concerning the need for further information on the infective dose of microorganisms. These were that epidemiological stu-

dies give useful information on the numbers of micro- organisms causing infection in a particular food poison- ing episode but provide no information on the MID (minimum infective dose), and that extrapolation of the data to other foodstuffs situations was not possible because of the vast range of factors that may affect the apparent infective dose (see above). Thus any gener- ated dose-response curves would have to take these factors into account, and particularly the response of different at risk groups, e.g. the young, old, pregnant and immunocompromised. It was further considered that experiments in animals cannot be used to predict response in humans (and particularly the human MID), although animals are useful for establishing the effects of different factors on the initiation of disease and for studying the disease process. The overall conclusion was that it was difficult to determine precise rela- tionships between a particular concentration of an organism, the probability of initiation of infection in man and the severity of any ensuing disease, except possibly for specific foods and defined sectors of a population. This fact was well demonstrated in a recent US FDA study (D. Archer, personal communication 1993) where a group of experts was asked to predict the human disease response in terms of mild, moderate or severe illness by 15 foodborne pathogens when present in food at one of three concentrations. The experts differed hugely in their estimates but the most consis- tent response was for Campylobacter jejmi whose ability to initiate disease is less affected than other foodborne pathogens by such factors as age and im- munocompetence. Glynn and Bradley (1992) analysed epidemiological data from 68 outbreaks of typhoid and 49 outbreaks of salmonella food poisoning and, based on reported severity (e.g. number of patients hospital- ized), found a dose-response relationship for severity of disease caused by foodborne disease-causing sal- monella but not by S. typhi.

Our current knowledge of how disease initiation is affected by different concentrations of microorganisms in foods is poor, but with better knowledge of the disease processes and factors affecting this it may possible to to develop dose-response models for the major pathogens that are at least applicable to the not-at-risk section of the population; such a model for pathogenic microorganisms in drinking water has been developed (Haas, 1983; Rose and Gerba, 1991). This has recently been extended to assess the health risks associated with viral contamination of shellfish, based on human feeding studies of a number of viruses from which dose-response curves and probabilities of infec- tion from exposure to a single virus particle were calculated using the Beta-Distribution Probability Model of Haas (Rose, 1993).

Exposure assessment

Exposure assessment concerns determining the prob- ability of consumption of a sufficient number of micro- organisms to initiate infection and disease. Added to

Food Control 1995 Volume 6 Number 1 31

Microbiological safety of food: A.C. Baird-Parker

* I”rErrIca

Figure 2 Exposure assessment of a microbial hazard. MID, mini- mum infective dose; -, frequency distribution of microbes; - - -, percentage infection (confidence limits shown by arrows, reflecting population sensitivity)

the difficulty caused by the idiosyncratic response of man to infection by foodborne disease-causing micro- organisms, there is the fact that microorganisms are usually highly heterogeneously distributed in foods. This distribution often changes throughout the food chain as a result of microbial growth or death during storage and preparation for consumption and this com- plicates exposure assessment. Any risk model must take into account microbial distributions. Mossel and Drion (1979) based their risk model on the assumption of random (Poisson) distribution of microorganisms in food, but we know that microbial distributions more generally correspond to log normal distributions with variable amounts of skew (Kilsby and Pugh, 1981). Taking account of the heterogenous distribution of microorganisms in food and the varied response of individuals to infection, it is not surprising that not all individuals exposed to a food contaminated with an infecting dose foodborne disease-causing organism be- come ill. This is illustrated in Figure 2, which shows that only those persons consuming a particular concentra- tion of microorganisms will become ill, and the prob- ability of illness also depends on the sensitivity of the exposed population. Few measurements appear to have been made of the distributions of infections arising from low levels of microbial contamination other than those by Haas (1983) and Rose (1993). These workers make the assumption that infecting organisms are randomly distributed in water/shellfish, that a single organism may cause infection and susceptibility to disease is normally distributed in a population; they also make an assumption as to the average amount of contaminated material that would be consumed. Rec- ognizing that many of the assumptions are probably wrong, these workers are to be congratulated for tackling microbiological risk assessment in a logical way.

Risk characterization

This is the outcome of hazard and exposure assessment and is generally expressed as a cumulative probability of occurrence of the hazard being assessed. In deciding whether a risk is acceptable or not, it is necessary to recognize that absolute safety is impossible to achieve

and that an acceptable risk of illness in a population exposed to a microbiological hazard must be decided. Ideally this should be done by close working together of industry, consumer groups and the responsible health authorities taking account of socio-economic and other aspects of such a decision. In the risk assessment model developed for the water and shellfish industry, (Rose and Gerba, 1991; Rose, 1993) the US Environment Agency proposal for risks from the consumption of water was used, ie. one infection/lo4 persons per year exposed was an acceptable risk of infection in a popula- tion; Mossel and Drion (1980) used a mean frequency of infection for enteric pathogens of one infection in a whole population during 100 years. These differences probably reflect the pragmatic views of an agency and the more idealistic views of academia. However, in any consideration of acceptability of risk, account must always be taken of the severity of the hazard. Thus in any assessment involving a life-threatening microorgan- ism such as Clostridium botulinum, industry will always aim to achieve a level of safety that is much higher than that applied to a mild foodborne illness-causing organ- ism such as Clostridium perfringens. Thus, for a canned food, an exposure level to Clostridium botulinurn con- tamination of <l can in 1012 is acceptable, whereas for non-life-threatening or spoilage organisms an exposure level of 4 can in lo4 is acceptable.

Thus in considering what is an acceptable risk, industry will take account of epidemiological data relevant to illness (dose and severity); target popula- tion of consumer; and the probability of circumstances outside their control giving rise to a health risk. On the basis of such an analysis, the degree of security that must be designed to a particular food operation is defined and, in the absence of sound data on which to base a risk assessment, the aim is always to build in additional safety factors. However, as Macler and Regli (1993) discuss in their paper on microbial risk assess- ment and drinking water standards, when considering an acceptable risk is important to recognize that, in reducing the risk of exposure to our agent, one must be careful not to increase the risk of another. As an example, they quote the use of high levels of chlorine to reduce microbial contamination of water; an example more relevant to the food industry could be the use of excessive levels of preservatives. Thus there is always a need to balance risks and, in some parts of our world, this may be a pragmatic decision that if we do not eat we will starve to death, but if we eat we may die. Such decisions do not, of course, come into food industry safety assessments, but there must always be socio- economic considerations in any risk assessment.

Formal risk assessment of a foodborne pathogen will always be difficult because of the uncertainty, unpre- dictability and, to some extent, the specificity of much of the data needed for hazard and exposure assessment. Industry, for moral and self-interest reasons does not wish to market unsafe foods and may wish to operate to a higher safety standard (lower risk) than that adopted by health authorities. The latter are concerned with all

32 Food Control 1995 Volume 6 Number 1

CONDITIONS UNDER WHICH FOOD HANDLED

Figure 3 ICMSF classification of health risks. For explanation of cases, see text

types of hazards to health in a population and may prefer to concentrate available resources on those hazards where there are greater risks and most political pressures for action.

The following section indicates how risk assessment procedures are applied by the food industry to assure the microbiological safety of industrial foods.

APPLICATION OF RISK ASSESSMENT PROCEDURES

Use of hazard characterization and hazard/risk ranking of foods and food operations

Health authorities and some sections of industry apply procedures whereby the microbiological hazards and risks of products and processes are ranked into categor- ies according to an estimate of their relative risks. This is a useful initial procedure in any risk assessment as it enables prioritization of action. Examples included those based mainly on a combination of food product characteristics, potential for growth and susceptibility of the consumer (National Academy of Sciences, 1969; Richmond Committee, 1990); those based on a com- bination of organism characteristics and potential for growth/survival (ICMSF, 1986); those based on a com- bination of food type, method of processing and num- bers of consumers exposed to risk, used for ranking food processors for the purpose of inspection (US Food Safety Act, 1990); those using combination of epidemiology, food handling procedures and number of persons served, for ranking catering establishments (Bryan, 1982).

Use of measurement of microbial numbers

Traditionally, microbiologists have attempted to reflect their judgement of risk by ascribing limits to concentra- tions of specific microorganisms regarded to be of concern in a particular foodstuff. This is followed by setting a means of controlling risk based on measure- ment of microbial numbers, to test whether or not a

Microbiological safety of food: A.C. Baird-Parker

specified concentration is exceeded. Such limits may be reflected in specifications developed by producers and purchasers of food or standards used by official bodies. This measurement approach has been developed exten- sively by the International Commission on Microbiolo- gical Specifications for Food. This organisation (ICMSF, 1986) developed a matrix of progressively more stringent sampling plans (numbers of sample units tested and stringency of compliance) based on: an expert judgement of severity of a disease caused by a particular organism; ability of the food to support growth; and how the food is prepared for consumption. The matrix developed is illustrated in Figure 3. The stringency of the sampling plans were related by the ICMSF to ‘Cases’, defined as ‘a set of circumstances relating to a hazard a food represents and to its anticipated subsequent treatment’. Thus a good con- taminated with S. typhi would be considered a severe hazard and Case 13,14 or 15 would apply depending on how the food is subsequently handled. For instance, if it is to be cooked prior to consumption, the sampling plan appropriate to Case 13 would be applied, whereas if the food is ready-to-eat and could support the growth of S. typhi a more stringent plan appropriate to Case 15 would be applied. The matrix, and the two- and three-class Attribute Sampling Plans associated with its use are used internationally as the basis for selecting sampling plans for end-product testing of foods. However, it is increasingly recognized that, although these plans are statistically sound and based firmly on hazard identification and risk assessment principles, they give poor security of safety of a batch of food. This is because the relatively small number of samples that can realistically be examined in the laboratory are un- likely to reflect the true levels of microorganisms in a batch of food. This heterogenous distribution of micro- organisms in foods means that the microorganism levels measured in the sample are unlikely to reflect the true average level of organisms in the batch or where presence/absence testing is used, absence in a sample does not mean absence in the batch (Mossel, 1977; Sharpe, 1980; Kilsby, 1982). Indeed, even when 60 sample unit from a batch of product are tested (for absence of a microorganism in a particular sample) and, assuming random distribution of the microorgan- ism, there is only a 50% chance of detecting contamin- ated product sample units, when the contamination level of product sample units is up to 1% (ICMSF, 1986). However, microbiological analyses give useful trend information and hence useful information on the performance of a food operation when accumulated results from a number of food batches are considered over a period of several months.

The performance of control methods based on the measurement of microbial numbers can be somewhat improved by applying sampling plans based on statistics such as ‘variables statistics’ which take account of the distribution of microorganism in a particular food. Variables-based plans are particularly useful to a food manufacturer who can determine the type of microbial

Food Control 1995 Volume 6 Number 1 33

Microbiological safety of food: AC. Baird-Parker

distribution and degree of variance of microorganisms in a particular product and hence improve the accuracy of an analysis (ICMSF, 1988). Where very low numbers of a pathogen are heterogeneously distributed in a batch it is possible to use sequential sampling methods where small quantities of product, e.g. 1 g, are taken at frequent intervals during production of a food batch and thoroughly mixed together to form a single analy- tical sample that is much more representative of the microbiological status of a production batch. This will give a higher probability of finding whether small numbers of a heterogenous distributed microorganism are present, than taking a smaller number of larger sized samples to an equivalent analytical sample weight; see also Kilsby and Pugh (1981) for further methods of improving the reliability of measurement techniques. However, control strategies based on measurement alone will never be able to assure micro- biological safety and generally this approach is being replaced by others, with microbiological measurements being used for more productive roles.

Use of design to a performance standard

An entirely different approach used by industry to assure the microbiological safety of its products is one based on meeting a particular performance standard; this means operating a process to deliver a certain kill, or inhibit a particular number of microorganisms. This approach makes assumptions as to levels of different pathogenic microorganisms likely to be introduced into a food product via raw materials or during subsequent processing and distribution, and also requires a deci- sion as to the limit(s) of acceptability of specific (or general groups of) microorganisms in the final product. Thus, like the measurement approach, it is based on an assessment of risk associated with an end product. It is not new and one of the best examples of its application is the performance standard for the safety of thermally processed low acid (pH 4.6 and above) canned foods which dates back to the 1920s. The standard, the so-called ‘botulinurn cook’ is a heat treatment designed to reduce the probability of survival Clostridium botuli- num in a single container of product to 10-l*. This heat process is based on the work of Esty and Meyer (1922) on the heat resistance of spores of more than 100 strains of Clostridium botulinum. The reasons why 10-l* was chosen as the standard are unknown to the author, but could be based on the assumption that on average one spore of C. botulinum could be present in each contain- er of a food prior to canning and that 1012 was the likely output of the US canning industry over a ten-year period. Some years later Ball and his associates de- veloped a means of calculating the thermal process needed to be given to different sizes of cans, product types and retort conditions based on modelling Esty and Meyer’s data. Thus they observed a log-linear destruction rate of the spores (from which could be calculated the D value) and also they noted a linear relationship between the log of the D value and

temperature (from which they derived the term z value). The D and z values form the basis of the mathematical model used to calculate the lethal rates of spores subject to different thermal processing tempera- tures (Stumbo, 1973). This model was introduced in the 1940s and for more than 50 years has proved its effectiveness. Thus it has stood the test of time despite increasing recognition that the concept of D and z value is an oversimplification of the effects of heat on the destruction of microorganisms (Gould, 1989).

Similar performance standards have been developed for pasteurized milks and, more recently, for chilled foods, where a probability of contamination of the pasteurized product with vegetative infectious disease- causing organisms of less then 10m6 is generally agreed to be an acceptable process standard for these pro- ducts. It is possible to extend the performance standard approach to further areas of food microbiology. Thus a further example of a performance standard approach is that used by Pivnick and Petrasovits (1973) who de- veloped a model for heat processing of canned cured meat products based on the measurement of destruc- tion and inhibition factors in the product using the summation of these factors (the heat process was calculated and the degree of inhibition by the combina- tion of heat and curing salts was measured) to devise an overall protection factor equivalent to the botulinurn cook. Hauschild and Simonsen (1985) further de- veloped the approach to provide a basis for safety evaluation of commercially used processes for self- stable cured meats.

Use of hazard identification and assessment (HACCP) in establishing process design

Increasingly, industry applies a more integrated approach to food safety based on the use of HACCP concept. There are many excellent documents on HACCP and the best of these apply systematic and quantitative procedures for hazard identification and assessment (NACMCF, 1992; CFDRA, 1992; FAO/ WHO, 1993; ILSI, 1993). The modern approach to HACCP is based on the use of multidisciplinary teams of experts applying a series of searching questions, concerning potential hazards and their control, in a systematic and formalized manner to all stages in a food operation. Much of this systematic approach is derived from HAZOP which is a technique that was originally used by the chemical industry to identify explosion and chemical hazards (Mayes and Kilsby, 1992).

In order to apply HACCP it is necessary to have good knowledge of the types of pathogenic organisms that may be contaminating a food and how these might change in numbers during production, distribution and preparation for consumption. Thus we need to under- stand how the numbers and types of microbes are affected by the structure and composition of the food, processing conditions and further may change during distribution, storage and use. Such knowledge will usually be found in books and journals on food micro-

34 Food Control 1995 Volume 6 Number 1

Microbiological safety of food: AC. Baird-Parker

biology but is often difficult to collate these in a form suitable for answering the questions likely to be asked in a HACCP study. Thus specific microbiological data bases are being developed and one of the most detailed of these will shortly be published by the ICMSF (ICMSF, 1994); this data will also be published as a PC database providing the data in a form that can be even more easily interrogated by a technical expert.

Parallel with the development of HACCP has been the introduction of mathematical models which are able to predict the growth, survival and death of microbes in foods and, in particular, how they are affected by such parameters as a,, pH, temperature, preservative con- tent and packaging conditions. The types of models range from simple response surface models that relate time to a particular event, such as the production of toxin or a cell count, to more complex models that are able to predict the effects of change in temperatures on

microbial numbers, as affected by changes in formula- tion and processing conditions (Cole, 1991). Predictive models will also be expected to replace microbiological challenge testing in foods, as a means of determining whether a potential pathogen will be able to survive a particular process and/or distribution regime, as it is increasingly demonstrated that there is good correla- tion between the predictions from the use of models, and the results of challenge testing.

and assistance from Dr M.H. Brown in preparing this paper.

REFERENCES

Baumann, H. (1974) The HACCP concept and microbiological hazard categories. Food Technol. 28, 30-34, 74

Bell, R.G. (1993) Development of the principles and practices of meat hygiene: a microbiologist’s perspective. Food Control 4, 125-133

Bryan, F.L. (1982) Foodborne disease risk assessment of food service establishments in a community. J. Food Prof. 45, 93-100

Cole, M.B. (1991) Databases in modern food microbiology. Trends Food Sci. Technol. 2, 293-297

Corlett, D.A. and Stier, R.F. (1991) Risk assessment within the HACCP system. Food Control 2, 71-72

D’Aoust, J.-Y. (1989) Salmonella. In: Foodborne Bacterial Pathogens (Ed. M.P. Doyle) Marcel Dekker, New York, pp. 328-445

Doyle, M.P. (1989) Foodborne Bacterial Pathogens Marcel Dekker, New York

Esty, J.R. and Meyer, K.F. (1922) The heat resistance of the spores of C. botulinus and allied anaerobes. J. Infect. Dis. 31, 650-663

FAO/WHO (1993) Report of the 26th Session of the Codex Commit- tee on Food Hygiene (Washington DC, l-5 March, 1993). Appendix II. Guidelines for the Application of the Hazard Anal& sis Critical Control Point IHACCP) Svstem Alinorm 93l13A. FAO/WHO, Rome ’ ’

Glynn, J.R. and Bradley, D.J. (1992). The relationship between infecting dose and severity of disease in reported outbreaks of salmonella infections. Epidemiol. Infect. 109, 371-388

THE WAY FORWARD

Gould, G.W. (1989) Heat injury and inactivation. In: Mechanism of Action of Food Preservation Procedures (Ed. G. W. Gould) Elsevier Applied Science, Amsterdam, pp. 11-42

Industrial food safety concepts based on risk assess- ment will continue to evolve as more information becomes available on which to base effective hazard identification and risk assessment procedures. We need to understand more about how microbes behave in food and the extent to which they are able to respond to their environment, switch genes and particularly de- velop means to change their resistance to preservatives and preservation systems used by the food industry. We need to understand the disease processes and particu- larly the molecular basis whereby microbes intiate infection and disease in man and how man may develop resistance to disease. We need to develop dose- response models and agree procedures to establish a scientific basis for establishing microbiological and other acceptance criteria for foods. As we develop mechanistic models based on physiological and mole- cular understanding of how microbes behave in foods we will also develop more accurate predictive models. We will also develop better ways to observe and detect microorganisms in foods. All such knowledge will be essential if we are going to be able to safely apply the most recent methods of preserving foods (Mertens and Knoor, 1992; Selman, 1993) and also improve the application of existing ones.

ACKNOWLEDGEMENT

The author wishes to acknowledge the useful advice

Haas, C.N. (1983) Estimation of risk due to low doses of microorgan- isms. A comparison of alternative methodologies. Am. J. Epidemiol. 118, 573-582

Hathaway, S.C. (1993) Risk assessment procedures used by the Codex Alimentarius Commission and its subsidiary and advisory bodies. Food Control 4, 189-201

Hauschild, A.H.W. and Bryan, F.L. (1980) Estimate of cases of food and water-borne illness in Canada and the United States. J. Food Prot. 43, 435-446

Hauschild, A.H.W. and Simonsen, B. (1985) Safety of shelf-stable canned cured meats. J. Food Prot. 48, 997-1009

ICMSF (1980) Microbial Ecology of Foods Vol. 1 and 2, Academic Press, New York

ICMSF (1986) In: Microorganisms in Foods 2. Sampling for Micro- biological Analysis: Principles and Specific Applications 2nd Edn, University of Toronto Press, Toronto, p. 82.

ICMSF (1988) In: Microorganisms in Foods 4. Application of the Hazard Analvsis Critical Control Point (HACCP) Svstems to Ensure Micrdbiological Safety and Quality Blackwkll icientific, Oxford

ICMSF (1994) Microorganisms in Foods. Characteristics of Microbial Pathogens. Chapman & Hall, London

ILSI (International Life Science Institute, Europe) (1993) A Simple Guide to Understanding and Applying the Hazard Analysis and Critical Control Point Concept ILSI Press, Brussels

ISLI (International Life Science Institute, Europe) (1994) A Scientific Basis for Regulations on Pathogenic Microorganisms in Foods ILSI Press, Brussels

Kaplan, S. and Garrick, B.J. (1981) On the quantitative definition of risk. Risk Analysis 1, 11-27

Kilsby, D.C. (1982) Sampling schemes and limits. In: Meat Micro- biology (Ed. M.H. Brown) Applied Science Publishers, London, pp. 387-42 1

Kilsby, D.C. and Pugh, M.E. (1981) The relevance of the distribution of microorganisms within batches of food to the control of microbiological hazards for foods. J. Appl. Bacterial. 51, 345-354

Food Control 1995 Volume 6 Number 1 35

Microbiological safety of food: A.C. Baird-Parker

Levine, M.M., NaBn, D.R., Hoover, D.L., Bergquist, E.J., Homick, R.B. and Young, C.R. (1979) Immunity to enterotoxigenic Escherichia coli. Infect. Immun. 23, 729-736

Macier, B.A. and Regii, S. (1993) Use of microbial risk assessment in setting US drinking water standards. ht. J. Food Microbial. 18, 245-2.56

Mayes, T. and Kiisby, D.C. (1989) The use of HAZOP hazard analysis to identify critical control points for the microbiological safety of food. Food Qual. Pref. 1, 53-57

Mayes, T. (1992) Simple user’s guide to the hazard analysis critical control point concept for control of food microbiological safety. Food Control 3, 14-19

McClure, P.J., Blackbum, C., Cole, M.B. et al. (in press) UK approach to modeliing the growth, survival and death of micro- organisms. ht. J. Food Microbial.

McCuBough, N.B. and Eiseie, C.W. (1951) Experimental human salmonellosis. II. Immunity following experimental illness with Salmonella meleagridis and Salmonella anatum. J. Immunol. 64, 595-608

Mertens, B. and Knonr, D. (1992) Developments in non-thermal processes for food preservation. Food Process. May, 124-133

Meyer, K.F. (1928) Ueber Botulismus Handbuch der pathog. Mikro- organismen 4th ed. Kolle

M-1, D.A.A. (1977) Microbiology of Foods. Occurrence, Preven- tion and Monitoring of Hazards and Deterioration. Faculty of Veterinary Medicine University of Utrecht.

Mossei, D.A.A. and Drion, E.F. (1980) Risk analysis as applied to the protection of the consumer against food transmitted disease. In: Food Microbiology and Technology (Ed. B. Jarvis, J. Christian and J. Michener) Medicinia Viva, Parma, pp. 417-430

Mossei, D.A.A. and Struijk, C.B. (1992) The contribution of micro- bial ecology to management and monitoring the safety, quality and acceptability (SQA) of foods. J. Appl. Bacterial. Symp. Suppl. 73, lS-22s

National Academy of Sciences( 1969) An Evaluadon of the Salmonella Problem. National Academy of Sciences, Washington DC

Notermans, S. and van der Geissen, A. (1993) Foodborne diseases in the 1980s and 1990s. The Dutch experience. Food Control 4, 122-124

Pivinck, H. and Petrasovits, A. (1973) A rationale for the safety of canned shelf-stable cured meats : Protection = Destruction + Inhibition. In: I9me Reunion Europeane des Chercheurs en Viande, Paris

Richmond Committee (1990) The Microbiological Safery of Food Part 1 (Report of the committee on the Microbiological Safety of Food) HMSO, London

Rose, J.B. (1993) Impact of shelf fish associated risk disease in the United States. Absrr. 80th Ann. Meet Int. Assoc. Milk Food Environ. Sanitarians Atlanta, August l-4, Abstract No. 118

Rose, J.B. and Gerba, C.P. (1991) Use of risk assessment for development of microbiological standards Water Sci. Technol. 24, 29-34

Seiman, J. (1993) New technologies for the food industry. Food Sci. Technol. Today 6, 205-209

Sharpe, A.N. (1980) Food Microbiology. A Framework for the Future Charles C. Thomas, Springfield, IL

Stumbo, CR. (1973) Thermobacreriology in Food Processing 2nd Edn, Academic Press, New York

CFDRA (Campden Food and Drink Research Association) (1992) HACCP: A Practical Guide. Technical Manual No. 38, Campden Food and Drink Research Association, Chipping Campden

UK Food Safety Act (1990) Code of Practice No. 9. Food Hygiene Inspection, HMSO, London

Varnun, A.H. and Evans, M.G. (1991) Foodborne Pathogens: an Illustrated Text Wolfe, London

NACMCF (National Advisory Committee on Microbiological Criteria WHO (1992) WHO Surveillance Programme for Control of Food- for Food (1992) Hazard Analysis and Critical Control Point borne Infections and Intoxicarions in Europe. Fifth report 1985- System (adopted March 20, 1992). Int. J. Food Microbial. 16, 1989. Institute of Veterinary Medicine, Robert von Ostertag l-23 Institute, Berlin

36 Food Control 1995 Volume 6 Number 1