Food Safety Hazard Guidebook

Richard Lawley, Laurie Curtis, Judy Davis

• Publisher: Royal Society of Chemistry
• Year: 2015
• ISBN:
  9781782625629
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Food Science
• Index: Technology & Engineering

Food safety is important and consumers have a right to expect that those who supply the food that they buy have taken every care to manufacture products that will do them no harm. Those with a responsibility for the regulation of the global food industry recognise this principle and legislate accordingly and the business of managing and regulating the safety of the food supply chain has come a long way in the last 25 years or so. Prompted by the emergence of new food safety hazards, such as the bacterial pathogens Listeria monocytogenes and E. coli O157, powerful new techniques for evaluating and managing the risks presented by these threats have been developed. For example, hazard analysis critical control point, or HACCP, has now become the food safety management system of choice worldwide. Although the food safety management tools are now widely available, they are still virtually useless unless they are supported by adequate and accurate information. HACCP does not work unless its practitioners have access to enough data and scientific knowledge to enable them to understand hazards and how to control them effectively. The Food Safety Hazard Guidebook is an attempt to address the problem of accessing the available information by distilling the key facts about a wide range of individual food safety hazards into a single text. The result is a guidebook, rather than an encyclopaedia, which acts as a portal for the immense and ever expanding body of scientific knowledge that exists for food safety. It is an easy-to-use information resource for anyone with a professional interest in the safety of the food supply. The book is easy to navigate and presents concise and carefully researched factual information on a wide range of biological and chemical hazards in a clear format that is designed to support risk analysis exercises and HACCP studies. It covers a broad range of established and emerging food safety hazards and includes details of authoritative sources of further information (many web-based) for those seeking to examine a topic in greater depth. The section on food allergens is a particularly valuable component of the book, the chapters on fish toxins are also useful and unusual in a book of this kind and bacterial pathogens are comprehensively covered. One of the most important features of the book is the wide scope of the content and the highly structured format designed to help the reader find information quickly. Other key benefits to the reader are: -The wide range of biological and chemical hazards covered in a single book -Written specifically with food industry professionals in mind -Easy to navigate and accessible for the non-expert -Clear and concise presentation of factual information presented in a format that lends itself to use in risk assessment exercises -Inclusion of references and web links to reliable sources of further information on each chapter -specifically designed for practical use by a professional readership.

Section 1: Biological Hazards

CHAPTER 1.1

Bacteria

1.1.1 AEROMONAS

Hazard Identification

What are Aeromonas?

Aeromonas species are gram-negative, non-spore-forming, bacteria, many of which are psychrotrophic (i.e. able to grow at low temperatures). Older references may state that these organisms are in the family Vibrionaceae, but they have recently been classified in a new family, the Aeromonadaceae, and this family now includes at least 14 described Aeromonas species.

Although a number of these species have been associated with human disease, the role of Aeromonas species as food-borne pathogens has yet to be confirmed. Aeromonas hydrophila, Aeromonas caviae, Aeromonas veronii biovar sobria and Aeromonas trota are the main species that are thought to cause gastrointestinal disease in man and it is considered that the main vehicle for these organisms is drinking water. Many Aeromonas species can be divided into two groups based on the temperature range at which strains are able to grow, and within a specific species some strains are psychrotophic, while others are mesophilic (not able to grow below 10 °C). For A. hydrophila, evidence suggests that those strains that are pathogenic to humans are mesophilic, whereas psychrotrophic strains are pathogenic to fish.

Occurrence in Foods

Aeromonas species are common contaminants in unprocessed foods and on occasions numbers can be high, exceeding 10⁶ cfu g⁻¹. Because of their widespread occurrence it is thought likely that not all strains of Aeromonas species are pathogenic. Aeromonas species have been isolated from the following food commodities: fresh vegetables; salads; fish; seafood; raw meats including beef, lamb, pork and poultry; and raw milk as well as high-pH cheeses produced from raw milk. Aeromonas species have also, on occasions, been isolated from some processed foods including pasteurised milk, whipped cream, ice cream and ready-to-eat animal products.

Possible gastroenteritis-causing species have been isolated from most of the above food groups. However, A. caviae is more commonly isolated from vegetables and salad while A. hydrophilia is more commonly isolated from meat, fish and poultry.

Hazard Characterisation

Effects on Health

Although there is increasing evidence to suggest that A. hydrophila, A. caviae and A. veronii biovar sobria are causative agents of food-borne gastroenteritis in humans, this is still a subject of debate. However, aeromonads are often detected in gastrointestinal infections.

The infectious dose is unknown, although data suggests that it is probably high, probably >10⁶ cells. Volunteer feeding studies involving ingesting high numbers of A. hydrophila cells (>10⁷) have been inconclusive, whereas the organism has been isolated from the stools of divers who became ill after taking in small amounts of contaminated water. Gastroenteritis associated with Aeromonas species is most frequently reported in young children, although it can occur in individuals of any age with the number of cases peaking in the summer months.

It is thought that when ingested, these organisms can cause gastrointestinal disease in healthy individuals, chronic enterocolitis in the elderly and septicaemia in the immunocompromised. Symptoms are thought to start to occur within 24–48 hours of ingestion of cells. Infection can manifest itself in one of two distinct forms. The more common form is a cholera-like illness (watery diarrhoea accompanied by a mild fever), sometimes accompanied by vomiting in children less than two years old. The less common form is a dysentery-like illness (diarrhoea with blood and mucus in the stools). The disease is usually self-limiting, lasting 1–7 days. Occasionally however, the diarrhoea can last for several months, or even longer (12 months plus). Rare cases of haemolytic uremic syndrome, following infection with Aeromonas species, have been linked to verocytotoxin-producing aeromonads.

Incidence and Outbreaks

Most Aeromonas infections are thought to be caused by contaminated water and there are few reported outbreaks of Aeromonas-associated gastroenteritis where food is the suspected vehicle of infection. These few incidents are mostly associated with seafood products such as raw oysters and clams, sashimi, cooked prawns, shrimp cocktail and raw fermented fish. The literature suggests that other food groups such as edible land snails, egg salad and smorgasbord (comprising shrimp and various ready-to-eat meat products) have also been involved.

Sources

Aeromonas species are ubiquitous, although the main source of the organisms is generally accepted as water. The organisms are found in flowing and stagnant fresh water, in water supplies (including chlorinated water), sewage and in marine waters, particularly those that border with fresh water such as in estuaries. Aeromonas species are also often found in household environments such as drains and sinks, and can be isolated from soil.

Aeromonads are found in aquatic animals such as frogs, fish and leeches, in reptiles and in domestic animals such as pigs, sheep, poultry and cows. They can also be carried by humans without symptoms on occasions, although carriage rates are higher in tropical or developing regions.

Growth and Survival Characteristics

The growth temperature range for Aeromonas species is variable, but is reported to be between <5 °C and 45 °C. Within a particular species there can be psychrotrophic strains (capable of growth at chill temperatures) and mesophilic strains (cannot grow below 10 °C). Although the optimum temperature for growth is generally reported as 28 °C, this figure is likely to vary depending on strain. Although environmental strains may not grow at 37 °C, many clinical strains can grow at 5–7 °C. A. hydrophila is reported to grow from 1–42 °C, with an optimum temperature of 28 °C.

Aeromonads are reported to survive freezing temperatures and have been isolated from frozen foods after storage for approximately two years.

The optimum pH range for the growth of aeromonads is between 6.5 and 7.5. The organisms are tolerant of pH values of up to 10 and many strains will grow down to pH 5.5 or less (under otherwise ideal conditions), but this characteristic is uncommon at chill temperatures. Aeromonads are inactivated at pH values <4.5.

Many aeromonads will not grow at salt levels >4%, although there are reports of some strains growing at concentrations of 6%. Studies have shown that when foods are stored at chill temperatures, Aeromonas species are unlikely to grow when the salt levels are more than 3–3.5% and pH values are below 6.0.

Aeromonas species are facultative anaerobes (capable of growth with or without oxygen). At chill temperatures however, it has been reported that growth rate is either unaffected, or possibly reduced, when fish is modified atmosphere/vacuum packaged. Modified atmospheres containing high levels of oxygen (>70%) have been shown to retard the growth of A. caviae on ready-to-eat vegetables at refrigeration temperatures.

Aeromonas species are not notably resistant to preservatives or sanitisers.

It is thought that their presence in chlorinated water is the result of post-treatment contamination or inefficiencies in the chlorination process.

Thermal Resistance

Aeromonads are not heat-resistant organisms and are readily inactivated by pasteurisation or equivalent processes. Decimal reduction times (D-values) of 3.20–6.23 min at 48 °C in raw milk have been recorded.

Control Options

Processing

At present, research suggests that if some Aeromonas strains are indeed food-borne pathogens, it is foods containing high numbers of the organisms that pose the greatest health risk.

Measures to reduce the likelihood of high numbers occurring should include: using treated water supplies in food processing; keeping foods chilled; and the thorough, frequent cleaning of equipment used to process foods, especially those that are not later cooked by the consumer, e.g. salads and vegetables.

Aeromonas species are easily inactivated by pasteurisation, or equivalent processes used by the food industry. Preventing the recontamination of heat-processed products, particularly those with a high water activity and neutral pH that are to be stored chilled, should ensure that aeromonads are not a potential health risk in these foods. Measures to reduce the risk of recontamination include keeping raw and cooked foods separate and implementing good handling and packaging practices.

Product Use

Aeromonas species should be considered as possible pathogens and it has been suggested that very young children, the elderly and the immunocompromised should avoid foods that could be contaminated with high numbers of these organisms.

Legislation

There is no specific legislation in the EU or the USA on levels of Aeromonas species in foods.

Sources of Further Information

Published

Janda, J.M. and Abbott, S.L. The genus Aeromonas: taxonomy, pathogenicity, and infection. Clinical Microbiology Reviews, 2010, 23(1), 35–73.

Daskalov, H. The importance of Aeromonas hydrophila in food safety. Food Control, 2006, 17, 474–83.

Isonhood, J.H. and Drake, M. Aeromonas species in foods. Journal of Food Protection, 2002, 65(3), 575–82.

On the Web

Guidelines for drinking water quality. Addendum: Microbiological agent in drinking water, 2nd edn. Aeromonas – World Health Organization. (2002). http://www.who.int/water_sanitation_health/dwq/en/admicrob2.pdf

1.1.2 ARCOBACTER

Hazard Identification

What is Arcobacter?

Arcobacters are potentially pathogenic, gram-negative, non-spore-forming bacteria, often described as aerotolerant Campylobacter-like organisms. Arcobacters are closely related to Campylobacter, and species in both genera share some similar morphological and metabolic characteristics. Both genera belong to the family Campylobacteraceae, however Arcobacter species can be differentiated from Campylobacter species by their ability to grow in air as well as at lower temperatures. There are currently nine described Arcobacter species, but it is Arcobacter butzleri, and more rarely Arcobacter cryaerophilus, that have been implicated in cases of human illness. On two occasions however, Arcobacter skirrowi has been linked to human infection, including in an individual suffering from chronic diarrhoea.

It is thought that the consumption of food contaminated with Arcobacter species may play a role in the transmission of these pathogens, although this has not yet been conclusively demonstrated. The most significant source of the organisms is thought to be contaminated water sources, however the organisms are also considered possible zoonotic agents (i.e. direct transmission may occur from animals to humans).

Occurrence in Foods

Arcobacters are associated with foods of animal origin and have been detected in beef, poultry, pork and lamb, but are most frequently found in poultry and pork products. Chicken carcasses and poultry processing plants are often contaminated with Arcobacter species and the organisms have been isolated from retail chicken and turkey products. However, evidence suggests that eggs are not usually contaminated with these bacteria. They have also been found in raw milk and shellfish (clams and mussels). Arcobacters are not routinely examined for in foods, and so their prevalence in other food types is unknown.

Hazard Characterisation

Effects on Health

Arcobacter butzleri is the most common Arcobacter species implicated in human disease. Those most at risk from developing the symptoms associated with Arcobacter infection are very young children, although any age group is susceptible. Asymptomatic infections are reported to occur.

The infective dose and incubation time is unknown. Clinical symptoms include abdominal pain, nausea and acute watery diarrhoea, typically lasting 3–15 days, although this can persist or re-occur on occasions for up to two months. Occasionally, vomiting, fever and chills are reported. Extra-intestinal disease such as septicaemia has also been documented occasionally.

Incidence and Outbreaks

The incidence of Arcobacter enteritis is unknown, and outbreaks caused by Arcobacter species have rarely been reported. One reason for this may be because these organisms are not routinely ...