Microbiology Australia, bringing Microbiologists together

Food safety

Producing safe food is essential for protecting the health of consumers and for ensuring the sustainability and profitability of food industries, including primary production, food manufacture, food service and retail. Food safety hazards may result from contamination of food with microbial, physical or chemical hazards. This edition of Microbiology Australia focuses on microbial food safety hazards, including prions, viruses, bacteria and fungi. Technological advancements throughout history, such as pasteurisation, canning and refrigeration, have significantly improved the safety of our food supply; however, foodborne illness remains a global problem impacting on millions of people each year. A recent example is the large outbreak of E. coli O104:H4 that occurred during 2011 in Germany and many other countries across Europe and North America, which affected more than 4,000 people resulting in 50 deaths. The outbreak was associated with seeds used for sprouting that had originated from Egypt. The causative agent, E. coli O104:H4, had acquired new virulence properties in the form of toxin genes carried by bacteriophage, creating a highly pathogenic strain. This outbreak highlighted some of the difficulties faced by those involved in keeping the food we eat safe. Many of these challenges are discussed throughout the articles in this edition of Microbiology Australia.

Narelle Fegan 13-May-2013

The OzFoodNet story: 2000 to present day

OzFoodNet is a network of epidemiologists whose primary interest is foodborne disease. The network is now over 10 years old and in this time, there have been many research studies and outbreak investigations undertaken by the network. A considerable body of published work exists that details the achievements and workings of the OzFoodNet network and the OzFoodNet sites. Lessons have been learnt from outbreak investigations, with improved surveillance systems developed for pathogens such as Listeria monocytogenes. The work of OzFoodNet plays an important part in informing food safety policy and regulations.

Michelle Green and Gerard Fitzsimmons 13-May-2013

Foodborne viruses: a focus on challenges associated with detection methods

Human enteric viruses are now recognised as one of the commonest causes of foodborne disease with norovirus and hepatitis A virus (HAV) the main viruses implicated in foodborne outbreaks. Norovirus is the main cause of acute nonbacterial gastroenteritis worldwide. Foods at risk of virus contamination are bivalve shellfish, fresh produce, manually prepared ready to eat (RTE) foods and bakery products. Analysis of foods for virus presence is challenging for many reasons. Complex food matrices present processing problems for efficient recovery and detection of viruses, current molecular methods do not allow for determination of virus infectivity and low virus copy number in foods means that exquisitely sensitive methods and multiple controls are required for virus detection. There are still no international standard methods for viral analysis of foods. However significant progress towards a standard method for detection of norovirus and HAV in foodstuffs has been made by a European Committee for Standardisation (CEN) technical working group. This method is due for publication in 2013 as a two-part joint ISO/CEN Technical Specification. In later years it will be replaced by a fully validated standard.

Gail E Greening 13-May-2013

Campylobacter survival through poultry processing

Australia has recorded around 100 cases of campylobacteriosis per 100,000 population, each year, since the mid-1990’s. Campylobacter jejuni and C. coli are recognized as the main species isolated from clinical cases. Approximately 30% of cases have been linked to poultry. Through poultry processing, from slaughter to packaging, the prevalence and concentration of Campylobacter can be reduced. Published Australian data on the effect of current processing conditions are minimal. Data from other countries suggests that the stages of scalding and immersion chilling can have significant impact on the prevalence and concentration of Campylobacter. Understanding the complexities of these processing stages (physical, chemical and microbiological) and their effect on Campylobacter species may lead to improved control during processing and hence improved public health outcomes.

Lesley Duffy 13-May-2013

Mycotoxins and food

Mycotoxins are toxic secondary metabolites produced by filamentous fungi that may occur in almost all food commodities but particularly in cereals, oilseeds and nuts. They are recognised as an unavoidable risk and are found in the world’s most important food and feed crops, including maize, wheat, and barley. When present in foods in sufficiently high levels, mycotoxins pose a significant food safety risk and health hazard. Besides negative health impacts, mycotoxin contamination of food and feeds has a major worldwide economic impact. Mycotoxin contamination of foods is the subject of increasing international importance due to a number of worldwide issues, including globalisation of food trade, global food security and climate change. Innovative strategies to meet the menace of mycotoxin contamination are required, and a greater understanding of the ecology of mycotoxigenic fungi and the molecular regulation of mycotoxin production may aide in the development of such strategies.

Nai Tran-Dinh 13-May-2013

Antimicrobial resistance in food associated Salmonella

Salmonella enterica is one of the leading causes of foodborne disease worldwide. Infection with Salmonella results in symptoms ranging from mild gastroenteritis through to severe complications such as septicemia and even death. These infections place a significant financial and health burden on the economies of both developed and developing countries. The emergence of antibiotic resistance in bacteria is of current international concern and has added an extra dimension to the issue of foodborne salmonellosis. Understanding and controlling the spread of antibiotic resistance among foodborne Salmonella is a goal that requires a global approach but one that needs to be tailored to local scenarios.

Boey Y Cheng, Amy HT Teh, Patric TC Chua and Gary A Dykes 13-May-2013

Listeria monocytogenes: illuminating adaptation with proteomics

With increased consumption of minimally processed ready-to-eat foods the potential for exposure to Listeria monocytogenes has increased. Thus, there is a need to maintain a balance between food convenience and safety. L. monocytogenes is not a homogenous species; certain strains are more resilient to stressful conditions while others are potentially more virulent. To understand the basis of these differences we are applying proteomics to determine the molecular mechanism of adaptations of L. monocytogenes in food-relevant environments. The goal is to define how this species grows, behaves and survives thus allowing us to fine tune food safety risk management, especially when developing new minimal food processes or considering introduction of unpasteurised food such as raw milk cheeses.

John P Bowman, Rolf E Nilsson, Chawalit Kocharunchitt and Tom Ross 13-May-2013

Baseline studies for pathogens in meat

Baseline microbiological studies, seeking to take a “snapshot” of the quality or safety of product produced across the nation at a point in time, are a valuable adjunct to other sources of information on quality or safety of foods. They have been used by the Australian red meat industry as a point of reference, to promote trade, and as a starting point for further research.

Ian Jenson 13-May-2013

Foodborne pathogenic E. coli (focus on STEC)

Foodborne pathogenic E. coli continue to emerge and evolve as significant human pathogens. With cattle and other ruminants acting as natural reservoirs, they contaminate food directly via contamination of animals at slaughter or indirectly via the use of contaminated manure or water during food production. E. coli O157 remains the predominant disease causing serotype although additional serotypes such as O26 and O111, along with E. coli possessing novel combinations of virulence genes, highlight the increasing complexity associated with reducing the prevalence of foodborne pathogenic E. coli. Variability in the severity of disease caused by different E. coli provides insight into the significance of virulence factors thereby enabling the design of possible control methods such as vaccines. The continuing burden of foodborne pathogenic E. coli presents a challenge for food producers and researchers to overcome to ensure an ongoing supply of safe and healthy food.

Robert S Barlow and Glen E Mellor 13-May-2013

Microbiological risk assessment: making sense of an increasingly complex world

As our understanding of microbiological pathogens and their interaction with hosts expands, the complexity of assessing the risks posed by these hazards is also increasing. This is compounded by the extension of food production pathways, with multiple processes and/or new technologies used to produce the food that consumers desire. While based on principles developed for assessing toxicological and carcinogenic hazards, microbiological risk assessment throws up many challenges due to the ability of some microorganisms (bacteria) to multiply, or become inactivated, as food moves through the production to consumption continuum. In addition, microorganisms themselves are not static entities but are constantly changing through natural selection and exchange of genetic material.

Duncan Craig 13-May-2013

Bovine spongiform encephalopathy and food safety

Bovine spongiform encephalopathy (BSE) is a fatal disease of cattle, caused by infective proteins known as prions. A prion (PrP^Sc) is a mis-folded isoform of the glycoprotein PrP^C, which is highly expressed in the nervous system. Prions replicate by coercing PrP^C to refold into PrP^Sc. The BSE epidemic was propagated by rendering dead cattle to produce meal which was then included in cattle feed. Consumption of BSE PrP^Sc from contaminated beef resulted in over 200 human cases of variant Creutzfeldt-Jakob (vCJD) disease, which is invariably fatal. There were rare cases of person-to-person vCJD transmission by blood transfusion. Variant CJD is now very rare, due to adoption of measures that prevent the feeding of ruminant protein to ruminants and the contamination of beef with the tissues that harbour PrP^Sc. Beef from countries with these control systems are safe for human consumption.

Rosalind Dalefield and Scott Crerar 13-May-2013

Listeria surveillance in Australia from the laboratory perspective

Listeria monocytogenes surveillance requires robust laboratory support in detection and organism characterisation. Such laboratory support includes ensuring all relevant isolates are secured and uniformly typed to allow detection of clusters and attribution to potential source. Different typing have different strengths. The move toward sequencing of the whole genome and its subsequent analysis although presenting new challenges to laboratories and practitioners receiving the outputs alike is proving of great utility by providing information of genetic distance between isolates. Australia has established surveillance integrating laboratory typing with epidemiological information relating to human cases. Extending this model to include the potential sources of L. monocytogenes does and has led to early detection of sources thus mitigating the risk to all stakeholders and vulnerable consumers.

Geoff Hogg, Agnes Tan and Joy Gregory 13-May-2013

Food poisoning due to Clostridium perfringens

“No other food poisoning bacterium is so uniquely poised to take advantage of the slackness of human beings involved in food preparation.” (John Bates – Food Poisoning lectures). Clostridium perfringens, a Gram-positive anaerobic spore-forming bacillus, has been responsible for a large number of food poisoning events in Australia. Frequently, these are spectacular outbreaks involving large numbers of diners at catered events. While the organism is perhaps better known in clinical laboratories as an agent of gas gangrene and deep tissue infections, in Public Health laboratories it is recognised as one of the major causes of food poisoning in Australia. While these outbreaks can cause high morbidity with severe abdominal cramps and diarrhoea lasting 24 hours, generally, fatal cases are rare, except in the very young and the elderly. For this reason, outbreaks in nursing homes or elderly patients in hospitals need to be identified quickly and their symptoms managed to avoid severe dehydration and shock.

John Bates 13-May-2013

Salmonella and egg-related outbreaks

Non-typhoidal Salmonella infections are a significant public health issue in Australia, with record numbers of both disease notifications and outbreaks being reported in recent years^1,2. Epidemiology plays an important role in Salmonella outbreak investigation, helping to identify raw and minimally cooked eggs as an increasingly common cause for these events. Of particular relevance to disease caused by Australian eggs is Salmonella enterica subsp. enterica serovar Typhimurium. A crucial element in demonstrating this serovars presence throughout the food chain is the ability to trace suspect eggs to their source. High product turnover makes this challenging but through the adoption of integrated surveillance practices and harmonised laboratory methods, a more effective response may emerge.

Cameron RM Moffatt and Jennie Musto 13-May-2013

Foodborne campylobacteriosis in Australia

Thermophilic Campylobacter are an important cause of human illness worldwide. Campylobacter reservoirs include a wide variety of wild birds, poultry, farm animals, domestic pets and natural water systems. In Australia, infection is mainly associated with foodborne transmission, though other routes of exposure including waterborne and direct zoonotic transmission are not uncommon. Most cases of infection appear to be sporadic in nature, with outbreaks rarely reported. Epidemiological and microbiological evidence suggests chicken meat is the principal source of infection among cases. A recent study estimated there are more than 50,000 cases of Campylobacter infection attributed to chicken meat each year in Australia. When outbreaks are detected, they are most often associated with the consumption of poultry, contaminated water and occasionally unpasteurised milk. The lack of recognised foodborne outbreaks of campylobacteriosis could be due to organism-related factors such as the inability of thermophilic Campylobacter to multiply on food left at room temperature, their microaerophilic nature and their susceptibility to drying. However, it is likely that outbreaks of Campylobacter infection are also under-reported in developed countries due to the current lack of a suitable phenotypic or genotypic typing method for routine surveillance and outbreak detection. The future development of improved typing methods for detecting outbreaks should enable further sources and risk factors for Campylobacter infection to be determined.

Russell Stafford 13-May-2013

Food safety plans: three problems to address when analysing microbiological hazards

Food safety programs set out how safe food is produced. The primary objective of designing food safety plans is to ensure food is safe and suitable for human consumption. However if the design of the food safety plan is affected by lack of knowledge of the biological, chemical and physical (BCP) hazards of the food production process, then food safety may not be assured. This paper focuses on three problems when analysing the microbiological hazards that can affect the quality of the food safety plan and which may result in unsafe food and a false sense of security for the food manufacturer.

Prue Bramwell 13-May-2013

Microbiological testing of foods: what, why, how

Complexity in food testing arises from the food (matrix), the need to detect low numbers of target microorganisms in the presence of potentially similar background microflora, the potential use of testing to demonstrate compliance and the high cost (not just financial) of getting it wrong. Microbiological criteria for food specify the method of analysis¹ because “test results are dependent on the analytical method used”². Several bodies are involved in the development of standardised methods, and laboratories may have to run several methods for the same target to meet client needs. The current review of Standard 1.6.1 of the Food Standards Code³ and the July 2012 collaboration agreement struck between the International Organization for Standardization (ISO) and the Association of Analytical Chemists (AOAC International)⁴ should hopefully reduce the workload for food laboratories.

Agnes Tan and Numani Weerasuriya 13-May-2013

Advanced food preservation technologies

Food preservation has been practiced by humans for millennia through fermentation, salting and drying. The industrialisation of food manufacture brought processes like canning and freezing to control microbial safety and enzymatic spoilage of foodstuffs. However, this often comes at the expense of nutritional and sensorial quality attributes and, thus, novel food processing technologies continue to be developed to serve the increasing demand for healthy and eco-friendly food products. In contrast to thermal processing, these new technologies make use of physical stressors other than just heat to kill microorganisms, using high pressure, electric fields, cool plasma or ultraviolet irradiation. The underlying inactivation mechanisms, efficiencies and limitations of these technologies are currently still under investigation and will be highlighted in this paper.

Roman Buckow and Michelle Bull 13-May-2013

Cooking meat at home

One of the five keys to safer food promoted by the World Health Organization for consumers is “cook thoroughly” as cooking food properly kills almost all dangerous microorganisms¹. While this simple message is similarly promoted throughout Australia, beliefs and self-reported behaviours among consumers concerning cooking can vary. Here we describe consumer surveys on cooking meat as an example.

Patricia Desmarchelier and Juliana Madden 13-May-2013