Update on food safety in the Australian poultry industry

I. INTRODUCTION

In Australia Salmonella spp. are frequently involved in egg and egg product-associated foodborne outbreaks. On the other hand, campylobacteriosis is associated with the consumption of contaminated chicken meat (Sexton, 2016). The Salmonella and Campylobacter shedding in poultry flocks can be highly variable across different flocks and farms; as a result, the level of product (chicken meat and/or eggs) contamination is largely attributed to the flock management. The refrigeration of the product in supply chain and handling can also influence the safety of the poultry products. For the past several decades, both in Australia and other parts of the world, campylobacteriosis has been the most notified foodborne infection. The consumption of inadequately cooked or undercooked chicken meat and chicken meat products is one of the primary sources of human campylobacteriosis (Bryan & Doyle, 1995). The industry and regulatory agencies are often focussed on achieving the best practices to reduce Campylobacter contamination during processing to ensure food safety for the consumers. Different intervention strategies have been applied across the supply chain, from bird rearing in the poultry farms through to the poultry meat production in the processing plants, to reduce the level of Campylobacter in the food chain. Strict biosecurity measures on farms prevent the spreading of Campylobacter within the farm and between different farms, while the processing plants apply multiple decontamination methods to prevent bacterial crosscontamination in chicken meat (Umaraw et al., 2017). Worldwide, contaminated eggs and egg products are frequently implicated in outbreaks of human salmonellosis (Chousalkar & Gole, 2016). Salmonella Enteritidis (S. Enteritidis) and Salmonella Typhimurium (S. Typhimurium) serovars have dominated the epidemiology of Salmonella and are the most common causes of human salmonellosis (Hendriksen et al., 2011). Thorough cooking of eggs can destroy most, if not all, bacteria present, including Salmonella, and will pose a low risk to human health. If egg products or food items are prepared from raw or lightly cooked egg contents however, this will not destroy all Salmonella (if present). A rough estimate of the presence of Salmonella (all species, not just pathogenic) on eggs is greater than 1 in 20,000 (Arnold et al., 2014). Considering the estimated production of eggs in Australia and per capita consumption, the risk of foodborne illness in general is very low for humans consuming eggs.

II. FOOD SAFETY IN AUSTRALIAN CHICKEN MEAT INDUSTRY

Chicken meat remains the most consumed animal protein in Australia (50.1 kg/person/year), comparable to the consumption of pork, sheep, beef and veal combined (ACMF, 2023). The chicken meat industry is dominated by large vertically integrated companies, with operations including breeder farms, hatcheries, grower farms, processing plants and feed mills.

There have been multiple longitudinal studies conducted in the egg layer industry due to high-risks of Salmonella outbreaks associated with eggs and egg-based products, however published studies are limited within the chicken meat industry (Abraham et al., 2019; Ford et al., 2018; N.-L. Willson & K. K. Chousalkar, 2023) with most surveillance conducted in-house. In Australia, Salmonella Typhimurium has been the leading cause of salmonellosis for over two decades, representing 84% of serovars linked to outbreaks between 2001-2016 (Ford et al., 2018). For Campylobacter spp., however a large proportion of isolates from notified Australian cases are not speciated (Cribb et al., 2022). The prevalence of Campylobacter spp. on raw poultry products at retail is high (Walker et al., 2019) and annual notifications of illness are increasing. Salmonella infection notification rates however are decreasing (NNDSS, 2022).

A recent study in Australia investigating the prevalence of Salmonella in broiler breeders and hatcheries found low detection rates for Salmonella (8% positive during rearing and 1.9% positive during production) over a 40 week surveillance period (N.-L. Willson & K. K. Chousalkar, 2023). There was also no association with serovars found in the hatchery and from the breeder flock they originated from, supporting studies in the UK that demonstrate contamination of eggs likely occurs from established infections within the hatchery rather that continued infection from breeder flocks (Withenshaw et al., 2021). Risk factors associated with Campylobacter colonisation include increasing animal age, number of sheds on farm, production type, stocking density, flock size, presence of other animals, partial depopulation and the type of nipple drinkers (Alter & Reich, 2021). Similar risk factors are associated with Salmonella(Chousalkar et al., 2017) and transmission vectors for both are heavily influenced by adequate biosecurity.

Gut health plays an integral role in the colonisation of foodborne pathogens, with the overarching aim in production to reduce the prevalence of carriage in poultry, thereby mitigating disease risk to the community. The first three days post hatch is a critical window for chick intestinal health as the microbiota is in early development and susceptible to colonisation, particularly with Salmonella (Ijaz et al., 2021). Although infection can be induced early in experimental chicks, Campylobacter will not generally be observed prior to 2-3 weeks in commercial flocks with a colonisation ‘lag-phase’ observed for multiple Campylobacter spp. but the rapid spread throughout the flock (Sahin et al., 2002). Once colonisation is established, bacterial shedding occurs, particularly in response to production stressors (N.-L. Willson & K. K. Chousalkar, 2023).

III. CONTROL OF FOOD BORNE PATHOGENS IN THE CHICKEN MEAT INDUSTRY

Campylobacter and Salmonella often establish persistent colonisation in the gastrointestinal tract of poultry (Hermans et al., 2012). Bacterial shedding from birds can be intermittent on farm but proliferation of both bacterial species has been linked with transport stress (Whyte et al., 2001) representing a significant risk for the downstream chicken meat supply chain. During processing, chicken carcasses can become contaminated with bacteria from feathers, skin, and ruptured intestinal tracts and cross-contamination of carcasses can also occur during the different stages of processing (Cox & Pavic, 2010). Thus, controlling bacteria throughout the chicken meat supply chain requires a multi-faceted approach that involves interventions at various states from farm to fork.

The source of Campylobacter and Salmonella on a farm can include residual litter, rodents, insects, feed, or water that can result in flock-to-flock infection (Battersby et al., 2016). Thus, the first line of defence against bacterial introduction is at the farm level. The Australian chicken meat industry has impleted strict biosecurity measures and several interventions to minimise the risk of bacterial contamination. This includes maintaining proper hygiene, regular cleaning and disinfection of poultry sheds and equipment in between batches, and clean water sources. In addition, all Australian commercial broiler breeder flocks are vaccinated with a live, attenuated Salmonella vaccine (N.-L. Willson & K. Chousalkar, 2023). Implementing a comprehensive vaccination program can reduce the prevalence of bacteria in individual flocks thereby minimizing on farm contamination as well as in the chicken meat supply chain. Currently, there is no commercially available poultry vaccine for Campylobacter.

Controlling bacteria in the chicken meat supply chain also involves strategies such as feed management. While Campylobacter is not commonly detected in feed components, Salmonella can be present in components of poultry feed (Ricke et al., 2020). Implementing measures such as proper storage, handling, and processing of feed can help minimise the risk of bacterial contamination. Feed supplements such as biochar, zeolite, and organic acids have been shown to reduce loads of foodborne bacterial pathogens in the poultry gastrointestinal tract (Prasai et al., 2016; Ricke et al., 2020).

Australian poultry meat processing plants use several interventions to reduce bacterial contamination of chicken carcasses including an inside/outside wash with water, chilling carcasses to 4°C, and immersion chilling in chlorinated water (Cox & Pavic, 2010). The efficacy of sodium hypochlorite, however, is dependent on organic load and total bacterial load (Lillard, 1980; Muhandiramlage et al., 2020). The Australian New Zealand Food Standards code permits the use of peroxyacetic acid (PAA) and acidified sodium chlorite (ASC) for use as food sanitizers (FSANZ, 2005) but chlorine remains the most commonly used sanitizer in the Australian poultry industry. Both PAA and ASC have been shown to reduce microorganisms linked with foodborne gastrointestinal disease on naturally contaminated bird carcasses obtained from Australian processing plants (Chousalkar et al., 2019; McWhorter et al., 2022; Sexton et al., 2007). The processing plants use strict hygiene protocols, such as regular cleaning and sanitisation of processing equipment and facilities. Regular testing and monitoring of chicken meat is also carried out to detect and control bacterial contamination.

IV. FOOD SAFETY IN EGG INDUSTRY

In Australia, longitudinal studies were conducted to study the shedding of Salmonella in cage (V. C. Gole, C. G. Caraguel, et al., 2014) and free range production systems (Gole et al., 2017; McWhorter & Chousalkar, 2019) and found the load and the prevalence of Salmonella is dependent on the individual farm and or flock management. There are a number of bacteria found on egghsell surface (Chousalkar & Roberts, 2012); however, from food safety perspective, Salmonella plays a more important role. As reviewed in Gantois et al., (Gantois et al., 2009), not all chicken-associated Salmonella serotypes have the potential to transmit vertically. For example, S. Enteritidis transmits both vertically and horizontally, while S. Typhimurium predominantly contaminate eggs through horizontal route of transmission. During horizontal transmission, Salmonella can survive on the eggshell surface, in shell pores and egg internal contents at various temperatures (Khan et al., 2021). At room temperature, Salmonella can penetrate into the egg internal contents (Lin et al., 2021), which results in the ultimate contamination of albumen and yolk.

Egg white has antibacterial properties and the alkaline pH and reduced iron level in albumen make it harsh environment for Salmonella replication. The antimicrobial activities of albumen is significantly reduced at higher temperatures (e.g. 45°C) (Baron et al., 2020). In poultry production, intact eggs typically will have less than 10 Colony Forming Units/egg of Salmonella (Humphrey et al., 1989); however, 106 CFUs/egg has also been reported on the shell surface (V. C. Gole, V. Torok, et al., 2014) . The load of Salmonella within albumen or yolk depends upon multiple conditions including the egg storage temperature, level of contamination shell quality characteristics. In the egg, Salmonella up-regulates various genes involved in cell metabolism and virulence (Clavijo et al., 2006); however, at lower storage temperatures (e.g. 4°C), Salmonella will not replicate exponentially, due to its metabolic arrest. To overcome the antimicrobial properties of albumen, Salmonella regulates genes, such as ybgC, yoaE and cpxR for its survivability (Huang et al., 2020; Qin et al., 2019). Once Salmonella translocates from the albumen to yolk within an intact egg, its growth can be significantly increased at higher storage temperature (Khan et al., 2021). Yolk favours the upregulation of metabolic pathways in Salmonella involved in type II secretion system, infection process and epithelial cell invasion of host (Xu et al., 2022). Therefore, it is recommended to store eggs at lower temperatures in the food supply chain in some countries.

V. CONTROL OF FOOD BORNE PATHOGENS IN THE EGG INDUSTRY

The Australian egg industry use many intervention strategies such as flock vaccinations, probiotics, in-feed organic acids, egg washing, farm hygiene and biosecurity etc. The effectiveness of each intervention such as vaccination (McWhorter & Chousalkar, 2018), use of probiotics (Khan & Chousalkar, 2021), and egg washing (Vaibhav C Gole et al., 2014) have been tested, however it is important to note that these biosecurity measures do not offer complete elimination of Salmonella spp. Stress can influence the Salmonella shedding in a flock and ultimately affect the load of Salmonella on eggs (V. C. Gole, V. Torok, et al., 2014). Egg washing reduces Salmonella on the shell surface but viable cells can still survive in the shell pores (McWhorter & Chousalkar, 2020). Therefore, it is paramount to store the washed eggs at appropriate temperature. It is important to note that egg washing is not practised in some parts of the world, such as Europe.

Major commercial egg producers in Australia are represented by Australian Egg Corporation Limited (AECL). The AECL has a voluntary egg quality program which provides guidelines for food safety, biosecurity, environmental use, hen health, welfare and labelling for the national egg industry. The Australia Eggs has voluntary Codes of Practice for assisting egg producers. These codes provide guidance on hygienic egg production, storage, packaging and distribution of shell eggs and egg products for human consumption. The recommended temperature for egg storage on farm, during transport and at the retail outlet is below 15 °C (+ /- 3°C). There is a S. Enteritidis monitoring and accreditation programme for commercial egg producers exporting eggs to overseas market. In Australia S.Typhimurium has been a predominant cause of local foodborne outbreaks attributed to the poultry egg products (Ford et al., 2018) . Recently, there have been some outbreaks of S. Enteritidis in some free range layer flocks (Collins et al., 2023). The efficacy of current S. Typhimurium vaccine has been tested against S. Enteritidis in experimental pen trials but currently there is no S. Enteritidis vaccine in Australia.

VI. CONCLUDING REMARKS

Despite several improved interventions, reducing the level of Salmonella and Campylobacter spp. remains a significant challenge for the industry. Communication between regulators and industry is paramount to control poultry product related foodborne outbreaks, and collaborative efforts are required to design and implement the control strategies. Continious education of the general public on safe handling of eggs and chicken meat is also necessary. Foodborne illnesses are frequently linked to poor poultry handling practices and subsequent cross-contamination in the kitchen environment. For example, washing or rinsing raw meat and poultry products can result in cross-contamination because the juices and wash water may come into contact with other foods, surfaces, and utensils (Shumaker et al., 2022). Previous studies found that foodborne pathogens such as Salmonella and Campylobacter are partially preventable through improvements in consumer preparation of Poultry products (Luber et al., 2006). It has been found that using hot water and detergent to clean hands and utensils after chicken preparation/handling in the kitchen achieved a 50% reduction in bacterial contamination (Cogan et al., 2002).

Previous studies concluded that despite guidance from food safety agencies, adherence to current recommended chicken meat and egg handling practices is low. The industry peak bodies and state regulatory authorities have included factsheets and resources on their websites to educate consumers on safe chicken meat and egg handling practices (Kosa et al., 2015). The impact of these educational materials on consumer awareness remains unclear.

Presented at the 35th Annual Australian Poultry Science Symposium 2024. For information on the latest and future editions, click here.