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Study reveals that antibiotic-resistant bacteria are present in Chile’s egg production


eggs, plate, white background


A study conducted by researchers at the University of Chile and the University of Maryland investigated the prevalence of Salmonella, a type of bacteria that causes illness and death worldwide, in eggs from different production systems in Chile. The study also looked at antimicrobial-resistant traits in Salmonella and the food safety knowledge of consumers. 


Salmonella is one of the leading causes of foodborne disease worldwide, usually related to contaminated poultry or eggs. It is capable of infecting virtually any organism with an intestinal tract and is responsible for more than 50,000 human deaths per year through the consumption of contaminated eggs, chicken, or pork. 


The study analyzed 426 egg samples and did not observe significant differences in the presence of Salmonella in different egg production systems (cage, cage-free, and free-range). Two samples (1.1%, 2/186) were contaminated with Salmonella serotype Enteritidis, which is resistant to nalidixic, an important antibiotic that treats animal and human infections. 


“Eggs contaminated with Salmonella bacteria can make people sick if not well cooked or if they contaminate other surfaces and spread to other foods. Infections with drug-resistant Salmonella can be more severe and result in higher rates of hospitalization and death,” said Patricia Tatemoto, Animal Welfare and Research Manager at Sinergia Animal, an international animal protection organization. 


A threat to public health


More than 70% of antibiotics sold worldwide are not used in people but in animals raised on intensive farms., According to the researchers, antibiotics in the poultry industry and other animal production systems are used for therapeutic and preventive control of diseases and to improve feed efficiency and productivity. However, their improper use might result in the dangerous accumulation of these chemicals in animal tissues and eggs and promote the selection of resistant bacteria. The main concern with antimicrobial resistance is not being able to treat animal and human infections, thus reducing the chances of using complementary therapies, such as chemotherapy and surgery. 


The World Health Organization (WHO) states that the misuse of antibiotics, which occurs at a large scale in factory farms, could lead to more deaths than cancer in the near future. A study published in The Lancet estimates that 4.95 million people died of diseases associated with antimicrobial resistance in 2019 alone. This number could rise to 10 million deaths annually by 2050 if the trend continues.


“Antibiotics are misused on billions of animals to prevent infections resulting from precarious conditions, high housing densities, and the fragile health of genetically selected animals, aiming for maximum productivity. The chronic stress these animals are subjected to also causes them to lose the natural immune response that would usually partially protect them against infections,” explains Tatemoto.


The study reports that Chilean consumers demonstrated adequate knowledge of food safety regarding the hazards related to egg contamination in the household; however, many still engage in practices that risk spreading foodborne illnesses, such as cross-contamination and the deliberate consumption of raw or undercooked eggs. Such poor hygiene practices are responsible for 25% of foodborne outbreaks.


Differences in production systems


There is rising interest in understanding the presence of Salmonella in various hen housing systems (cages and cage-free systems). A review article concludes that it appears highly unlikely that moving from conventional cages to cage-free systems will increase Salmonella infections in laying hen flocks. According to the authors, factors such as biosecurity, vaccination, and the professional skills of farmers are of utmost importance to minimize the presence of Salmonella in laying hen flocks. Likewise, a systematic review concludes that Salmonella occurrence in laying hen flocks is multifactorial and that many risk factors are largely related to management practices, which are correctable. 


The European Food Safety Authority has conducted the world’s largest study on this issue and concluded that cage systems have a higher prevalence of Salmonella than cage-free systems.


Most laying hens in Chile are raised in battery cages, a very intensive egg-production system that confines several hens together in small wire cages. Each hen spends her life within a space smaller than an A4 sheet of paper and cannot walk freely nor properly open her wings. The extreme confinement and lack of physical exercise commonly cause high frustration levels and painful bone fractures. 


“It is time for the animal agriculture industry in Chile to move away from very intensive production systems. It is important to consider more sustainable protocols for increasing the resilience of food systems and protecting public health. Ensuring higher welfare levels for farm animals can mitigate the immunosuppression caused by chronic stress. Although variables like the maturity of systems must also be considered, improving animal welfare, reducing the use of antibiotics, and informing consumers are essential and urgent steps to improve conventional food systems,” says Tatemoto.


About Sinergia Animal


Sinergia Animal promotes healthy, sustainable food choices and improves animal welfare in countries of the Global South, including Chile.


The study “Prevalence of Salmonella in Eggs from Conventional and Cage-Free Egg Production Systems and the Role of Consumers in Reducing Household Contamination” was published in The Lancet and conducted by Doina Solís, Ninoska Cordero, Maritza Quezada-Reyes, Carla Escobar-Astete, Magaly Toro, Paola Navarrete, and Angélica Reyes-Jara. Sinergia Animal sponsored the study with the support of the Tiny Beam Fund.


“Sinergia Animal recognizes that basing the animal protection movement on science increases its credibility, thereby increasing the potential to leverage actions that will lessen animal suffering. Our campaigns and messaging are more trusted, and our progress is more effective if they are based on scientific and technical information. We are committed to being a science-based organization and only use reliable information to influence public opinion,” explains Tatemoto.

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