Salmonella And Chicken Eggs

Max Pixel

Hi guys,

Have you ever heard about Salmonella? People who were unfamiliar with this kind of disease might just have thought it for a typical food-related illness. Even though they were considered as one of the commonest food-borne agents that can cause food poisoning, it's not always Salmonella which causes you to suffer from watery diarrhoea or any other related food poisoning symptoms; it's probable but not always. However, it is worth noting that, the figure which was presented in various studies regarding the occurrences of food poisoning related to Salmonella in Malaysia might have been underestimated (high incidence of unreported cases). This can be due to a few factors such as poor access to a proper healthcare, financial limitation, lack of knowledge and limited resources for diagnosing Salmonellosis.

In 2016, it was documented in a journal published by Thung TY et al. regarding a 20% incidence of Salmonella-infected meat which was identified among 120 chicken meat. That was quite significant won't you say? Even though the number seems small (24 meat affected) but treatments required for treating such illness is quite significant. A financial record which has been documented by the United States Department of Agriculture (USDA) in 2015 specifically for treating food-borne illnesses related to Salmonella infection has shown an extremely expensive figure (around 3.7 billion dollars). The infection is especially prevalent among countries which were producing a large number of poultry products such as eggs and not surprisingly, Malaysia is one of them. It was estimated that the number of chickens meat produced in Malaysia alone were approximately 1.44 million tonnes a year to supply the high domestic demands due to the fact that Malaysian were one of the highest poultries meat consumers in the world (around 40 kg/year).

Despite the fact stated above, the number of sales recorded in any of the large processing facilities (specifically for poultry products) still remains average. This is due to the fact that, most of the necessities related to food were provided and usually bought at the wet markets which are quite popular in most of the Asian countries. I'm not having any problems with the concept of having wet markets in any country; it just that any fresh products which were sold in that particular places were exposed to the surrounding environment at a certain temperature which is optimal for bacterial growth. However, the price of a poultry product sold in wet markets was relatively cheaper than the price of the poultry product sold by any poultry's processing facilities making it one of the most reasonable places to be chosen by consumers when it comes to making a decision regarding where to buy chickens for lunch/dinner.

What Do You Need To Know About Salmonella?

Project Manhattan - Wikimedia (CC BY-SA 3.0)

Before we discussed regarding eggs and salmonella, there are a few things you should know about the bacterium itself since knowing the basic structure of this organism and how it operates would make it much clear regarding the importance of choosing food products which are free from this kind invading pathogen. Unlike some microbial organisms, the existence of Salmonella is ubiquitous. It can be found literally everywhere, I'm not sure if it is applied to the north and south pole due to the fact that they were quite an unsuitable habitat for them to live in, but generally, they can be found anywhere on earth. Even if it is not common, there were a few cases of antibiotic-resistant Salmonella species which has arisen possibly due to antibiotic abuse but we're not going to focus on that part. Maybe soon, sometimes in the future.

Salmonella is a flagellated bacterium which means in most of the cases, they were able to propel themselves to a specific point in the body to cause a specific kind of pathology. Other than that, they were Gram-negative (pink in gram staining) bacteria which are usually identified through 3 primary antigens that can be found on the bacteria surface:

• H antigen (flagellum)
• O antigen (somatic - usually found on the outer membrane of the bacterium)
• Vi antigen (this kind of antigen only possessed by a few subspecies of Salmonella)

The most important part which determines the virility of the organism is a complexly-shaped lipopolysaccharide which acts like an endotoxin of the bacterial species. The complex constitutes of three important structure; the central portion is composed of a structure called the R core which is sandwiched between two other structures, the outer coating protein called the O-polysaccharide and the inner structure called the A coat. The R core which has been the central structure of Salmonella's endotoxin were also found in various other disease-causing Gram-negative bacteria which make it easier to produce an antibiotic to counteract all of them. It is also one of the possible reasons why antibiotic resistance has arisen from this type of bacteria, too many infections can be treated by a single antibiotic and repeated exposure can cause mutations which will allow them to survive the onslaught.

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The outer coating which is made up of polysaccharides is an important antigen which usually determines their virulence. It consists of a series of interconnected sugar molecule which measures the capability for the bacteria to cause diseases; a shorter chain of O-sugar would simply mean that the bacterium is less virulence than its counterpart (a longer O-sugar chain Salmonella). Even though, there were quite a number of diseases which can be caused by the bacteria in the Salmonella species, most of them cater for a specific kind of disease:

• Gastroenteritis is usually caused by Salmonella typhymurium and Salmonella enteritidis
• Enteric fever is usually caused by Salmonella typhi and Salmonella paratyphi-A
• Focal infections were usually caused by a much rare Salmonella choleraesuis

However, that doesn't rule out the other uncommon species of Salmonella if, for example, a patient is diagnosed with enteric fever. The ability for a Salmonella species to cause a specific kind of disease would depend on a few factors:

• The structure of the outer lipopolysaccharides coating
• The ability for an individual bacterium to invade a cell
• The ability for an individual bacterium to replicate in the host cell
• The virulence factor (toxin)

Pixabay

Some steps in the mechanisms of how Salmonella cause symptoms in an individual were not known. Typically, when someone eats contaminated foods which contain the bacteria, their ileum (the distal part of the small intestine) and the proximal part of the colon would be colonised by the bacteria. This would lead to the invasion of the mucosal membrane which will allow the bacteria to exert its toxic effect causing an acute inflammatory response with or without ulceration of the surface epithelium. This will activate adenylate cyclase which will results in an uncontrolled secretion hence the diarrhoea. Unfortunately, the infection is not quite simple as the toxin produced by Salmonella can go systemic. In some strain of resistance salmonella, they can cause damage to multiple organs depending on where do they end up with but that is very rare.

Whether or not someone will recover from such infection, will depend on the integrity of the host immune system and a few other protective mechanisms that will resist intestinal colonisation such as low pH stomach juice, the degree of the intestinal motility, the normal flora of the intestine and presence of mucosal antibodies.

How Do Salmonella Affect The Chicken's Egg?

Contaminated chicken's eggs have been the primary sources of Salmonella infection in human population, causing about 53% from the overall cases that have been reported to the Centre for Disease Control and Prevention (CDC) between the years of 1985 to 2002 (Harriet Whiley, 2015). There are two possible pathways that can be taken which will end up with the formation of contaminated eggs that will be sold to consumers. In the direct pathway, the infection originated from the hen's reproductive system while in an indirect pathway, the causes can be attributed to the environment of the egg production site which may include, the type of food being fed to the individual hen, how the hen's foods were being prepared, the hygiene level of the egg production site, the temperature and condition during the egg's storage, etc.

The thing is, even if the eggs being sold were contaminated with Salmonella, most of the time, the bacteria would be killed during the cooking process provided the egg is cooked well with an appropriate temperature. In recent years, the utilisation of products which contain a raw form of eggs such as mayonnaise, ice-cream and milkshakes have been increasing and this effectively causing the probability of foods which are contaminated to be consumed by an individual increase. Nevertheless, despite all of the possible exposure towards the virility of Salmonella, the chances for a healthy individual to be infected were low (courtesy of various protective mechanisms). For example, on 13 April 2018, approximately 207 million eggs were distributed in 9 out of 50 states in the United State of America. All of the eggs were sold but the number of people who were diagnosed with Salmonellosis was 22. It's an extremely low figure even though a lot of things should be considered:

• The number of chickens or eggs which were infected by the bacteria were not determined. The number can be small with respect to the total so 22 doesn't really tell anything.

• In a study conducted by the European Union regarding Salmonella has revealed that only 1 out of 57 cases of Salmonella were reported. So if we consider the figure to be an accurate representation of unreported cases, the actual number of people who were affected should be 1254 people. It's still small compared to the number of eggs being sold but take note that, the number of people who bought a specific amount of eggs cannot be determined and we don't even know how many of them who were eating a half-cooked or raw eggs as opposed to a properly-cooked egg.

Kate Ter Haar - Flickr (CC BY 2.0)

Other than the mucosal lining of the human's intestine, Salmonella can invade the mucosa of a hen's ovary and intestine making it safe to assume that the actual problem can be originated from the way the chicken was raised (how their food was given, how they were taken care of); however, it's still difficult to determine in which level do the Salmonella started to affect the production of a healthy chicken egg. Other than that, this particular bacteria can diffuse in when they were in contact with uninfected chicken eggs. This is why the condition of the storage unit which is used to store these eggs should be monitored as well. Even with the greatest care which a facility can provide, the rate of infected eggs can only be reduced to as far as 1:20,000 ratio. The eggs should be cooked adequately (usually until the white and yolk portion has become firm) to minimise the number of pathogens which might be lurking on the inside of our precious foods.

If any of you have any symptoms which possibly can be caused by any kind of food poisonings such as fever, vomiting and diarrhoea, it will be wise to consult a physician for a proper mode of treatment as sometimes, the symptoms can be quite severe which might lead to even worse consequences. Oh yeah, do not take any kind of antibiotics unless prescribed by the attending physician. Antibiotics can sometimes, make things worse, as it would affect the population of flora in the intestine giving much opportunities to the Salmonella to invade.

Sources

• Salmonella
• Salmonella: A review on pathogenesis, epidemiology and antibiotic resistance
• 200 Million Eggs Recalled: How Does Salmonella Get into Eggs, Anyway?
• Salmonella and Eggs: From Production to Plate
• Prevalence of Salmonella in poultry processing environments in wet markets in Penang and Perlis, Malaysia
• USDA Gain Report
• Prevalence and antibiotic resistance of Salmonella Enteritidis and Salmonella Typhimurium in raw chicken meat at retail markets in Malaysia.

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