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https://www.fda.gov/food/laboratory-methods-food/bam-chapter-5-salmonella
Literature review for Salmonella enterica serovars
Introduction about Salmonella enterica serovars and why this bacterium is a concern
Foodborne illness is one of the most concerning health problems in the world. There are one in ten people who are ill, and around thirtythree million people of healthy life are lost every year (World Health Organization, 2018) because of foodborne diseases. Without of doubt to state that foodborne disease outbreaks not only affect human health but cause economic loss in the food and relative industries. Salmonellosis disease in humans, which is caused by salmonella bacteria, is the most common foodborne microorganism in the world (Bintsis, 2017). It is also listed as one of the four key global reasons that cause diarrhoeal disease (World Health Organization, 2018).
Salmonella is a rod-shaped bacterium, gram-negative facultative, intracellular pathogen, and it is also a member of the Enterobacteriaceae family. The diameter is approximately 0.7 to 1.5m and the length of 2 to 5 m. Salmonella bacteria was acknowledged by an American veterinary pathologist, Daniel Elmer Salmon, and his assistant Theobald Smith in 1885 from the common hog cholera in the pig. Smith discovered the bacteria firstly by isolating the species of bacteria from the illness pig, however, the name of the bacterium was after Salmon (Schultz, 2008), it was called Salmonella cholerae-suis in the beginning.
Andino & Hanning, (2015) confirmed that there are around 2579 Salmonella serovars that were discovered and treated by scientists, epidemiologists, and food microbiologists. It is complicated to classify Salmonella bacteria, for example, it is classified based on phage typing, resistance to antibiotics, and antigenic patterns (Bhunia, 2018). Therefore, to simplify all the salmonellae have been catalogued into two major species, that are Salmonella enterica, and Salmonella bongori. However, Salmonella enterica species are heard as the most, and Salmonella enterica serovar is also one of the most important agents of foodborne sickness. The species Salmonella enterica has been divided into six subspecies (subsp.) that include Salmonella enterica subsp. enterica (group I); Salmonella enterica subsp. salmamae (groupII); Salmonella enterica subsp. arizonae (group IIIa); Salmonella enterica subsp. diarrizonae (group IIIb); Salmonella enterica subsp. houtenae (group IV); Salmonella enterica subsp. indica (group VI).
Jay, et al, (2005) also stated that treating Salmonella serovars as species is not valid anymore. For example, Salmonella Typhimurium should be Salmonella enterica serovar Typhimurium. Therefore, salmonella is placed into three groups for epidemiology purposes. It includes infecting humans only serovars, the hosted-adapted serovars and un-adapted serovars.
Salmonella enterica is a zoonotic pathogen (Knodler, Elfenbein, 2019) that is really concerned with the health of humans and animals in the world. More than 2600 Salmonella enterica serovars are also the reason cause significant morbidity, evenly in some cases mortality in some serious cases for the human body as well as animals. According to the World Health Organization (WHO), Salmonella enterica affects over 17 million people in the whole world every year. CDC (2022) estimated that Salmonella bacteria makes around 1.35 million people sick, 26500 people are hospitalized, and 420 deaths yearly in the United State.
What is the primary source of salmonella bacteria?
Salmonella bacteria in-habitat primarily in the intestinal tract of animals such as birds, reptiles, farm animals, humans and occasionally insects (Ray et al 2005). The faeces with bacteria is excreted, and then the bacteria are transmitted by insects or other organisms; it is called the intestinal form reservoir source. The intestinal form may also be found in the water, wild animals, birds, etc,.. consume the contaminated water and spread the bacteria.
How does salmonella enterica cause diseases?
Salmonella bacteria usually in-habitats in the intestines of people, animals, and birds. Humans get infected with salmonella bacteria by consuming food, and water which is contaminated by faeces. Franz and Bruggen (2008) mentioned the infection dose by Salmonella bacteria is very low from 10 to 100 cells based on some outbreaks in history. They can grow in the temperature range from 5-450C (optimum 35-370C), pH from 6-7, some still can grow at pH 4.1.
Salmonellosis, which is presentative with two main manifestations typhoid and gastroenteritis, is a disease that is salmonella bacteria. Annually, there are 16 million people who experienced typhoid fever, 1.3 million cases of gastroenteritis, and around three million deaths in the world (Bhunia, 2018). The symptoms consist of nausea, vomiting, abdominal pain, headache, chills, and diarrhoea; it is also accompanied by prostration, muscular, weakness, faintness, moderate fever, restlessness, and drowsiness (Knodler et al, 2019).
After invading the human body, Salmonella enterica serovar Typhi (S. Typhi), which causes Typhoid fever, will translocate via mucosal microfold (M) cells or dendritic cells, and then multiplies in the submucosal layer. Then it will be transferred to the liver and spleen; in here, it will leave and enter the blood circulation and reach the gall bladder. In the next step, the bacteria are shed into the intestine for the second round of infection through M cells. S. Typhi produces Vi antigen which allows the bacteria to survive inside phagocytes; Vi antigen also keeps a role as a vaccine candidate against typhoid fever. The typhoid fever symptom appears within 1-2 weeks and lasts for 2-3 days.
What is the case study, how to prevent and what is the statistic for the case study and prevention?
One interesting case study about the outbreak of Salmonella enterica serotype Newport (S. Newport), which was associated with tomato farms in 2005, was done by Greene et al (2007) in the United State. The case study investigated the outbreaks of S. Newport infection because of the contamination in tomatoes on the Eastern shore of Virginia. The two outbreaks in 2002, and 2005 were caused by the same rare strain (a pan-susceptible S. Newport), in the similar geographical distribution of the cases, and the same Pulsed-field electrophoresis of bacteria. This serotype was also identified in the irrigation ponds two years apart (Green et al, 2007); it made 510 people sick in 26 states in 2002, and another 72 patients (aged from 5 months to 75 years, 42 were female, 8 were hospitalized, no death) in 16 states from July November 2005.
In the case study, the hypothesis of the possible sources of S. Newport infection was developed due to prevent similar outbreaks in the future by telephone and in-person interviews for 29 patient cases and 140 matched controls in the neighbourhood. Until 20th September 2005, 24 additional isolates indistinguishable were identified from the outbreak strain. The case study found that there were 26 (90%) of 29 cases ate at least one in a restaurant (26 patients ate in 26 different restaurants) during the outbreaks happened, compared with 58 (41%) of 140 control (mOR (the odds ratio)15.3, 95% CI 3.6 138.8; if the mOR is greater than 1.0, the exposure might be a risk factor for the disease (SDC, 2013)); there were 2 of 29 cases missing a response, assuming that they not eaten a tomato, for the control cases 12 of 140 with missing values, assuming that they ate tomatoes. The result was mOR for tomatoes which was large and statistically significant with an mOR of 4.8, 95% CI 1.9-13.4, which means the infection was highly associated with eating tomatoes.
The outbreak strain bacteria were found in irrigation pond water on the Eastern shore of Virginia. The water was supplied directly into the soil, not fruits. One grower used pond water to dissolve the pesticide to treat tomato fruits, the investigation showed that cross contaminations were possible. Through this case study, Green et al said that contaminated tomatoes were not undertaken for recall; besides, tomatoes were also demonstrated as the vehicle for the multistate Salmonella outbreak. The author suggested that the contamination may occur early in the distribution chain, on the farm or packing house rather than at the restaurant. The primary source of the contamination was probably domestic faeces or wild animals. Another interesting point in the case study, the dilute concentration of pesticides did not affect the survival of Salmonella; contaminated stem and flower tomatoes can yield contaminated fruits, and the bacteria could be spread; without of doubt concluding that the Salmonella bacteria can survive a long time and adapt to different environmental condition. In summary, this outbreak is a great example to raise awareness about the microbiology hazard in the mass production of fresh products. Due to prevent a similar outbreak in the future, some further environmental and laboratory research should be conducted to determine the source of pathogens. It should be done by the industry, government agencies, and academic organizations. For example, in the study, the surface water is easier to contaminate than the protected wells, so the monitoring or preventing method is necessary.
What is the natural environment of salmonella enterica?
Salmonella bacteria can survive in many different environmental conditions, and it can also interact with both humans and animals (Murry, 2000). The water from the pond may be the source of salmonella bacteria from the excretion of the animals like faeces. The serotypes of Salmonella bacteria are also found in live organisms such as birds, animals, inserts, rodents, and poultry. How can Salmonella bacteria survive in the wide environmental inches?
According to Jay et al (2005), the neutral pH is the optimum environment to grow these bacteria; above 9.0 or below 4.0 is bactericidal. The temperature of 450C is the upper limit for the growth of Salmonella, the lowest is 5.50. The water activity (aw) is below 0.94 in media with neutral pH; if the higher aw, the pH value should be adjusted down to optimize the growth. Salmonella is also unable to tolerate high salt concentrations.
What is the source of the contamination?
The source of contamination is usually related to food processing or animals activities, pollution from humans, farming activities, or consumption of contaminated pond water (Murry, 2000). To be simple, salmonella contaminates raw products (vegetables, poultry, meat, etc..) and then brings the contamination into the kitchen environment.
Firstly, (Bhunia, 2018) poultry is a major source of cross-contamination. Poultry farming is usually operated under a high-density population, the colonized bird can spread the bacteria to the others; some serotypes of Salmonella enterica can survive in the empty poultry shed for at least one year (Way, 2000). From the poultry, the bacteria are transmitted to humans through slaughter and evisceration processing. Eggs are also the source of transmission because the bacteria are reserved in the ovary of the laying hen.
Some evidence showed that the contamination source was the failure of hygiene processing such as in milk and dairy products. One outbreak in England and Wales was from cheese containing S. goldcoast bacteria; the reason was the serious faults in the pasteurization process (Humphrey, 2000).
The rapid method of isolation and identification of salmonella enterica is based on molecular such as PCR. Note: around 1500 words for this part
The rapid methods to identify Salmonella are more convenient and faster than the current conventional method, especially, when large numbers of samples need to be investigated (Zee and Hui, 2000). The rapid methods take from 24 to 52 hours for the whole process: screening for, detecting, and identifying. The test kits for rapid testing are developed from many different technologies that include isolation techniques, and non-isolation methods.
According to Ray (2005), there are two groups of molecular genetic methods which are polymer chain reaction (PCR), Lux Gene Luminescence, Ice Nucleation Assay, and Nucleic acid (DNA) Probes.
Frontiers of Food Microbiology
Assignment 1, Semester 2 2021
DUE DATE: 26th August, 4 PM
AUTonline: Turnitin and Hard copy in my Pigeon Hole
From the following list of following micro-organisms choose ONE and write a literature review (~3000 words) outlining the significance of this organism and the molecular based methods to identify and enumerate it in food.
Salmonella enteritica
Include in your answer:
Why is it a concern?
How does it cause disease
Case, Prevalence, Statistics.
Details of the natural environment of the organism.
Likely sources of contamination.
Rapid methods of isolation and identification.
Focus on molecular based methods such as PCR.
Use references from:
Review papers
Scientific articles
Scientific Journal Articles
Review papers
Reputable websites from Organisations, ie:
Ministry of Primary Industries (MPI)
Food and Drug Administration (FDA)
Center for Disease Control (CDC)
