In this series, we’re making an effort to get to know the
enemies of food safety by taking a look at pathogens and potential hazards that
cause foodborne illness in humans. Our last article was on listeria,
and in this article, we’ll move onto one of the most notorious, and most
common, causes of food poisoning, Salmonella.
Salmonella is a genus of rod-shaped bacteria, with the main
species of concern to humans being Salmonella enterica, which is found
worldwide in all warm-blooded animals. Strains of Salmonella can cause a
variety of nasty illnesses, most notably typhoid fever and food poisoning.
Salmonella bacteria are part of the Enterobacteriaceae
family, and they are primarily non-spore-forming, motile bacteria around 2 to 5
µm long. They can survive with or without oxygen and water, and through
freezing, but they are killed by heat of 75°C after 10 minutes.
The bacteria were first discovered in 1880 by Karl Eberth in
typhoid patients, and 4 years later the pathogen was successfully grown in the
laboratory by Georg Theodor Gaffky. The name Salmonella was after Daniel Elmer
Salmon, a veterinary pathologist who ran the USDA’s microorganism research
program in the 1800s. He had discovered Salmonella in pigs that had died of hog
cholera, or classical swine fever.
When a human becomes infected with Salmonella bacteria, it
generally results in food poisoning. This usually occurs when humans ingest
foods containing a high concentration of Salmonella, which then infects the
body through the digestive tract. Adults can fight off quite a large number
before infection, but infants and young children are much more susceptible.
The infection can only take hold once living salmonellae
reach the gastrointestinal tract. Some of the microorganisms are killed in the
stomach, with gastric acid responsible for the majority, but some can still
survive, embedding in the walls of the stomach and intestine, and sometimes
oesophagus, and once these bacteria reach the end of their incubation period
they release endotoxins, which cause enteritis and gastrointestinal disorder,
or food poisoning.
Typhoidal Salmonella is an even nastier form of the bacteria
that has adapted to humans and some higher primates. This version is much
better at making it through intestine walls and eventually infecting organs.
Symptoms are similar at the start, but can worsen into shock, whether
hypovolemic, septic or both.
Preceding symptoms, common to both types, are what most
people associate with Salmonella and food poisoning. In most cases, they show
up as diarrhoea, stomach cramps and sometimes vomiting and fever. Usually, it
takes 12 to 72 hours for the symptoms to develop after swallowing an infectious
dose of salmonella; they then typically last 4 to 7 days, with the majority of
people recovering without treatment.
Treatment,
if necessary, consists of several options. The main concern is to stay well
hydrated, as this is the major danger of Salmonella. Drink plenty of fluids to
offset those lost due to diarrhoea or vomiting. Your doctor might recommend a
rehydration solution, available from your pharmacist. Sometimes, serious cases
may be treated with antibiotics, and you must be sure to finish the course if
this is the case for you. Also make sure to stay at home until 48 hours after
symptoms have stopped, as you can still be infectious during this period.
But how can you avoid treatment entirely by preventing Salmonella
infection? Well, the key to that is good hygiene and food preparation
standards. Wash your hands before preparing and eating food, after handling raw
food, after going to the toilet, after contact with pets, or after working in
the garden.
In terms of food preparation, keep cooked food away from raw
food, and store raw foods below cooked in the fridge. Wash raw fruit & veg
well before eating, and make sure that cooked food (especially meat) is cooked
thoroughly. If you have a food thermometer, food should be cooked at temperatures of at least 75°C for 10
minutes.
Salmonella has been causing a whole slew of problems
throughout history, from food poisoning, to the much direr outbreaks of
typhoid. Perhaps the most infamous case of typhoid was that of Typhoid Mary, a
private cook who was a healthy carrier of the disease, who then spread it to
many people, causing the deaths of at least 3, and maybe more.
However, the disease goes back way further than that, with
one typhoid fever outbreak in 430 B.C. apparently wiping out one third of the
population of Athens when the city was one of the most powerful in the world.
Two of the worst Salmonella outbreaks in recent history are
the 1985 Milk Farm Dairy outbreak, with 5295 infected and 9 deaths after a contaminated batch of 2% pasteurised
milk, and the 2008 Peanut Corporation of America scandal, that led to 9 deaths
and 691 people affected across 46 states after negligence from said company. It
also led to imprisonment for senior executives of the firm, and one of the
largest food recalls in American history, and was one of the worst food safety scandals of all time.
Overall, Salmonella represents one of the most enduring and
unpopular bugs in human history, with a nasty propensity to adapt and survive,
and equally nasty effects on the human body. Thankfully, modern food safety
techniques and standards have reduced infections, and modern medicine is much
better at dealing with those ones that do make it through. Still, make sure you
wash your hands!
Sam Franklin
With
a master’s in Literature, Sam inhales books and anything readable, spending his
working hours reformulating the info he gathers into digestible articles. When
not reading or writing, he likes to put his camera to work around the world,
snapping street photography from Stockholm to Tokyo. Too much of this time
spent in Japan teaching English has nurtured a weakness for sashimi, Japanese
whisky, and robot cafés.
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