Food Contamination
Because the same nutrients in foods are also the same nutrients microbes need for their growth, food spoilage is inevitable. However, most infectious agents do not multiply on foods, but use them as a vector to gain entrance to the human body.
Food Poisoning results from many sources. Some of them include the following: Bacillus cereus, Campylobacter jejuni, Clostridium perfringens, Escherichia coli, Salmonella typhimurium, Staphylococcus aureus, Vibrio parahaemolyticus, and Yersinia enterocolitica. Infection from them usually causes the same basic symptoms of acute gastroenteritis, abdominal discomfort and pain, and diarrhea, but symptoms vary -- from mild gastric distress to death -- depending on the type of bacterial infection. Transmission is usually passed via the fecal/oral route with the ingestion of the pathogen on contaminated food.
Foodborne diseases affects roughly seventy-six million people each year in the US, which is more common and deadlier than bacterial meningitis, toxic shock syndrome, and the flesh-eating strep combined. Typical bacteria that cause most of the epidemics include Salmonella, Campylobacter, and Shigella. More recently, such mutant strains as Escherichia coli 0157:H7, Listeria monocytogenes, Cyclospora cayetanensis, and caliciviruses are becoming more commonplace.
Water contamination is usually because of the presence of three bacteria and are indicators of fecal contamination -- E. coli, Clostridium perfringens, and enterococci. In the case of water contamination by Klebsiella pneumoniae, it should not be assumed that the contamination came from a fecal source. The bacterium is also found in soil and runoff can contaminate water.
Meat held at room temperature often invites bacteria from the family Enterobacteriaceae. This also happens with strains of Staphylococci, micrococci, and aerobic Gram-positive spore-forming bacilli. Refrigeration suppresses these microbes, but can allow the growth of such other organisms as pseudomonas. Eating raw meats, fish, and milk is becoming more of a hazard and should be avoided. Suspect, too, are salads prepared in restaurants where meats and vegetables share a common surface during preparation.
Color can often indicate the type of microbe involved in the spoilage:
- Black spots on meat are the result of Cladosporium species.
- White spots are from Sporotrichum carnis.
- Yellow or green spots form as a result of the Penicillium species.
- A rainbow effect, often seen on bacon and fish, is caused by a spoilage bacteria known as Photobacteria that can break down ATP to produce visible light. After a couple of days, this bacterium can grow sufficiently to enable raw fish to glow in the dark!
Spoiled milk, as opposed to fermented products, is caused by such capsulated organisms as Lactococcus cremoris or Enterobacter aerogenes, leaving the milk to form unpleasant strands. Various strains of clostridium can also cause milk to spoil. Contaminated ice cream in Minnesota in 1994 caused an estimated quarter of a million people to become ill. Despite this, it took a full three months before the Salmonella-type bacterium was tracked down and appropriate action taken. This is not an inspiring record designed to instill confidence in the public health system. On the other hand, when a contaminant is suspected, much food is wasted in an effort to track down a few questionable samples.
Stores of rotten black potatoes that turn into an oozing mess are the result of an Erwinia contamination.
A liver fluke, Fasciola hepatica, can be contracted by humans, mainly from eating watercress harvested from beds where infected snails live.
Listeria monocytogenes is a Gram-positive bacillus capable of growing at temperatures of 0°C (32°F) and lower. It is relatively heat-resistant, having been isolated from pasteurized products. Another reason for it being an easy microbe to be passed on is its ability to remain on the hands for long periods of time -- at least eight hours -- and is not easily removed by conventional handwashing.
Foods associated with this microbe are soft cheeses, pates, and raw vegetable dishes. Pre-cut foods are most at risk for developing listeria contamination. Most people remain relatively unaffected, except for pregnant women and newborns, where often fatal cases of meningitis and/or septicemia develop.
Almost half of all food poisonings in Japan are caused by Vibrio parahaemolyticus, a marine bacterium found off the coast there, as well as in America and southwest England. Almost all food poisonings have been the result of undercooked fish. Such was the case in an air flight from Hong Kong to the UK, where lobster salad was served. Fortunately, the new crew, picked up in India enroute, did not eat any of the salad as all others aboard were ill by the time the flight ended. Obviously, the incubation period is relatively short -- the time it took to fly from Hong Kong to the UK.
Food Contamination
