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Bacteria are among the earliest forms of life that appeared on earth billions of years ago. Bacteria live on or in just about every type of material; there are thousands of species of bacteria. Under certain circumstances, some bacteria transform into spores that become a dormant form of bacteria. Bacteria can cause disease by invading tissues or by producing toxins, and some can do both.
Bacteria are living organisms which are microscopic and unicellular - lacking a cellular nucleus — and are classed as prokaryotes containing DNA. Bacteria are the only prokaryotes. All other life forms are eukaryotes, creatures whose cells have nuclei. However, they are generally capable of “free-living” and therefore they possess all the biosynthetic machinery that is needed for this. Bacteria multiply by binary fission and there is no sexual interaction. They are basically one of three different shapes, bacilli, ball-shaped, and helical-shaped. Bacteria have been found to tolerate temperatures beyond the boiling point and subzero temperatures. They consume everything from sugars to sunlight, sulfur and iron. One species of bacteria (Deinococcus radiodurans) can withstand blasts of radiation 1,000 times more lethal than what humans can endure.
While pathogenic bacteria are notorious for cholera, tuberculosis, and gonorrhea, etc., such disease-causing species are a comparatively tiny fraction of the bacteria as a whole. Bacteria are both harmful and useful to the environment and animals, including humans. Antibiotics are given and classified as either bactericidal (killing bacteria) or bacteriostatic (slowing effects of bacteria.) The time, course, and severity of a disease depend upon the balance between the virulence of the infecting agent and the success with which the immune system combats the organism. Latency refers to a situation where an agent persists in a dormant, inactive form without causing damage, but can reactivate to cause problems at a later date. An example is herpes simplex virus, which may lie dormant within dorsal root ganglia after the primary infection, and may periodically reactivate to cause cold sores.
There are over 220 known bacterial toxins and they can be divided into two groups, endotoxins and exotoxins. An endotoxin is a component of the cell wall of all gram negative bacteria while the exotoxins include a huge number of proteins that are secreted from the bacterial cell which are mostly, but not exclusively, produced by gram positive bacteria.
Exotoxins are often divided up into three main groups, although not every toxin falls neatly into these categories. Cytotoxins destroy host cells. Neurotoxins interfere with neural transmission, examples being the toxins of Clostridium tetani and Clostridium botulinum. Enterotoxins affect the cells lining the gastrointestinal tract; the enterotoxins of Staphylococcus aureus and many of the toxins produced by Escherichia coli are examples of this.
A myriad of microbes and toxic substances can contaminate foods. There are more then 250 known foodborne diseases. Most are infectious and are caused by bacteria, viruses, and parasites. Other foodborne diseases are essentially poisonings caused by toxins and chemicals contaminating the food. According to the CDC around 80 million people a year in the U.S. contract foodborne diseases, accounting for 325,000 hospitalizations and more than 5,000 deaths. Foodborne illness is caused by drinking or eating food containing bacteria, viruses or parasites. Foods containing toxic chemicals can cause foodborne diseases as well.
We know that there are more than two hundred types of bacteria, viruses and parasites that can cause foodborne diseases. Reactions to these germs can range from mild gastric discomfort to death. The easiest way to prevent foodborne illness is to properly handle and cook foods. This includes washing hands and utensils carefully and cooking meat thoroughly. Foodborne microbes and toxins enter the body through the gastrointestinal tract and often cause the first symptoms there. Nausea, vomiting, abdominal cramps, and diarrhea are frequent symptoms. The most common foodborne infections are caused by three bacteria and viruses (although there are a few others that will be discussed herein). campylobacter, salmonella, and E. Coli.
Campylobacter bacterium has two species which are said to be the cause of campylobacter enteritis – they are Campylobacter coli and Campylobacter jejuni; the latter was found to be more prevalent, especially on poultry products and unpasteurized milk. Campylobacter jejuni, C. fetus, and C. coli are the types that usually cause campylobacteriosis in people. C. Jejuni causes most cases of the illness.
According to CDC, C. Jejuni is the leading cause of bacterial diarrheal illness in the United States, affecting an estimated 2.4 million people every year. Campylobacter is the most common bacterial cause of diarrheal illness in the world, and, the leading cause of bacterial food poisoning, a disease characterized by unpleasant attack of acute diarrhea that could last up to 5 days.
The bacteria live in the intestines of healthy birds and most raw poultry meat has Campylobacter on it. Eating undercooked chicken or other food that has been contaminated with juices dripping from raw chicken is the most frequent source of this infection. C. Jejuni primarily affects children less than 5 years old and young adults (15 to 29 years old).
Campylobacter enteritis disease is essentially a food-borne zoonosis, which means that the principal vehicle (carrier) of infection is raw or undercooked meat. Transmission is through direct consumption of infected animal meat (cattle, swine, chicken). Any kind of animal meat is likely to be contaminated with the bacterium. Products of poultry, especially broiler chickens are said to be the main source of the microbes Campylobacteriosis is disease caused by campylobacter and though not usual, can be spread person to person, especially with children.
Thus, infections come from handling raw poultry, eating undercooked poultry, drinking non-chlorinated water or raw milk, or handling infected animal or human feces. Most frequently, poultry and cattle waste are the sources of the bacteria, but feces from puppies, kittens, and birds also may be contaminated.
If infected with Campylobacter there may be no symptoms or there may be the following symptoms:
Laboratory tests are needed to identify Campylobacter in stool.
Most people infected with Campylobacter will get better with no special treatment. Erythromycin may be used to treat diarrhea caused by Campylobacter.
Some people infected with Campylobacter develop arthritis. A small number of people with campylobacteriosis may develop Guillain-Barré Syndrome (GBS), the leading cause of acute paralysis in this country. These rare conditions develop from 2 to 4 weeks after a Campylobacter infection and usually after diarrheal symptoms have disappeared.
In 1982, scientists identified the first dangerous strain of E-coli in the United States. The type of harmful E. coli most commonly found in this country is named O157:H7, referring to the chemical compounds found on the bacterium’s surface. This type produces one or more related, powerful toxins that can severely damage the lining of the intestines. Other types, including O26:H11 and O111:H8, also have been found in this country and can cause human disease.
E. coli 0157:H7
There are five unique classes of E. coli that can cause gastroenteritis and are, therefore, termed enterovirulent.
The more dangerous type is called enterohemorrhagic E. coli, or EHEC. The EHEC often causes bloody diarrhea and can lead to kidney failure in children or individuals with weakened immune systems. In about 5% of the cases, a life-threatening complication called hemolytic uremic syndrome can occur several weeks after the initial symptoms of gastroenteritis. This can result in anemia, bleeding and kidney failure. Cattle are the main sources of E. coli O157:H7, but other domestic and wild mammals also can harbor these bacteria.
E. Coli bacteria and its toxins have been found in:
E. Coli O157:H7 toxin can damage intestinal lining and cause other symptoms including:
Enterotoxigenic E. coli (ETEC), which produce a toxin similar to Cholera toxin, can cause diarrhea. These strains typically cause so-called travelers diarrhea because they commonly contaminate food and water in developing countries.
Enteropathogenic E. coli (EPEC) are associated with persistent diarrhea (lasting 2 weeks or more) and are more common in developing countries where they can be transmitted by contaminated water or contact with infected animals
Laboratory tests are needed to identify E. coli in stool.
Infections with E. coli O157:H7 will recover within 5 to10 days without treatment.
Hemolytic uremic syndrome (HUS), a serious complication of EHEC can lead to kidney failure. In North America, HUS is the most common cause of acute kidney failure in children, who are particularly prone to this complication.
Salmonellosis, or salmonella, is an infection caused by Salmonella bacteria. Salmonella is widespread in the intestines of birds, reptiles and mammals. Salmonella infections are increasing in the United States. In persons with poor underlying health or weakened immune systems, salmonella can invade the bloodstream and cause life-threatening infections. While the occurrence of different types of salmonella varies from country to country, Salmonella Typhimurium and S. Enteritidis are the two most commonly found in the United States.
An antibiotic-resistant strain of S. Typhimurium, called Definitive Type 104 (DT104), was first found in the United Kingdom and then in the United States. It is the second most common strain (after S. enteritidis) of salmonella found in humans. This strain poses a major threat because it is resistant to several antibiotics normally used to treat people with salmonella infections.
Salmonellosis may occur in small, contained outbreaks in the general population or in large outbreaks in hospitals, restaurants, or institutions for children or the elderly. While the disease is found worldwide, health experts most often report cases in North America and Europe. Every year, CDC receives reports of 40,000 cases of salmonellosis in the United States. However, the agency estimates that 1.4 million people in this country are infected, and that 1,000 people die each year with salmonellosis. Symptoms are most severe in the elderly, infants, and people with chronic conditions. People with AIDS are particularly vulnerable to salmonellosis-often suffering from recurring episodes.
Salmonella bacteria can be found in food products such as raw poultry, eggs, and beef; also occasionally on unwashed fruit. Food prepared on surfaces that previously were in contact with raw meat or meat products can, in turn, become contaminated with the bacteria.
In recent years, CDC has received reports of several cases of salmonellosis from eating raw alfalfa sprouts grown in contaminated soil. Salmonella infection frequently occurs after handling pets, particularly reptiles like snakes, turtles, and lizards. Some people who may be asymptomatic, but carry the bacteria can spread the disease by not washing their hands before preparing food for others.
The following symptoms usually begin from 12 hours to 3 days after infection.
Laboratory tests are needed to identify salmonella in stool if infected.
With severe diarrhea, intravenous fluids might be required. If the infection spreads from the intestines into the bloodstream, antibiotics such as Ampicillin might be required.
Reiter’s syndrome is a complication of salmonella. This syndrome can last for months or years and can lead to arthritis.
Unless treated properly, salmonella can escape from the intestine and spread by blood to other organs, sometimes leading to death.
Botulism is a rare but serious illness caused by the toxin produced by Clostridium botulinum bacteria. This toxin affects the nerves and if untreated, can cause paralysis and respiratory failure. Each year, U.S. health care providers report an average of 110 cases of food, infant, and wound botulism to CDC. About 10 to 30 outbreaks of foodborne botulism are reported every year. It is mentioned here because it has been used as a bioweapon and is therefore important for nurses to recognize. Botulinum will also be discussed later in the course under BioWar.
Often, cases of foodborne botulism come from home-canned foods with low acid content, such as asparagus, green beans, beets, and corn. C. Botulinum is anaerobic, which means it can survive and grow with little or no oxygen. Therefore, it can survive very well in sealed containers. Outbreaks of the infection, however, are often from more unusual sources such as chili peppers, tomatoes, and improperly handled baked potatoes wrapped in aluminum foil.
Laboratory tests are needed to identify C. botulinum toxin in blood or stool
Diagnosed early, treatment for foodborne botulism can be done successfully with an antitoxin that blocks the action of the bacterial toxin.
C. botulinum toxin is one of the most potent toxins known in nature, Paralysis of the arms, legs, trunk may occur. Exposure to the toxin, particularly in an aerosolized form, can be fatal.
Positive Uses of C. Botulinum
In 2000, FDA approved this toxin to treat cervical dystonia, a neurological movement disorder causing severe neck and shoulder contractions. In April 2002, FDA approved a form known as Botox to temporarily improve the appearance of moderate to severe frown lines between the eyebrows.
Shigellosis, also called bacillary dysentery, is an infectious disease caused by shigella bacteria. Four main types of shigella cause infection:
The CDC estimates that more than 400,000 cases occur every year in the United States. Healthcare providers report about 18,000 cases to CDC each year.
Sonnei is the most common type of shigella in developed countries, including the United States. Outbreaks of shigellosis frequently occur in tropical climates especially in areas with severe crowding and/or poor hygiene that sometimes occur in day care and institutional settings. An extremely low number of bacteria (10 to 100) are needed to transmit the infection.
Antibiotics such as ampicillin or ciprofloxacin might be required. Anti-diarrheal medicines may make the illness worse.
S. dysenteriae type 1 produces shiga toxin and can lead to life-threatening hemolytic uremic syndrome (HUS), the same complication that develops in some cases of infection with E. coli bacteria (enterohemorrhagic E. coli or EHEC).
Cholera is a major source of water-and foodborne sickness and death in the developing countries of Asia, Africa, and South America, particularly during epidemics and in refugee settings. It is endemic in the subcontinent of India, as well as in Russia, and sub-Saharan Africa. Scientific studies have shown that Vibrio cholerae bacteria, which cause cholera, constantly adapt to changes in the environment.
Individual cholera bacteria can join together to form large mats called biofilms. Biofilms protect the bacteria from environmental stresses and make the pathogen more resistant to being disinfected by chlorine. When conditions become favorable, other genes allow the bacteria to revert to their original forms. This is one method V. cholerae uses to survive harsh conditions. Better understanding of how the pathogen can shift will help researchers develop new ways to control it during epidemics.
Infection with S. typhi can be fatal if untreated, but it is not common in the United States. Typhoid fever frequently is found in developing countries, usually in contaminated water. It’s also a risk in areas where flooding or earthquakes cause sewer systems to overflow. Appropriate antibiotics are usually effective for treating typhoid fever; although the incidence of antibiotic-resistant S. typhi is increasing in some parts of the world.
In general, the following principles should be followed to prevent the transmission of the foodborne diseases discussed above.