Bacteria and Food Poisoning

The U.S. Centers for Disease Control and Prevention (CDC) estimates that around 80 million people a year in the U.S. alone contract food poisoning or other foodborne diseases.
Foodborne illness is caused by eating or drinking food that contains disease causing agents. The most common causes of foodborne diseases are bacteria, viruses, and parasites. Foods containing toxic chemicals can cause foodborne diseases as well.
There are over 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 your hands and utensils carefully and cooking meat thoroughly.
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Below is a list of a few bacteria that cause foodborne diseases, along with the foods that are associated with them, as well as symptoms that are likely to develop from ingesting the contaminated foods.
Bacteria and Food Poisoning
Microbe - Aeromonas hydrophila
Affiliated Foods - Fish, Shellfish, Beef, Pork, Lamb, and Poultry
Diseases - Gastroenteritis, Septicemia
Symptoms - Diarrhea, Blood and Mucus in Stool

Microbe - Bacillus cereu
Affiliated Foods - Meats, Milk, Rice, Potato, and Cheese Products
Diseases - B. cereus Food Poisoning
Symptoms - Diarrhea, Abdominal Cramps, Nausea

Microbe - Campylobacter jejuni
Affiliated Foods - Raw Chicken, Unpasteurized Milk, Non-chlorinated Water
Diseases - B. cereus Campylobacteriosis
Symptoms - Diarrhea, Abdominal Cramps, Nausea and Fever, Headache and Muscle Pain

Microbe - Clostridium botulinum
Affiliated Foods - Canned Foods Including: Vegetables, Meats, and Soups
Diseases - Foodborne Botulism
Symptoms - Weakness, Double Vision and Vertigo, Difficulty in Speaking, Swallowing, and Breathing, Constipation

Microbe - Clostridium perfringens
Affiliated Foods - Non-refrigerated Prepared Foods: Meats and Meat Products, Gravy
Diseases - Perfringens Food Poisoning
Symptoms - Severe Abdominal Cramps, Diarrhea

Microbe - Escherichia coli O157:H7
Affiliated Foods - Undercooked Meats, Raw Ground Beef
Diseases - Hemorrhagic colitis
Symptoms - Severe Abdominal Pain, Watery and Bloody Diarrhea, Vomiting

Microbe - Listeria monocytogenes
Affiliated Foods - Dairy Products, Raw Vegetables, Raw Meats, Smoked Fish
Diseases - Listeriosis
Symptoms - Flu-like Symptoms, Persistent Fever, Nausea and Vomiting, Diarrhea

Microbe - Salmonella spp.
Affiliated Foods - Poultry and Eggs, Milk and Dairy Products, Raw Meats, Fish, Shrimp, Peanut Butter
Diseases - Salmonellosis
Symptoms - Nausea, Vomiting, Abdominal Pain, Fever, Headache, Diarrhea

Microbe - Shigella spp
Affiliated Foods - Poultry, Milk and Dairy Products, Raw Vegetables, Fecally contaminated water, Salads: Potato, Chicken, Tuna, Shrimp
Diseases - Shigellosis
Symptoms - Diarrhea, Abdominal Pain, Fever, Vomiting, Blood or Mucus in Stool

Microbe - Staphylococcus aureus
Affiliated Foods - Poultry and Egg Products, Meat Products, Dairy Products
Diseases - Staphyloenterotoxicosis, Staphyloenterotoxemia
Symptoms - Abdominal Cramping, Nausea and Vomiting, Prostration

Microbe - Vibrio cholerae
Affiliated Foods - Contaminated Water, Shellfish
Diseases - Cholera
Symptoms - Watery Diarrhea, Abdominal Pain, Dehydration, Vomiting, Shock
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Viruses Can Turn Harmless E. Coli Dangerous....^_^

Viruses attacking E. coli, (electron microscopy picture). (Credit: Image courtesy of Norwegian School of Veterinary Science)

Bacteriophage Structure© Gary E. Kaiser

For her doctorate, Camilla Sekse studied how viral DNA can be transmitted from pathogenic to non-pathogenic E. coli. Viruses that infect bacteria in this way are called bacteriophages. Her findings reveal that such transmission of bateriophage between bacteria can occur, and that in the case of E. coli it can transform a harmless bacterium into one capable of causing disease in man.

Escherichia coli is a complex group of gut bacteria that are found in all warm-blooded animals and are for the most part harmless. A few, however, cause disease in man and animals. The E. coli bacteria that produce a poison called Shiga toxin can produce a range of effects in man. One common effect is bloody diarrhoea followed by complications such as kidney failure (haemolytic uraemic syndrome). The bacteria may be spread through contaminated food or water, or from contact with animals.

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A combination of qualities necessary to produce disease
A sequence of favourable circumstances needs to exist before E. coli can produce disease. The most important of these is the ability to produce Shiga toxin. The gene that codes for Shiga toxin is not innate, but is contained within bacteriophages. In other words, the bacterium needs first to be infected by a bacteriophage coding for Shiga toxin in order to produce the toxin itself.
In her work, Camilla Sekse studied E. coli O103:H25 bacteria isolated both from foodstuffs and patients from the E. coli outbreak of 2006. She and her colleagues discovered special features of these E. coli bacteria that separate them from ordinary, benign forms. This discovery lead to it being easier to demonstrate E. coli O103:H25 in suspect food products.

Dangerous bacteria in our environment
It seems that E. coli O103:H25 has existed in Norway for some time, since this bacterium was also found to be a cause of the kidney failure outbreaks both in 2003 and 2005. Studies of the entire genome of this bacterium have shown that it more closely resembles the enteropathogenic E. coli (bacteria that cause diarrhoea) than the more common, Shiga toxin-producing E. coli, namely E. coli O157:H7.
Escherichia coli bacteria that are not disease-causing can absorb and lose bacteriophages coding for Shiga toxin, and can be important in the spread of these bacteriophages in the environment, even though they don't themselves cause disease. It appears that some E. coli bacteria can both more easily absorb and lose bacteriophages that contain the gene for Shiga toxin, and this may well be the case for E. coli O103:H25.
The work was primarily carried out at the Department Food Safety & Environment of the Norwegian School of Veterinary Science. Parts of the study were done in close collaboration with scientists of the University of Barcelona and at the Technical University of Denmark in Copenhagen, and in co-operation with the Norwegian Institute of Public Health in Oslo. The project was financed by the Research Council of Norway and the Norwegian School of Veterinary Science.

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Bacterial Reproduction

Bacteria are prokaryotic organisms that reproduce asexually. Bacterial reproduction most commonly occurs by a kind of cell division called binary fission. Binary fission results in the formation of two bacterial cells that are genetically identical.

Bacterial Cell Structure

Bacterial cells typically contain the following structures: a cell wall, cell membrane, cytoplasm, ribosomes, plasmids, flagella, and a nucleiod region.

• Cell Wall - Outer covering of the cell that protects the bacterial cell and gives it shape.
• Cytoplasm - A gel-like substance composed mainly of water that also contains enzymes, salts, cell components, and various organic molecules.

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• Cell Membrane or Plasma Membrane - Surrounds the cell's cytoplasm and regulates the flow of substances in and out of the cell.
• Flagella - Long, whip-like protrusion that aids in cellular locomotion.
• Ribosomes - Cell structures responsible for protein production.
• Plasmids - Gene carrying, circular DNA structures that are not involved in reproduction.
• Nucleiod Region - Area of the cytoplasm that contains the single bacterial DNA molecule.

Bacterial Reproduction:

AsexualMost bacteria reproduce by binary fission. During binary fission, the single DNA molecule replicates and both copies attach to the cell membrane.The cell membrane begins to grow between the two DNA molecules. Once the bacterium just about doubles its original size, the cell membrane begins to pinch inward.A cell wall then forms between the two DNA molecules dividing the original cell into two identical daughter cells.

Bacterial Recombination:

Binary fission is an effective way for bacteria to reproduce, however it does produce problems. Since the cells produced through this type of reproduction are identical, they are all susceptible to the same types of antibiotics. In order to incorporate some genetic variation, bacteria use a process called recombination. Bacterial recombination can be accomplished through conjugation, transformation, or transduction.

Conjugation

Some bacteria are capable of transferring pieces of their genes to other bacteria that they come in contact with. During conjugation, one bacterium connects itself to another through a protein tube structure called a pilus. Genes are transferred from one bacterium to the other through this tube.

Transformation

Some bacteria are capable of taking up DNA from their environment. These DNA remnants most commonly come from dead bacterial cells. During transformation, the bacterium binds the DNA and transports it across the bacterial cell membrane. The new DNA is then incorporated into the bacterial cell's DNA.

Transduction

Transduction is a type of recombination that involves the exchanging of bacterial DNA through bacteriophages. Bacteriophages are viruses that infect bacteria. There are two types of transduction: generalized and specialized transduction.Once a bacteriophage attaches to a bacterium, it inserts its genome into the bacterium. The viral genome, enzymes, and viral components are then replicated and assembled within the host bacterium. The newly formed bacteriophages then lyse or split open the bacterium, releasing the replicated viruses.During the assembling process however, some of the host's bacterial DNA may become encased in the viral capsid instead of the viral genome. When this bacteriophage infects another bacterium, it injects the DNA fragment from the previous bacterium. This DNA fragment then becomes inserted into the DNA of the new bacterium. This type of transduction is called generalized transduction.In specialized transduction, fragments of the host bacterium's DNA become incorporated into the viral genomes of the new bacteriophages. The DNA fragments can then be transfered to any new bacteria that these bacteriophages infect.
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How Safe is the Air Indoors?

What is in the air in your home, where you work, or in public buildings? There may be bioaerosols — airborne biological contaminants. Aerobiological health hazards affect everyone on a daily basis and include allergens, mold spores, bacteria, and viruses that cause infectious diseases. How can these hazards be controlled indoors?

Aspergillus fumigatus is a fungus whose spores are common inhalation pollutants that pose a health hazard. Photo: Centers for Disease Control and Prevention.

Aerobiological engineering is a field of study that combines elements of engineering and microbiology that focus on reducing the risk of airborne disease by controlling the aerobiology of our indoor environments. It offers some solutions to the hazards of bioaerosols:

• Existing technologies can collectively control these bioaerosols if we retrofit old buildings or specifically design new buildings to control airborne microbes.
• By re-engineering our buildings on city-wide scales, the population can be broadly protected and potentially immunized against epidemics.
• Developing standards for indoor environments and educating the public are critical steps to transforming our disease-prone society.

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Aerobiological health threats

Contagious diseases are the most dangerous and costly threats posed to building occupants today, including influenza, SARS, tuberculosis, pneumonia, and meningitis. Emerging pathogens such as avian flu and the resurgence of old diseases like plague, scarlet fever, whooping cough, and measles highlight the increasing vulnerability of populations to epidemic disease.

Evolving drug resistance, especially among hospital-acquired infections, complicates treatment of microbial agents, and physicians see their once abundant arsenal of antibiotics shrinking faster than new miracle drugs can be developed. Vaccines, once thought to be magic bullets, seem insufficient by themselves to combat airborne pathogens that can be transmitted freely in our unprotected buildings and have the potential to spread globally and cause pandemics.

Relatively mundane health threats like mold, dander, and allergens burden homes, schools, and offices, while the threat of bioterrorism leaves our buildings vulnerable to manmade epidemics that could decimate cities. Such formidable challenges can be placed into a manageable context if we recognize that protecting our buildings against the most common microbes simultaneously protects against the most dangerous threats as well.

Air- and surface-cleaning technologies

The technologies needed to create healthy buildings already exist, but they are not implemented widely enough to interdict epidemics. Optimized combinations of filtration and ultraviolet germicidal irradiation (UVGI) can be used to remove airborne microbes with high efficiencies. Combining and optimizing these technologies is the most cost effective means of disinfecting indoor air.

• Filtration removes airborne particles including mold spores, many bacteria, and allergens.
• UVGI eliminates many harmful bacteria and viruses.

Existing buildings can be retrofitted with air disinfection systems, but the most economic long-term solution is to construct new buildings that maintain aerobiological cleanliness by design. Air circulation is often poor in older buildings, and there are limits to what retrofitted air-cleaning systems can do for them. New buildings can be built in which the airflow is more evenly distributed and in which effectiveness of air cleaning can be maximized.2 A variety of other technologies, including photocatalytic oxidation (PCO), ozone, pulsed light, and antimicrobial materials, are also available options for air and surface biocontamination problems.

Criteria for rating healthy buildings

Modern air disinfection systems can achieve high levels of air cleaning, but limited budgets often require us to ask exactly how much air cleaning is needed to protect health. This question ultimately hinges on how buildings rate:

• aerobiologically — the indoor levels of airborne microbes
• epidemiologically — the infection risk of the building

Airborne levels of microbes

Indoor air contains a great variety of bioaerosols, most of which are relatively harmless to healthy humans. The concentration of airborne microbes in indoor environments, treated collectively without regard to species, provides a reasonable indication of overall aerobiological air quality. Levels of bacteria and fungi vary by season, with lows in winter, and increase with occupancy, as people are the primary source of contagious pathogens. Airborne levels are measured in terms of colony-forming units (cfu) of bacteria or fungi per cubic meter. Some hospital operating rooms are designed to maintain levels as low as 10 cfu/m3, although this level often proves difficult to achieve. Levels in homes and offices need not be this low, making solutions there less cost-prohibitive.

Infection risk

The infection risk (IR) of any building might be estimated by collecting data on infection rates and symptoms or through methods of risk analysis.3 Another approach is to estimate the risk using computer models of building airflow to calculate daily doses of inhaled contaminants. Airborne levels can be easily, if not always accurately, assessed with air samplers. The IR to an occupant in a particular building can be evaluated from epidemiological data. The IR can also be inversely viewed as the percentage of occupants protected from infection, a parameter called the building protection factor (BPF).

The BPF is the complement of the IR— a low IR implies a high BPF— and it can be used to rate and compare buildings under a common design basis. The BPF is primarily a function of the volume, airflow, outside air fraction, and removal efficiency of the air disinfection system. Being an intrinsic property of the building, it applies generically to all microbial species.4
Buildings differ according to their operating parameters. A completely unprotected building may have a BPF of 0% to 1%, whereas a building that maximizes protection of occupants may have a BPF of up to 99%. BPF can be considerably improved in existing buildings through the addition of air cleaning or other ventilation system improvements.

At least four general categories of buildings have been suggested:

1. Problem buildings foster aerobiological problems or act as amplifiers. Their airborne levels may exceed 10,000 cfu/m3. IR can approach 99% or more and BPF 1% or less.
2. Normal buildings have average airborne levels, about 500 to 5000 cfu/m3. Typically, IR is about 50% to 75% and BPF about 25% to 50%.
3. Healthy buildings promote good air quality and health or are above average. Airborne levels are 100 to 1000 cfu/m3. Typically, IR is less than 50% and BPF 50% or higher.
4. Immune buildings are designed to actively prevent airborne disease transmission. Airborne levels are as low as 10 cfu/m3. IR is less than 10% and BPF 90% or higher.

Disease-free buildings

Buildings concentrate allergens due mainly to the protective effects of shade, warmth, substrate materials, and moisture. For the same basic reasons, they act as vectors (carriers) for contagious airborne diseases. Humans have been building enclosed habitats for perhaps half a million years, and in this course of time airborne pathogens evolved the ability to survive indoors just long enough to transmit to new hosts. They have adapted to our enclosed habitats so completely that they cannot survive outdoors. This evolutionary process accelerated when man began husbanding animals, from which almost all human pathogens seem to have jumped species. The evolutionary process continues today as emerging pathogens adapt to indoor transmission, and the number of new disease species has increased exponentially over time, in concert with the size and density of the human population.

By designing our habitats strictly for human comfort, we have unwittingly fostered the adaptation and proliferation of dangerous pathogens. It is only by re-engineering our buildings to eliminate, rather than foster, airborne disease transmission that we can reverse this evolutionary trend. By immunizing enough buildings against disease, it is theoretically possible to develop herd immunity in a community or city. The percentage of buildings that would need to be immunized to block an airborne epidemic is similar to the percentage of a population vaccinated to achieve herd immunity, and depending on the contagiousness of the species, this may be as low as 30%.

In addition to air disinfection and improved delivery of clean air, there are other factors that can aid in the development of healthy buildings. Rugs, carpets, furniture, draperies, and the like can absorb mold spores and regenerate new ones if they become wet. Material selectivity can be one beneficial approach, and other alternatives include the use of self-disinfecting materials, pressurization, and isolation of zones within buildings, including the provision of buffer zones between the inside and outdoor air and the creation of clean inner zones safe from airborne health threats.

Regulating healthy buildings

Implementing changes to building construction on a vast enough scale to control epidemics would require governmental programs. As yet there are virtually no existing standards or laws regarding the aerobiological healthiness of buildings. It is curious to note that airborne chemical contaminants are regulated in many states while airborne pathogens, which cause far more fatalities, are not.

The key to regulation is the development of aerobiological air quality standards. Several organizations and government agencies are involved in the control of disease epidemics, including the Centers for Disease Control and Prevention (CDC), National Institute of Occupational Safety and Health (NIOSH), and World Health Organization (WHO), but none of them is responsible for regulating the living environments in which these diseases are transmitted.

The task of improving air quality in homes, schools, and offices has mostly fallen to independent professional societies. The American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) has had a long and active interest in air quality, healthy buildings, and green buildings, and it is currently developing new programs in these directions. The International Ultraviolet Association (IUVA) is currently drafting a set of guidelines to assist in the design, development, implementation, and testing of UVGI and other air- and surface-cleaning systems.

Aerobiologically green buildings

Green building design is a field geared toward constructing sustainable indoor environments without damaging the environment. Green is clean, as they say, and healthy. The concept of human health is intrinsic to both this field and to aerobiological engineering, and common ground can be found through the exploration of aerobiologically green buildings that implement sustainable technologies for air and surface cleaning.

An example of where these fields overlap is the selection of building materials and furnishings that are both ecofriendly and less likely to contribute to health problems. Solar exposure can provide benefits, since sunlight can destroy mold spores, bacteria, and viruses. Radiant floor heating is an energy-efficient alternative to covering floors with carpets, as are dedicated outside air systems that efficiently control humidity. Although forced air is generally considered a necessity for air cleaning, buildings can also be naturally ventilated using wind energy.

Hygienic protocols

Engineering may go a long way toward the control of airborne diseases, but it may not be sufficient to eradicate them if other transmission routes remain unattenuated. Direct contact may be the dominant route of infection for many pathogens considered airborne, and engineering alone cannot control unhygienic human behavior. People must be educated to protect themselves, and for this purpose we need to define a set of protocols for human hygiene. These might include hand-washing procedures, quarantining contagious individuals, and other commonsense practices that can be taught in elementary school.

Many office workers today are so motivated they come to work during the contagious phase of their infection, placing other workers at risk. Economic losses from lost work and diminished productivity can be staggering. Working at home and in-office quarantine are two options for employers.

What can the individual do?

The most important thing individuals can do to protect themselves against airborne disease is to become educated about sources and transmission routes of airborne pathogens. Proximity to a contagious individual for as little as one hour can cause a secondary infection. Families with children must be especially careful since the youngest children tend to bring home diseases from schools, which are then transmitted to the rest of the family. Frequent hand washing and isolating sick children in bedrooms is one approach to protecting the rest of the family.

In regard to allergens, the home environment can be improved in some simple ways even without air cleaning. Old rugs and carpets that absorb spores can be cleaned, removed, or replaced with alternatives such as linoleum or other growth-resistant materials, and the amount of sunlight entering a home can be increased in various ways.

Misconceptions about disease must be dispelled. For example:

• The myth that colds and flus come from outdoor air has persisted since the ancient world and is kept alive every time children are told to “bundle up or you’ll catch a cold.”
• Another popular misconception is that some disease is beneficial, or that disease makes you stronger, but such fuzzy ideas are not grounded in science. Acquired immunity from pathogenic disease is always specific, never providing any general protection, and is often temporary at best. It is true our bodies are filled with friendly bacteria that were once parasites, but if selection for antibiotic resistance is allowed to continue, millions could become victims of unnecessary plagues.

Conclusion

Humanity stepped beyond the hardships of living in the elements by building habitats, but modern human culture and technology have created new contingencies and unexpected problems. It is well within human capabilities to redesign buildings and cities to be resistant to epidemic airborne disease, which is arguably the most serious threat we face today. Human health is a global concern, and achieving it begins with education, redesign of living environments, and large-scale implementation of aerobiological standards. The ultimate goal of these efforts must be disease eradication; all other remedies are merely triage and half-measures that fail to deal directly with the environments that are the root of the airborne disease problem today.

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Newly Discovered Protein Kills Anthrax Bacteria By Exploding Their Cell Walls

Not all biological weapons are created equal. They are separated into categories A through C, category A biological agents being the scariest: They are easy to spread, kill effectively and call for special actions by the pubic health system. One of these worrisome organisms is anthrax, which has already received its fair share of media attention. But work in Vince Fischetti’s laboratory at Rockefeller University suggests that a newly discovered protein could be used to fight anthrax infections and even decontaminate areas in which anthrax spores have been released.

“Anthrax is the most efficient biowarfare agent. Its spores are stable and easy to produce, and once someone inhales them, there is only a 48-hour window when antibiotics can be used,” says Fischetti. “We’ve found a new protein that could both potentially expand that treatment window and be used as a large-scale decontaminant of anthrax spores.” Because anthrax spores are resistant to most of the chemicals that emergency workers rely on to sterilize contaminated areas, a solution based on the protein would be a powerful tool for cleaning up after an anthrax attack.

A bacillus bacterium, a close relative of anthrax, begins to explode after being treated with PlyPH. The PlyPH protein, discovered by Rockefeller scientists, offers several advantages over existing anthrax treatments. (Image courtesy of Rockefeller University)

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All bacteria, anthrax included, have natural predators called bacteriophage. Just as viruses infect people, bacteriophage infect bacteria, reproduce, and then kill their host cell by bursting out to find their next target. The bacteriophage use special proteins, called lysins, to bore holes in the bacteria, causing them to literally explode. Fischetti and colleagues identified one of these lysins, called PlyG, in 2004, and showed that it could be used to help treat animals and humans infected by anthrax. Now, they have identified a second lysin, which they have named PlyPH, with special properties that make it not only a good therapeutic agent, but also useful for large-scale decontamination of areas like buildings and military equipment.

The new protein has several advantages. Most lysins, including PlyG, are only active in a very specific pH range of six to seven, so that they work very effectively in our bloodstream, but may not useful in many environmental conditions. “PlyPH works in an extremely wide pH range, from as low as four to as high as eight,” says Fischetti. “I don’t know of any other lytic enzyme that has such a broad range of activity.”

In addition, PlyPH, like PlyG, is highly specific in terms of the types of bacteria it affects. When Fischetti and colleagues added PlyPH to different bacterial species, only the anthrax bacteria were killed. This is a great benefit over antibiotics, which kill many different kinds of bacteria, including many helpful species. Because it is so specific, the chances of anthrax becoming resistant to PlyPH, as it is to many of the antibiotics currently available to treat it, are extremely low.

“We have never seen bacterial resistance to a lysin,” says Fischetti. “PlyPH and PlyG are probably the most specific lysins we, or anyone, has ever identified — they only kill anthrax and its very close relatives. This feature, and the wide pH range offered by PlyPH, is why we think it could be used as an environmental decontaminant.”

Fischetti hopes to combine PlyPH with a non-toxic aqueous substance developed by a group in California that will germinate any anthrax spores it comes in contact with. As the spores germinate, the PlyPH protein will kill them, usually in a matter of minutes. The combined solution could be used in buildings, on transportation equipment, on clothing, even on skin, providing a safe, easy way to fight the spread of anthrax in the event of a mass release.
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Bacterial Reproduction

Bacteria are prokaryotic organisms that reproduce asexually. Bacterial reproduction most commonly occurs by a kind of cell division called binary fission. Binary fission results in the formation of two bacterial cells that are genetically identical.

Bacterial Cell Structure

Bacterial cells typically contain the following structures: a cell wall, cell membrane, cytoplasm, ribosomes, plasmids, flagella, and a nucleiod region.

• Cell Wall - Outer covering of the cell that protects the bacterial cell and gives it shape.
• Cytoplasm - A gel-like substance composed mainly of water that also contains enzymes, salts, cell components, and various organic molecules.
• Cell Membrane or Plasma Membrane - Surrounds the cell's cytoplasm and regulates the flow of substances in and out of the cell.
• Flagella - Long, whip-like protrusion that aids in cellular locomotion.
• Ribosomes - Cell structures responsible for protein production.
• Plasmids - Gene carrying, circular DNA structures that are not involved in reproduction.
• Nucleiod Region - Area of the cytoplasm that contains the single bacterial DNA molecule.

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Bacterial Reproduction: Asexual

Most bacteria reproduce by binary fission. During binary fission, the single DNA molecule replicates and both copies attach to the cell membrane.

The cell membrane begins to grow between the two DNA molecules. Once the bacterium just about doubles its original size, the cell membrane begins to pinch inward.

A cell wall then forms between the two DNA molecules dividing the original cell into two identical daughter cells.

Bacterial Recombination:

Binary fission is an effective way for bacteria to reproduce, however it does produce problems. Since the cells produced through this type of reproduction are identical, they are all susceptible to the same types of antibiotics. In order to incorporate some genetic variation, bacteria use a process called recombination. Bacterial recombination can be accomplished through conjugation, transformation, or transduction.

Conjugation

Some bacteria are capable of transferring pieces of their genes to other bacteria that they come in contact with. During conjugation, one bacterium connects itself to another through a protein tube structure called a pilus. Genes are transferred from one bacterium to the other through this tube.

Transformation

Some bacteria are capable of taking up DNA from their environment. These DNA remnants most commonly come from dead bacterial cells. During transformation, the bacterium binds the DNA and transports it across the bacterial cell membrane. The new DNA is then incorporated into the bacterial cell's DNA.

Transduction

Transduction is a type of recombination that involves the exchanging of bacterial DNA through bacteriophages. Bacteriophages are viruses that infect bacteria. There are two types of transduction: generalized and specialized transduction.

Once a bacteriophage attaches to a bacterium, it inserts its genome into the bacterium. The viral genome, enzymes, and viral components are then replicated and assembled within the host bacterium. The newly formed bacteriophages then lyse or split open the bacterium, releasing the replicated viruses.

During the assembling process however, some of the host's bacterial DNA may become encased in the viral capsid instead of the viral genome. When this bacteriophage infects another bacterium, it injects the DNA fragment from the previous bacterium. This DNA fragment then becomes inserted into the DNA of the new bacterium. This type of transduction is called generalized transduction.

In specialized transduction, fragments of the host bacterium's DNA become incorporated into the viral genomes of the new bacteriophages. The DNA fragments can then be transfered to any new bacteria that these bacteriophages infect.

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Bacteria: Friend or Foe?

Bacteria are all around us and most people only consider these prokaryotic organisms to be disease causing parasites. While it is true that bacteria are responsible for a large number of human diseases, they also make it possible for certain elements such as carbon, nitrogen, and oxygen to be returned to the atmosphere.

Life as we know it would not exist without bacteria to decompose waste and dead organisms. These bacteria ensure that the cycle of chemical exchange between organisms and their environment is continuous.

The decision as to whether bacteria are friend or foe becomes more difficult when both the positive and negative aspects of the relationship between humans and bacteria are considered. Let's discuss three types of symbiotic relationships: commensalism, mutualism, and parasitism.
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Commensalism is a relationship that is beneficial to the bacteria which live off of the host, but does not help or harm the host. Most of the bacteria that reside within the bodies of humans are commensalistic.

In a mutualistic relationship, both the bacteria and the host benefit. For example, there are several kinds of bacteria which live inside the mouth, nose, throat, and intestines of humans and animals. These bacteria receive a place to live and feed while keeping other harmful microbes from taking up residence.

A parasitic relationship is one in which the bacteria benefit while the host is harmed. Pathogenic parasites, which cause disease, do so by resisting the host's defenses and growing at the expense of the host. These bacteria produce poisonous substances called endotoxins and exotoxins which are responsible for the symptoms that occur with an illness.

When all of the facts are considered, bacteria are more helpful than harmful. Humans have exploited bacteria for a wide variety of uses, such as: making cheese and butter, decomposing waste in sewage plants, and developing antibiotics. Bacteria have been able to survive without us, but we could never live without them.

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