Spinach, Swine, and E. Coli
E. coli O157:H7 is a strain of Escherichia coli bacterium. Unlike the other strains which are harmless, this one can cause illness with the Shiga-like toxin it produces. This subtype of the bacterium can be found in the intestines of healthy farm animals: cattle, goats, and sheep. It is distinguished from other E. coli by its specific surface markers, the abbreviation of which can be found in the name. This type of E. coli is included in a class of dangerous E. coli, called enterohemorrhagic. E. coli O157:H7 was discovered in 1982, during a severe outbreak of bloody diarrhea, associated with the consumption of contaminated hamburgers. It is negative for invasiveness, unlike other E. coli, does not produce any colonization factors, and is not hemolytic (Roberts, 2001).
The contamination of bagged baby spinach with E. coli occurred because of infection of baby spinach by cattle feces that showed positive for the O157:H7 strain. As the method of this bacterium’s invasion is mostly fecal-oral, the E. coli traveled with the cattle’s feces through the water on a spinach field and this way people got infected by contaminated fresh produce that was not properly washed or thermally processed.
The time between being exposed to the bacteria and becoming ill is 3-4 days. Bloody diarrhea and abdominal cramps are the main symptoms of E. coli O157:H7 affection. Sometimes the diarrhea is free of blood and there are no other symptoms visible. The fever is insignificant, and the disease lasts 5-10 days. The hemolytic uremic syndrome is one of the complications of contamination with this strain of bacteria. It is common in the elderly, as well as in children. Acute kidney failure is accompanied by the destruction of erythrocytes. This complication affects about 8 % of those infected by E. coli O157:H7. Comparing to other food-borne illnesses, for example, Campylobacter jejuni caused enteritis, which besides diarrhea is characterized by abdominal pain, high fever, the E. coli infection is not so rich in symptoms.
E. coli O157:H7 outbreak in several Taco Bell restaurants was linked to contamination of lettuce, shredded cheese, and ground beef by this strain of bacteria. However lettuce is considered to be the most probable product to transfer the pathogen, as the cheese underwent the process of pasteurization, and ground beef was cooked.
Pulsed-field gel electrophoresis (PFGE) subtyping is used as an epidemiological standard in the study of pathogens. This test facilitated discriminating among different strains of bacteria and therefore identifying geographically dispersed bacterial outbreaks. The procedure consists of running periodically reversed voltage through a standard gel so that each DNA band runs in the opposite direction. PFGE subtyping results for geographically dispersed cases are submitted by laboratories to a national database, and from there are compared to determine whether there is a common source. This determination is guided using PFGE subtypes. If a common infection source has been discovered, and the bacteria had been isolated from this source, subtyping allows determining, if it is an outbreak strain (Thompson, 2000).
A Virus Killer Cocktail
Cranberry juice is believed to reduce urinary tract infections in women. Bacteriuria caused by a bacterial infection in the bladder is very common, especially in elderly women. Cranberry juice inhibits the adherence of bacterial cells to the lining of the bladder. This decreases the rate of inflammation caused by bacteria and also stops pyuria, which is common for infection of the bladder (Zamula).
Reovirus is a rare type of virus that belongs to a family of pathogens that affect the respiratory system and the gastrointestinal tract. The virus occurs in humans, and most cases are not severe. It is detected in feces, and urine, as well as nasal secretions, blood, and cerebrospinal fluid. The genome of this virus consists of 10-12 segments which are divided according to their size into 3 categories: L, M, and S. Although the role of reovirus in human pathology are uncertain, it is believed to cause several acute non-specific illnesses associated with respiratory and enteral tract. However, the virus is considered an opportunistic pathogen.
Cranberry juice consists of two major constituents – fructose, and a large polymeric compound. Fructose has nothing to do with the bactericidal effect of the juice, whereas the polymeric compound is found only in cranberry and also blueberry juice. A 100% cranberry juice contains specific tannin, called hippuric acid. This substance shifts down the level of pH, making the urine more acidic. This prevents the bacteria from adhering to the epithelium of the urinal tracts, as a certain pH level is required for this reaction (“Misconceptions about Infection Causes” 9).
The intestinal monkey rotavirus SA-11 was used along with a pool of intestinal reoviruses to create a model of the intestinal virus system. The virus responded to cranberry juice treatment by losing its ability to attach itself to erythrocytes. It was also unable to infect its host cells. Using electron microscopy the scientists were able to determine that there were no viral particles in the host cells treated with cranberry juice. Thus, cranberry juice proved to be an effective antiviral agent, by inducing an antiviral effect on the disease-producing agents.
A viral particle is also known as a vision. It consists of a nucleic acid, which is surrounded by a protective protein coat, called a capsid. The lowering of the number of virions in the bloodstream causes a decrease of general intoxication in the organism, as a smaller amount of viral particles infects less somatic cells, which release toxic products under the influence of virus integrating into their DNA. The toxic products of viral metabolism are the main pathogenic factor that causes the manifestation of disease symptoms, and because a smaller amount of virions are affecting the body, the clinical signs of the disease become less visible. However, as the level of virions in the blood is low, the virus may still exist within the cells in its latent form, and cause a later relapse (Lwoff, 1962).
Drug Resistance and Penguins
The ability of bacteria to resist some antibiotics is a naturally developed phenomenon. The ultraviolet radiation influences the induction of the lytic cycle in Antarctic bacteria, which leads to the liberation of virions and bacteriophages into the environment. Bacteriophages in their turn can transduce antibiotic resistance genes to sensitive bacteria. Transduction of antibiotic resistance is the major factor of insensitivity to antibiotics in bacteria found in Antarctic penguins (Dooley 393).
The researchers traveled to the Antarctic to study antibiotic-resistant bacteria for two reasons. First of all, the Antarctic is exposed to UV radiation by far more than any other geographic location, as the polar day lasts 6 months of the year. The ozone layer over the North Pole is also thinner than anywhere else, this means that the area is exposed to more UV light and there is more chance of bacterial antibiotic resistance development. The second reason the researchers went this far was the fact of Antarctic isolation from all other parts of the world, which meant no chance of bacteria ever being in contact with antibiotics. Therefore the microorganisms couldn’t adapt to a certain kind of antibiotic, which meant that the antibiotic resistance was due to natural reasons.
Small doses of ultraviolet radiation with long-wavelength (UV-A) play a vital role in the generation of vitamin D in the skin. For humans, long exposure to even long wavelengths of UV radiation may cause harmful effects, such as sunburns, and cataracts. The radiation at a shorter wavelength of 290-320 nm (UV-B) causes the damage of DNA at a molecular level. Due to exposition to short-wavelength doses of UV radiation that DNA may change its shape, as it absorbs the ultraviolet. This causes the protein-building enzymes to be unable to read the DNA and create distorted proteins. UV-B radiation can suppress the immune system of vertebrates, and also induces skin cancer in humans. Mammals exposed to such radiation also suffer from cataracts and snow blindness. An increased rate of UV-B radiation over the Antarctic reduces the plankton’s ability to photosynthesize. This reduces the amount of oxygen produced, as well as the amount of plankton itself. Plankton is a major food source for aquatic ecosystems, and its reduction significantly influences the life of vertebrates (Dees 166).
A process by which the bacterial DNA is transferred from one bacterium to another through a virus is called transduction or transfection. The viruses that afflict bacteria are called bacteriophages. Having entered a bacterial cell, the bacteriophage integrates into the host DNA/RNA for the bacteria to produce copies of the virus. These copies (virions) exit the cell and may infect other bacteria. Transduction may occur through the lytic or lysogenic cycle. During a lysogenic cycle, the phage is integrated into bacteria’s DNA and can stay inactive for many generations. The lytic cycle may be induced by various factors, for example, UV radiation. Under the influence of the lysogen (UV) the phage activates and lyses the bacterial cell, releasing the virions into the environment. The virions released from such a cell may capture part of the bacterial DNA, and when infecting different bacteria, transduce this foreign DNA into the new host cell. If by any chance the primarily infected bacteria were resistant to antibiotics, this quality will be exchanged to the newly infected cell (Burdette iii).
Pseudolysogeny, just like lysogeny is a state of a phage that has infected a bacterial cell. Unlike lysogeny, which includes integration of phage into the DNA material and becoming dormant for a long time, during pseudolysogeny there bacteriophage coexists within the host cell without constant inheritance of the phage’s genetic material, however, this coexistence is unstable. This condition determines infection and sensitivity to phage progeny within the same culture. Little research has been done on this topic, as pseudolysogeny is difficult to study. During pseudolysogeny, the bacterium’s metabolism experiences nutritional changes, pigment, and toxin production (Gaudillière and Rheinberger v). RecA gene is a protein that is very well conserved, especially among eubacterial species. It has much use in the field of microbiology, as with its help the researchers can differentiate heterofermentative species. This is done utilizing comparing the gene sequence of recA. (Yamanaka et al.)
Enterococci and Fast Food
Enterococci are facultative anaerobes that usually occur in pairs and are Gram-positive. Two types of enterococci are common to the human intestines. One – E, faecalis, and the other – E. faecium. Sometimes, especially under low immune status, these organisms tend to cause human illnesses. They might be the etiologic factor for such diseases, like urinary tract infections, bacteremia, infection of the heart valves (bacterial endocarditis), infection of the brain (meningitis), diverticulitis. It is also known that this bacterium colonizes open wounds and ulcers, causing wound and ulcer infections.
These bacteria may be detected on uncooked fruits and vegetables. As enterococci live in the intestines of most farm animals, they get released along with their feces and possibly contaminate vegetables and fruits, or water that is being used for plant irrigation. The numbers of enterococci are especially high in the summer, as the air temperature is favorable during the hot season. It is also more likely for the enterococci to spread over a vast territory, water irrigation is used mostly in the summer, and water intensifies the dissemination of these bacteria.
Most enterococci that contaminate food products and water are antibiotic-resistant. This is due to the production of an enzyme called beta-lactamase by the bacterial cell. This enzyme inactivates the Penicillin G before the antibiotic reaches its target. Another mechanism may be the alteration of penicillin-binding proteins, so the antibiotic is unable to properly attach and destroy bacterial cells. Enterococci are known for their penicillin, Vancomycin, and Linezolid resistance (Patterson, 1989).
Houseflies play an important role in the contamination of food by enterococci. As they tend to feed on human and animal feces, they might carry the pathogenic bacteria on their tarsi and contaminate fruits vegetables, and other alimentary products. Agricultural industries are also critical for enterococci dissemination, as they control the quality of the water with which the plants are being irrigated, as well as the water that is used to process the agricultural products. If this water is of low quality, with a high level of enterococci bacteria, then the produce of the industry will become a source of bacterial contamination.
Horizontal gene transfer is a transfer of genetic material from one bacterial organism to another that is not its progeny. This type of genetic material transfer is common for prokaryotes, and also may occur in unicellular eukaryotes. There are three widespread mechanisms of horizontal gene transfer. Transduction occurs when genetic material is being transferred from one organism to another via a bacteriophage. Transformation is characterized by a cell’s genetic alteration by a foreign genetic agent. The last mechanism of horizontal gene transfer is bacterial conjugation when bacterial cells establish physical contact, through which they exchange genetic information (Marri, 2007).
Shear Force and the Bacteriophage
Shear force is the energy that causes different levels of sedimentation among bacteriophages during centrifugation. As the device is rotating, the shear force causes the phages with greater molecular weight to precipitate faster than those that weigh less. If we know the rotation speed of the centrifuge, we can determine the molecular weight of bacteriophages according to their sedimentation.
M-13 bacteriophage is a virus that consists of single-stranded DNA, encapsulated in 2700 major coat protein copies, and 5 different copies of minor coat proteins. These minor coat proteins attach to a specific receptor on its host – Escherichia coli. This virus is non-lytic, however, the infected cells are notices to decrease their growth. A lot of research is being done with the M-13 phage and its role in nanotechnology and nanostructures. The M-13 bacteriophage can affect several strains of bacteria due to its M-13 p3 tip which binds to the To1A protein on the bacterial pilus. It can potentially infect all bacteria that carry this type of protein (Kuhn, 1987).
Problematic bacteria that are present within hospitals are pneumococcus, which is resistant to penicillin-type antibiotics. Not very sensitive to penicillin and vancomycin are enterococcus bacteria as well. Staphylococcus aureus is also quite resistant to antibiotic treatment pathogens. It is very adaptable to penicillin, however can be treated with oxacillin. There are also some strains of streptococcus pyogenes that are resistant to macrolide antibiotics but show sensitivity to penicillin. Streptococcus pneumonia is a beta-lactams resistant bacterium that is the major cause of pneumonia, meningitis, arthritis, and bacteremia.
Bacteriophages are currently being looked at as a future type of treatment for several bacteria-induced diseases. As phages are viruses that attach the bacterial organisms, they can be administered in form of intravenous injections that take the phages through the bloodstream directly to the loci of the pathologic process. However, this type of treatment requires further research.
References
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Lwoff, André. Biological Order. Cambridge, MA: M.I.T Press, 1962.
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Yamanaka, Takeharu, et al. “The TAO-Gen Algorithm for Identifying Gene Interaction Networks with Application to SOS Repair in E. Coli.” Environmental Health Perspectives 112.16 (2004): 1614+.
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