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Bacteria
Bacteria are small “prokaryotes”; they do not possess nuclei or intracellular organelles. Most bacteria are free living and can grow in humans, other animals and in the environment. They are the smallest living cell with an average size of one micron [1/1000 of a millimeter]. Bacteria make up the major component of our normal body flora. Bacteria are found all over the earth and are thought to be one of the first life forms. They can survive in the deepest oceans, the highest mountains and even in the arctic ice. They can colonize in any environment; acid/alkali, boiling/freezing and with/without oxygen. Their survival lies in their ability to go dormant for extended periods.
Bacteria divide by asexual binary fission. Under ideal conditions, bacteria divide every 20 minutes and it is estimated that the mutation rate is, at the lowest, one in every 100 million cells. It follows that in the colon, at normal growth, one million mutant bacteria will be produced every 20 minutes. It is clear that the intestinal bacteria have a great capacity to react to any adverse conditions to which they are exposed. This includes the administration of antibiotics to fight infections. It is no coincidence that the intestinal bacteria are a major reservoir of antibiotic resistant genes.
Pathogenic bacteria include Staphylococcus aureus which can produce toxins [toxic shock syndrome] and in its more resistant form becomes methicillin-resistant Staphylococcus aureus [MRSA]. Methicillin-resistant Staphylococcus aureus has mutated over time to develop a resistance to most antibiotics, causing infections that can be life threatening and difficult to treat. Sixty percent of Staph infections are now drug resistant, up from 2% in 1974. MRSA occurs most frequently in patients with weakened immune systems undergoing invasive procedures in hospitals and nursing homes.
Streptococcus pyogenes, solely a pathogen of humans, is responsible for rheumatic fever, skin infections and necrotizing fasciitis [a rare but deadly skin and deep tissue infection].
Pseudomonas aeruginosa is the fourth most commonly isolated hospital acquired pathogen. Ubiquitous in any moist environment, it can rapidly contaminate a moist endoscope with biofilm. It has been found in endoscope irrigation systems, automated reprocessors and even in the hospital water supply. It can be quite virulent and produces many toxins. There have been more than 200 reported cases of Pseudomonas aeruginosa transmission from endoscopes. Patients having bronchoscopies and ERCP are especially at risk for this pathogen. These infections cause discomfort, lengthy hospital stays and may result in death in critically ill patients.
Escherichia coli is a member of the large and diverse family of gram negative rods known as enterobacteriaceae. Although part of the normal intestinal flora, some strains are more pathogenic and can cause meningitis and septicemia. Escherichia coli is one of the three most common causes of diarrheal disease worldwide. A number of different E. coli strains can release toxins that cause a secretory diarrhea and urinary infections. Other members of this genus include Salmonella, Klebsiella and Serratia.
Helicobacter pylori is another solely human pathogen that has adapted to living in the harsh acidic environment of the stomach. It is estimated that half of the world’s population is colonized or infected with H. pylori. It adapts to the acidic stomach environment by secreting an enzyme, urease, which converts urea into bicarbonate and ammonia, creating a cloud of neutralizing chemicals to support bacterial growth. It then initiates an inflammatory response causing gastritis. This infection may be passed to the health care worker if proper personal protection is not used. Peptic ulcer disease can develop and H. Pylori may cause two forms of cancer: carcinoma of the stomach and a lymphoid tumor called maltoma.
Mycobacterium tuberculosis is an especially resistant bacteria with a waxy cell wall that causes particular staining properties called acid fast. This cell wall makes it resistant to destruction by drying and many chemical agents. Tuberculosis germs coughed into the air [or on a contaminated instrument] can remain alive and viable for weeks or months, much longer than other bacteria. Although it does not form spores, the resting form of these bacteria can survive many years without food or water. Because Mycobacterium tuberculosis is found in the stomach as well as the lungs, the infection is easily spread by a contaminated instrument. Many high level disinfectants are tested for potency using Mycobacterium tuberculosis. More resistant forms of Mycobacterium tuberculosis have been discovered in the HIV/AIDS populations.
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