Structure and Ecology of E.Coli
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- NURUL ATIKAH
Since the ancient time until today, the modern day area, human had been living with various microorganism like bacteria, archaea, algae, fungi, protozoa and viruses (Pelczar, 2014). Basically they are living in all environment in the world. They exist in the hot spring. Water, soil and even in the air that we breathe. Due to their microscopic size, human are not able to see them with naked eyes. Thus, they can only be seen by using the microscope. Each of the microorganism are different from each other based on their distinctive characteristics.
Bacteria is believed to live in the Earth a long time ago and actually predate the dinosaur themselves (What are Bacteria, 2015). Some bacteria is good and beneficial to human being like Lactobacillus acidophilus. On the other hand, there are also numerous infectious bacteria that can be harmful to human body. They have the ability to cause sickness and even lead to death.
One of the most popular pathogenic bacteria is Escherichia Coli or commonly called E. coli. Many people know that E. coli can cause diarrhea if they ate foods or drinks that are contaminated with E. coli. Actually, there are many types of E. coli that can cause different types and level of diarrhea. This assignment is going to discuss on the E. coli itself, its structure, ecology and mode of transmission. Then, the diseases caused by different types of E. coli and the treatment required to treat the infections.
This bacteria was first discovered in 1885 by a German microbiologist Theodor von Escherich when he isolated it from the feces of a newborn. It was first name as Bacterium coli Commune and later was renamed to Escherichia Coli until today.
E. coli was a gram negative non-sporing rod-shaped bacteria which normally lives in the lower gastrointestinal tract of warm-blooded animals E. colican also be found in environments at higher temperature, such as on the edge of hot springs. It is one of many bacterialspeciesthat inhabit our digestive tract in large numbers. E. coli is a facultative anaerobes which can live both in the presence and absence of oxygen. While in the colon the bacterium performs fermentation or anaerobic respiration but can switch to aerobic respiration when it is passed out of the colon and deposited on an aerobic environmental surface (Hartsock, n.d). But of course the bacteria will grow better with the present of oxygen because it can use its nutrients more efficiently during aerobic growth and therefore generate more energy and grow faster.
Environmental resources of elements like carbon, hydrogen, nitrogen, oxygen, phosphorus and sulphur are essential to bacteria and other living organisms to build their cellular component and survive. Growth factor is the addition to those building blocks. E. coli is well adapted to its habitat. According to Todar, the wild-type E. coli do not required any growth factor. This is because it has the ability to produce its own growth factor with the adequate supply of the essential elements. However a lot of energy is required to make every single growth factor required. So, if E coli is being supplied with those growth factors it will be able to grow and reproduce much faster.
E. coli is a mesophilic bacteria. It can grows and divides between the temperatures of 10ËšC to 45ËšC. But its optimum temperature is 37ËšC or 98.6ËšF. This temperature is normal since E. coli lives and evolves in human colon and the normal body temperature for human is also 37ËšC. It is a need for the bacteria to have the same optimum temperature as the host to make sure it can grow effectively. Hartsock said that the growth rate of E. coli will slow down if it is removed from the 37ËšC environment, but it will not die. The optimum pH for growth is 6.0 to 8.0
It is important to note that E. coli can be divided to numerous strains and most of the strains are not pathogens. Most of them are harmless and exist as part of the normal flora of the human gut. Nordqvist (2014) stated that E. coli also has many beneficial functions. For example, helping in digestion processes, food breakdown and absorption, and vitamin K production. E. coliis also commonly used as an indicator to indicate how much human feces is in the water in the field of water purification. This is due to a significant larger amount ofE. coliin human feces than other bacterial organisms.
INFECTIONS CAUSED BY E. COLI
On the other hand, there are also E. coli strains that can be considered as pathogens. Compared to other bacteria like Vibrio cholerae and Listeria monocytogenes that are one-disease organisms, E. coli strains can cause various types of disease. Diseases that can be cause by E. coli strains infections are diarrhea, dysentery (bloody diarrhea), hemolytic uremic syndrome, HUS (kidney failure), bladder infections, septicemia, pneumonia and meningitis. Because each strain can cause different types of disease, it is important to identify particular strains or groups of strains so that the disease caused by each strain can be identified. The infections that can be caused by pathogenic E. coli can be divided into two categories which are gastrointestinal infections and urinary tract infection (UTI). The strains are called diarrheagenic E. coli strains and E. coli of extraintestinal infections. Currently, there are at least six diarrheagenic E. coli virotypes that have been identified: enterotoxigenic E. coli (ETEC), enteroaggregative E. coli (EAggEC), diffusely adhering E. coli (DAEC), enteropathogenic E. coli (EPEC), enterohemorrhagic E. coli (EHEC) and enteroinvasive E. coli. (EIEC), (Salyers & Whitt, 2002, p. 408).
The first strain is enteropathogenic E. coli or EPEC. Adherence of EPEC strain produces an alterations in the structure of host mucosal cell. The normal mucosal absorptive cell have numerous microvilli on their apical surfaces. But the cell which the EPEC strain have adhered exhibit elongated microvilli at the place where the bacteria are not bounded and there are no microvilli present at the place where the bacteria are bound. This is called attaching and effacing.
Rather than producing exotoxins, the diarrhea may be caused primarily by bacteria invasion of host cell and subversion of signal transduction system that control ion flow. According to U.S Food and Drugs Administration (FDA), infantile diarrhea is the name of the disease usually associated with EPEC especially in the developing countries. Adults also can get this EPEC diarrhea, and this types of diarrhea is sometimes included in the ‘traveler’s diarrhea’. EPEC may not be as invasive as Shigella but it still cause inflammatory moderate inflammatory response. The symptoms of this disease are watery diarrhea, bloody diarrhea, abdominal cramps, vomiting, malaise, headache, fever, chills and abdominal pain. The infectious dose of EPEC in healthy adults has been estimated to be 10^6 organisms. Todar (2012) stated that some types of EPEC are referred to as diffusely adherent E. coli (DAEC), based on specific patterns of adherence.
The third strain is enterotoxigenic E. coli or ETEC. Centre for Disease control and Prevention, CDC (2006) stated in their website that this strain is the main cause for the ‘traveler’s diarrhea’. One of the symptoms caused is diarrhea but with no fever. This strain adheres to the host cell and produced a choleralike toxin called heat-labile toxin (LT) and a second diarrheal toxin called heat-stabile toxin (ST) that act on mucosal cell to cause diarrhea. The transmission of ETEC is only by the fecal-oral route. ETEC only cause a mild inflammatory diarrhea towards the host cells but it can be fatal especially in infants and children in the developing countries. This strainis the second leading cause of death in children less than 5 years of age. The infectious dose of ETEC for adults has been estimated to be at least 10^8 cells, but may be lower in children and elderly.
The forth strain is enteroaggregative E. coli or EAggEC which can only be found in human. These bacteria were named ‘‘enteroadherent-aggregative E. coli,’’ although the name was subsequently shortened to enteroaggregative E. coli (EAggEC), (Steiner, Lima, Nataro, Guerrant, 1998). This strain had emerged as the emerging as an important cause of persistent diarrhea, especially in children in the developing world. EAggEC is basically resembles ETEC in many ways like they are not invasive, they both only cause mild inflammatory response and do not change the structure of the intestinal mucosal cell they adhere. But what make them differ is the EAggEC strains tend to clump in small aggregates like a ‘‘stacked-brick’’ pattern and adhere to the intestinal mucosa.
EAggEC strains possess a variety of virulence factors. These include producing an enterotoxin similar to the heat-stable enterotoxin of ETEC, putative haemolysins and toxins, and various types of fimbriae and outer membrane proteins that may be involved in the adhesion process.
The fifth strain is enteroinvasive E. coli or EIEC which also can be found only in human. EIEC closely resembles and often mistaken as Shigella because of the same pathogenic mechanisms and inflammatory response they cause. The symptom they produce is dysentery, including a dysentery like diarrhea with fever. Besides, both organisms are invasive and do not produce LT or ST toxin. EIEC invades the host and destroy the colonic tissue that lead to dysentery. At least 10^6 of EIEC organisms are required to cause illness in healthy adults.
The sixth strain is enterohemorrhagic E. coli or EHEC which also known as E. coli O157:H7. EHEC are considered to be "moderately invasive". It do not invade the mucosal cell but produces toxins, known as verotoxins or Shiga-like toxins because of their similarity to the toxins produced byShigella species. The symptoms for EHEC infections are abdominal cramp, fever, vomiting and diarrhea. There are also some cases which the diarrhea progress into bloody diarrhea (haemorrhagic colitis). Most patients will recover in 10 days interval but for some small portion of patients like children and the elderly, the infection will lead to a life threatening disease such as hemolytic uremic syndrome (HUS). HUS is characterized by acute renal failure, hemolytic anemia and thrombocytopenia (WHO, 2011). The infectious dose for O157:H7 is low which is estimated to be 10 to 100 cells.
CAUSES AND PREVENTION
The main cause and mode of transmission for E. coli is foodborne and waterborne. Human and animals can be infected with this bacteria when they consume contaminated foods and drinks. Water that is contaminated with sewage and feces can cause a great harm to human and certain animals. Firstly, the water supply system is the one that should be put into observation. Having a water supply that is free from sewage is everyone’s right. The aging water supply system, the leaking pipes that can allow sewage-bearing pipes to leak into tap water-bearing pipes should be change. The government of all countries play a great part in this matter. Besides, people should not swim in public pool or lakes that are susceptible to the sewage and feces.
It is known that E. coli can be transmitted through food that we eat. For example meat products. The meat maybe contaminated with the intestinal contents during slaughter. Food irradiation would help to kill the bacteria and microorganisms inside the ground meat. There are three sources of radiation that are used for food irradiation, gamma rays, x-rays and electron beam. FDA had listed the benefits of food irradiation. First, it helps to kill and eliminate organisms that cause foodborne infections like E. coli and Salmonella. Other than that, irradiation also helps to preserve foods for a long time, acts as the pest-control by destroying the insects that are harmful to the fruits and delay sprouting and ripening to increase longevity. Lastly, irradiation also used to sterilize food so that it can be stored for years without the need of being freeze. On the other hand, people also should adhere to the proper way of preparing and cooking foods. All foods should be handle safely to ensure that the foods are safe enough to be eaten. The meat should be cook thoroughly under high temperature to kill the bacteria contaminating the meat.
Plants and fruits can also become the agents in transmitting E. coli. People should wash all fruits and vegetables thoroughly before eating them especially when they want to eat them raw. Do not drink can drinks or milk unless they are pasteurized. Cross-contamination also should be avoided. Make sure that the utensils that are used during cooking and eating are clean. For example, wash the cutting board before you use it.
E. coli infections also can be caused by human to human transmission through their contact with fecal matter. To avoid this, people should practice meticulous personal hygiene. Practice the correct steps of hand washing to prevent the bacteria from being transmitted to other person. For infants, the best way to fight E. coli infections is through breast-feeding. But for the bottle-feed infants, make sure that the way of preparing the milk is clean and safe. Besides, if the baby have diarrhea, change the diaper frequently and do not wait for it to full to avoid transmission of feces.
As a conclusion, Escherichia coli or E. coli initially is a good bacteria that help human with the process that happen in the gastrointestinal tract. But, there are some of the strain from these bacteria that considered as diarrheagenic E. coli such as ETEC, EAggEC, DAEC, EPEC, EHEC, EIEC. Even though all of these strains may have the same mode of transmission which are foodborne or waterborne, they may differ in the way how they cause the infections in our body. Some may be the invasive types, and some secrete toxin that can affect other cells in the body. Both human and animals can be infected with this bacteria.
Taking care of one’s personal hygiene is the best way to control and prevent the E. coli infections. Adhere to the correct way of hand hygiene, wash the fruits and vegetables before eating them and do not eat or drink unpasteurized milk and canned foods or drinks. All human are prone to be infected with this bacteria including the babies. It is the best for the mothers to keep breast-feeding their babies to protect them from being infected with E. coli.
Salyers, A. A., & Whitt, D. D. (2002). Diarrheagenic Escherichia Coli. Bacterial Pathogenesis: A Molecular Approach, 407-420.
U.S. Food and Drug Administration (FDA). (2014). Food Irradiation: What You Need to Know. Retrieved from http://www.fda.gov/Food/ResourcesForYou/Consumers/ucm261680.htm
Marks, J. W. (2014). E. coli 0157:H7 (Escherichia coli 0157:H7 infection). Retrieved from http://www.medicinenet.com/e_coli__0157h7/article.htm#e_coli_0157h7_facts
Centers for Disease Control and Prevention (CDC). (2006). Traveler’s Diarrhea. National Center for Immunization and Respiratory Diseases: Division of Bacterial Diseases. Retrieved from http://www.cdc.gov/ncidod/dbmd/diseaseinfo/travelersdiarrhea_g.htm
Todar, K. (2012). Escherichia coli in the Gastrointestinal Tract. Todar’s Online Textbook of Bacteriology. Retrieved from http://textbookofbacteriology.net/e.coli_2.html
Hartsock, A. (n.d.). Growth Requirements of E. coli. and Auxotrophs. Retrieved by http://educationportal.com/academy/lesson/growthrequirementsofecoliandauxotrophs.html
Nordqvist, C. (2014). What is E. coli? (escherichia coli. Retrieved from http://www.medicalnewstoday.com/articles/68511.php
Pelczar, R. M. (2014). Microbiology: Bacteria (eubacteria and archaea). Encyclopedia Britannica. Retrieved from http://global.britannica.com/EBchecked/topic/380246/microbiology/48790/Bacteriaeubacteriaandarchaea
 The cell wall composition have less peptidoglycan and are structurally more complex, with an outer membrane that contains lipopolysaccharides
 The essential metabolites that are important to an organism but that organism is unable to synthesize them.
 Short fingerlike projections
 This is a problem for travelers from developed countries with good hygiene who visit countries with poor hygiene standards.
 Peptides that can be destroyedoralteredbyheat.
 Peptides that can keep their 3D structure and remain active at temperatures as high as 100°C.
 Food irradiation (the application of ionizing radiation to food) is a technology that improves the safety and extends the shelf life of foods byreducing or eliminating microorganisms and insects
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