Natural Environment of Escherichia Coli - Lab Report Example

Natural Environment of Escherichia Coli Introduction: Escherichia coli is an enteric micro-organism that belongs to the Enterobacteriaceae family, consisting of Shigella, Salmonella, Enterobacteria, Klebsislla, Serratius, Proteus and others. Specifically, it tests negative to the Gram staining procedure because of the peculiarity of its cell membrane and other cytoarchitectural components. It has a rod-like shape and is a very important bacterium. Microbiologists and other scientists have ascribed so much importance to Escherichia coli because it is responsible for various diseases. Examples of which include urinary tract infections or UTIs (of which E.coli is the commonest cause), nosocomial or hospital-acquired pneumonia and neonatal meningitis. It also causes bloody and non-bloody diarrhea and is transmitted via the feco-oral route (thus it is important to wash hands and foods very well in addition to proper handling and disposal of sewage, feces etc). E.coli and other enterobacteriaceae are the commonest pathogens in existence, alongside the Staphylococci and Streptococci. Habitat/Ecological Niche of E.coli: E.coli is regarded as part of the normal flora of the animal and human body. It is usually present in the colon (large intestine) i.e. its natural habitat is mainly the gastrointestinal tract. By virtue of its enteric location, E.coli can be present in very high concentrations (reaching levels up to 108 per gram) in human feces. Nutritional and energy requirements of E.coli: E.coli is a facultative anaerobe depending on the prevailing circumstances i.e. E.coli can make use of oxygen when it is present or generate energy by anaerobiosis in an oxygen-poor environment. In other word, E.coli can metabolize nutrients by respiration or fermentation. E.coli also carries out the fermentation of quite a number of carbohydrates. It has been firmed that E.coli grows well on meat extract medium without adding sodium chloride and also reproduce well on MacConkey’s agar. E.coli also ferments lactose rapidly. In fermentation, a substance (preferable an organic compound) will accept the hydrogen ion being donated as against respiration in which oxygen is the hydrogen acceptor. The process of fermentation is different from respiration in terms of energy yield. Energy yield is greater than that from fermentation and this can be up to as much as a factor of 10. Aim/purpose of the experiments The experiments was conducted in order to demonstrate the growth type and rate as well as the growth pattern of the E.coli in relation with particular factors such as temperature or time. Hypothesis It was hypothesized that E.coli will produce a growth with a particular pattern which can be shown as a growth curse, when measured amounts of bacteria inoculations are added to the fresh liquid media (when can be MacConkey’s agar) L. Broth which was used in this experiments. Methods In order to demonstrate bacterial growth, the experiments had to be done in a systematic manner in order to get precise results, minimize errors and improve analysis. 1ml of E.coli in inoculums from a saturated culture was added to a fresh sample of 50ml of L-Broth. The L-Broth is expected to produce a unique and particularly nutrient –rich environment that will encourage the growth of E.coli. The ideal broth (culture or nutrient medium) contains a steady source of organic energy (hydrogen ion donors) and hydrogen ion acceptor. It can also contain other important substances such as carbon and nitrogen for the synthesis of compounds. Minerals such as sulfur, phosphorus, calcium, magnesium and some other trace elements should be present in order to trigger activation off the enzymes. After some minutes, it was observed that the viable cell count, a measure of cell concentration, had changed. This change is measurable by the turbidity of the culture. For example, when the suspension is barely turbid, E.coli contains 107 cells per milliliter while a fairly turbid suspension can have up to about 108 or more cells per milliliter of the culture. Clearly, there were changes in our turbid metric measurement of the culture prepared thus signifying growth. However, it must also be noted that the relationship between the viable count and turbidity can vary during the growth and death of the organisms present in the culture. Therefore, it is very possible for the bacterial cells to lose viability without eliciting a corresponding loss of the culture turbidly. The simplest way however, to measure the cell mass is by conducting the photometric absorption measurement. Observations made during the experiments A typical bacterial growth curve is in various phases and can be characterized by the generation time (this is the average time required for cell numbers to double and can also be determined by accurate measurement of the biomass density (dry weight or protein content percentage determination). Bacteria increase in number in a logarithmic progression (n = 2G) where G is the time required for a reproduction cycle and it varies for different bacteria. In our experiments, the phases of the bacterial growth curve were demonstrated and statistically proven by the particle counting (turbid metric density measurements) of all the cells concluding the viable and non-viable ones). For the sake of the experiments and clarity, it is important to state a general overview of the phases of bacterial growth. These include the following 1) Lag phase 2) Acceleration phase 3) Exponential phase 4) Deceleration phase 5) Stationary phase 6) Decline or death phase 1. The lag phase: This is the first phase and the major event is the increase in the mass of the E.coli per unit of volume but there is actually no net increase in cell count. It is also the phase at which the cells adapt to their environment once they are depleted of vital materials. 2. Acceleration phase: As the name of this phase implies, there is a gradual acceleration of the growth of the E.coli before the growth becomes exponential. 3. Exponential phase: This phase is also referred to as the ‘log phase’ and logarithmic manner. The increase is so steep that the cell count can reach 109/ml. 4. Deceleration phase: In this stage, there is a decrease in the rate of growth and the number of surviving cells. 5. Stationary phase: At this level, the E.coli cells have used up all the essential nutrients present in the broth. This is in addition to the fact that there is a total accumulation of metabolites and free radicals which are cytotoxic (cell-damaging). 6. Decline or death phase: At this final phase, the cells die due to the accumulation of toxic materials and the lack of essential nutrients that have been used up. The E.coli was grown on L-broth for our experiments. However, it can also be cultured on endo agar. Endo agar is a combined selective/indicator medium. The red color of the bacterial colony and the agar is an indication of the metabolic breakdown of lactose. CONCLUSION Interpretation of Results: The results derived at the end of the experiments revealed very interesting relationships between the different parameters used in conducting the experiments. These parameters included the various time intervals, absorbance and the turbidimetric measurements introduced later to assess the growth of bacteria in the culture. For the experiments conducted at 30 degrees centigrade, three teams were involved and were duly numbered teams 1 to 3. At the start of the experiments, four different time intervals were used in the measurement. The following is the breakdown of each of the teams’ results: Team No. 1: At the first time interval, the value recorded was 0.099 which increased greatly to 0.163 at the reading conducted at the second time interval. For the third time interval, there was a further increase in the values recorded to 0.249 which subsequently spiked up to 0.361. This was the highest value recorded by team No.1. At the end of the experiment for the first team, it was observed that there was a continuous rise in the values with time and this peaked at 0.361. Team No.2: The second team also recorded a progressive increase in the recordings made. However, there are detectable changes in the values recorded by the first team. Firstly, the first value for team 2 was 0.031 as against 0.099 recorded by team 1. Then, there was a relatively slow rate of increase in the values between the 2nd and 3rd intervals (from 0.106 to 0.154) in team 2 as compared with 0.163 to 0.249 in the first team. Also, the highest value in team 2 (0.226) was quite different from that of team 1 which recorded a value of 0.361. Team No.3: The values recorded by this team were generally the highest overall values but also showed gradual increase (0.136, 0.175, 0.31 and 0.398). This team also recorded the highest overall value of 0.398. The variation in the values recorded can be attributed to operator and tools errors such as errors of parallax or contamination of the sample. Other factors that could be responsible for some of the unusual figures include uncontrollable but minute changes in the temperature, aeration and pressure of the environment in which the experiments were conducted. On the whole, the increasing values recorded supported the hypothesis of binary fission type of growth of micro-organisms such as E.coli as proposed earlier. Works Cited: 1. Eric M. Chen & Sanjay S. Kasturi, Déjà Review of Microbiology and Immunology, McGraw-Hill, 2007, p.59-66. 2. Arthur G. Johnson et al, Microbiology and Immunology , Board Review Series, 4th Edition, Lippincott Williams & Wilkins, 2002, p.58-67 Read More