Task Stream 2

Microbiology can be broken down into categorizations based upon the environmental conditions necessary for organisms in which to grow. Two large categories of microorganisms are those requiring oxygen to live (obligate aerobes) and those which can grow with oxygen but have the ability to also grow without it (facultative aerobes). The obligate aerobes produce more energy from nutrients than anaerobes by using oxygen as the “final electron acceptor in the electron transport chain, which produces most of the ATP in these organisms”(Betsy & Keogh, 2005, p.104). The facultative microorganisms are able to use oxygen but can also go without by using fermentation or anaerobic respiration when it is not available (Betsy & Keogh,2005). The microorganisms being cultured in our first task (Lactobacillus acidophilus and Staphylococcus epidermidis) are obligate aerobes.

Microorganisms can grow in a variety of conditions with temperature being one of those variables, but the types we frequently encounter in our environment thrive in fairly warm temperatures. Both Lactobacillus acidophilus and Staphylococcus epidermidis are examples of these, which are referred to as mesophiles. Extreme temperatures (as in deep freezing or auotoclaves for example) are effective in destroying microorganisms due to their inability to thrive outside of more moderate temperatures). Growth of these two organisms would be optimized by remaining between 25 and 40 degrees celsius (Betsy & Keogh, 2005). The higher end of this range should increase the rate of growth as it causes a higher rate of metabolism, which is why our experiments suggest using an incubation box if our house is not overly warm.

There are many ways we actually benefit from enhancing the growth of microorganisms and on the flip side are the ways we depend greatly upon eliminating as much growth as possible. One example of the former is baking bread by using yeast. This process needs a warm environment to facilitate fermentation (growth of yeast) in order for the bread to rise. A second example of beneficial organisms is in the use of a compost bin to create rich soil for gardens. These bins are filled with organic matter such as vegetable scraps and need bacteria to break them down into the resulting mulch of organic nutrients to put back into the soil.

An obvious environment in which growth must be deterred is the hospital setting. Two critical methods used to eliminate pathogens include autoclaving and sterilizing instruments for surgeries as contaminated equipment could easily transfer microorganisms to exposed areas of the body that are typically enclosed (for example, open heart surgery wherein the chest is opened). Any incision can become a portal of entry for bacteria to colonize readily. Once the patient has been sutured up, the organisms have their own incubator (the warm body) and can grow unchecked until they have progressed to the point signs develop on the surface (like hot inflamed skin, fever or pus).

Also in the hospital setting patients frequently have elevated blood sugars from such things as stress of illness or steroid treatments, which makes the availability of nutrients (sugar in the blood) for growth even more readily available. Furthermore, patients already have many microorganisms already on their skin(some that can be pathogenic such as varieties of Staphylococcus) and some patients are actually hospitalized to treat already existing infections. In these cases, preventing growth and trying to eliminate the existing harmful pathogens are priorities. Ways to do this include using oral hygiene antiseptic systems for ventilated patients since the mouth is a huge reservoir for organisms that can develop into conditions such as pneumonia (Magill,2014) and oral or intravenous antibiotics specific to organisms (based on sensitivity cultures done in the hospital lab).

Many patient are also immunocompromised from chemotherapy or transplant medications to prevent organ rejection. These populations are easy targets for opportunistic “bugs”. These populations require strict isolation to minimize potential exposure to pathogens carried by others with stronger immune systems. Ways to do this are with frequent hand washing (physical and chemical control), antiseptic hand gels (chemical controls), isolation masks and gowns and isolation of infected bodily wastes.

Hospitals also make efforts on a basic level to control/deter the growth of microorganisms, such as keeping the air dehumidified and the temperature fairly cool, especially in the OR. Avoidance of introducing pathogens is done with sterile technique (as in placing central lines and in surgery). Destruction of organisms that may already be present on equipment is done by the aforementioned autoclave and sterilization process.

Four forms of culture media are discussed in the introductory portion of this course. The first type is the nutrient broth, which essentially is a solution containing basic elements for metabolism and is a very non-specialized environment in which many types of microorganisms can grow. Agar is a pure culture base that is composed of material not metabolized by bacteria, basically a “blank slate” on which the cells can grow. Our course covers three versions using this medium. The agar slant (in which the agar solidifies at an angle in a test tube in order to increase the available surface area on which cells can grow, which would typically be those needing a lot of oxygen). The agar stab is a basic upright test tube in which the agar has gelled, which maximizes the area for cells that either do not require oxygen or specifically need to avoid it and therefore settle lower down from the surface away from oxygen exposure. And finally the agar dishes/plates (also known as Petri dishes). These are useful in smears and growing sections of cells as it provides a large wide surface area on which it is much easier to spread separate samples or different concentrations of the same sample for comparison on the same dish). For our samples, growth in 24hrs has resulted in only sediment at the bottom of both test tube samples and is hard to even qualify as growth since the amount present has not increased beyond the baseline measurement. This is likely due to each organism's generation period, which very in time just as gestation times vary between animals. The cells are likely in the Lag Phase—the time in which they are very metabolically active while “gearing up to divide” by synthesizing DNA and enzymes (Betsy & Keogh, 2005).

Growth in 48hrs resulted in an increase in turbidity in the Lactobacillus acidophilus sample, although there was still sediment remaining. This is likely due to the cells being in the Log phase. The Staphylococcus epidermidis sample appeared to have a cloudy area towards the surface of the liquid, described as a “pellicle” but is hard to say for certain that it wasn't just floating material from the cotton swab or even dead skin cells that have now been “shed” from the swab.

After having another 24hrs to grow, both samples had increased amounts of the characteristics observed (turbidity and a pellicle being better defined). Factors that may have contributed to this delay include possible temperature variability as the room in which they were stored was not tightly controlled and air conditioning is in use during these summer months. Oxygen should have been readily available as the caps were very loose. The nutrient composition in the solutions provided could potentially be deficient in certain factors the organisms need, as I am unfamiliar with the exact amounts given to us as well as what is exactly required of these bacteria.

References

Betsy, T., & Keogh, J. (2005). Microbiology Demystified. Blacklick, OH, USA:
McGraw-Hill Professional Publishing. Retrieved from http://www.ebrary.com Magill, S.(2014). Multiple Point-Prevalence Survey of Health Care-Associated
Infections. New England Journal of Medicine,370,1198-208.