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Experiment 11: Fomite Transmission Essay

There are three elements necessary for the spread of infection. First there has to be a source of an infective organism. This source can be endogenous or exogenous. Endogenous sources of infection reside on or in the host’s body. In contrast exogenous sources arise from outside. Second there has to be a mode of transmission. Described in below are the three primary modes of transmission, vertical, horizontal or contact. Lastly there has to be a susceptible host. Susceptibility of the host to infection generally is determined by the integrity of the host’s immune system and their ability to fend off the infective organism. (Alonzo, p.79)

What Increases Host Susceptibility to Infection

Susceptibility to infection is always a battle between the source’s ability to infect versus the host’s ability to resist infection. Factors such as age, stress, immunity and overall condition of health of the host define the host’s susceptibility to infection. (Alonzo, p.79)

Description of Three Primary Modes of Pathogen Transmission

The three primary modes of pathogen transmission are vertical, horizontal, and contact. Vertical transmission occurs from mother to child, usually via the placenta. Horizontal transmission occurs from person to person, for example sexual contact. In the contact mode of transmission the contact can
be either direct (exposure to body) or indirect (inanimate objects), ie: fomites.

Description of Eight sites to Test

For my eight sites to test for presence of microorganisms I chose the following: 1. Couch Cushion
2. TV Remote
3. Computer Keyboard
4. Door Knob
5. Air Conditioner Filter
6. Toilet Handle
7. Refrigerator Door Handle
8. Clean silverware

Explanation of results of the Tests

The results of the tests or cultures at 72 hours incubation are as follows: 1. Couch cushion- These colonies were observed to be large (dime size) with irregular edges, white in color and flat. 2. TV Remote- Two distinct round colonies. The larger of the two has a gray color and mounding, resembling a mold culture. The smaller one is white with some clusters. 3. Computer Keyboard- These cultures appeared to be one colony, round with white color and flat. 4. Door Knob- No growth observed.

5. Air Conditioner Filter- Large multiple colonies were observed that were tan in color, round, raised and in clusters. 6. Toilet Handle- No growth observed.
7. Refrigerator Door- Four distinct small, round, tan colonies with some mounding. 8. Clean Silverware- No growth observed.

Expected Results Versus Observed Results

I expected growth of microorganisms on everything that human hands would
touch. While expected growth occurred on the TV remote, computer keyboard and refrigerator door, I was surprised not to see growth on the toilet handle and door knob. The house had been recently cleaned hours before the test, which could account for the lack of growth. Surprisingly the largest colonies grown were located on the air conditioner filter. I was glad to see the clean silverware (which had been washed in dishwasher on high temp setting) did not exhibit growth, demonstrating how heat and detergents can limit growth of microorganisms. References

Alonzo, C (2008) Microbiology. Englewood, CO: Hands on Labs

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