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INTRODUCTIONThe objective of this lab was to isolate antibiotic resistant bacteria. The

bacteria that were used in this lab were taken from several random soil

samples in the Harrisonburg area. After an incubation period these samples

began to grow different species of soil microbes. Soil microbes are a type of

bacteria that aid in decomposition and help to recycle elements, including

carbon and nitrogen, for the use of other organisms. The soil microbes,

which are microscopic cells, form into colonies. The colonies are a group of

cells that can be seen by the naked eye which are formed by the division of

one or more cells. All colonies are random in shape, size, and color. One

such group of soil microbes are the actinomycetes. Actinomycetes are

known to be antibiotic producers that form into long filamentous structures at

a slow rate and are gram-positive. Antibiotics are, as suggested in the name,

kill or inhibit the life of organisms. As antibiotics work to kill or inhibit a

cells life a zone of inhibition forms around the colony, or targeted cells. The

zone of inhibition is a blank area around antibiotic producing bacteria that

occurs because other bacteria cant grow around it. (Hurney, et al. , 2008).

Bacterial colonies are very hard to tell apart. There are, however,

several different morphologies that help to distinguish between different

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colonies. Three such colony morphologies include filamentous, circular, and

spiral shaped. The filamentous bacterial colonies are long and rod-shaped.

Actinomycetes are most often rod-shaped, filamentous structures that are

cream colored. The circular shaped colonies are, as suggested by the name

small circles. The spiral shaped colonies are lines that rotate into a spiral

pattern. (Hurney, et al. , 2008).

We chose bacterial colonies that were farther away from most of the

colonies. We chose these because they exhibited a filamentous structure

with a greenish hue and black lines within it. In the center of the colony

there were curvy lines and there was not a smooth edge on the outer ring of

the colony. The outer edge was darker while the center was much lighter in

color. We chose this particular colony because it displayed characteristics of an actinomycete. Actinomycetes are usually antibiotic producers, which is

why we chose to use this colony in order to promote the growth of an

antibiotic.

Antibiotics select to only work on prokaryotes because of their

peptidoglycan cell wall. Eukaryotes dont have this feature, making it harder

for antibiotics to affect them. The antibiotic penicillin targets the

peptidoglycan cell wall of bacteria, which is only found in prokaryotes.

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Other antibiotics focus exclusively on the inhibition of protein synthesis.

(Hurney, et al. , 2008).

In this lab, we tested whether bacteria A or bacteria B isolated from soil

produces an antibiotic that inhibits the growth of other bacteria. If this

hypothesis is correct then a zone of inhibition will form around the antibiotic

producing microbe (Hurney, et al. , 2008).

Works Cited

Hurney, CA, A. Pesce, and SK Babcock. 2008. Organisms, a laboratory

manual for Bio 114, Sixth Edition, Hayden-McNeil Publishing Inc.,Plymouth, MI, 172-174 pp.