In our final attempt to identify our unknown soil microorganism, we tested the antibiotic sensitivity in comparison to known bacteria. The antibiotics used included Azithromycin, Chloramphenicol, Carbenicillim, and Erythromycin. The bacteria controls tested in comparison included Pseudomonas aeruginosa, Staphylococcus aureus, and Klebsiella pneumonia.
After creating a lawn of bacteria on individual part dishes, the four antibiotics, contained in antibiotic disks, were distributed evenly across the medium. After incubating the plates for 24 hours, we recorded the presence and size of zones of inhibition, which indicates sensitivity to the antibiotic.
Our unknown microbe was not resistant to any of the tested antibiotics, but did vary in sensitivity. The order of sensitivity, in decreasing order, was Erythromycin, Azithromycin, Chloramphenicol, and Carbenicillim. The unknown was more sensitive to Erythromycin compared to the other bacteria. Our microbe's sensitivity to Azithromycin was similar to that of S. aureus and K. pneumonia. Chloramphenicol did not have as much an affect on the unknown as it did S. aureus and K. pneumonia, though P. aeruginosa was resistant to its affects. Carbenicillim affected the unknown similarly to K. pneumonia.
Azithromycin affects a wide range of bacteria including some gram positive and gram negative. Chloramphenicol affects both gram positive and negative bacteria, as well as most anaerobic organisms. Carbenicillim, a sub group of penicillin, affects most gram negative bacteria but has limited affect on gram positive organisms. Erythromycin affects a similar range of bacteria, including gram positive organisms, but extends further to include atypical bacteria as well.
The high sensitivity to Erythromycin supports our previous conclusion that our unknown microbe is gram-positive. But it may be an indication that our organism is atypical. The varying sensitivity to the different antibiotics does allow for clear interpretation to identify our unknown.
Each week has brought new discoveries in our search for the identity of our unknown microorganisms. Unfortunately not every experiment presented clear, definitive answers, therefore educated guesses were necessary in proceeding. Also, with the collection of data came contradicting results. Attempting to follow the dichotomous key was often a puzzle and varied each week. Though we may not be able to pinpoint the exact identity of our microbe, we are able to narrow down our options.
From the date collected throughout the semester we know that our bacteria is gram-positive and originally believed it to be rod-shaped. But after hemolysis testing revealing alpha hemolysis on the blood agar plate, we must reevaluate our previous morphological conclusion. We determined that our organism is catalase positive, which contradicts our hemolysis findings. The glucose and coagulase tests should be run next in order to help determine the our microbes identity. Whether our unknown organism oxidizes or ferments glucose, or tests positive or negative for coagulase would narrow the possible organisms down to Micrococcus spp., S. aureus, and S. epidermis. S. aureus may be ruled out because our antibiotic testing did not reflect similar results between the bacteria and our unknown. There is also the possibility of Streptococcus spp., as determined from the hemolysis test, but an optochin susceptibility test would need to be run to determine the specific strain.
http://apps.who.int/iris/bitstream/10665/93142/1/EML_18_eng.pdf?ua=1
Kibwage, I O et al. “Antibacterial Activities of Erythromycins A, B, C, and D and Some of Their Derivatives.” Antimicrobial Agents and Chemotherapy 28.5 (1985): 630–633. Print.
http://www.toku-e.com/Upload/Products/PDS/20120618001452.pdf
http://www.toku-e.com/Assets/MIC/Carbenicillin%20disodium%20USP.pdf
-Palmer Miller
 |
| Unknown Microbe |
 |
| P. aeruginosa |
 |
| S. aureus |
 |
| K. pneumonia |
The resulting data was recorded for analyzation in the following table:
Organisms
|
Antibiotics
| |||
Azithromycin
|
Chloramphenicol
|
Carbenicillim
|
Erythromycin
| |
Unknown
|
Sensitive
8mm
|
Sensitive
5mm
|
Sensitive
1mm
|
Sensitive
12mm
|
P. aeruginosa
|
Sensitive
1mm
|
Resistant
|
Sensitive
4mm
|
Resistant
|
S. aureus
|
Sensitive
6mm
|
Sensitive
10mm
|
Sensitive
25mm
|
Sensitive
9mm
|
K. pneumonia
|
Sensitive
7mm
|
Sensitive
8mm
|
Sensitive
2mm
|
Sensitive
1mm
|
Azithromycin affects a wide range of bacteria including some gram positive and gram negative. Chloramphenicol affects both gram positive and negative bacteria, as well as most anaerobic organisms. Carbenicillim, a sub group of penicillin, affects most gram negative bacteria but has limited affect on gram positive organisms. Erythromycin affects a similar range of bacteria, including gram positive organisms, but extends further to include atypical bacteria as well.
The high sensitivity to Erythromycin supports our previous conclusion that our unknown microbe is gram-positive. But it may be an indication that our organism is atypical. The varying sensitivity to the different antibiotics does allow for clear interpretation to identify our unknown.
Each week has brought new discoveries in our search for the identity of our unknown microorganisms. Unfortunately not every experiment presented clear, definitive answers, therefore educated guesses were necessary in proceeding. Also, with the collection of data came contradicting results. Attempting to follow the dichotomous key was often a puzzle and varied each week. Though we may not be able to pinpoint the exact identity of our microbe, we are able to narrow down our options.
From the date collected throughout the semester we know that our bacteria is gram-positive and originally believed it to be rod-shaped. But after hemolysis testing revealing alpha hemolysis on the blood agar plate, we must reevaluate our previous morphological conclusion. We determined that our organism is catalase positive, which contradicts our hemolysis findings. The glucose and coagulase tests should be run next in order to help determine the our microbes identity. Whether our unknown organism oxidizes or ferments glucose, or tests positive or negative for coagulase would narrow the possible organisms down to Micrococcus spp., S. aureus, and S. epidermis. S. aureus may be ruled out because our antibiotic testing did not reflect similar results between the bacteria and our unknown. There is also the possibility of Streptococcus spp., as determined from the hemolysis test, but an optochin susceptibility test would need to be run to determine the specific strain.
http://apps.who.int/iris/bitstream/10665/93142/1/EML_18_eng.pdf?ua=1
Kibwage, I O et al. “Antibacterial Activities of Erythromycins A, B, C, and D and Some of Their Derivatives.” Antimicrobial Agents and Chemotherapy 28.5 (1985): 630–633. Print.
http://www.toku-e.com/Upload/Products/PDS/20120618001452.pdf
http://www.toku-e.com/Assets/MIC/Carbenicillin%20disodium%20USP.pdf
-Palmer Miller
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