Bacteriology 102 – Exp. 7:
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Check your notes taken during your observation of all 12 known cultures with this "official" key. Do not memorize this table! It is most important that you have seen positive and negative reactions in the various media and realize what they represent. The gram reactions indicated below are for the "ideal" situation – i.e., young cultures. As you have seen, increasing age of cultures can lead to shortening of cells and less reliability in obtaining the correct gram reaction. Gram-positive cultures which have a tendency to "turn gram-negative" (and also an opposite case) are indicated in the list of the 12 cultures on pages 30-31. Note that all of the cultures grow in the presence of air, so that leaves out organisms of which oxygen relationship category? We did not test our cultures with Thioglycollate Medium in this experiment, but we did two tests whose results correlate with what we expect for organisms in the three remaining oxygen relationship categories. |
| organism | gram rx. | cellular shape & arrange- ment | glucose fermen- tation* | lactose fermen- tation* | nitrate reduc- tion to nitrite | nitrate reduc- tion to N2 | motility | indole produc- tion | starch hydro- lysis | catalase rx. | colonial characteristics |
| Escherichia coli |
– | short rods | FG | FG | + | – | + | + | – | + | Check your notes regarding colony characteristics which you made during your observation of the 12 cultures in Period 2 of Exp. 7.1. Note that only three (SM, CV and ML) were brightly pigmented (red, purple and yellow, respectively); the others were white or off-white. |
| Klebsiella pneumoniae |
– | short rods | FG | FG | + | – | – | – | – | + | |
| Serratia marcescens |
– | short rods | FG or F | (F) or – | + | – | + | – | – | + | |
| Pseudomonas fluorescens |
– | rods | – | – | – | + | + or – | – | – | + | |
| Chromobacterium violaceum |
– | rods | F | – | + | – | + | – | – | + | |
| Micrococcus luteus |
+ | cocci in clusters | – | – | – | – | – | – | – | + | |
| Staphylococcus epidermidis |
+ | cocci in clusters | F | F | + | – | – | – | – | + | |
| Enterococcus faecalis |
+ | cocci in chains | F | F | (+) or – | – | – | – | – | – | |
| Lactobacillus plantarum |
+ | rods | F | F | (+) or – | – | – | – | – | – | |
| Bacillus subtilis |
+ | rods | – | – | + | – | + or – | – | + | + | |
| Bacillus cereus |
+ | large rods | F | – | + | – | + or – | – | + | + | |
| Bacillus polymyxa |
+ | rods | FG | FG | + | – | + or – | – | + | + | |
| Bacillus megaterium** |
+ | large rods | – | – | – | – | + or – | – | + | + |
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* For Glucose and Lactose Fermentation Broths: |
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Page last modified on 10/10/06 at 6:00 PM, CDT.  |