Our unknown was a sample appearing to be urine. There was no turbidity, indicating few bacteria. Before trying to concentrate the sample, we streaked it onto a general purpose medium (TSA) to see if we would get colonies. After 2 days incubation at 37  degrees, 3 colony types grew. These were Gram stained. Two were Gram positive (a rod and a coccus) and one was a Gram negative rod. Because Staphylococcus saprophyticus is a possible cause of urinary tract infections, the Gram positive coccus was inoculated onto mannitol salt agar. Staphylococcus should grow on this medium and S. aureus and S. saprophyticus ferment mannitol producing a yellow color in the agar. The G+ coccus grew but did not ferment mannitol, so we considered it to be part of the normal microbiota.

Because E. coli and other enteric bacteria are common causes of urinary tract infections, we streaked the Gram negative isolate onto MacConkey agar. There was no color change in the colony, indicating that it was probably not E. coli. At first we didn't think much had grown on the plate, but after the instructor told us to look more closely we saw that the bacterium had spread over the whole surface of the plate, meaning that it is highly motile. According to the textbook, this is a common characteristic of Proteus, an enteric bacterium that sometimes causes urinary tract infections. One test that helps differentiate Proteus from other enteric bacteria is the urease test. Our test turned a bright fuschia purple, indicating a positive test. We were then allowed to do a Biolog test. First, we did an oxidase test to confirm that our isolate was likely an enteric bacterium. The test was negative, meaning we had to use the "Ent" standard to adjust the turbidity and to add several drops of thioglycollate solution when setting up our plate.  After reading the result, we entered the data into the computer which said that our isolate was Proteus mirabilis (90% probablility). The Biolog printout is attached. Table 1 shows the data that we collected.

isolate: Gram- Gram + rod Gram + coccus
MSA ND ND growth, no fermentation
MacConkey growth, no color change    
motility very much    
urease positive    
oxidase negative