Week 2, Day 3

May 22, 2013

Today we entered lab and began the usual series of events: grabbing a lab coat, washing our hands, cleaning our station, retrieving our samples. We also retrieved the samples we made last class: starch, casein, gelatin, triglyceride, litmus milk, and motility. These samples will be used to determine what our bacteria is capable of hydrolyzing. We tested out starch culture to see if our bacteria had hydrolyzed the starch in the starch agar plate. We flooded the starch agar surface with Gram's iodine to see if a clear area would be visible around our bacterial growth, which would indicate a positive test for starch hydrolysis. After waiting the 30-60 seconds for the iodine to set, we noticed a somewhat clear snake-like streak in the Petri dish where our bacteria had been streaked the previous day, but no clear area surrounding it. Our professor told us that the test was negative, meaning our bacteria did not hydrolyze the starch. We looked over the remaining samples, but our professor had us incubate them for another day, so we will examine them further in future and post the results for each at that time.

Tryglyceride Plate

Skim Milk Plate

Starch Plate

Motility Test

Gelatin Tube

Applying Iodine to Starch Plate

Flooded Plate (Negative, thinner streak on top)

The remainder of lab was spent inoculating different samples of compounds. Our professor brought out tubes of maltose, sucrose, glucose, lactose, MR-VP (Methyl Red, Voges-Proskauer), citrate, tryptophan (amino acid), nitrate, TSIA (triple sugar iron agar), and urea. We inoculated each tube with a loop-full of bacteria from our streak plate, except for the citrate and TSIA tube which where slants. For the TSIA slant we used a loop-full of bacteria to make a slant streak sample; and for the citrate slant we used the inoculating needle to stab our bacteria about three-fourths of the way down the tube and then streaked the needle across the surface of the slant before removing it.

Maltose

Lactose

Glucose

Sucrose

Citrate

TSIA

MR-VP

Tryptophan

Nitrate

Urea

After checking to make sure each tube was labeled properly, we placed the tubes in the 25°C incubator replaced our other samples from the previous day into their respective incubators (shared samples were placed in the 30°C incubator), and put our pure cultures into the fridge for storage. We cleaned our benches, washed our hands, and took of our lab coats for the day.