My Mixed Culture

So, the rules are that I cannot employ any outside, expert biology advice, so if you are an expert and can tell what this is (haha), then you mustn't tell me. I think it's pretty impossible to tell from just a gram stain, though.

So, for the uninformed, gram positive and negative refer to the different kinds of walls in bacteria. They pick up stain differently. Gram + and Gram - are two major categories of bacteria types, so this is what we start with for a test. The sample is smeared carefully (and thinly) on a slide, air-dried, and "heat fixed" by passing it through a bunsen burner flame twice. Then it is stained with crystal violet for 20 seconds, rinsed with H20, stained with Gram's iodine for one minute, rinsed with H20, stained with safranin for one minute, rinsed with H20, and then blotted dry. It is then observed under oil immersion on the microscope. You put a dot of oil on the slide and the lens touches the oil when it is focused properly.

This is my mixed sample. It was very hard to tell on my last stains which was mixed, but I'm pretty positive I have gram positive and negative rods mixed here. The positive ones are the big purple ones and the negative are the smaller pink ones. The gram positive wall retains the crystal violet dye and rinses out of the negative ones when you put on Gram's iodine. Then the pink dye is added, which the gram negative retains.

This is the first stain I did that I thought came out well, but I was still hesitant to say that there were two types of rods in there. I thought maybe there were rods and cocci (spheres). 

This sample is a little thick, but it convinced me that I was indeed seeing two types of rods in the mix in the other slide as well. I believe the negative rods are Serratia marcescens, which grows pink at 25 C but not at 37 C (my sample on the counter grew pink, with a greenish tinge, and grew tan/colorless in the incubator).