Diagnosis of an Infected Patient

We are given a sputum sample from a patient that may be infected with a bacterium from one of the following genera: Bacillus, Escherichia, or Mycoplasma. In order to determine which bacterium is the cause of the infection, we will need to examine the sample under microscopy, as well as stain it. Looking at the sample with a microscope and knowing what the anatomical differences between each genera are is the first step in identifying the bacterium. The first possible bacterium is Bacillus. SInce Bacilli divide only on their short axis, there are fewer groupings of them. Most times they will appear as single bacilli and look like rods. If they appear as pairs they are called diplobacilli and streptobacilli if in chains. They may have open ends like straws or tapered ends like cigars. There are also coccobacilli that look much like cocci. Escherichia, or E. coli, is a rod shaped bacteria. There are many strains of E. coli and many are not harmful to humans and animals. There are some, however, that will cause illness in the form of gastrointestinal distress. There is often vomiting and diarrhea. The last, Mycoplasma, are very small with no cell walls. They are the smallest known bacteria and when first discovered they were mistaken for viruses because of their small size. Despite their small size, they can grow and reproduce outside of living host cells.
To help further identify the bacteria, we can then stain the specimen and then view it under a microscope. For the Bacillus and Escherichia, we can use the Gram stain. The Gram stain is a differential stain that determines if a bacteria is gram-positive or gram-negative. To do this we need to first cover a heat-fixed smear with a primary stain. In this case it will be a basic purple dye. Next the dye is washed off and the smear is covered with iodine. This