According to Dr. Gary E. Kaiser, bacteria come in three basic shapes: coccus, which are arranged in pairs, bacillus, which are rods, and spirals. These are the main types students learn in basic biology courses, and they are easy to identify using powerful magnification and the naked eye. However, using a magnifying lense is not a very precise method, as many different bacteria can share the same shape. Therefore, this process only narrows down the identity of a bacteria to a minor degree.
Science encyclopedia JRank.org states that the gram stain method was developed in 1884 by Christian Gram. It uses iodine drops to stain a cell, illuminating its once invisible cell wall. Once you can see the cell wall, you can further narrow down the type of bacteria you are observing.
Antigenicity functions by having scientists introduce foreign bodies to the bacteria and observing how the immune system reacts to them. Depending on the type of bacteria and how it lives, it will either react defensively, offensively or passively to another organism. This helps scientists classify how bacteria behave.
DNA is the ultimate method of identifying and classifying bacteria because it looks at similarities between the molecular makeup of different bacteria. If individuals can see which bacteria are similar and different on a molecular level, they can make assumptions about their origins. However, this type of analysis requires extensive scientific equipment and training.