The materials and methods section generally contains details of the procedure the experimenter followed. This section should have sufficient information that allows the person reading the lab report to understand how the experiment was performed. For example, a microbiology lab report on acid fast staining needs to specify the organism used, the type of culture in which it was grown, and the method used to visualize the stained organisms. Provide details of specific precautions you followed and the reasons behind them. If you followed a procedure already available in a laboratory manual, you do not need to repeat that information; a reference to the name of the manual, its author and year of publication will suffice.
When composing the materials and methods section, it is important to settle upon the appropriate level of detail. To get a clear picture of whether some information is to be included, carry out a simple test. Ask yourself if the information you seek to present would be of relevance to another researcher wishing to duplicate the experiment. For example, it may be sufficient to state that sterilized glassware was used in a particular procedure. You do not need to go into details of how to carry out the sterilization, however, unless there is a specific modification you introduced in this process.
When providing information about the equipment, reagents, cultures, glassware and instruments you used in the experiment, you do not need to list them at the beginning of the materials and methods section. It is sufficient to cite these as and when they appear in the course of your narrative about the experiment. It is nonetheless very important to mention the specific model and make of the instrument or equipment, as well as grades of culture media and other reagents you used, to ensure that a researcher reproducing your experiment would achieve the same results.
Considering that the lab report gives an account of a procedure you already completed, write the materials and methods section in the past tense. It is scientific tradition to write reports in the passive voice. Find out if your teacher has specific requirements for this aspect, and compose your report accordingly. When citing the name of a microorganism, remember to use the upper case for the name of the genus and lower case for the species, and italicize the entire name of the organism. After you first cite the complete name of the organism in your report, you may subsequently abbreviate the genus name to its first letter, followed by a period. For example, you may cite "Staphylococcus aureus" as "S. aureus."