Summerize into three theory statments

Differential staining In microscopy and histology, staining is a technique to increase contrast in biological samples. Stains and dyes may interact with specific tissues, cell populations, organelles or proteins within the sample, which allows them to be more easily discerned or quantified. Differential staining is the process of differentiating between different kinds of cells. In microbiology, there are various clinically useful differential stains. The most widely used is the Gram stain. For the identification of unknown bacteria, differential staining can be combined with other techniques, such as differential and/or selective media or biochemical tests. Bacterial culturing Bacterial culturing is the practice of growing bacteria in the lab. The nutrients bacteria need are provided by the culture medium. Bacteria can be grown in liquid culture or on media made solid by the addition of agar, which gives culture media a gel-like consistency. Other conditions that are important for bacterial growth, such as the temperature and gas composition, are regulated by the incubator. A culture that contains only a single type of 2 Copyright Labster ApS 2020 All Rights Reserved microorganism is called a pure culture. Some clinical samples taken from normally sterile environments such as the blood or cerebrospinal fluid are already pure cultures. Samples from sites with diverse microflora such as nasal samples or stool samples are likely to be a mixture of different microorganisms. In this case, a pure culture can be obtained and maintained through specific culture conditions and good aseptic technique. Bacterial metabolism Like all cells, bacteria take up nutrients from the environment and transform them into energy and cellular components. Enzymes, proteins with catalytic activity, are required to carry out many of the reactions necessary for metabolism. Metabolic processes and enzymatic characteristics vary between bacterial strains and species. Such differences are exploited by differential or selective media and biochemical tests. Host-microbe interactions Microorganisms are found everywhere and encounters between humans and microbes are frequent. Additionally, different parts of the human body are colonized by bacteria. These bacteria may be harmless or beneficial (commensals), or disease-causing (pathogenic). Pathogens can be transmitted directly or indirectly (through ingesting contaminated food or water or touching contaminated surfaces). Humans have various defenses against the transmission of microorganisms, such as the skin or mucous membranes as physical barriers, the flow of saliva or mucus to carry away microbes or low pH or bile salts, which damage microorganisms. Commensal bacteria (also known as the normal flora, microbiota or collectively as the microbiome) can also help protect against pathoge