The importance of antibiotics to medicine has led to much research into their discovery and production. Microorganisms used in fermentation are rarely identical to the wild type. This is because species are often genetically modified to produce the maximum amount of antibiotics. The impact factor of journal provides quantitative assessment tool for grading, evaluating, sorting and comparing journals of similar kind. It reflects the average number of citations to recent articles published in science and social science journals in a particular year or period, and is frequently used as a proxy for the relative importance of a journal within its field.