Antibiotics are widely used in genetic engineering in order to carry out a nonnatural function and/or express a synthetic gene resistant to a specific antibiotic. Thus, theneed for complete sterilization of the culture of some bacteria is not as important with the addition of low doses of antibiotics. Antibiotics are defined as chemicals that interferewith some cellular mechanisms making cell growth slower and some cells may even die. Some unicellular and simple multicellular organisms produce antibiotics in a natural way to compete with other organisms in their environment [223]. However, some of these antibiotics can have a negative impact on the product that bacteria is producing, in this case BC. In this context, Henning and Catchmark [224] evaluated the effect of ampicillin, chloramphenicol and kanamycin, antibiotics to which Gluconacetobacter hansenii is inherently resistant, on the properties of the BC produced. Ampicillin increased bundle thickness but some noncellulosic deposits appeared.Both ampicillin and chloramphenicol inhibited biomass production (Fig. 5.12) and induced filamentation behavior.Antibiotic stress can cause the production of additional exopolysaccharides.