E. F. Gale

Assimilation of Amino Acids by Gram-Positive Bacteria and Some Actions of Antibiotics Thereon

Publisher Summary This chapter discusses the assimilation of amino acids by gram-positive bacteria. The growth of the bacterial cell involves, and is the result of, synthesis of all its components. Many bacteria can synthesize protein from ammonia and a carbon source, such as glucose. “Biochemical mutants” of molds and bacteria have indicated the probable biosynthetic pathways and individual steps in pathways that have been studied with cell-free extracts of microorganisms. Species of bacteria that are unable to synthesize amino acids, assimilates the preformed substances, to form suitable material for the study. Experimental correlations among the various processes are observed, and certain stages in the processes are found to be sensitive to antibiotics and growth inhibitors.

Nature and Development of Phenotypic Resistance to Amphotericin B in Candida albicans

Publisher Summary Resistance to amphotericin in Candida albicans begins to increase when cultures pass into the stationary phase of growth and may reach very high values if incubation continues in the absence of an external source of carbon and energy, especially at an acid pH value and in the absence of sources of reducing potential. The evidence that has accumulated in the course of the studies mentioned in the chapter indicates that this resistance can be attributed to the development in the wall of a barrier to the penetration of the antibiotic to target sites in the cytoplasmic membrane. This barrier involves (1→3)-β-glucan chains and its action in the impeding passage of the antibiotic increases as these chains increase in length and form a tightly cross-linked network within the cell wall. Rupture of β-chains by the action of β-glucanases decreases resistance, while blocking chain extension or increasing chain instability by the incorporation of glucose analogues prevents further increase in the resistance.