title: Response of developing branched bacteria to adverse environments. I. Membrane-transfer techniques for assessment and SEM visualization of drug activity against Nocardia asteroides.
abstract: Membrane-transfer technique (MTT) is proposed as a method for assessing antimicrobial activity against branched bacteria at different phases of development. After preliminary cultivation up to the desired stage, colonies developing on membranes are transferred onto media containing various concentrations of drugs to be tested. Different exposure times and drug combinations are possible. Following exposure to the toxicant, membranes can be examined macroscopically, by light or electron microscopy and/or transferred to drug-free media to evaluate viability and possible recovery. Some results on the effects of benzylpenicillin, fusidic acid, gentamicin and sulfadiazine on the morphology of Nocardia asteroides, as detected by scanning electron microscopy, are presented. The progression of alterations, due to increasing exposures to various concentrations of gentamicin, has also been followed. Minimal inhibitory concentration values for the same antibiotic vary according to the growth phase; in particular in the early developmental stages they appear directly related. Advantages of MTT over classical "antigermination" tests in assessing susceptibility to different toxicants and its possible application to the study of environmental effects on morphogenesis of branched bacteria are discussed.
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D008567:Membranes, Artificial; D008826:Microbial Sensitivity Tests; D008855:Microscopy, Electron, Scanning; D009616:Nocardia asteroides / Q000187:drug effects* / Q000648:ultrastructure; D013997:Time Factors
chemical_list: D000900:Anti-Bacterial Agents; D008567:Membranes, Artificial