Downstream processing antibiotic production

Extraction is a process that utilizes the difference in solubility of the product of interest between two immiscible phases. Liquid-liquid extraction is commonly used in classical biotechnological downstream processing for production of antibiotics and other small molecules. The second liquid phase is usually a water immiscible organic solvent. Reciprocating plate, Podbielniak centrifugal extractors, Delaval contactors, and Westfalia extraction-decanters are examples of some of the equipment available for carrying out extraction. 

The growing interest in various )5-lactam antibiotics, especially the cephalosporins, over the last decade has called upon improvement in their production methods via modification of either the basic process and the microbial strain or the downstream processing techniques. The product recovery may involve various methods of extraction and purification which play an important role in the overall process economics [12]. During recent years much attention has been given to the development of liquid membrane (LM) processes which usually exhibit high extraction rates and selectivity as compared to those achievable in conventional solvent extraction and adsorption processes. 

Low-molecular-weight products, generally secondary metabolites such as alcohols, carboxylic and amino acids, antibiotics, and vitamins, can be recovered using many of the standard operations such as liquid-liquid extraction, adsorption and ion-exchange, described elsewhere in this handbook. Proteins require special attention, however, as they are sufficiendy more complex, their function depending on the integrity of a delicate three-dimensional tertiary structure that can be disrupted if the protein is not handled correcdy. For this reason, this section focuses primarily on protein separations. Cell separations, as a necessary part of die downstream processing sequence, are also covered. 

Process-related impurities encompass those that are derived from the manufacturing process, that is, cell substrates (e.g., host cell proteins, host cell DNA), cell culture (e.g., inducers, antibiotics, or media components), or downstream processing. Product-related impurities (e.g., precursors and certain degradation products) are molecular variants arising during manufacture and/or storage that do not have properties comparable with those of the desired product with respect to activity, efficacy, and safety. 

Process-related impurities encompass aU possible material that is used during manufacture and which might still be present in the final product These include cell components (e.g., host cell protein, DNA and RNA) and components of the cell culture medium (e.g., antibiotics, inducers, media). In addition, possible downstream-derived components (e.g., enzymes, (bio)-chemical reagents, inorganic salts and solvents) must be considered. Any adventitiously introduced material which is not part of the manufacturing process of either DS or DP is considered as a contaminant. For viral products and processes, special attention is paid to endogenous or adventitious viruses, which should ideally not be present or at least be removed/inac-tivated by the manufacturing process. 

Despite these potential problems, many microbial biocatalysts have been identified with sufficient selectivity and sensitivity to allow their use in single analyte determination. The low cost, stability, and ease of use makes such analyses attractive. The most commonly reported application for such sensors is process control, both in fermentation and downstream monitoring. A wide range of fermentation products have been monitored by microbial biosensors including alcohols, amino acids, antibiotics, organic acids, peptides, and vitamins. 

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