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Microbial contamination is a rare cause of culture failure in experienced laboratories and is largely preventable. As noted earlier, AF itself has bacteriocidal properties. If overwhelming microbial contamination is apparent within 24 hours after setup, it is probably due to improper handling of the specimen between amniocentesis and delivery to the laboratory (e.g. leakage from loose screw caps or poorly packaged syringes).

Approximately 10–20 percent of all samples are cell rich and their turbidity should not be a source of anxiety with regard to possible contamination. This also holds for brownish fluids containing cellular debris and granules in addition to erythrocytes. Seguin and Palmer⁶⁶⁹ measured cell growth from clear, cloudy (cell‐rich), bloody, and dark brown fluids. They showed that cloudy fluids yield better growth than clear ones. They confirmed earlier observations⁶⁷⁰ that very bloody fluids adversely affect the cloning efficiency. If bacterial or yeast contamination arises during the course of cell culture, it is by no means hopeless to attempt to salvage such cultures. Penicillin‐, streptomycin‐, or fungicide‐supplemented media are used to feed cultures daily after initial frequent washings. Increased chromosomal breakage rates and elevated rates of pseudomosaicism may be observed in such salvaged cultures but if the metaphase cells are analyzable, this rarely interferes with interpretation of the results.