ABSTRACT
Many procedures are adopted within standard tests, and within routine laboratory experiments, which prepare inocula for performance tests, after their growth in suitable media. In order to standardize cell density, procedures are generally adopted that relate cell numbers to optical opacity/density and subsequently either dilute the cells, with fresh medium or diluent, or concentrate them. Washed cell suspensions are routinely prepared, for evaluations of antimicrobial effectiveness and for studies of microbial physiology, by successive centrifugation and resuspension steps. Provided that care is taken with the choice of washing and resuspension media such that temperature, nutrient, and osmotic shocks are minimized, then such processes are not expected to elicit any damaging effect. Filtration is often used as an alternative to centrifugation for the separation of bacterial cells from growth medium. Bacteria-proof filter membranes by the application of negative pressure to the underside of the filter or positive pressure to the culture.
