Microbial growth resistance testing

LIMITATIONS OF ACCELERATED MICROBIAL GROWTH RESISTANCE TESTING... 

USP <1191> Stability Considerations in Dispensing Practice At appropriate time intervals, samples of the product are assayed for potency by use of a stability-indicating method, observed for physical changes, and, where applicable, tested for sterility and or for resistance to microbial growth and for toxicity and bioavailability... 

The outdoor exposure tests to determine the resistance of plastic materials to microbial attack are carried out many different ways (9). The simplest technique is to expose plastic material to an outdoor environment in geographical locations where weather conditions are favorable to microbial growth. The alternate method is called the soil burial method. This method calls for burying the specimens for four weeks and observing the effects of microorganisms of the specimens. 

The Rothamsted Carbon Model (RothC) uses a five pool structure, decomposable plant material (DPM), resistant plant materials (RPM), microbial biomass, humified organic matter, and inert organic matter to assess carbon turnover (Coleman and Jenkinson 1996 Guo et al. 2007). The first four pools decompose by first-order kinetics. The decay rate constants are modified by temperature, soil moisture, and indirectly by clay content. RothC does not include a plant growth sub-module, and therefore NHC inputs must be known, estimated, or calculated by inverse modeling. Skjemstad et al. (2004) tested an approach for populating the different pools based on measured values. 

Currently, advanced molecular methods represent an invaluable tool in the study of food ecosystems and the strains responsible of fermentation processes. At the same time, especially in industrial or applied microbiology, phenotypic tests, which were used widely in the past for microbial identification, are still being considered for the characterization of strain metabolic properties, growth performance, resistance to industrial processes, and shelf life. However, due to their poor reproducibility and low discriminatory power, phenotypic methods have been almost abandoned for identification purposes. Their low taxonomic resolution often leads to differentiation only at the genus level, and they require a labor-intensive approach. On the contrary, genotypic techniques provide a more robust classification and identification, and their costs, over the years, have been decreasing. 

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