An investigation into the use of an electronic nose to predict the class and growth phase of two potentially pathogenic microorganisms , Eschericha coli (E. coli) and Staphylococcus aureus (S. aureus), has been performed. In order to do this we have developed an automated system to sample, with a high degree of reproducibility, the head space of bacterial cultures grown in a standard nutrient medium. Head spaces have been examined by using an array of six different metal oxide semiconducting gas sensors and classified by a multi-layer perceptron (MLP) with a back-propagation (BP) learning algorithm. The performance of 36 different pre-processing algorithms has been studied on the basis of nine different sensor parameters and four different normalization techniques. The best MLP was found to classify successfully 100% of the unknown S. aureus samples and 92% of the unknown E. coli samples, on the basis of a set of 360 training vectors and 360 test vectors taken from the lag, log and stationary growth phases. The real growth phase of the bacteria was determined from optical cell counts and was predicted from the head space samples with an accuracy of 81%. We conclude that these results show considerable promise in that the correct prediction of the type and growth phase of pathogenic bacteria may help both in the more rapid treatment of bacterial infections and in the more efficient testing of new antibiotic drugs.

No abstract

No abstract

Intact cells of chemostat-grown Methylococcus capsulatus (Bath) assimilated CO, such that approximately 2.5% (w/w) of cell carbon arose from CO, during growth with methane as carbon substrate. Radiolabelling studies suggested that CO, was fixed by both ribulose-1,5-bisphosphate (RuBP) carboxylase and known heterotrophic .mechanisms. The. pattern of CO, fixation was similar to that in heterotrophically grown autotrophs. Enzyme analysis suggested the presence of a complete Calvin cycle but attempts to grow the organism autotrophically were unsuccessful. A specific phosphoglycollate phosphatase, required for the metabolism of phosphoglycollate arising as a result of RuBP oxygenase activity, was present. The product of this reaction, glycollate, was further metabolized by reactions of the serine cycle, used for C, assimilation in type I1 methylotrophs. The possession of this pathway explains both the presence of hydroxypyruvate reductase and the results of ['4Clformate uptake reported by other workers. The relationship between RuBP carboxylase/oxygenase and net carbon assimilation is discussed.