Crawford S. Dow

The prediction of bacteria type and culture growth phase by an electronic nose with a multi-layer perceptron network

An investigation into the use of an electronic nose to predict the class and growth phase of two potentially pathogenic micro-organisms, 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 anti-biotic drugs.

An electronic nose system for monitoring the quality of potable water

A measurement system has been developed for the testing of cyanobacteria in water, and it consists of three main stages: the odour sampling system, an electronic nose (e-nose) and a CellFacts instrument that analyses liquid samples. The e-nose system, which employs an array of six commercial odour sensors, has been used to monitor not only different strains but also the growth phase of cyanobacteria (i.e. blue-green algae) in water over a 40-day period. Principal components analysis (PCA), multi-layer perceptron (MLP), learning vector quantisation (LVQ) and Fuzzy ARTMAP were used to analyse the response of the sensors. The optimal MLP network was found to classify correctly 97.1% of the unknown nontoxic and 100% of the unknown toxic cyanobacteria. The optimal LVQ and Fuzzy ARTMAP algorithms were able to classify 100% of both strains of cyanobacteria samples. The accuracy of MLP, LVQ and Fuzzy ARTMAP in terms of predicting four different growth phases of toxic cyanobacteria was 92.3%, 95.1% and 92.3%, respectively. These results show the potential application of neural network based e-noses to test the quality of potable water as an alternative to instruments, such as liquid chromatography or optical microscopy.

Rhodopseudomonas blastica sp.nov.: a Member of the Rhodospirillaceae

Summary: Inoculation of samples from a small eutrophic pond into pyruvate/malate medium at neutral pH yielded a new species of the Rhodospirillaceae described here as Rhodopseudomonas blastica. The cells are ovoid to rod-shaped, 1 to 2.5 μm long and 0.6 to 0.8 μm wide, non-motile and multiply by a process of sessile budding. The photosynthetic membrane system consists of lamellae parallel to and underlying the cell membrane. The photopigments consist of bacteriochlorophyll a and carotenoids of the spheroidene group. Cells can grow anaerobically in the light using a wide range of organic compounds. Aerobic growth in the dark is also possible. Nicotinic acid and thiamin are required as growth factors. Good photolithotrophic growth with H2 is possible, but sulphide and thiosulphate cannot be used as electron donors. As this species has properties lying between the two groups of existing Rhodopseudomonas species, i.e. those which show intercalary growth and those which multiply by budding (asymmetric polar growth), a new species is hereby proposed.

Ribulose-1,5-bisphosphate Carboxylase/Oxygenase and Carbon Assimilation in Methylococcus capsulatus (Bath)

SUMMARY: Intact cells of chemostat-grown Methylococcus capsulatus (Bath) assimilated CO2 such that approximately 2.5% (w/w) of cell carbon arose from CO2 during growth with methane as carbon substrate. Radiolabelling studies suggested that CO2 was fixed by both ribulose-1,5-bisphosphate (RuBP) carboxylase and known heterotrophic mechanisms. The pattern of CO2 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 C1 assimilation in type II methylotrophs. The possession of this pathway explains both the presence of hydroxypyruvate reductase and the results of [14C]formate uptake reported by other workers. The relationship between RuBP carboxylase/oxygenase and net carbon assimilation is discussed.

Nucleoids of Caulobacter crescentus CB15

SUMMARY: Nucleoids isolated from heterogeneous populations of Caulobacter crescentus were invariably associated with the cell envelope. The cell types from which nucleoids were derived were easily identifiable because of the distinctive dimorphic cell cycle of this organism. Sucrose density gradient centrifugation of an exponentially growing culture, gently lysed at 10 °C, gave two classes of envelope-associated nucleoids. One, a broad slow sedimenting band with a sedimentation coefficient of 5600S, was comprised primarily of nucleoids from stalked cells. The other, a tight fast sedimenting band with a sedimentation coefficient of 7100S, was comprised of nucleoids from flagellate and pre-divisional cells. The DNA packing and nucleoid morphology of each class of nucleoids was examined by electron microscopy.

Data reduction in headspace analysis of blood and urine samples for robust bacterial identification

This paper demonstrates the application of chemical headspace analysis to the problem of classifying the presence of bacteria in biomedical samples by using computational tools. Blood and urine samples of disparate forms were analysed using a Cyrano Sciences C320 electronic nose together with an Agilent 4440 Chemosensor. The high dimensional data sets resulting from these devices present computational problems for parameter estimation of discriminant models. A variety of data reduction and pattern recognition techniques were employed in an attempt to optimise the classification process. A 100% successful classification rate for the blood data from the Agilent 4440 was achieved by combining a Sammon mapping with a radial basis function neural network. In comparison a successful classification rate of 80% was achieved for the urine data from the C320 which were analysed using a novel nonlinear time series model.

Simplified Vegetative Cell Cycle of Rhodomicrobium vannielii

Summary: Homogeneous swarm cell populations of Rhodomicrobium vannielii, selected from the late-exponential phase of growth, when cultured photoheterotrophically on solid medium yield two distinct colony types. These reflect two vegetative cell cycle expressions, one composed of the characteristic multicellular complexes, the other of a “simplified” cell cycle composed of prosthecate, reproductive cells and motile swarm cells. This simplified cell cycle has been characterized and its derivation is discussed. The implication of the CO2 concentration as a factor in the control of expression of this cell cycle is also considered.

A new method to evaluate spontaneous platelet aggregation in type 2 diabetes by Cellfacts

BACKGROUND The alterations in the functional activities of platelets in diabetes produce an increase of spontaneous platelet aggregation (SPA) and release of platelet-derived microparticles. Platelet-derived microparticles are shed from platelets during activation by high shear stress, collagen and certain agonists. Although the physiologic role of microparticles has been difficult to assess, the characterization of their biological activity is of interest in view of a possible role in hemostasis and coagulation and their reported involvement in thrombotic disease. METHODS We propose a new, simple method to evaluate spontaneous platelet aggregation and release of platelet-derived microparticles by the Cellfacts analyser (Microbial System Limited (MSL), Coventry, England) that uses electrical sensing flow impedance determination to detect the size particles and the cells in a conductive fluid. Platelet-rich plasma (PRP) from type 2 diabetes was employed for this study. The importance of platelet-activating factor (PAF) on spontaneous platelet aggregation was evaluated and the effect of vitamin E and WEB 2086-BS, an antagonist of platelet-activating factor, was measured. RESULTS AND CONCLUSIONS Data presented show that Cellfacts could be an easy and fast instrument to check the state of platelets in patients with alterations in the functionality of platelets, and to follow the effect of pharmacological therapy on spontaneous platelet aggregation and the release of platelet-derived microparticles.

Isolation, characterization and topographical relationships of pigment−protein complexes from membranes of Rhodomicrobium vannielii

Summary: Pigment-protein complexes from Rhodomicrobium vannielii were prepared by detergent solubilization of intra-cytoplasmic membranes followed by gel electrophoresis or sucrose gradient centrifugation. These procedures gave rise to two native pigmented complexes. The major one (designated B800-865) was associated with two polypeptides of Mr 11000 and 13000 and was identified with the ‘accessory’ light-harvesting complex II found in other members of the Rhodospirillaceae. The minor complex (designated B885-RC) contained both reaction centre and light-harvesting bacteriochlorophyll. Detergent fractionation and reversible chemical cross-linking, followed by two-dimensional polyacrylamide gel electrophoresis, indicated a specific relationship between a membrane-bound cytochrome c-553 and the Mr 31000 subunit of the reaction centre.

The Tricarboxylic Acid Cycle of Heterogeneous and Swarmer Cell Populations of Rhodomicrobium vannielii Rm5

Summary: Studies on the tricarboxylic acid cycle of Rhodomicrobium vannielii Rm5 demonstrated that, unlike other Rhodospirillaceae, this organism has a functionally incomplete cycle, broken at 2-oxoglutarate dehydrogenase, under photoheterotrophic conditions. This enzyme was, however, synthesized when Rm. vannielii was grown under microaerophilic chemoheterotrophic conditions. The citrate synthase exhibited responses to inhibitors characteristic of Gram-negative organisms but, unlike many microbes exhibiting an incomplete cycle, was not inhibited by 2-oxoglutarate. Both NAD- and NADP-linked isocitrate dehydrogenase activity was detectable but the functional roles of these enzymes are unclear. No significant differences in enzyme activities or inhibitor sensitivities of enzymes were detected between heterogeneous cultures and synchronous swarmer cell populations.