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Biomedical subjects

A M Cook

Publications and source records attributed to A M Cook.

At least 19 recordsLinked to original sources
PubMed1992

Aeromonas spp as a potential cause of diarrhoea in children.

AIMS: To determine the prevalence of Aeromonas spp in the faeces of children and the association with symptoms of gastroenteritis. METHODS: Faecal specimens (n = 1026) were cultured for Aeromonas spp using three selective media and an enrichment broth at both 30 degrees C and 37 degrees C. The isolation of Aeromonas spp was correlated with symptoms of gastroenteritis, previous antibiotic use, and environmental temperature. RESULTS: Aeromonas spp (n = 28) from 26 (2.5%) patients were recovered. Bile salt, Irgasan, and brilliant green agar was the most efficient selective culture medium. Eleven of the patients had symptoms of gastroenteritis, usually mild diarrhoea of two to three days' duration, in the absence of other recognised enteropathogens. A caviae was a particularly frequent isolate (nine out of 11 cases) in symptomatic individuals. Only one out of seven Aeromonas spp recovered by enrichment culture alone was possibly associated with symptoms of gastroenteritis. There was a close correlation between the environmental temperature and isolation of Aeromonas spp. CONCLUSIONS: Aeromonas spp and particularly A caviae may cause gastroenteritis in children, most often during warmer months of the year. Culture for these potential enteropathogens could be confined to summer and autumn months. Bile salt, Irgasan, and brilliant green selective agar, but not alkaline peptone water enrichment, is an efficient culture medium for recovering possibly clinically important isolates.

Aeromonas↗
PubMed1992

Phenotypic methods for speciating clinical Aeromonas isolates.

AIMS: To establish the suitability of currently available phenotypic methods for speciation of clinical Aeromonas isolates in diagnostic microbiology laboratories. METHODS: Using 62 Aeromonas spp, three schemes based on biochemical reactions were compared: a series of conventional tests; a system based on the suicide phenomenon, comprising two tubes in total; and a commercially available test, API 20 NE, augmented with a plate assay for beta haemolysin production. The whole cell and outer membrane protein (OMP) profiles of strains were examined by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS PAGE), according to the results of the above schemes, to determine the intra-species homogeneity. RESULTS: Ninety per cent of strains were identified satisfactorily according to conventional criteria. For these strains, agreement was obtained using the suicide phenomenon and API schemes in 93% and 88% of cases, respectively. The three schemes concurred for 82% of strains. Whole cell protein profiles were unsuitable for comparing strains within a species. However, OMP patterns were similar for 89% of A caviae and 63% of A hydrophila. CONCLUSION: Phenospeciation of clinical Aeromonas isolates by the scheme based on the suicide phenomenon is simple to perform and accurate, and suitable for use in the diagnostic laboratory. OMP profiles are potentially useful for confirming the identity of A caviae and most A hydrophila, but not A sobria.

Aeromonas↗
PubMed1992

Audit in action: significant reduction of double-contrast barium enema screening time with no loss of examination quality.

The double-contrast barium enema is an examination of high radiation exposure to the patient. As part of a departmental audit, our own fluoroscopic screening times were being recorded. A study was undertaken to see if a determined effort could reduce the screening time without having a detrimental effect on the quality of the examinations. Methods of screening time reduction were identified and then implemented by two radiologists. In the period before the study the average screening time for radiologists A and B was 2.6 min and 3.2 min, respectively (over 56 examinations). After implementation of the changes, the average screening time for both was 0.9 min (over 50 examinations). This is a statistically significant reduction (p less than 0.01). The examinations were assessed independently by a gastroradiologist. No difference in the quality of the examinations was identified. We conclude that a significant reduction of screening time for the double-contrast barium enema can be achieved without loss of examination quality.

Barium Sulfate↗
PubMed1991

4-Sulphobenzoate 3,4-dioxygenase. Purification and properties of a desulphonative two-component enzyme system from Comamonas testosteroni T-2.

Cell-free extracts of Comamonas testosteroni T-2 grown in toluene-p-sulphonate/salts medium catalyse the conversion of p-sulphobenzoate (PSB) into protocatechuate and sulphite by an NADH-requiring and Fe2(+)-activated dioxygenase. Anion-exchange chromatography of extracts yielded red (A) and yellow (B) protein fractions, both of which were necessary for dioxygenative activity. Further purification of each fraction by hydrophobic interaction chromatography and gel filtration led to two homogeneous protein components (A and B), which together converted 1 mol each of PSB, O2 and NADH into 1 mol each of protocatechuate, sulphite and, presumably, NAD+. The system was named 4-sulphobenzoate 3,4-dioxygenase (PSB dioxygenase system). Monomeric component B (Mr 36,000) was determined to be a reductase that contained 1 mol of FMN and about 2 mol each of iron and inorganic sulphur per mol. This component transferred electrons from NADH to the oxygenase component (A) or to, e.g., cytochrome c. Homodimeric component A (subunit Mr 50,000) of the PSB dioxygenase system contained one [2Fe-2S] centre per subunit and its u.v.-visible-absorption spectrum corresponded to a Rieske-type iron-sulphur centre. The requirement for activation by iron was interpreted as partial loss of mononuclear iron during purification of component A. Component A could be reduced by dithionite or by NADH plus catalytic amounts of component B. The PSB dioxygenase system displayed a narrow substrate range: none of 18 sulphonated or non-sulphonated analogues of PSB showed significant substrate-dependent O2 uptake. The physical properties of the PSB dioxygenase system resemble those of other bacterial multi-component dioxygenase, especially phthalate dioxygenase. However, it differs from most characterized systems in its overall reaction; the product is a vicinal diphenol, and not a dihydrodiol.

Amino Acids↗
PubMed1991

Dichloromethane utilized by an anaerobic mixed culture: acetogenesis and methanogenesis.

Dichloromethane (8.9 mg/l) was eliminated from industrially polluted, anaerobic groundwater in a fixed-bed reactor (43 m3) which was packed with activated charcoal and operated continuously for over three years. The elimination of dichloromethane over this period was some ten-fold in excess of the sorptive capacity of the charcoal, and the elimination (3.7 mg/h.[kg of charcoal]: residence time, 49 h) was tentatively attributed to dehalogenative microorganisms immobilized on the charcoal. Anaerobic enrichment cultures, with dichloromethane as the sole added source of carbon and energy, were inoculated with material from the reactor. Reproducibly complete substrate disappearance in subcultures was observed when traces of groundwater (1%) or yeast extract (0.01%) were supplied. Fed-batch experiments under an atmosphere of CO2 plus N2 led to the conversion in 11 days of 11 mM dichloromethane to 3 mM acetate and 2 mM methane, with a growth yield of 0.4 g of protein/mol of dichloromethane; insignificant amounts (less than 1 microM) of chloromethane accumulated. Methanogenesis could be inhibited by 50 mM 2-bromoethane sulfonate without any effect on the dehalogenation rate. The maximum dehalogenation rate was 0.13 mmol dichloromethane/h.l (2.6 mkat/kg of protein).

Acetates↗
PubMed1991

4-Toluene sulfonate methyl-monooxygenase from Comamonas testosteroni T-2: purification and some properties of the oxygenase component.

Comamonas testosteroni T-2 synthesizes an inducible enzyme system that oxygenates 4-toluene sulfontate (TS) to 4-sulfobenzyl alcohol when grown in TS-salts medium. We purified this TS methyl-monooxygenase system (TSMOS) and found it to consist of two components. A monomeric, iron-sulfur flavoprotein (component B), which has been shown to act as a reductase in the 4-sulfobenzoate dioxygenase system of this organism (H. H. Locher, T. Leisinger, and A. M. Cook, Biochem. J. 274:833-842, 1991), carried electrons from NADH to component M, an oxygenase. This oxygenase had the UV-visible spectral characteristics of an iron-sulfur protein. Mrs of about 152,000 for the native oxygenase and of 43,000 under denaturing conditions indicated a homotri- or homotetrameric enzyme, whose N-terminal amino acids and amino acid composition were determined. The activity of the purified enzyme was enhanced about fivefold by the addition of Fe2+. In the presence of O2 and NADH, components B and M together catalyzed the stoichiometric transformation of TS or p-toluate to the corresponding alcohol. The reaction was confirmed as oxygenation of the methyl group by observation of an oxygen atom from 18O2 in carboxybenzyl alcohol. The substrate range of TSMOS included carboxylated analogs of TS (p- and m-toluates and 4-ethylbenzoate), whereas p-xylene, toluene, and p-cresol were not substrates. TSMOS also catalyzed demethylation; 4-methoxybenzoate was transformed to 4-hydroxybenzoate and formaldehyde.

Amino Acids↗
PubMed1990

Initial steps in the degradation of benzene sulfonic acid, 4-toluene sulfonic acids, and orthanilic acid in Alcaligenes sp. strain O-1.

Alcaligenes sp. strain O-1 grew with benzene sulfonate (BS) as sole carbon source for growth with either NH4+ or NH4+ plus orthanilate (2-aminobenzene sulfonate, OS) as the source(s) of nitrogen. The intracellular desulfonative enzyme did not degrade 3- or 4-aminobenzene sulfonates in the medium, although the enzyme in cell extracts degraded these compounds. We deduce the presence of a selective permeability barrier to sulfonates and conclude that the first step in sulfonate metabolism is transport into the cell. Cell-free desulfonation of BS in standard reaction mixtures required 2 mol of O2 per mol. One mol of O2 was required for a catechol 2,3-dioxygenase. When meta ring cleavage was inhibited with 3-chlorocatechol in desalted extracts, about 1 mol each of O2 and of NAD(P)H per mol of BS were required for the reaction, and SO3(2-) and catechol were recovered in high yield. Catechol was shown to be formed by dioxygenation in an experiment involving 18O2. 4-Toluene sulfonate was subject to NAD(P)H-dependent dioxygenation to yield SO3(2-) and 4-methylcatechol, which was subject to meta cleavage. OS also required 2 mol of O2 per mol and NAD(P)H for degradation, and SO3(2-) and NH4+ were recovered quantitatively. Inhibition of ring cleavage with 3-chlorocatechol reduced the oxygen requirement to 1 mol per mol of OS SO3(2-) (1 mol) and an unidentified organic intermediate, but no NH4+, were observed.

Alcaligenes↗
PubMed1979

Phosphate and soil binding: factors limiting bacterial degradation of ionic phosphorus-containing pesticide metabolites.

Soils that had a high binding capacity for inorganic orthophosphate (Pi) had reduced capacities to bind ionic alkyl phosphorus compounds. Only ionic methylphosphonate (MPn) and ionic phenylphosphonate exhibited moderate binding. Pseudomonas testosteroni used either MPn or Pi as a sole phosphorus source and exhibited diauxic utilization of MPn and Pi. The utilization of MPn was suppressed in the presence of Pi. This suppression was abolished by a Pi-binding soil. The soil did not have a significant effect on the maximum rate of degradation of either MPn or the poorly bound ionic O-isopropyl methylphosphonate, whereas the amount of MPn (but not the amount of O-isopropyl methylphosphonate) metabolized was reduced in the presence of soil

Biodegradation, Environmental↗
PubMed1978

Phosphorus-containing pesticide breakdown products: quantitative utilization as phosphorus sources by bacteria.

Bacteria were isolated that could utilize representatives of the following ionic phosphorus-containing breakdown products of organophosphorus pesticides as sole phosphorus sources: dialkyl phosphates, dialkyl phosphorothioates, dialkyl phosphorodithioates, alkyl arylphosphonates, alkyl arylphosphonothioates, and alkyl alkylphosphonates. Utilization of each organophosphorus compound, which was complete for 7 of 12 compounds studied, was confirmed by determination of protein yield from the amount of phosphorus source consumed. This is the first report of the utilization of an ionic dialkyl thiophosphate or dithiophosphate by microorganisms.

Bacteria↗
PubMed1978

Phosphonate utilization by bacteria.

Bacteria able to use at least one of 13 ionic alkylphosphonates of O-alkyl or O,O-dialkyl alkylphosphonates as phosphorus sources were isolated from sewage and soil. Four of these isolates used 2-aminoethylphosphonic acid (AEP) as a sole carbon, nitrogen, and phosphorus source. None of the other phosphonates served as a carbon source for the organisms. One isolate, identified as Pseudomonas putida, grew with AEP as its sole carbon, nitrogen, and phosphorus source and released nearly all of the organic phosphorus as orthophosphate and 72% of the AEP nitrogen as ammonium. This is the first demonstration of utilization of a phosphonoalkyl moiety as a sole carbon source. Cell-free extracts of P. putida contained an inducible enzyme system that required pyruvate and pyridoxal phosphate to release orthophosphate from AEP; acetaldehyde was tentatively identified as a second product. Phosphite inhibited the enzyme system.

Aminoethylphosphonic Acid↗
PubMed1976

Regulation of growth of Acinetobacter calcoaceticus NCIB8250 on benzyl alcohol in batch culture.

Formation of benzoate and catechol during oxidation of benzyl alcohol by washed suspensions of Acinetobacter calcoaceticus NCIB8250 confirmed earlier results indicating that this organism metabolizes benzyl alcohol via benzaldehyde, benzoate, and the 3-oxoadipate pathway. There was no evidence for feedback inhibition of benzyl alcohol dehydrogenase or benzaldehyde dehydrogenase II. Examination of growth curves and patterns of substrate utilization, as well as measurement of enzyme activities, showed that benzyl alcohol dehydrogenase and benzaldehyde dehydrogenase II are repressed when A. calcoaceticus utilizes L-mandelate or phenylglyoxylate. Growth of bacteria on L-mandelate prior to their inoculation into benzyl alcohol/salts medium leads to an exceptionally long lag period before benzyl alcohol is used at the maximum rate. Benzyl alcohol metabolism is also suppressed during growth on benzoate.

Acinetobacter↗
PubMed1975

Regulation of growth of Acinetobacter calcoaceticus NCIB8250 on L-mandelate in batch culture.

Batch culture of Acinetobacter calcoaceticus in L-mandelate- or phenylglyoxylate-salts medium showed an unusual non-exponential pattern unless the inoculum had been grown on benzyl alcohol. There were transient accumulations of benzaldehyde and benzyl alcohol caused by the limitation of L-mandelate oxidation by low activities of benzaldehyde dehydrogenase and the diversion of reducing power to the formation of benzyl alcohol. In vivo enzymic activities were estimated from patterns of substrate utilization in batch cultures containing pairs of substrates. When bacteria previously grown in L-mandelate-salts medium were inoculated into media containing L-mandelate and a second carbon source, metabolism of L-mandelate was arithmetical in the presence of benzoate, catechol or succinate, but accelerated on exhaustion of the second substrate. This indicated repression of the enzymes involved in L-mandelate oxidation. Inoculation of bacteria grown in benzoate-salts medium into medium containing L-mandelate and benzoate gave diauxie with initial utilization of benzoate. Similar experiments showed that benzoate oxidation was not repressed by catechol and only partially repressed by succinate. Measurement of L-mandelate dehydrogenase, phenylglyoxylate carboxy-lyase and benzaldehyde dehydrogenase I in bacterial extracts showed no evidence for feedback inhibition by intermediates of the pathway. The rates of L-mandelate and benzoate utilization by bacterial suspensions were inhibited by succinate and catechol but not by other intermediates of the pathway.

Acinetobacter↗