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PubMed1976

Growth of Enterobacter aerogenes in a chemostat with double nutrient limitations.

The behavior of Enterobacter aerogenes during growth in chemostats limited by single and double nutrient restrictions was examined. On the assumption that different essential nutrients act to limit growth in different ways, we selected pairs of nutrients likely to affect different aspects of metabolism. Results show that macromolecular cell composition can be controlled by using more than one nutrient restriction. The polysaccharide content of the cells is readily manipulated by the ratio of carbon to nitrogen in the inlet nutrients. Also, at low dilution rates, ratios of protein to ribonucleic acid are dependent on the ratio of phosphate to nitrogen in the input nutrients. An examination of both acetic acid and metabolite production (as measured by ultraviolet absorbance of culture filtrates) showed that accumulation of these products was dependent on both dilution rate and type of nutrient limitation(s). These results were examined in terms of the problems of translation of batch to continuous culture processes and the use of selected nutrient limitations to control noncellular product formation.

Ammonia↗
PubMed1977

Nitrogen-fixing Enterobacter agglomerans isolated from guts of wood-eating termites.

Two strains of facultatively anaerobic, N2-fixing bacteria were isolated from guts of Coptotermes formosanus and identified as Enterobacter agglomerans. The deoxyribonucleic acid base composition of isolates was 52.6 and 53.1 mol% guanine plus cytosine. Both isolates and a known strain of E. agglomerans carried out a mixed acid type of glucose fermentation. N2 fixation by E. agglomerans was inhibited by O2; consequently, N2 served as an N source only for cells growing anaerobically in media lacking a major source of combined N. However, peptone, NH4Cl, or KNO3 served as an N source under either aerobic or anaerobic conditions. It was estimated that 2 x 10(2) cells of E. agglomerans were present per termite gut. This value was 100-fold lower than expected, based on N2 fixation, low recoveries of E. agglomerans may be related to the marked decrease in N2 fixation rates observed when intact termites or their extracted guts were manipulated for the isolation of bacteria. It was concluded that the N2-fixing activity of E. agglomerans may be important to the N economy of C. formosanus.

Anaerobiosis↗
PubMed1989

Isolation and Characterization of an Enterobacter cloacae Strain That Reduces Hexavalent Chromium under Anaerobic Conditions.

An Enterobacter cloacae strain (HO1) capable of reducing hexavalent chromium (chromate) was isolated from activated sludge. This bacterium was resistant to chromate under both aerobic and anaerobic conditions. Only the anaerobic culture of the E. cloacae isolate showed chromate reduction. In the anaerobic culture, yellow turned white with chromate and the turbidity increased as the reduction proceeded, suggesting that insoluble chromium hydroxide was formed. E. cloacae is likely to utilize toxic chromate as an electron acceptor anaerobically because (i) the anaerobic growth of E. cloacae HO1 accompanied the decrease of toxic chromate in culture medium, (ii) the chromate-reducing activity was rapidly inhibited by oxygen, and (iii) the reduction occurred more rapidly in glycerol- or acetate-grown cells than in glucose-grown cells. The chromate reduction in E. cloacae HO1 was observed at pH 6.0 to 8.5 (optimum pH, 7.0) and at 10 to 40 degrees C (optimum, 30 degrees C).

Journal Article↗
PubMed1993

Cloning and Characterization of Aerobactin Biosynthesis Genes of the Biological Control Agent Enterobacter cloacae.

Five strains of Enterobacter cloacae that are biological control agents of Pythium damping-off diseases produced the hydroxamate siderophore aerobactin under iron-limiting conditions. Genes determining aerobactin biosynthesis of the biocontrol strain E. cloacae EcCT-501 were localized to a 12.3-kb region, which conferred aerobactin production to Escherichia coli DH5alpha. The aerobactin biosynthesis genes of E. cloacae hybridized to those of the pColV-K30 plasmid of E. coli, but restriction patterns of the aerobactin regions of pColV-K30 and E. cloacae differed. A derivative strain with a deletion in the aerobactin biosynthesis locus was as effective as strain EcCT-501 in biological control of Pythium damping-off of cucumber. Thus, aerobactin production did not contribute significantly to the biological control activity of EcCT-501 under the conditions of this study.

Journal Article↗
PubMed1994

Optimization of Novel Extracellular Polysaccharide Production by an Enterobacter sp, on Wood Hydrolysates.

An environmental isolate identified as Enterobacter cloacae has been found to produce a highly viscous, anionic extracellular polysaccharide (EPS) from a weak mineral acid hydrolysate of hardwood. Production of this EPS has been optimized on the hydrolysate (initial pH, 6.3; NH(4)Cl amendment, 0.1%) so that crude yields approaching 9.83 g/liter were obtained. Although this EPS is polydisperse, its molecular mass as determined by gel exclusion chromatography centers at approximately 1,700 kDa. Solutions of this EPS have been examined rheologically under a variety of conditions and compare favorably with both xanthan and alginate.

Journal Article↗
PubMed1996

Physiologic Mechanisms Involved in Accumulation of 3-Hydroxypropionaldehyde during Fermentation of Glycerol by Enterobacter agglomerans.

When grown in 700 mM glycerol within the pH range 6.0 to 7.5, anaerobic pH-regulated cultures of Enterobacter agglomerans exhibited an extracellular accumulation of 3-hydroxypropionaldehyde (3-HPA). This phenomenon, which causes fermentation cessation, occurred earlier when pH was low. In contrast, substrate consumption was complete at pH 8. Levels of glycerol-catabolizing enzymes, i.e., glycerol dehydrogenase and dihydroxyacetone kinase for the oxidative route and glycerol dehydratase and 1,3-propanediol dehydrogenase for the reductive route, as well as the nucleotide pools were determined periodically in the pH 7- and pH 8-regulated cultures. A NAD/NADH ratio of 1.7 was correlated with the beginning of the production of the inhibitory metabolite. Further accumulation was dependent on the ratio of glycerol dehydratase activity to 1,3-propanediol dehydrogenase activity. For a ratio higher than 1, 3-HPA was produced until fermentation ceased, which occurred for the pH 7-regulated culture. At pH 8, a value below 1 was noticed and 3-HPA accumulation was transient, while the NAD/NADH ratio decreased. The low rate of glycerol dissimilation following the appearance of 3-HPA in the culture medium was attributed to the strong inhibitory effect exerted by 3-HPA on glycerol dehydrogenase activity.

Journal Article↗
PubMed1997

Reduction of Selenium Oxyanions by Enterobacter cloacae SLD1a-1: Isolation and Growth of the Bacterium and Its Expulsion of Selenium Particles.

A facultative bacterium capable of removing the selenium (Se) oxyanions selenate (SeO(inf4)(sup2-)) and selenite (SeO(inf3)(sup2-)) from solution culture in flasks open to the atmosphere was isolated and studied with the goal of assessing its potential for use in bioremediation of seleniferous agricultural drainage water. Elemental Se (Se(sup0)) was confirmed as a product of the reaction. The organism, identified as Enterobacter cloacae and designated strain SLD1a-1 (ATCC 700258), removed from 61.5 to 94.5% of added SeO(inf4)(sup2-) (the primary species present in agricultural drainage water) at concentrations from 13 to 1,266 (mu)M. Equimolar amounts of nitrate (NO(inf3)(sup-)), which interferes with SeO(inf4)(sup2-) reduction in some organisms, did not influence the reaction in growth experiments but had a slight inhibitory effect in a washed-cell suspension. Washed-cell suspension experiments also showed that (i) SeO(inf3)(sup2-) is a transitory intermediate in reduction of SeO(inf4)(sup2-), being produced and rapidly reduced concomitantly; (ii) NO(inf3)(sup-) is also reduced concomitantly and at a much higher rate than SeO(inf4)(sup2-); and (iii) although enzymatic, reduction of either oxyanion does not appear to be an inducible process. Transmission electron microscopy revealed that precipitate particles are <0.1 (mu)m in diameter, and these particles were observed free in the medium. Evidence indicates that SLD1a-1 uses SeO(inf4)(sup2-) as an alternate electron acceptor and that the reaction occurs via a membrane-associated reductase(s) followed by rapid expulsion of the Se particles.

Journal Article↗
PubMed2004

Fluorogenic selective and differential medium for isolation of Enterobacter sakazakii.

4-Methylumbelliferyl-alpha-D-glucoside, the fluorogenic substrate of alpha-glucosidase, was used as a selective marker to develop a differential medium for Enterobacter sakazakii. This bacterium showed strong fluorogenic characteristics clearly distinguishable from other microorganisms. On the basis of reducing background noise, an optimum basal medium and nitrogen source were selected. Incubation conditions were optimized.

Cronobacter sakazakii↗
PubMed2006

Effects of preculturing conditions on lag time and specific growth rate of Enterobacter sakazakii in reconstituted powdered infant formula.

Enterobacter sakazakii can be present, although in low levels, in dry powdered infant formulae, and it has been linked to cases of meningitis in neonates, especially those born prematurely. In order to prevent illness, product contamination at manufacture and during preparation, as well as growth after reconstitution, must be minimized by appropriate control measures. In this publication, several determinants of the growth of E. sakazakii in reconstituted infant formula are reported. The following key growth parameters were determined: lag time, specific growth rate, and maximum population density. Cells were harvested at different phases of growth and spiked into powdered infant formula. After reconstitution in sterile water, E. sakazakii was able to grow at temperatures between 8 and 47 degrees C. The estimated optimal growth temperature was 39.4 degrees C, whereas the optimal specific growth rate was 2.31 h(-1). The effect of temperature on the specific growth rate was described with two secondary growth models. The resulting minimum and maximum temperatures estimated with the secondary Rosso equation were 3.6 degrees C and 47.6 degrees C, respectively. The estimated lag time varied from 83.3 +/- 18.7 h at 10 degrees C to 1.73 +/- 0.43 h at 37 degrees C and could be described with the hyperbolic model and reciprocal square root relation. Cells harvested at different phases of growth did not exhibit significant differences in either specific growth rate or lag time. Strains did not have different lag times, and lag times were short given that the cells had spent several (3 to 10) days in dry powdered infant formula. The growth rates and lag times at various temperatures obtained in this study may help in calculations of the period for which reconstituted infant formula can be stored at a specific temperature without detrimental impact on health.

Animals↗
PubMed1975

Methyl violet: a selective agent for differentiation of Klebsiella pneumoniae from Enterobacter aerogenes and other gram-negative organisms.

Three selective media for differentiation of Klebsiella pneumoniae from Enterobacter aerogenes on the basis of colonial morphology were evaluated. Using methyl violet 2B as a selective agent, strains of K. pneumoniae isolated from urine, fresh water, and fresh produce were tested against other members of Enterobacteriaceae in addition to strains of Aeromonas hydrophila and Pseudomonas aeruginosa. Comparison of colonial morphology showed K. pneumoniae produced larger, smoother colonies than other bacteria tested. These media were developed to aid in presumptive separation of K. pneumoniae from E. aerogenes in the monitoring of bacterial quality of water.

Aeromonas↗
PubMed1975

Effect of substrates on acetoin production by Torulopsis colliculosa and Enterobacter species.

Under optimal conditions, Torulopsis colliculosa NRRL 172 and Enterobacter B-87 (ATCC 27613) produced 50 to 500 mg of acetoin per g of substrate. Whereas cane molasses, gur, glucose, and sucrose were suitable substrates for acetoin production, lactose and mannitol supported very good growth but yielded little or no acetoin. Production of acetoin increased with increases in the concentration of glucose, yeast extract, and peptone. Combination of substrates and intermittent feeding of substrate failed to increase the yields.

Acetoin↗
PubMed1976

Partial purification and properties of Enterobacter cloacae heat-stable enterotoxin.

Cell free preparations of the whole-cell lysate and ultrafiltration (UF) fractions of broth cultures of a strain of Enterobacter cloacae, isolated from a Puerto Rican with tropical sprue, were assayed for their ability to induce in vivo net water secretion in the rat jejunum. The whole-cell lysate and UM-10 retentate of broth cultures were inactive. The UM-2 retentate and filtrate were active at a concentration of 100 mug/ml or more; the toxigenic activity was entirely retained, and increased to 1 mug/ml, by a UM-05 membrane; washing this retentate yielded a fraction with an activity of 10 ng/ml. Stationary aerobic culture conditions yielded the most active UF fractions when ammonium sulfate was used as the precipitating agent, whereas anaerobic culture conditions produced the most active fractions in broth cultures precipitated by acetone. Passage of the active acetone-precipitated UF fractions through a Sephadex G-25 column yielded eluate pools with enhanced toxigenic activity in, or adjacent to, the void volume, but maximum activity of the ammonium sulfate-precipitated UM-05 retentate eluated at a Kav of 0.38 to 0.52. Neither of the most active gel filtration elution fractions of the UM-05 retentates contained detectable carbohydrate, suggesting that the toxin is not associated with endotoxin. Toxigenic activity was unaltered by exposure to a temperature of 100C for 30 min, lowering the pH to 1, or incubation with either Pronase or trypsin. These observations indicate that the strain of E. cloacae under study elaborates a heat-stable enterotoxin htat has approximately the same molecular weight and shares many of the characteristics of the heat-stable enterotoxin produced by some strains of Escherichia coli and Klebsiella pneumoniae.

Aerobiosis↗
PubMed1982

Evaluation of three differential media for detection of Enterobacter agglomerans (Erwinia herbicola).

Dextrin-fuchsine-sulfite medium (DFS), Rimler-Shotts agar (RS), and a new lysine-ornithine-mannitol agar (LOM) were tested for detection of Enterobacter agglomerans. In human stools, LOM and DFS were most sensitive at coliform-to-E. agglomerans ratios of less than or equal to 10(2) and E. agglomerans inocula of greater than 10(2) per plate. Both LOM and DFS detected one strain in 254 stools, but RS proved to be inhibitory.

Culture Media↗
PubMed1996

Molecular epidemiology of Enterobacter aerogenes acquisition: one-year prospective study in two intensive care units.

To evaluate the respective contributions of patient-to-patient transmission and endogenous acquisition of Enterobacter aerogenes isolates, we conducted a prospective epidemiologic study in two intensive care units (ICUs) between May 1994 and April 1995. We collected a total of 185 E. aerogenes isolates: 130 from 51 patients in a surgical ICU (SICU), 45 from 26 patients in a medical ICU (MICU), and 10 from the environments in these two ICUs. All isolates were typed by random amplification of polymorphic DNA and enterobacterial repetitive intergenic consensus PCR. Among the 175 clinical isolate, we observed 40 different profiles by random amplification of polymorphic DNA and 36 different profiles by enterobacterial repetitive intergenic consensus PCR. We identified a ubiquitous and prevalent clone, corresponding to 58% of SICU and 41% of MICU clinical isolates. Three epidemiologically related strains were specific to each ICU and represented 17% of SICU and 24% of MICU clinical isolates; unique type strains represented 17 and 29% of SICU and MICU clinical isolates, respectively, and E. aerogenes strains which were spread to a limited degree and which were isolated less than five times during the 1-year study period represented 8 and 6% of SICU and MICU clinical isolates, respectively. Our results show that E. aerogenes is acquired in the ICU in three different ways: patient-to-patient spread of a prevalent or an epidemiologically related strain, acquisition de novo of a strain from patients' own flora, and acquisition of a nonendemic strain followed by occasional patient-to-patient transmission. The findings point out the importance of patient-to-patient transmission in E. aerogenes acquisition and suggest that changes in E. aerogenes ecology in the hospital have taken place during the past decade.

Adult↗
PubMed1998

Molecular epidemiological study of nosocomial Enterobacter aerogenes isolates in a Belgian hospital.

In 1995, the rate of isolation of Enterobacter aerogenes in the Saint-Pierre University Hospital in Brussels, Belgium, was higher than that in the preceding years. A total of 45 nosocomial E. aerogenes strains were collected from 33 patients of different units during that year, and they were isolated from 19 respiratory specimens, 13 pus specimens, 7 blood specimens, 4 urinary specimens, 1 catheter specimen, and 1 heparin vial. The strains were analyzed to determine their epidemiological relatedness and were characterized by their antibiotic resistance pattern determination, plasmid profiling, and genomic fingerprinting by macrorestriction analysis with pulsed-field gel electrophoresis (PFGE). The majority of the strains (82%) were multiply resistant to different commonly used antibiotics. Two major plasmid profiles were found: most strains (64%) harbored two plasmids of different sizes, whereas the others (20%) contained a single plasmid. PFGE with SpeI and/or XbaI restriction enzymes revealed that a single clone (80%) was responsible for causing infections or colonizations throughout the year, and this result was concordant with those obtained by plasmid profiling, with slight variations. By comparing the results of these three methods, PFGE and plasmid profiling were found to be the techniques best suited for investigating the epidemiological relatedness of E. aerogenes strains, and they are therefore proposed as useful tools for the investigation of nosocomial outbreaks caused by this organism.

Adult↗
PubMed1975

R factor in Enterobacter cloacae resistant to silver sulfadiazine.

A strain of Enterobacter cloacae resistant to silver sulfadiazine was recovered from a unit in which this antimicrobial agent was in use. This strain was found to harbor an R factor responsible for resistance to carbenicillin, kanamycin and ampicillin. These antibiotic resistances were transferable to Escherichia coli by mating. Resistance to silver sulfadiazine was not, however, transmissible.

Ampicillin↗