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Biomedical subjects

M Hermansson

Publications and source records attributed to M Hermansson.

At least 19 recordsLinked to original sources
PubMed2006

Performance of direct biofiltration of surface water for reduction of biodegradable organic matter and biofilm formation potential.

Direct biofiltration of surface water may be considered as pre-treatment for membrane filtration, in order to reduce fouling. The biofiltration process was investigated with regard to biodegradable organic matter and biofilm formation, covering the annual variations under moderately cold climate conditions. Granular activated carbon (GAC) and two types of crushed expanded clay (EC) were compared as filter media. To assess the biological properties of the biofilters, viable biomass and respiratory activity was examined. Biofiltration removed assimilable organic carbon (AOC) and biodegradable dissolved organic carbon (BDOC) by about 30% and also reduced the bacterial concentration in the water phase. Also, biofilm formation in the treated water was reduced by 80-90% during summer and winter conditions. The reductions in the investigated parameters were similar in the biofilters with GAC and EC. Likewise, a similar amount and development of biomass was found in the GAC and EC biofilters of comparable grain size with a pronounced stratification from top to bottom of the filter bed. The specific respiratory activity of the biofilter biomass was dependent on raw water temperature. Even though slight correlations between BDOC removal and temperature or respiratory activity were observed, AOC and BDOC removals were mainly dependent on the feed water concentrations of these compounds. The results indicate that direct biofiltration of surface water, by reducing AOC, BDOC and biofilm formation in the water, may be an advantageous pre-treatment for membrane filtration processes.

Biodegradation, Environmental↗
PubMed2006

Influence of flocculation and settling properties of activated sludge in relation to secondary settler performance.

Floc characteristics were studied at a full scale activated sludge treatment plant with a unique process solution incorporating pre-denitrification with post-nitrification in nitrifying trickling filters. Since greater nitrogen removal is achieved when more secondary settled wastewater is recirculated to the trickling filters, the secondary settlers are always operated close to their maximal capacity. The flocculation and settling properties are therefore crucial and have an effect on the overall plant performance. Since the plant is operated at a short sludge age, these properties change quickly, resulting in variable maximal secondary settler capacity. The dynamics in floc structure and microbial community composition were studied and correlated to the secondary settler performance. Fluorescence in situ hybridisation was used to investigate the microbial community structure and their spatial distribution. The floc structure could to some extent be related to the flocculation and settling properties of the sludge. Even small differences had an influence suggesting that colloidal properties also play a significant role in determining the floc properties. No correlation between microbial community composition and settling properties could be established with the group-specific probes investigated.

Environmental Restoration and Remediation↗
PubMed2005

Community survey of ammonia-oxidizing bacteria in full-scale activated sludge processes with different solids retention time.

AIMS: To study the effects of different solids retention time (SRT) on the nitrification activity and community composition of ammonia-oxidizing bacteria (AOB) in two full-scale activated sludge processes during a 5-month period. METHODS AND RESULTS: The AOB community composition was analysed using fluorescence in situ hybridization (FISH) and denaturing gradient gel electrophoresis (DGGE), and the identified populations were enumerated by quantitative FISH. Potential nitrification rates were determined in batch tests and the in situ rates were calculated from mass balances of nitrogen in the plants. Increased SRT reduced the nitrification activity, but neither the number per mixed liquor suspended solids nor community composition of AOB were affected. Two dominant AOB populations related to Nitrosomonas europaea and Nitrosomonas oligotropha were identified by FISH, whereas only the latter could be detected by DGGE. CONCLUSIONS: The effect of a longer SRT on the activity was probably because of physiological changes in the AOB community rather than a change in community composition. SIGNIFICANCE AND IMPACT OF THE STUDY: Physiological alterations of a stable AOB community are possible and may stabilize activated sludge processes. The commonly used FISH probes designed to target all beta-proteobacterial AOB does not detect certain Nitrosomonas oligotropha populations, leading to an underestimation of AOB if a wider set of probes is not used.

Ammonia↗
PubMed2001

Formation of helical hairpins during membrane protein integration into the endoplasmic reticulum membrane. Role of the N and C-terminal flanking regions.

The helical hairpin, two closely spaced transmembrane helices separated by a short turn, is a common structural element in integral membrane proteins. Previous studies on the sequence determinants of helical hairpin formation have focussed on the role of polar and charged residues placed centrally in a long stretch of hydrophobic residues, and have yielded a "propensity scale" for the relative efficiency with which different residues promote the formation of helical hairpins. In this study, we shift our attention to the role of charged residues flanking the hydrophobic stretch. Clusters of charged residues are known to hinder membrane translocation, and thus flanking charged residues may conceivably force a long hydrophobic segment to form a helical hairpin even if there are no or only weakly turn-promoting residues in the hydrophobic stretch. We indeed find that Lys and, more surprisingly, Asp residues strongly affect helical hairpin formation when placed next to a poly-Leu-based transmembrane segment. We also find that a cluster of four consecutive Lys residues can affect the efficiency of helical hairpin formation even when placed approximately 30 residues downstream of the hydrophobic stretch. These observations have interesting implications for the way we picture membrane protein topogenesis within the context of the endoplasmic reticulum (ER) translocon.

Aspartic Acid↗
PubMed2001

Adhesion of type 1-fimbriated Escherichia coli to abiotic surfaces leads to altered composition of outer membrane proteins.

Phenotypic differences between planktonic bacteria and those attached to abiotic surfaces exist, but the mechanisms involved in the adhesion response of bacteria are not well understood. By the use of two-dimensional (2D) polyacrylamide gel electrophoresis, we have demonstrated that attachment of Escherichia coli to abiotic surfaces leads to alteration in the composition of outer membrane proteins. A major decrease in the abundance of resolved proteins was observed during adhesion of type 1-fimbriated E. coli strains, which was at least partly caused by proteolysis. Moreover, a study of fimbriated and nonfimbriated mutants revealed that these changes were due mainly to type 1 fimbria-mediated surface contact and that only a few changes occurred in the outer membranes of nonfimbriated mutant strains. Protein synthesis and proteolytic degradation were involved to different extents in adhesion of fimbriated and nonfimbriated cells. While protein synthesis appeared to affect adhesion of only the nonfimbriated strain, proteolytic activity mostly seemed to contribute to adhesion of the fimbriated strain. Using matrix-assisted laser desorption ionization-time of flight mass spectrometry, six of the proteins resolved by 2D analysis were identified as BtuB, EF-Tu, OmpA, OmpX, Slp, and TolC. While the first two proteins were unaffected by adhesion, the levels of the last four were moderately to strongly reduced. Based on the present results, it may be suggested that physical interactions between type 1 fimbriae and the surface are part of a surface-sensing mechanism in which protein turnover may contribute to the observed change in composition of outer membrane proteins. This change alters the surface characteristics of the cell envelope and may thus influence adhesion.

Bacterial Adhesion↗
PubMed2000

Formation of cytoplasmic turns between two closely spaced transmembrane helices during membrane protein integration into the ER membrane.

The helical hairpin, two closely spaced transmembrane helices separated by a short turn, is a recurring structural element in integral membrane proteins, and may serve as a compact unit that inserts into the membrane en bloc. Previously, we have determined the propensities of the 20 natural amino acids, when present in the middle of a long hydrophobic stretch, to induce the formation of a helical hairpin with a lumenally exposed turn during membrane protein assembly into the endoplasmic reticulum membrane. Here, we present results from a similar set of measurements, but with the turn placed on the cytoplasmic side of the membrane. We find that a significantly higher number of turn-promoting residues need to be present to induce a cytoplasmic turn compared to a lumenal turn, and that, in contrast to the lumenal turn, the positively charged residues Arg and Lys are the strongest turn-promoters in cytoplasmic turns. These results suggest that the process of turn formation between transmembrane helices is different for lumenal and cytoplasmic turns.

Amino Acid Sequence↗
PubMed1999

A turn propensity scale for transmembrane helices.

Using a model protein with a 40 residue hydrophobic transmembrane segment, we have measured the ability of all the 20 naturally occurring amino acids to form a tight turn when placed in the middle of the hydrophobic segment. Turn propensities in a transmembrane helix are found to be markedly different from those of globular proteins, and in most cases correlate closely with the hydrophobicity of the residue. The turn propensity scale may be used to improve current methods for membrane protein topology prediction.

Amino Acid Substitution↗
PubMed1999

Surgical approach and prognostic factors after peptic ulcer perforation.

OBJECTIVE: To find out which prognostic factors were important in predicting postoperative mortality and length of hospital stay in patients with perforated peptic ulcers. DESIGN: Retrospective study. SETTING: Teaching hospital, Lund, Sweden. SUBJECTS: 246 patients with perforated peptic ulcer who presented between January 1974 and December 1992. INTERVENTION: Cox proportional hazards analysis. MAIN OUTCOME MEASURES: Influence of age, sex, coexisting disease, duration of symptoms, site of perforation and operative technique on mortality and length of hospital stay. RESULTS: Age over 75 years (p = 0.002), coexisting cardiac or pulmonary disease (p = 0.02), perforation of the cardia or body of the stomach (p = 0.02), lapse of more than 12 hours between start of symptoms and operation (p = 0.006) and type of operation (p < 0.0001) had a significant influence on hospital mortality. Age over 75 years (p < 0.0001) and lapse of more than 12 hours between start of symptoms and operation (p = 0.03) significant influenced the likelihood of a prolonged stay in hospital. CONCLUSION: Patients with perforated peptic ulcers should be operated on as soon as possible. Simple closure is simple and safe with relatively low mortality and short stay in hospital.

Duodenal Ulcer↗
PubMed1999

Effect of ionic strength on initial interactions of Escherichia coli with surfaces, studied on-line by a novel quartz crystal microbalance technique.

A novel quartz crystal microbalance (QCM) technique was used to study the adhesion of nonfimbriated and fimbriated Escherichia coli mutant strains to hydrophilic and hydrophobic surfaces at different ionic strengths. This technique enabled us to measure both frequency shifts (Deltaf), i.e., the increase in mass on the surface, and dissipation shifts (DeltaD), i.e., the viscoelastic energy losses on the surface. Changes in the parameters measured by the extended QCM technique reflect the dynamic character of the adhesion process. We were able to show clear differences in the viscoelastic behavior of fimbriated and nonfimbriated cells attached to surfaces. The interactions between bacterial cells and quartz crystal surfaces at various ionic strengths followed different trends, depending on the cell surface structures in direct contact with the surface. While Deltaf and DeltaD per attached cell increased for nonfimbriated cells with increasing ionic strengths (particularly on hydrophobic surfaces), the adhesion of the fimbriated strain caused only low-level frequency and dissipation shifts on both kinds of surfaces at all ionic strengths tested. We propose that nonfimbriated cells may get better contact with increasing ionic strengths due to an increased area of contact between the cell and the surface, whereas fimbriated cells seem to have a flexible contact with the surface at all ionic strengths tested. The area of contact between fimbriated cells and the surface does not increase with increasing ionic strengths, but on hydrophobic surfaces each contact point seems to contribute relatively more to the total energy loss. Independent of ionic strength, attached cells undergo time-dependent interactions with the surface leading to increased contact area and viscoelastic losses per cell, which may be due to the establishment of a more intimate contact between the cell and the surface. Hence, the extended QCM technique provides new qualitative information about the direct contact of bacterial cells to surfaces and the adhesion mechanisms involved.

Bacterial Adhesion↗
PubMed1998

In Situ Detection of High Levels of Horizontal Plasmid Transfer in Marine Bacterial Communities.

Gene transfer of the conjugative plasmid pBF1 from Pseudomonas putida to indigenous bacteria in seawater was investigated with a detection system for gene transfer based on the green fluorescent protein (GFP) (C. Dahlberg et al., Mol. Biol. Evol. 15:385-390, 1998). pBF1 was tagged with the gfp gene controlled by a lac promoter which is down regulated in the donor cell by a chromosomal repressor (lacIq). The plasmid donor cells (Pseudomonas putida KT2442) subsequently do not express gfp. Transfer to recipient strains lacking the repressor results in expression of gfp. The transconjugant can subsequently be detected by epifluorescence microscopy on a single-cell level. By using this method, transfer of pBF1::gfp and expression of the gfp gene were first shown to occur during nutrient-limiting conditions to several defined recipient bacteria in artificial seawater. Second, we measured transfer of pBF1 from P. putida to the marine bacterial community directly in seawater samples, on a single-cell level, without limiting the detection of gene transfer to the culturable fraction of bacteria. Plasmid transfer was detected on surfaces and in bulk seawater. Seawater bacteria with different morphologies were shown to receive the plasmid. Gene transfer frequencies of 2.3 x 10(-6) to 2.2 x 10(-4) transconjugants per recipient were recorded after 3 days of incubation.

Journal Article↗
PubMed1998

A FISH cosmid 'cocktail' for detection of 13q deletions in chronic lymphocytic leukaemia--comparison with cytogenetics and Southern hybridization.

The most frequent structural chromosome abnormality in chronic lymphocytic leukaemia (CLL) is deletion at chromosome 13q14. Studies with Southern blot hybridisation have revealed deletions in the region located telomeric of the retinoblastoma gene in more than 40% of cases. The highest frequency of homozygous deletions has been found at the D13S319 locus and it is likely that a new tumour suppressor gene is located close to this region. We have analysed deletions in the D13S319 region in 20 selected CLL patients using conventional cytogenetic analysis, fluorescence in situ hybridisation (FISH) and Southern blot hybridisation. FISH and Southern hybridisation are equally efficient in detecting deleted clones in our study. However, FISH analysis indicate that subclones with different numbers of alleles in the D13S319 region can exist simultaneously. The cytogenetic analyses confirm that clones with different chromosomal abnormalities can occur in patients with CLL and that 13q14 deletions can be limited to one of these subclones. Furthermore, the FISH analyses show that trisomy 12 and deletion of 13q14 can occur in the same cell clone. Finally, our study confirms that mitogen stimulation of peripheral blood cells from CLL patients before FISH analysis may result in a sharp increase in normal appearing cells, which can hide leukaemic clones with deletions in the D13S319 region.

Blotting, Southern↗
PubMed1998

Growth hormone treatment prevents the decrease in insulin-like growth factor I gene expression in patients undergoing abdominal surgery.

Acquired GH resistance together with reduced skeletal muscle mass are found in patients with increased protein catabolism due, for example, to sepsis, trauma, or major surgery. Both administration of glutamine-containing parenteral nutrition and GH treatment have been found to diminish this catabolism. The effects of GH are mediated in part by insulin-like growth factor I (IGF-I) that is produced in the liver and locally in GH target tissues. The aim of this study was to investigate the effect of GH treatment on expression of the IGF-I gene and GH receptor (GHR) gene in skeletal muscle after major surgery. A new quantitative RT-PCR-based assay was established to measure IGF-I gene expression. Metabolically healthy patients, without significant preoperative weight loss, who were undergoing elective abdominal surgery were included in the study. Five patients (one woman and four men) were treated with daily injections of GH (0.3 IU/kg.day) in addition to being given total parenteral nutrition including glutamine (0.28 g/kg.day). The control group consisted of eight patients (three women and five men), who were given glutamine-enriched total parenteral nutrition but no GH. A muscle biopsy was taken from the lateral portion of the quadriceps femoris muscle preoperatively (day 0) after induction of anesthesia. A second biopsy was taken under local anesthesia on postoperative day 3. Total ribonucleic acid (RNA) was extracted from the muscle biopsies, and IGF-I messenger RNA (mRNA) and GHR mRNA were measured by competitive quantitative RT-PCR assays. IGF-I mRNA and GHR mRNA levels were related to the expression of a housekeeping gene (cyclophilin). In the control group, IGF-I mRNA levels decreased from 1505 +/- 265 (mean +/- SEM) transcripts/cpm cyclophilin on day 0 to 828 +/- 172 on day 3 (P < 0.05). In contrast, IGF-I mRNA levels did not change in the GH-treated group (1188 +/- 400 transcripts/cpm cyclophilin on day 0 vs. 1089 +/- 342 transcripts/cpm cyclophilin on day 3). No statistically significant changes were seen in GHR expression. We conclude that administration of GH prevents the reduction in IGF-I gene expression in skeletal muscle after abdominal surgery.

Abdomen↗
PubMed1997

Determination of bacterial cell surface hydrophobicity of single cells in cultures and in wastewater in situ.

Bacterial cell surface hydrophobicity is one of the most important factors that influence bacterial adhesion. A new method microsphere adhesion to cells, for measuring bacterial cell surface hydrophobicity was developed. Microsphere adhesion to cells is based on microscopic enumeration of hydrophobic, fluorescent microspheres attaching to the bacterial surface. Cell surface hydrophobicity estimated by microsphere adhesion to cells correlates well with adhesion of bacteria to hydrocarbons or hydrophobic interaction chromatography for a set of hydrophilic and hydrophobic bacteria (linear correlation coefficients, R2, were 0.845 and 0.981 respectively). We also used microsphere adhesion to cells to investigate the in situ properties of individual free-living bacteria directly in activated sludge. Results showed that the majority of the bacteria were hydrophilic, indicating the importance of cell surface hydrophobicity for bacterial adhesion in sludge, and for the overall success of the wastewater treatment process.

Bacterial Adhesion↗
PubMed1997

Conjugative plasmids isolated from bacteria in marine environments show various degrees of homology to each other and are not closely related to well-characterized plasmids.

Mercury resistance plasmids were exogenously isolated, i.e., recovered after transfer to a model recipient bacterium, from marine air-water interface, bulk water, and biofilm communities during incubation in artificial seawater without added nutrients. Ninety-five plasmids from different environments were classified by restriction endonuclease digestion, and 12 different structural plasmid groups were revealed. The plasmid types isolated from different habitats and from different sampling occasions showed little similarity to each other based on their restriction endonuclease patterns, indicating high variation and possibly a low transfer between microhabitats and/or a different composition of the microbial communities at different sites and times. With another approach in which probes derived from one of the isolated plasmids and a mercury resistance (mer) probe from Tn501 were used, similarities between plasmids from several different groups were found. The plasmids were further tested for their incompatibility by use of the collection of inc/rep probes (B/O, com9, FI, FII, HI1, HI2, I1, L/M, N, P, Q, U, W, Y) described by Couturier et al. (M. F. Couturier, P. Bex, L. Bergquist, and W. K. Maas, Microbiol. Rev. 52:375-395, 1988). Hybridizations did not reveal any identity between the 12 plasmid groups and any of the inc/rep probes tested. The results indicate that plasmids isolated from different marine habitats have replication and/or incompatibility systems that are different from the well-characterized plasmids that are commonly used in plasmid biology. This shows the need for the use of more relevant plasmids in studies of plasmid activity in the environment and development of new inc/rep probes for their characterization.

Bacteria↗
PubMed1997

Measurement of human growth hormone receptor messenger ribonucleic acid by a quantitative polymerase chain reaction-based assay: demonstration of reduced expression after elective surgery.

Studies of GH receptor (GHR) gene expression in human tissues have been hampered by the limited amount of tissue available for analysis and the low sensitivity of conventional methods. We have developed a quantitative reverse transcriptase-PCR assay for measurement of GHR messenger ribonucleic acid levels in small human tissue biopsies. To compensate for sample to sample variation, an internal RNA standard, which differs from the wild-type GHR transcript by only a few nucleotides, was reverse transcribed and amplified together with the GHR transcripts. PCR was carried out using one biotinylated primer to permit the purification of single stranded PCR products on streptavidin-coated microtiter plates. The ratio between the wild-type and mutated transcripts was determined by two separate minisequence reactions in which a primer, annealed immediately 3' of a variable nucleotide, was extended by a single 3H-labeled nucleotide, complementary to either the wild-type or mutated sequence. The assay range was 0.125-8 x 10(5) transcripts/sample, the mean intraassay coefficient of variation was 8.7%, and the lower limit of detection was 0.125 x 10(5) transcripts/sample. GHR messenger ribonucleic acid levels were detectable in small amounts (10-100 ng) of total RNA extracted from adipose tissue, skeletal muscle, and liver. The GHR gene expression in liver was approximately 10-fold higher than that in skeletal muscle, whereas intermediate levels were found in adipose tissue. In nine patients undergoing elective abdominal surgery, GHR gene expression in skeletal muscle was reduced on day 3 after surgery compared to the baseline level. The decrease in GHR gene expression was accompanied by a decrease in skeletal muscle glutamine. This suggests that the postoperative protein catabolism may be caused at least partly by acquired GH insensitivity due to reduced expression of the GHR gene.

Abdomen↗
PubMed1997

Peptic ulcer perforation before and after the introduction of H2-receptor blockers and proton pump inhibitors.

BACKGROUND: The aim of this retrospective study was to compare patients treated for perforated peptic ulcer before and after the introduction of the H2-receptor antagonists and proton pump inhibitors (PPI) with regard to their medical history, clinical features, methods of diagnosis and treatment, complications, and mortality. METHODS AND RESULTS: During the study period 1974 to 1992 we found a significant reduction in the incidence of peptic ulcer perforation (P < 0.001). Patients admitted during the later period of the study were older and more seriously ill. The incidence of perforation among men decreased, but that among women was stable, thus changing the sex ratio towards a female preponderance at the end of the study period. After the introduction of PPI the relative number of gastric perforations decreased compared with the number of perforations in the duodenum. A relatively higher proportion of patients with gastric perforations was taking acetylsalicylic acid or non-steroid, anti-inflammatory drugs at the time of admission compared with patients with duodenal perforation. Simple suture of the perforation was the operative procedure used in 80% of the patients. CONCLUSIONS: Even though patients were increasingly older and more ill, neither the mortality nor the rate of postoperative complications changed during the study period.

Age Factors↗
PubMed1995

Abundance of Tn3, Tn21, and Tn501 transposase (tnpA) sequences in bacterial community DNA from marine environments.

The occurrence of the tnpA genes of the transposons Tn3, Tn21, and Tn501 was assessed in total bacterial community DNA isolated from different marine environments. The PCR technique was employed, together with most probable number statistics, to determine the abundance of the target tnpA genes. All three genes could be detected, and the Tn21 tnpA sequences predominated in all samples. The smallest amount of total community DNA in which the Tn21 tnpA sequence could be detected was 0.037 ng, and on the basis of our results, we estimated that this sequence was present in 1 of 1,000 to 10,000 bacteria. Hybridization of the PCR products with the respective tnpA probes verified the Tn21 and Tn501 tnpA sequences but only some of the Tn3 tnpA amplification products. The distribution and dissemination of transposons in natural bacterial communities are discussed.

Bacteria↗