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PubMed2001

Microbial community analysis in the denitrification process of saline-wastewater by denaturing gradient gel electrophoresis of PCR-amplified 16S rDNA and the cultivation method.

The metallurgic wastewater generated from the processes of recovering precious metals from industrial wastes contains high concentrations of nitrogen compounds and salts. Biological nitrogen removal from this wastewater was attempted using a circulating bioreactor system equipped with an anaerobic packed bed or an anaerobic fluidized bed. The denitrification capability of the system with the anaerobic packed bed was more stable than that of the system with the anaerobic fluidized bed. The NOx removal rate of the anaerobic packed bed was as high as 97%. Microbial community analysis by denaturing gradient gel electrophoresis (DGGE) of PCR-amplified 16S ribosomal DNA (rDNA) fragments and the cultivation method revealed that the community diversity varied in accordance with wastewater composition such as the level of salinity and so on. Phylogenetic analysis suggested that the taxonomic affiliation of the dominant species in the anaerobic reactors was to the gamma-Proteobacteria including Halomonadaceae species. The PCR-DGGE method as a non-cultivation method was found to be a powerful tool for analysis of the microbial community, because the cultivation method could detect only a fraction of the microbial species present in these systems. The genetic diversity of the isolated bacteria belonging to the gamma-Proteobacteria which reduced both nitrate and nitrite in the anaerobic packed bed was higher than that of the bacteria in the anaerobic fluidized bed. This suggested that a genetically diverse microbial community stabilized the denitrifying performance in the anaerobic packed bed.

Journal Article↗
PubMed2004

Diversity and vertical distribution of magnetotactic bacteria along chemical gradients in freshwater microcosms.

The vertical distribution of magnetotactic bacteria along various physico-chemical gradients in freshwater microcosms was analyzed by a combined approach of viable cell counts, 16S rRNA gene analysis, microsensor profiling and biogeochemical methods. The occurrence of magnetotactic bacteria was restricted to a narrow sediment layer overlapping or closely below the maximum oxygen and nitrate penetration depth. Different species showed different preferences within vertical gradients, but the largest proportion (63-98%) of magnetotactic bacteria was detected within the suboxic zone. In one microcosm the community of magnetotactic bacteria was dominated by one species of a coccoid "Alphaproteobacterium", as detected by denaturing gradient gel electrophoresis in sediment horizons from 1 to 10 mm depth. Maximum numbers of magnetotactic bacteria were up to 1.5 x 10(7) cells/cm3, which corresponded to 1% of the total cell number in the upper sediment layer. The occurrence of magnetotactic bacteria coincided with the availability of significant amounts (6-60 microM) of soluble Fe(II), and in one sample with hydrogen sulfide (up to 40 microM). Although various trends were clearly observed, a strict correlation between the distribution of magnetotactic bacteria and individual geochemical parameters was absent. This is discussed in terms of metabolic adaptation of various strains of magnetotactic bacteria to stratified sediments and diversity of the magnetotactic bacterial communities.

Bacteria↗
PubMed2006

Improving rescreening in community clinics: does a system approach work?

Community clinics provide inadequate breast cancer screening services to low-income, racially- and ethnically-diverse communities. This study develops and evaluates the effectiveness of multifaceted organizational system interventions--operational assessments, tracking systems, reminder calls, tailored education, physician prompts and a tailored counseling call--on mammography rescreening rates within three community clinics. We used the Chronic Care Model and Put Prevention Into Practice framework to redesign breast screening delivery services within the California Cancer Detection Programs: Every Woman Counts (CDP:EWC), community clinic settings. We used a quasi-experimental design with a random selection of 400 patients at pre-intervention. To establish a post-intervention clinic's rescreening rate a new comparable cross-sectional random sample of 347 women was drawn. Measures A chart abstraction instrument was used to establish clinics' rescreening rates. Subjects participants at pre and post-intervention were low-income women 50 years of age and older who had received normal mammography results and had not been diagnosed with breast cancer in the last five years. General linear mixed model analysis revealed significant improvements for the organizational system redesign condition [pre-intervention rescreening rate: 32.1 percent v. post-intervention rescreening rate 50.2 percent, (p < .001)]. For the organizational system redesign plus tailored counseling call condition, there was maintenance in the rescreening rate following the intervention [pre-intervention: 44.4 percent v. post-intervention: 45.1 percent, (p > 0.05)]. Multilevel interventions directed at redesigning community clinics primary care breast cancer screening services, can improve mammography rescreening rates.

Aged↗
PubMed1988

Diagnostic yield of the autopsy in a university hospital and a community hospital.

To determine the extent to which autopsies yield unexpected findings that are relevant to the patient's death and whether cases with a high yield of such findings can be identified selectively, we studied a total of 233 autopsies at a university hospital and at a community hospital. The rates at which autopsies detected major unexpected findings whose premortem diagnosis would probably have improved survival were 11 percent at the university hospital and 12 percent at the community hospital. Major unexpected findings whose premortem diagnosis would not have prolonged survival were found in another 12 and 21 percent of cases, respectively. Pulmonary embolism and fungal infections in immuno-compromised hosts were the most common major unexpected findings. Neither we nor the patients' physicians were able to identify from the clinical data the autopsies likely to have high yields. Furthermore, the physicians' estimates of an autopsy's expected yield were similar for patients evaluated by autopsy and for matched patients who were not. We conclude that the autopsy continues to yield clinically relevant findings at a high level and that it is not currently possible to predict which cases will have high yields. Autopsies are vital to ensure the quality of medical care, and autopsy rates must be increased substantially if this role is to be fully realized.

Adolescent↗
PubMed2004

Risk factors for developing epilepsy after neonatal seizures.

The objective of this study was to determine clinical and polysomnographic risk factors that might be early predictors for the development of postnatal epilepsy in a cohort of infants with seizures. The study sample included 158 infants who presented two or more clinically proven seizures. Gestational, perinatal, and polysomnographic data were obtained retrospectively. A questionnaire designed to detect patients with epilepsy in the community was prospectively given to all families, and the positive cases were reassessed for confirmation of epilepsy. Epilepsy rate after neonatal seizures was 22% within 12 months of follow-up and 33.8% within 48 months. Transient electrolytic imbalance and perinatal asphyxia were the most frequent etiologic factors associated with neonatal seizures. More than one seizure type was detected in 17.3% (n = 22) of cases and strongly associated with central nervous system infection (relative risk [RR] = 3.02, 95% confidence interval [CI] = 1.24-7.40, P = 0.02). Focal symptomatic epilepsy (P = 0.01) and syndromes not determined as focal or generalized (P = 0.04) were also associated with central nervous system infection. Abnormal polysomnographic recordings (P = 0.09) and abnormal neurologic examination on discharge (P < 0.01) were correlated with postnatal epilepsy. No differences were observed between premature and term infants concerning outcome. Neonatal seizures were associated with a high incidence of postnatal epilepsy in the cohort, including epileptic syndromes with catastrophic evolution. Abnormal neurologic examination on discharge was a good predictor of an unfavorable outcome and abnormal polysomnographic recording a moderate predictor.

Asphyxia Neonatorum↗
PubMed2006

Dithiocarbamate fungicide thiram detection: comparison of bioluminescent and fluorescent whole-cell bioassays based on hsp22 stress promoter induction.

Detection of toxic substances interfering with endocrine system is one of the major preoccupations of the European community. A whole-cell bioassay for pollution detection based on stress induction has been designed. Well characterized toxicants, cadmium chloride and thiram (a dithiocarbamate fungicide), were used to optimize the detection conditions such as time-course conditions, cell line and reporter gene to be used. HeLa cells containing the firefly luciferase (luc) reporter gene under the control of the Drosophila melanogaster hsp22 promoter were compared to liver cells (HepG2) containing the same stress gene promoter fused either to the luc or the EGFP (Enhanced-Green Fluorescent Protein) gene. The sensitivity of the obtained bioassay was found to be enhanced by the concomitant use of liver cells and EGFP reporter gene. The detection limits of the toxicants were then lowered from 1 to 0.1 microM and from 1 to 0.01 microM for CdCl(2) and thiram, respectively.

Biological Assay↗
PubMed1999

Disease and disease control. International Leprosy Congress, Beijing, 7-12 September 1998. Workshop report.

Four workshops were conducted during the congress under the disease control theme. The workshops were on the issues of defining disease and antibacterial therapy, early case detection, sustaining leprosy control in low endemic situations, and the prevention of disability. These workshops spanned the spectrum of disease and its consequences through from early detection, the definition of disease to the prevention of disability. All of these topics being important contemporary issues challenging leprosy control programmes world wide. Despite the broad spectrum of the topics it was interesting to see that a number of important themes emerged which were common to all topics. It is possible to identify five major themes arising from the output of the workshops which are now described below. Each of the workshops adopted broad and comprehensive approaches to their topic. In the past, there has been narrowness in defining disease in terms of the need for chemotherapy. The approach taken in the workshop now is for a much more comprehensive approach looking at all the consequences of the disease process rather than the requirement for antibacterial chemotherapy. Similarly broad approaches were taken to low endemic situations, considering comprehensive approaches which are inclusive rather than exclusive. Disability prevention also continues this same theme of comprehensive approaches based on multidisciplinary involvement in prevention of the consequences of the disease process. The second major theme to be identified in the output of the workshops was the importance of relevance to patients and people affected by leprosy. It is no longer adequate to view programmes in terms of their acceptance to those running the programmes. Control programmes must be acceptable to the people they are designed to benefit. This even impacts on definitions of disease in terms of what matters to patients rather than only restricting this to disease pathology. Similarly, approaches to disability prevention are not merely about measurement of impairments due to nerve function deficit but rather consider the abilities and functions which are most important to the individuals affected. The third theme which spans all of the workshops is the need to develop partnerships with others in addressing the challenges of leprosy today. Each workshop identified important groups with which partnerships need to be developed included local patient groups, voluntary associations and primary health care services. All of these have a role to play, from early case detection right through to the prevention of disability and the sustaining of control under low endemic situations. The fourth important theme is sustainability of programmes which need to be developed for the long term benefit of those affected by disease rather than short term goals. Again, this impacts an area such as case detection methods which need to be sustained in the long term. Approaches such as intensive case detection through mass survey are not sustainable given changes to the patterns of disease, whereas involvement of communities and community participation in the process of early case detection is a much more sustainable approach. This is important, as programmes attain low endemic status and is also important in preventing disabilities where the progressive nature of secondary impairments following primary impairments may be lifelong. The final theme is that of the importance of training, as each area is recommending new approaches to be taken and for new people to be involved in leprosy programmes. The implications are that those to be involved need to be trained and that the training requirements will be different from those of the last ten years. Training programmes will need to adapt to a wider range of individuals and groups being involved in programmes and to much more comprehensive approaches. These implications for training are profound and training centres and training programmes rapidly

China↗
PubMed2006

Automated surveillance for adverse drug events at a community hospital and an academic medical center.

OBJECTIVES: To compare the rates and nature of ADEs at an academic medical center and a community hospital using a single computerized ADE surveillance system. DESIGN: Prospective cohort study of patients admitted to two tertiary care hospitals. Outcome Measure Adverse drug events identified by automated surveillance and voluntary reporting. METHODS: We implemented an automated surveillance system across an academic medical center and a community hospital. Potential events identified by the computer were reviewed in detail by medication safety pharmacists and scored for causality and severity. Findings were compared between the two hospitals, and with voluntary reports from nurses and pharmacists. RESULTS: Over the 8 month study period, 25,177 patients were admitted to the university hospital and 8,029 to the community hospital. There were 1,116 ADEs in 900 patients at the university hospital for an overall rate of 4.4 ADEs per 100 admissions. At the community hospital, 399 patients experienced 501 ADEs for a rate of 6.2 events per 100 admissions. Rates of antibiotic-associated colitis, drug-induced hypoglycemia, and anticoagulation-related ADEs were significantly higher at the community hospital compared with the university hospital. Computerized surveillance detected ADEs at a rate 3.6 times that of voluntary reporting at the university hospital and 12.3 times that at the community hospital. CONCLUSIONS: Operation of a common automated ADE surveillance system across hospitals permits meaningful comparison of ADE rates in different inpatient settings. Automated surveillance detects ADEs at rates far higher than voluntary reporting, and the difference may be greater in the community hospital setting. Community hospitals may experience higher rates of certain types of ADEs compared with academic medical centers.

Academic Medical Centers↗
PubMed2004

Measuring community preferences for public mental health services: pilot test of a mail survey method.

This study tested the feasibility of a simple mail survey approach to measuring community preferences for mental health services. A 38 item survey detected statistically significant differences in preferences for four central goals, finding that community members most value Focus on the Severely Mentally Ill, followed by Community Safety and Environment, Service Quality and Original Community Mental Health Goals. Some procedural problems were encountered that reduced the response rates, however, the study yielded information that suggests improved procedures for future surveys. Simple mail surveys appear to offer a potentially affordable, efficient way to assess community service priorities.

Adult↗
PubMed2002

1998-1999 rotavirus seasons in Juiz de Fora, Minas Gerais, Brazil: detection of an unusual G3P[4] epidemic strain.

An epidemiologic survey on the rotavirus strains causing gastroenteritis in young children was conducted in Juiz de Fora, Minas Gerais, in Southern Brazil during two consecutive seasons. Rotavirus was detected in 94 of the 1,056 fecal specimens collected from January 1998 to December 1999. Among the 13 discernible long electrophoretic profiles found, one was highly prevalent (73.4%) and represented the rotavirus strain responsible for the May-August winter epidemic outbreak of 1998, as clearly shown in a three-dimensional graph. This epidemic strain, designated JF98, was characterized as subgroup II and genotype G3P[4] by the original reverse transcription-PCR typing assays. Besides the unusual combination of G and P types, this G3 strain lacked reactivity with anti-G3-specific monoclonal antibodies and presented an uncommon pattern upon digestion of its cDNA-copied VP7 gene with the BstYI restriction enzyme. Strain JF98 affected primarily 6- to 24-month-old children and accounted for 85.5% of the severe rotavirus-associated dehydrating diarrhea cases that required hospitalization. As in our previous studies in neighboring Rio de Janeiro and São Paulo, a remarkably large proportion (44%) of mixed infections was detected, generating a complex set of circulating strains in the community, represented by the many distinct electropherotypes. Other common human types were detected as minor strains in single or in mixed infections, including the JF98 strain. Those were types G1, G4, G8, G9, P[8], and P[6], but not G2 or G5. One specimen contained a mixture of group A and C rotaviruses.

Brazil↗
PubMed2003

Gastric acid-suppressive therapy and community-acquired respiratory infections.

BACKGROUND: Bacteria and viruses have been detected in the stomach of patients during acid-suppressive therapy. AIM: To investigate whether subjects using acid-suppressive drugs more often develop community-acquired respiratory infections when compared to those who do not use acid-suppressive drugs. METHODS: 700 study subjects were recruited during a single week in December 2002. Information on the prevalence of clinical manifestations of infections and complications in the preceding month was assessed by questionnaire. Furthermore, subjects were asked to report antibiotic therapy and physician visits related to possible infection. RESULTS: Questionnaires were returned by 405 subjects (58%). Consumption of acid-suppressive drugs was reported by 91 individuals, of whom 79 used proton-pump inhibitors (20%) and 12 H2-receptor antagonists (3%). Overall, 101 (25%) responders reported clinical manifestations of respiratory infection in the preceding month. Subjects using acid-suppressive drugs were 2.34 times [95% confidence interval (CI) 1.4-4.1] more likely to have clinical manifestations of infection than individuals not using acid-suppressive drugs. Subjects using acid-suppressive drugs visited a physician 3.72 times more often (95% CI 2.1-6.8) for an infection and received antibiotic therapy 4.19 times more often (95% CI 2.2-8.1) in comparison to individuals not using acid-suppressive drugs. CONCLUSIONS: Subjects using acid-suppressive drugs more often reported community-acquired respiratory infections in comparison to those who did not use acid-suppressive drugs.

Adult↗
PubMed2006

Evaluation of community-based serologic screening for identification of chronic Salmonella typhi carriers in Vietnam.

OBJECTIVES: To determine the utility of screening anti-Vi antibodies to detect chronic Salmonella Typhi carriers in an endemic community. METHODS: We conducted a community-based serologic survey for anti-Vi antibodies to identify chronic Salmonella Typhi carriers in a typhoid endemic region in Vietnam. RESULTS: We tested sera from 3209 (67.2%) of 4772 eligible adults. The median age was 37 years (range 20-92), 57.3% were female, 4.6% reported a history of typhoid fever and 0.3% reported typhoid vaccination. Anti-Vi antibody titers tested in Vietnam were < 1:40 in 2759 (86.0%), 1:40 in 194 (6.0%), 1:80 in 168 (5.2%), 1:160 in 57 (1.8%), and > or = 1:320 in 31 (1.0%). On re-testing in the USA, an additional 19 sera with titers > or = 1:160 were identified. We collected 589 rectal swabs from 103 (96.3%) of 107 persons with Vi antibody titers > or = 1:160 and 183 swabs from 33 persons with antibody titers < 1:80. No Salmonella Typhi was isolated. CONCLUSIONS: Community-based serologic screening is a feasible, but impractical method for identifying chronic Salmonella Typhi carriers. Background levels of anti-Vi antibody titers in this endemic area may be high despite a low prevalence of chronic carriers.

Adult↗
PubMed2006

Population-based detection of systolic and diastolic dysfunction with amino-terminal pro-B-type natriuretic peptide.

BACKGROUND: There is limited information regarding the clinical utility of amino-terminal pro-B-type natriuretic peptide (NT-proBNP) for the detection of left ventricular (LV) dysfunction in the community. We evaluated predictors of circulating NT-proBNP levels and determined the utility of NT-proBNP to detect systolic and diastolic LV dysfunction in older adults. METHODS: A population-based sample of 1229 older adults (mean age 69.4 years, 50.1% women) underwent echocardiographic assessment of cardiac structure and function and measurement of circulating NT-proBNP levels. RESULTS: Predictors of NT-proBNP included age, female sex, body mass index, and cardiorenal parameters (diastolic dysfunction [DD] severity; LV mass and left atrial volume; right ventricular overload; decreasing ejection fraction [EF] and creatinine clearance). The performance of NT-proBNP to detect any degree of LV dysfunction, including mild DD, was poor (area under the curve 0.56-0.66). In contrast, the performance of NT-proBNP for the detection of EF < or = 40% and moderate-severe DD was strong with area under the curve of > 0.90 regardless of age and sex; history of hypertension, diabetes, coronary artery disease; or body mass category. The ability of NT-proBNP to detect EF < or = 40% and/or moderate-severe DD was optimized by using age/sex-specific limits. Of "false-positive" tests, 88% (124/141) were explained after considering cardiorenal determinants of NT-proBNP levels. CONCLUSIONS: Amino-terminal pro-B-type natriuretic peptide is a suboptimal marker of mild LV dysfunction, but performs strongly as a marker of EF < or = 40% and/or moderate-severe DD in the community. Most subjects with a positive NT-proBNP test, using age/sex-specific cutoffs, had prognostically significant abnormalities of cardiac structure or function.

Aged↗
PubMed1993

Analysis of pathogens isolated from urinary tract infections in Barbados.

The isolation of pathogens from urine specimens was surveyed during a six-month period when 1611 urine specimens were examined in the Public Health Laboratory, and 8769 were examined in the Microbiology Laboratory of the Queen Elizabeth Hospital. Significant growth (defined as > 10(4) organisms/ml urine) was detected in 393 (24.4%) of the urines cultured in the Public Health Laboratory and in 1218 (13.9%) of urines cultured in the Queen Elizabeth Hospital. The overall isolation rate was 15.5%; Gram-negative bacilli comprised 72.8% of the isolates, Gram-positive cocci 24.3% and yeasts 2.9%. Gram-negative bacilli were more commonly isolated from hospital patients, whereas Gram-positive cocci were relatively more common in community patients. The most common pathogens detected were coliforms (1233 isolates), streptococci (197) and coagulase-negative staphylococci (182); 50% of all isolates were sensitive to amoxycillin, 68% to cephradine, 61% to co-trimoxazole, 62% to nalidixic acid and 79% to nitrofurantoin. Anti-bacterial activity was detected in 130 (8%) of the urine specimens received in the Public Health Laboratory.

Anti-Bacterial Agents↗
PubMed2002

Psychological well-being in patients on 'adequate' doses of l-thyroxine: results of a large, controlled community-based questionnaire study.

OBJECTIVE: Over 1% of the UK population is receiving thyroid hormone replacement with l-thyroxine (T4). However, many patients complain of persistent lethargy and related symptoms on T4 even with normal TSH levels. To date there has been no large study to determine whether this is related to thyroxine replacement or coincidental psychological morbidity. We have therefore attempted to address this issue using a large, community-based study. DESIGN AND PATIENTS: Computerized prescribing records of five general practices were used to identify 961 patients who had been on thyroxine for a minimum of 4 months from a population of 63 000 (1.5%), along with age- and sex-matched controls. All 1922 individuals were sent a two-page questionnaire, made up of the short form of the General Health Questionnaire (GHQ-12), designed to detect minor psychiatric disorders in the community, and a 12-question 'thyroid symptom questionnaire' (TSQ) in the same format. A covering letter explained that we were interested in 'how patients felt on medication' and made no direct reference to thyroxine. MEASUREMENTS: Scores from the GHQ and TSQ were marked for each individual using the GHQ and Likert scoring methods. Patients' latest TSH measurements were obtained from laboratory records. Comparisons were then made on scores for the total GHQ-12, TSQ and individual questions between patients (P) and control (C) groups. Separate analyses were made comparing the patients with a normal TSH (nP) and the control group. RESULTS: Five hundred and ninety-seven (62%) of the patients (P) and 551 (57%) of the controls (C) responded and fully completed at least one of the two questionnaire. Three hundred and ninety-seven responding patients (nP) had a TSH estimation performed in the previous 12 months with the last result being in the local laboratory normal range for TSH (0.1-5.5 or 0.2-6.0 mU/l, according to the assay method used). The responding P, nP and C populations were well matched for age (59.96, 59.73, 59.35 years) and sex (85%, 83%, 87% female). The number of individuals scoring 3 or more on the GHQ-12 (indicating 'caseness') was 21% higher in P than C [185/572 (32.3%) vs. 137/535 (25.6%), P = 0.014] and 26% higher in nP than C [131/381 (34.4%) vs. 137/535 (25.6%), P < 0.005]. Stronger differences were seen with the TSQ scores [C = 187/535 (35.0%), P = 273/583 (46.8%), P < 0.001, P vs. C; and nP = 189/381 (48.6%), P < 0.001, nP vs. C]. Differences existed in chronic drug use and chronic disease prevalence between the control and patient groups, but the differences in GHQ and TSQ scores between the groups remained significant even after correction for these factors as well as age and sex in multiple regression analysis. CONCLUSIONS: This community-based study is the first evidence to indicate that patients on thyroxine replacement even with a normal TSH display significant impairment in psychological well-being compared to controls of similar age and sex. In view of the large numbers of people on thyroxine replacement, we believe that these differences, although not large, could contribute to significant psychological morbidity in a substantial number of individuals.

Adolescent↗
PubMed1988

Access to primary health care in urban Iceland.

The accessibility by telephone of primary health care was studied in Reykjavik and its surrounding municipalities. Comparison was also made between community run health centres and private practices. About 60% of the total population of Iceland live within the study area. The study used medical secretaries as patient substitutes. During the prescribed telephone time, all "patients" were able to make telephone contact with their practice facilities, and 80% reached their doctor within 10 min. The waiting time for non-acute appointments was never more than three days. The study did not detect any difference in accessibility between community run health centres and privately owned GP practices.

Appointments and Schedules↗
PubMed2004

Development and evaluation of microarray-based whole-genome hybridization for detection of microorganisms within the context of environmental applications.

The detection and identification of microorganisms in natural communities is a great challenge to biologists. Microarray-based genomic technology provides a promising high-throughput alternative to traditional microbial characterization. A novel prototype microarray containing whole genomic DNA, termed community genome array (CGA), was constructed and evaluated. Microarray hybridizations at 55 degrees C using 50% formamide permitted the examined bacteria to be distinguished at the species level, while strain-level differentiation was obtained at hybridization temperatures of 65 or 75 degrees C. The detection limit was estimated to be approximately 0.2 ng with genomic DNA from a single pure culture using a reduced hybridization volume (3 microL). Using mixtures of known amounts of DNA or a known number of cells from 14 or 16 different species, respectively, about 5 ng of genomic DNA or 2.5 x 10(5) cells were detected under the hybridization conditions used. In addition, strong linear relationships were observed between hybridization signal intensity and target DNA concentrations for pure cultures, a mixture of DNA templates, and a population of mixed cells (r2 = 0.95-0.98, P < 0.01). Finally, the prototype CGA revealed differences in microbial community composition in soil, river, and marine sediments. The results suggest that CGA hybridization has potential as a specific, sensitive, and quantitative tool for detection and identification of microorganisms in environmental samples.

Bacteria↗
PubMed1998

Application of molecular biological techniques to a seasonal study of ammonia oxidation in a eutrophic freshwater lake

The autotrophic ammonia-oxidizing bacteria in a eutrophic freshwater lake were studied over a 12-month period. Numbers of ammonia oxidisers in the lakewater were small throughout the year, and tangential-flow concentration was required to obtain meaningful estimates of most probable numbers. Sediments from littoral and profundal sites supported comparatively large populations of these bacteria, and the nitrification potential was high, particularly in summer samples from the littoral sediment surface. In enrichment cultures, lakewater samples nitrified at low (0.67 mM) ammonium concentrations only whereas sediment samples exhibited nitrification at high (12.5 mM) ammonium concentrations also. Enrichments at low ammonium concentration did not nitrify when inoculated into high-ammonium medium, but the converse was not true. This suggests that the water column contains a population of ammonia oxidizers that is sensitive to high ammonium concentrations. The observation of nitrification at high ammonium concentration by isolates from some winter lakewater samples, identified as nitrosospiras by 16S rRNA probing, is consistent with the hypothesis that sediment ammonia oxidizers enter the water column at overturn. With only one exception, nested PCR amplification enabled the detection of Nitrosospira 16S rDNA in all samples, but Nitrosomonas (N. europaea-eutropha lineage) 16S rDNA was never obtained. However, the latter were part of the sediment and water column communities, because their 16S rRNA could be detected by specific oligonucleotide probing of enrichment cultures. Furthermore, a specific PCR amplification regime for the Nitrosomonas europaea ammonia monooxygenase gene (amoA) yielded positive results when applied directly to sediment and lakewater samples. Patterns of Nitrosospira and Nitrosomonas detection by 16S rRNA oligonucleotide probing of sediment enrichment cultures were complex, but lakewater enrichments at low ammonium concentration were positive for nitrosomonads and not nitrosospiras. Analysis of enrichment cultures has therefore provided evidence for the existence of subpopulations within the lake ammonia-oxidizing community distinguishable on the basis of ammonium tolerance and possibly showing a seasonal distribution between the sediment and water column.

Journal Article↗