Inactive Sediment Research Articles

Evaluation of haem dipstick pad, urine protein, urine pH and urine protein:creatinine ratio results as a marker of bacteriuria in dogs and cats with inactive urine sediment.

Evaluation of haem dipstick pad, urine protein, urine pH and urine protein:creatinine ratio results as a marker of bacteriuria in dogs and cats with inactive urine sediment. Cats and dogs with contemporaneous urine dipstick, microscopic sediment analysis and microbiological culture and sensitivity results over a four-year period (2016 to 2020) were retrospectively identified. Dogs and cats with active urine sediments (at least five erythrocytes and/or five leukocytes per high-power field) and/or spermaturia were excluded. Association between urine pH, haem dipstick result, protein dipstick result and urine protein:creatinine ratio with bacteriuria were evaluated using binary logistic regression analysis. Likelihood ratios for bacteriuria were calculated at different diagnostic thresholds. A total of 668 and 169 dog and cat urine samples were included. Of these, 166 dogs (25%) had a positive urine culture, whilst only 29 cats (17%) had a positive urine culture. In dogs and cats, any positive haem dipstick result was significantly associated with bacteriuria, although only a ≥4+ haem positive result in dogs was associated with a small increase in the likelihood of a positive urine culture, and positive likelihood ratios did not support the use of haem dipstick results as a screening test for bacteriuria in cats. pH, urine protein:creatinine ratio and protein dipstick results were not associated with bacteriuria. Our findings provide proof of concept that haem dipstick pad results in dogs with inactive sediment and without spermaturia might be useful as a screening test for bacteriuria, although further studies are required to confirm these findings.

Organic Carbon Oxidation in the Sediment of the Ulleung Basin in the East Sea

We characterized the biogeochemical organic carbon (Corg) cycles in the surface sediment layer of the Ulleung Basin (UB) of the East Sea. The total oxygen uptake (TOU) rate and the diffusive oxygen uptake (DOU) rate of the sediment were measured using an autonomous in situ benthic lander equipped with a benthic chamber (KIOST BelcII) and a microprofiler (KIOST BelpII). The TOU rate was in the range of 1.51 to 1.93 mmol O2 m−2 d−1, about double the DOU rate. The high TOU/DOU ratio implies that the benthic biological activity in the upper sediment layer is one of the important factors controlling benthic remineralization. The in situ oxygen exposure time was about 20 days, which is comparable to the values of other continental margin sediments. The sedimentary Corg oxidation rates ranged from 6.4 to 6.5 g C m−2 yr−1, which accounted for ~2% of the primary production in UB. The Corg burial fluxes ranged from 3.14 ± 0.12 to 3.48 ± 0.60 g C m−2 yr−1, corresponding to more than 30% of the deposited Corg buried into the inactive sediment deep layer.

High incidence of proliferative and membranous nephritis in SLE patients with low proteinuria in the Accelerating Medicines Partnership.

Delayed detection of LN associates with worse outcomes. There are conflicting recommendations regarding a threshold level of proteinuria at which biopsy will likely yield actionable management. This study addressed the association of urine protein:creatinine ratios (UPCR) with clinical characteristics and investigated the incidence of proliferative and membranous histology in patients with a UPCR between 0.5 and 1. A total of 275 SLE patients (113 first biopsy, 162 repeat) were enrolled in the multicentre multi-ethnic/racial Accelerating Medicines Partnership across 15 US sites at the time of a clinically indicated renal biopsy. Patients were followed for 1 year. At biopsy, 54 patients had UPCR <1 and 221 had UPCR ≥1. Independent of UPCR or biopsy number, a majority (92%) of patients had class III, IV, V or mixed histology. Moreover, patients with UPCR <1 and class III, IV, V, or mixed had a median activity index of 4.5 and chronicity index of 3, yet 39% of these patients had an inactive sediment. Neither anti-dsDNA nor low complement distinguished class I or II from III, IV, V or mixed in patients with UPCR <1. Of 29 patients with baseline UPCR <1 and class III, IV, V or mixed, 23 (79%) had a UPCR <0.5 at 1 year. In this prospective study, three-quarters of patients with UPCR <1 had histology showing class III, IV, V or mixed with accompanying activity and chronicity despite an inactive sediment or normal serologies. These data support renal biopsy at thresholds lower than a UPCR of 1.

Prevalence of positive urine culture in the presence of inactive urine sediment in 1049 urine samples from dogs.

BackgroundUrinalysis (UA) is often used to screen for bacterial cystitis, regardless of sediment results, and followed up by quantitative urine culture (UC) for definitive diagnosis.ObjectivesDetermine prevalence of positive UCs in dogs with inactive urine sediments on routine UA.AnimalsA total of 1049 urine samples with inactive urine sediments and UCs collected from dogs presented to a veterinary specialty hospital between January 2018 and February 2020.MethodsRetrospective study of dogs with an inactive urine sediment on routine UA and follow‐up UCs. Signalment, UA findings, proteinuria, and UC results were recorded. Associations among these findings were assessed using multivariate logistic regression carried out using a backward stepwise method.ResultsOverall prevalence of positive UC was 3.4% (95% confidence interval [CI], 2.4‐4.8). Escherichia coli was the most commonly isolated bacteria. Only naturally voided samples were associated with increased prevalence of positive culture when compared to collection by cystocentesis or a non‐specified method. No statistically significant association with culture positivity was found for urine protein‐to‐creatinine ratio, urine specific gravity, urine pH, breed, age, or sex.Conclusions and Clinical ImportanceBased on the low prevalence (3.4%) of positive culture in urine samples from dogs with inactive sediment on routine UA and the relatively high cost of UC and sensitivity, cost‐benefit analysis including clinical suspicion of lower urinary tract disease should inform testing decisions, rather than routinely performing cultures on urine samples without active sediments.

Comparison of urinary protein-to-creatinine ration, serum albumin, serum creatinine and systolic arterial blood pressure of glomerular injury cases in dogs with chronic kidney disease

This study aims at assessing the prevalence of glomerular alterations in dogs with chronic kidney disease (CKD) and comparing the clinical and laboratory parameters. The tests conducted include a double-blind histopathological assay conducted by two pathologists, urine tests including inactive sediment, urinary protein-to-creatinine (UPC), serum albumin and serum creatinine, as well as measurement of the systolic arterial blood pressure. The prevalence of glomerular injuries was determined and the predominant injury was compared with a group comprised of the remaining injuries. The study included 24 dogs with CKD. The results revealed a predominance of membranous glomerular alterations 17/24 (70,83%), followed by glomerulosclerosis 3/24 (12,50%), membranoproliferative injuries 2/24, glomerulocystic atrophy 1/24 and glomerular amyloidosis 1/24. Amyloidosis presented the highest UPC while the membranoproliferative injury presented the lowest mean concentration of serum albumin. Higher values in the UPC did not correspond with lower mean serum albumin values. Glomerulosclerosis presented the highest mean systolic blood pressure and glomerular atrophy presented the highest creatinine values. When comparing membranous injuries with a group comprised of the remaining injuries, the UPC did not present significant differences between the groups. Renal amyloidosis was included in the group with the lowest systolic arterial blood pressure values while membranoproliferative injury was included in the group with highest UPC. The group called “others” presented the highest creatinine value. Dogs with CKD may present several types of glomerular injuries with similar clinical and laboratory profiles. This study observed a predominance of membranous glomerular injuries, followed by membranoproliferative injuries, glomerulocystic atrophy and amyloidosis.

Sedimentation and sediment geochemistry in a tropical mangrove channel meander, Sungai Kerteh, Peninsular Malaysia

Tropical mangrove swamps are commonly characterized by dense networks of tidal channels that may show pronounced meandering and dendritic patterns. Channel meanders are sometimes accompanied by cut-offs, and, like classical fluvial meanders, record changes in hydrology and sedimentation over time. Channel meandering can, thus, be an important process that contributes to spatial and temporal variability in the preserved record of the sedimentology and geochemistry of mangrove sediments. The aim of this study is to highlight changes in channel meander sedimentation in response to a meander cut-off in a tropical mangrove swamp. Two short sediment cores were sampled, respectively from a point bar (core KR1, 122 cm) at the junction with the neck cut-off and inside the cut-off (core KR2, 98 cm) in the Sungai Kerteh mangroves of Peninsular Malaysia. The profile comparison was based on sediment characteristics, total organic carbon (TOC), and selected elements (Fe, Na, Mg, Mn, Ba, and Sr). A smaller standard deviation of mean grain size (MGS) was found at the point bar (4.37 ± 0.51 ϕ) than in the cut-off (4.43 ± 1.76 ϕ), indicating a difference in flow velocity between the two settings. In turn, these changes in grain size influence channel meander evolution via associated changes in TOC and heavy metals. In order to clarify these relationships, we used principal components analysis and factor analysis. An increased accumulation of selected elements and TOC at the cut-off site from a depth of ~ 60 cm to the core-top segment was probably associated with a slowing down of sediment settling. A higher TOC recorded in the cut-off (2.74 ± 1.42%) compared to the point bar (1.14 ± 0.46%) suggests a propensity for prolonged in situ accumulation of organic matter in the abandoned meander bend. This study provides grain size and sediment geochemical information that is consistent with patterns of active and inactive sedimentation in the meander bends of mangrove channels.

Central Diabetes Insipidus in a Young Feline

Background: Central diabetes insipidus (CDI) is an endocrine disorder caused by the failure to produce, transport, or release ADH. This disease may show a primary etiology (idiopathic or congenital) or a secondary one (trauma or neoplasms). It is characterized by signs such as polyuria and polydipsia. The definitive diagnosis is obtained by the two-step water deprivation test; the absence of adequate urinary concentration in the first stage confirms the diagnosis of diabetes insipidus and, in the second stage, the response to the application of synthetic desmopressin confirms a central origin. Because CDI is rare in felines, the aim of this study was to report the occurrence of a case of CDI, probably of congenital primary origin, in an 8-month-old kitten.Case: An 8-month-old male feline, castrated, 3.2 kg, was brought to consultation with a report of polydipsia, polyuria, smaller size and weight, and lower activity when compared to his brother, for several months. On physical examination, lethargy, body score 2/5, and mild dehydration were noted, as well as deciduous teeth that should have already been replaced. Abdominal ultrasound and laboratory tests were requested, which ruled out chronic kidney disease (CKD), diabetes mellitus (DM), hyperadrenocorticism (HAC), and hyperthyroidism. Due to the fact that urinalysis evidenced hyposthenuria (urinary density [UD] 1.004), CDI was suspected. The patient underwent a water deprivation test and, after 7.5 h, lost 4.7% of his initial weight, while UD was 1.012, confirming the diagnosis of DI. The investigation then proceeded to the evaluation of the response to synthetic desmopressin by the application of 5 U IM. Two h later, UD was 1.019, confirming the diagnosis of CDI. The prescribed treatment was oral desmopressin at a dose of 100 μg BID. Upon return after 30 days, the feline had gained weight, was well hydrated, and the tutor reported higher activity. A new urinalysis showed a UD of 1.004 and inactive sediment. The tutor was asked to start administering the drug three times a day. However, noting that the patient’s quality of life had significantly improved, and wishing to spare the animal from the stress of taking medication once more a day, she chose not to modify the therapy and not to perform additional tests, due to financial limitation.Discussion: First, CKD, DM, HAC, and hyperthyroidism, more common conditions, were ruled out, and the investigation then proceeded to a water deprivation test. The feline lost 3% to 5% of the initial weight and UD was on the borderlinebetween hypo- and isosthenuria, as described in the literature for the diagnosis of DI. In the second stage of the test, slight urinary concentration was observed after the application of synthetic desmopressin, which confirmed the diagnosis of CDI. The dose of desmopressin prescribed for home treatment, 100 μg BID, was effective to relieve the clinical signs, but urine remained in hyposthenuria in the interval between administrations, suggesting that, for this patient, treatment would be more effective by administering the medication three times a day, in order to maintain an adequate serum concentration. Due to the diagnosis of CDI and the feline being young, the condition’s primary origin is believed to be congenital. It is also suspected that the patient may still have congenital hypothyroidism, due to the clinical signs of late tooth exchange and constant lethargy, in addition to laboratory results of thyroid hormones below reference levels. However, because thyroid tests were made by chemiluminescence, a repetition by radioimmunoassay is indicated. If hypothyroidism is confirmed,it would be possible to assume a common etiological factor between CDI and hypothyroidism, such as hypothalamicpituitary malformation.

The prevalence of positive urine cultures in 100 dogs with an inactive urine sediment

Objective: The purpose of this study was to determine the prevalence of positive quantitative urine cultures in dogs with an inactive urine sediment.
 Background: A urinalysis is a useful screening tool for the evaluation of evidence of bacterial cystitis and a quantitative urine culture is used for definitive diagnosis.
 Evidentiary value: A retrospective chart review from June 2012 to December 2017 at three private practice emergency and specialty referral hospitals examined urine samples obtained from 100 client-owned dogs.
 Methods: The signalment and clinicopathologic data was recorded for all canine patients that had urine samples obtained by cystocentesis that had an inactive sediment exam on urinalysis and subsequent quantitative urine cultures were performed.
 Results: The prevalence of positive quantitative urine cultures in all dogs with an inactive urine sediment at the aforementioned institutions was 6% (6/100). Escherichia coli was the most commonly isolated bacteria.
 Conclusion: Given the low prevalence of positive quantitative urine cultures in dogs with an inactive urine sediment and current guideline recommendations for management of subclinical bacteriuria, we do not recommend urine cultures for dogs without lower urinary tract signs. Further prospective study of patient subgroups, as well as controlled studies evaluating urine sample handling techniques using methods available to private practice practitioners are sorely needed.
 Application: Emergency and general practicing veterinarians should consider a quantitative urine culture for dogs with lower urinary tract signs, even with an inactive sediment examination, and on a case-by-case basis for dogs with pertinent systemic diseases or known risk factors for bacterial cystitis.
 

Clinicopathological findings in 41 dogs (2008-2018) naturally infected with Ehrlichia ewingii.

Background Ehrlichia ewingii is the most seroprevalent Ehrlichia‐infecting dogs in the southern and mid‐western United States. Fever, lameness, and polyarthritis are commonly reported findings in dogs naturally infected with E. ewingii.ObjectivesTo evaluate clinicopathologic findings in a population of dogs naturally infected with E. ewingii.AnimalsForty‐one dogs PCR positive for E. ewingii and PCR negative for other targeted vector‐borne organisms.MethodsRetrospective study. Clinical and clinicopathologic data including physical examination findings, CBC, serum biochemistry, urinalysis (UA), symmetric dimethylarginine (SDMA), and vector‐borne disease diagnostic results were reviewed.ResultsFrequent clinical diagnoses other than ehrlichiosis (28/41; 68.3%) were renal disease (7/41; 17.1%) and immune‐mediated hemolytic anemia (IMHA) (6/41; 14.6%). The most frequent physical examination finding was joint pain (14/41; 34.1%). Prominent hematologic and biochemical abnormalities included abnormal lymphocyte counts (22/36; 61.1%); neutrophilia (21/37; 56.8%); increased alkaline phosphatase (20/35; 57.1%) and alanine transaminase (14/35; 40%) activities; and increased SDMA concentration (11/34; 32.4%). Urinalysis abnormalities included proteinuria (20/27; 74%), most with inactive sediments (16/20; 80%). Dogs were seroreactive by Ehrlichia canis immunofluorescence assay (IFA; 17/39; 43.6%) and Ehrlichia ELISA (34/41; 82.9%). Seroreactivity by IFA for other vector‐borne pathogens included Bartonella (1/39; 2.6%), Rickettsia rickettsii (spotted‐fever group rickettsiae) (12/39; 30.8%), and Borrelia burgdorferi by ELISA (1/41; 2.4%).Conclusions and Clinical ImportanceRenal disease, IMHA, proteinuria, neutrophilia, abnormal lymphocytes, and increased liver enzyme activities were common in this group of E. ewingii‐infected dogs. Studies are needed to determine if E. ewingii contributes to comorbidities or is a precipitating factor in clinical syndromes in persistently infected dogs.

Sedimentological and geomorphological characteristics of Quaternary deposits in the Planica-Tamar Valley in the Julian Alps (NW Slovenia)

ABSTRACTWe present a geomorphological map on a scale of 1:15,000, with detailed sedimentological descriptions, and a general relative spatio-temporal depositional reconstruction of Quaternary sediments in the Planica-Tamar Valley (NW Slovenia). After the Last Glacial Maximum, the retreating Quaternary glacier deposited large amounts of glacial sediments. These were followed by Holocene sediments, which differ in their sedimentological characteristics, transport mechanisms, and morphology. These sediments are deposited as sedimentary bodies with complex depositional geometries. They form areas of active, partly active, and inactive sedimentation in response to local/regional climate and bedrock geology. Previous research of the valley was mainly focused on bedrock mapping, while almost completely neglecting Quaternary deposits. This work is the first broader analysis of Quaternary sedimentary deposits in the research area, which offers an insight into the complex geomorphological and sedimentological processes, which shape the current mountainous landscape.

Within-catchment variability in landscape connectivity measures in the Garang catchment, upper Yellow River

The degree of landscape connection has wide-ranging implications for sediment availability, frequency of transport, and the nature of sediment storage within a basin. Two methodological approaches for assessing landscape connectivity are applied within the Garang subcatchment of the upper Yellow River. A GIS-based geomorphometric index was calculated for the catchment and compared to a methodology linking interpretation of satellite imagery and field mapping of sediment storage to slope threshold analysis. Landscapes of the Garang catchment are highly contrasting and can be separated into three zones: i) a highly disconnected upper catchment of low-relief with large inactive sediment stores; ii) a transitional zone where present landscape dynamics are controlled in large part by past incisional processes in the form of large alluvial fan/terrace deposits; and iii) a highly connected and highly dissected landscape within the lower catchment that has little accommodation space for sediment storage. The geomorphometric index shows general agreement with the patterns in landscape connectivity observed through imagery and field investigations. However, it estimates similar levels of connectivity in landscapes with observed (dis)connectivity, reflecting limitations of the calculation. While rapidly calculated geomorphometric indices of landscape connectivity provide useful appraisals of relative within-catchment variability in systems such as the Garang catchment, caution is urged in conducting broader-scale analyses using the same tools. Findings from this study highlight the importance of field-informed appraisals of landscape dynamics, site-specific characteristics and the imprint of historical (evolutionary) context in making such comparative assessments.

Biodegradation potential of aquaculture chemotherapeutants in marine sediments

The commercial chemotherapeutant formulations SLICE® and AlphaMax® [active ingredients emamectin benzoate (EB) and deltamethrin respectively] are used in fin fish aquaculture to control parasitic sea lice. In some regions, the use of these substances has drawn concern from the commercial fishing industry regarding potential adverse effects on non-target organisms. In the present work, biodegradation of EB and deltamethrin, and their commercial formulations, was investigated over 135 days at 4 and 10°C in fresh marine sediments collected from underneath an active open net-pen salmon farm. EB incubated as either pure substance or commercial formulation was recalcitrant at both temperatures under abiotic and biotic conditions. Deltamethrin incubated alone or as its commercial formulation degraded slowly at 10°C (t1/2 = 330 ± 107 and 201 ± 27.1 days respectively). At 4°C, deltamethrin degradation was only significant following incubation as commercial formulation (t1/2 = 285 ±112 days). Degradation rates of EB and deltamethrin as pure substances versus their commercial formulations were not statistically different. Depletion of deltamethrin was observed in 10°C inactive sediments indicating that transformation occurred (at least in part) via an abiotic pathway. Overall, these data provide further insight into the fate and persistence of EB from the ongoing use of SLICE® in British Columbia's salmon aquaculture industry. AlphaMax® is not registered in Canada but is used in other salmon farming countries to control sea lice.

AB0536 Renal Biopsy in Patients with Systemic Lupus Erythematosus and Proteinuria Less than 0.5 G/24Hrs

BackgroundThe currently indications for a first renal biopsy in patients with systemic lupus erythematosus (SLE) are the presence of a confirmed 24 hours urinary proteins ≥0.5 g, an active urinary...

AB0379 Long-term renal outcome after remission induction with cyclophosphamide pulse therapy in patients with lupus nephritis – a single centre experience

BackgroundCyclophosphamide (Cyc) pulse therapy is the treatment of choice in patients with proliferative lupus nephritis (LN). Dependent on its definition, a remission of LN is achieved in 54 – 90...

THU0260 Low Risk of Renal Flares and of Negative Outcomes in Women with Lupus Nephritis Conceiving after Switching Mycophenolate Mofetil to Azathioprine

BackgroundA growing number of women with Lupus nephritis (LN) wish to fulfil their desire for having a child. A common concern is the optimal choice of immunosuppressive treatment during the...

SAT0184 Predictors of response to induction therapy in lupus nephritis

BackgroundSeveral prognostic factors have been described in lupus nephritis, which vary depending on the population studied. Few studies have examined these factors in relation to different stages of treatment.ObjectivesTo identify...

Low risk of renal flares and negative outcomes in women with lupus nephritis conceiving after switching from mycophenolate mofetil to azathioprine

MMF is teratogenic and needs to be replaced before pregnancy. This change may lead to flares. Our aim was to determine the risk of renal flares in women with LN who switched treatment from MMF to AZA before conception and to evaluate the outcome of their pregnancies. Medical records of women with LN counselled for pregnancy wish were reviewed. Women receiving treatment with either MMF or AZA (control group), with inactive lupus (SLEDAI ≤ 4) and quiescent LN (serum creatinine <1.5 mg/dl, inactive sediment and proteinuria <1 g/24 h for the preceding 6 months) were eligible for this study. We identified 54 women [23 treated with MMF (group 1) and 31 treated with AZA (group 2)]. MMF dosage was tapered and subsequently transferred to AZA, which was maintained throughout pregnancy. Three (13%) patients (group 1) vs none (group 2) developed a renal flare 3-6 months after transitioning from MMF to AZA (P = 0.14) before pregnancy ensued. The only parameter with a significant difference in those with flare compared with those without was younger age (median 27 vs 30 years; P = 0.03). Risk for adverse outcome within 48 pregnancies (pre-eclampsia 9%, preterm delivery 20.5%) increased with every milligramme of prednisone dosage [odds ratio (OR) 2.03] and every single unit of SLEDAI score (OR 3.92). Renal flares occurred post-partum in two women. No patient developed worsening of renal function. Replacing MMF with AZA in patients with quiescent LN for pregnancy planning rarely leads to renal flares. Pregnancy outcome was favourable.

A rare case of reversible acquired AA-type renal amyloidosis in a chronic filariasis patient receiving antifilarial therapy

Lymphatic filariasis is a major health problem in India with a large number of patients tending to be asymptomatic. In the Southeast and South Asian regions, Wuchereria bancrofti is the most prevalent parasite, causing filariasis in 99.4% of cases. While kidney involvement is a rare event in chronic filariasis, this case is unique because AA-type renal amyloidosis occurs in chronic W. bancrofti infection. We present here a unique case of lymphatic filariasis. The patient, a 25-year-old male who was previously diagnosed with right lower limb filarial lymphedema and had undergone lymphovenous anastomosis, was admitted for evaluation of persistent nephrotic-range proteinuria. Autoimmune markers in the form of anti-nuclear antibodies, anti-double-stranded DNA and anti-neutrophil cytoplasmic antibody were negative; C3 was normal. Urine analysis revealed inactive sediment with moderate proteinuria. Both serum and urine electrophoresis were negative for paraproteins and bone marrow aspirate and biopsy were normal. Evidence of active filarial infection was established on the basis of microfilariae in the peripheral smear and a positive W. bancrofti antigen test. Kidney biopsy revealed renal amyloidosis when stained with Congo red and anti-AA immunostain. The patient's proteinuria improved on conservative management with angiotensin-converting enzyme inhibitors and a course of antifilarial drugs. His proteinuria returned to <1g/24h with normalization of renal function and no significant proteinuria on periodic follow-up at 6-month and 1-year intervals. Repeat kidney biopsy after 1.5years showed regression of amyloidosis. Repeat demonstration of filarial antigen and microfilariae in the peripheral smear were negative on multiple occasions during the follow-up period. Although various chronic infections can lead to secondary renal amyloidosis, this is the first case reported in world literature where secondary amyloidosis developed as a complication of chronic filarial infection due to W. bancrofti. This is probably also the first case reported in world literature where renal amyloidosis has an etiological association with W. bancrofti infection and where patient symptoms improved with antifilarial and antiproteinuric management.

Evidence for microbial iron reduction in a landfill leachate-polluted aquifer (Vejen, Denmark).

Aquifer sediment samples obtained from the anaerobic part of a landfill leachate plume in Vejen, Denmark, were suspended in groundwater or in an artificial medium and incubated. The strictly anaerobic suspensions were tested for reduction of ferric iron [Fe(III)] oxides, which was measured as an increase in the concentration of dissolved Fe(II). Iron reduction did not occur when the medium was inoculated with inactive sediment and when the organisms in the inoculated medium were killed by formaldehyde, by chloroform, or by pasteurization, whereas the level of iron reduction was significant when living bacteria were present. Mixed cultures were obtained from the sediment samples, and differences in apparent iron reduction rates among the different cultures were maintained during several transfers. In addition, iron reduction was observed in unamended incubation mixtures containing whole sediment and groundwater. Synthetic amorphous Fe(III) oxides, as well as naturally occurring sediment-bound Fe(III) oxides, could be reduced by the cultures. Together, our results provide evidence that iron-reducing bacteria are present and microbial iron reduction occurs in the polluted aquifer sediments which we studied.