Calculating the limit of detection for a dilution series

AIMS

Microbial samples are often serially diluted to estimate the number of microbes in a sample, whether as colony-forming units of bacteria or algae, plaque forming units of viruses, or cells under a microscope. There are at least three possible definitions for the limit of detection (LOD) for dilution series counts in microbiology. The statistical definition that we explore is that the LOD is the number of microbes in a sample that can be detected with high probability (commonly 0.95).

METHODS AND RESULTS

Our approach extends results from the field of chemistry using the negative binomial distribution that overcomes the simplistic assumption that counts are Poisson. The LOD is a function of statistical power (one minus the rate of false negatives), the amount of over-dispersion compared to Poisson counts, the lowest countable dilution, the volume plated, and the number of independent samples. We illustrate our methods using a data set from Pseuodomonas aeruginosa biofilms.

CONCLUSIONS

The techniques presented here can be applied to determine the LOD for any counting process in any field of science whenever only zero counts are observed.

SIGNIFICANCE AND IMPACT OF STUDY

We define the LOD when counting microbes from dilution experiments. The practical and accessible calculation of the LOD will allow for a more confident accounting of how many microbes can be detected in a sample.

Range extension and conservation status of the rare Solanaceae shrub, Solanum conocarpum

Background

The British Virgin Islands and the US Virgin Islands, two island groups located in the Caribbean archipelago, hold unique plant diversity and high endemism. Until recently, Solanumconocarpum was considered a rare plant species endemic to the island of St. John in the US Virgin Islands. Ongoing botanical surveys in this region are revealing new populations and refining our understanding of the distribution of these narrow endemic plant species. The objective of this paper is to assess the conservation status of S.conocarpum, including a review of its geographic range, population numbers, threats and conservation actions needed for its long-term survival.

New information

In this paper, we present new occurrences for S.conocarpum, extending its geographic range to a new island, Tortola and new territory, the British Virgin Islands. Despite this range expansion, this species is evaluated as Endangered (EN), based on Criteria B1b(iii,v)+2b(iii,v)+C2a(i), according to the IUCN Red List Categories and Criteria. The extent of occurrence (EOO = 46 km²) and area of occupancy (AOO = 20 km²) are highly restricted. On St. John (US Virgin Islands), the historically recorded individuals at Reef Bay, Europa Ridge and Sabbat Point are now considered extirpated due to disturbance from development compounded by invasive species, as well as the impact of feral ungulates and drought stress. These threats are impacting the species across the whole island of St. John and contributing to a continuing decline of suitable habitat, despite the island being a National Park. On the island of Tortola, the species occurs on unprotected lands subject to development and habitat modification and decline by feral ungulates. Based on these threats acting separately across the two islands, two locations were defined. The estimated total number of mature individuals ranges between 150 and 250, with the largest subpopulation at Nanny Point in the US Virgin Islands, containing 108 mature individuals. Conservation action, focused on protecting this species' habitat, is urgently needed.

Reassessment of Varronia bellonis - a threatened, endemic plant from Puerto Rico

Background

Varroniabellonis (Urb.) Britton is a lianescent or recumbent shrub that is endemic to Puerto Rico where it is restricted to specific geology types with a limited extent on the western half of the Island. The species occurs on serpentinite geology covered by serpentine-derived soils in the west-central mountains and on limestone geology in the the northern karst region. The species area of occupancy is estimated to range between 108 km² and 268 km² and its extent of occurrence to be between 644 km² and 852 km². The number of locations are estimated to be four. There are 418 known mature individuals in the wild (Hamilton 2020a). The species was previously assessed as Critically Endangered (Linsky and Sustache 2014), based on available information. However, an international team have been collaborating to conserve the species and, based on new information derived from this work, the species is reassessed as Endangered (EN), based on Criteria B1ab(i,ii,iii,iv,v)+2ab(i,ii,iii,iv,v), according to the IUCN Red List Categories and Criteria (version 3.1) and guidelines (IUCN Standards and Petitions Committee 2019).

New information

Areas of suitable habitat across the native range of the threatened plant, V.bellonis, were surveyed by a team of experts between 2016 and 2019 to determine the species habitat preferences, identify threats to the species survival and provide an up-to-date meta-population status. The new information enabled members of the international team to reassess the species status and will enable sound and scientifically-based recovery actions to be recommended that can secure Varroniabellonis populations for the future. Parallel efforts are ongoing to explore the species population genetics and reproductive biology.

Conservation status of native plant hybrids in the British Virgin Islands

Background

Hybridization is an evolutionary event present in the natural world. Several studies suggest that natural hybridization is an important process in plant evolution, creating new genetic combinations which can play a vital role in speciation (Soltis and Soltis 2009, Soltis 2013, Neri et al. 2017, Taylor and Larson 2019). Therefore, it is important to understand and protect naturally occurring hybrids, conserving their ecological novelties and new traits, such as the ability to explore new niches, different from those of the parental species (Soltis 2013, Supple and Shapiro 2018).

The British Virgin Islands (BVI) is a UK Overseas Territory situated in the Caribbean biodiversity hotspot (Myers et al. 2000). To date, three natural hybrids are known to occur within this territory: Tillandsia×lineatispica Mez, Anthurium×selloanum K.Koch and Coccolobakrugii × C.uvifera R.A.Howard (Howard 1957, Acevedo-Rodriguez and Strong 2005, Acevedo-Rodriguez and Strong 2012).

Tillandsia×lineatispica is endemic to the Puerto Rican Bank, occurring in Puerto Rico, the US Virgin Islands (USVI) and the British Virgin Islands with an extent of occurrence estimated to be 3,390 km² and a limited number of locations. The suitable habitat for this hybrid is declining mainly due to the negative impacts of feral ungulates, development for tourism and residential infrastructure and the impact of human-induced wildfires. In addition, it is suspected that the global population does not exceed 10,000 individuals with the largest subpopulation on Beef Island in the BVI thought to have no more than 1,000 mature individuals. This hybrid is therefore evaluated as Vulnerable, based on IUCN Red List Criteria, B1a(iii)+2b(iii) + C2a(i).

Anthurium×selloanum is an endemic hybrid to BVI and USVI with a very restricted extent of occurrence which was estimated to range between 103 km² and 207 km² and an area of occupancy which was estimated to range between 56 km² and 188 km² and a limited number of locations. The suitable habitat of this species is declining mainly due to the negative impacts of feral ungulates, development for tourism and residential infrastructure and the negative impact of recreation activities in protected areas. This species is therefore evaluated as Endangered, based on IUCN Red List Criteria B1a+ b(iii) + B2a+b(iii).

Coccolobakrugii × C.uvifera is native to the BVI, USVI, Puerto Rico, Dominican Republic, Haiti and Anguilla. It is estimated to have an extent of occurrence of 89,412 km². This value exceeds the threshold for any threatened category. Despite an observed continuing decline of suitable habitat for this species, which is being degraded mainly through ongoing development pressures, this species occurs in more than 10 locations. It is therefore assessed as Least Concern (LC).

New information

In this paper, we discuss the conservation status of all the known, naturally occurring, native hybrids in the the British Virgin Islands and we provide distribution data, including new records, from across these hybrid species ranges. Although conservation assessments of hybrids are out of the scope of the published IUCN Red List of Threatened Species (IUCN Standards and Petitions Committee 2019), we use the IUCN Red List Criteria and Categories (version 3.1) to establish an equivalent conservation status of these hybrids and discuss conservation action due to the potential evolutionary importance of these naturally occurring hybrids. These assessments provide the necessary baseline information for prioritising species conservation and making informed management decisions, such as establishing the BVI's Tropical Important Plant Areas (TIPAS) network (Sanchez et al. 2019).

New island record and conservation status of Puerto Rican Bank endemic plant species, Ruehssia woodburyana (Acev.-Rodr.) Goyder, comb. nov., formally transferred from Marsdenia

Background

Thought to be endemic to the Commonwealth of Puerto Rico, Ruehssiawoodburyana (Apocynaceae) was recently discovered at a single location on Norman Island in the British Virgin Islands. Despite an increase in the extent of occurrence and area of occupancy, this species meta-population is very limited with a total of 37 individuals known in the wild. The largest subpopulation, on Mona Island, has only 26 individuals. The species suitable habitat is experiencing a continuing decline due to urban development, grazing by feral ungulates and human-induced forest fires. Conservation action is urgently needed and should be directed towards establishing genetically representative ex situ collections, such as seed for long term storage and live material for propagation. This species is evaluated as Critically Endangered (CR), based on Criteria C2a(i)+D, according to the IUCN Red List Categories and Criteria (version 3.1) and guidelines (Subcommittee IUCN Standards and Petitions 2016).

New information

Extensive and regular surveys to the region enable the discovery of new plant records for different countries and islands. In this paper, we record a new island record for Ruehssiawoodburyana on Norman Island, in the British Virgin Islands and discuss the species conservation status. Marsdeniawoodburyana is transferred to the genus Ruehssia to reflect the resurrection of that genus for species of Marsdenia native to the New World.

Hard Surface Carrier Test as a Quantitative Test of Disinfection: A Collaborative Study

The hard surface carrier test (HSCT) recently was proposed as a qualitative test for disinfectant efficacy. A collaborative study of HSCT led to a suggested performance standard of ≤2 or 3 positive carriers out of 60 tested. Subsequently, it was discovered that HSCT can be used as a quantitative test, because the HSCT protocol requires measurement of inoculum level on some carriers. The data allow estimation of the log10 reduction in number of active bacteria. Producers, consumers, and policymakers will be better able to discuss merits of alternative performance standards if the focus is on log reduction of organisms rather than on number of positive carriers. Data from the collaborative study were reanalyzed from this quantitative viewpoint. If the point estimate of log reduction is LR and the 99% lower confidence limit estimate is LLR, the LR values ranged from 7.0 to 9.0 and the LLR values were greater than 6.0 for all disinfectants except the negative control formulation. The total variance for estimated LR is the sum of inter laboratory and intralaboratory variances. The total variance for LR was 0.095 for Pseudomonas aeruginosa, 0.251 for Staphylococcus aureus, and 0.118 for Salmonella choleraesuis. Percentages of the variance due to interlaboratory variability were 11% for P. aeruginosa, 52% for S. aureus, and 25% for S. choleraesuis. Chances of making false-effective and false-ineffective decisions can be calculated for the quantitative HSCT. The performance standard can be based on LLR.

Repeatability and Reproducibility of Germicide Tests: A Literature Review

The results of a quantitative antimicrobial assay can be summarized by the log reduction value. For an assay to be proposed as a standard method, it is usually necessary to conduct a collaborative study to demonstrate that the repeatability and reproducibility standard deviations (SDs) of the log reduction values are sufficiently small. It is not clear, however, precisely how small those SDs should be. This paper describes the results of a literature review conducted to determine the range of repeatability and reproducibility SDs for standard quantitative antimicrobial assays. The underlying premise is that, for an assay to have been accepted as a standard method, its repeatability and reproducibility SDs must have been sufficiently small. This premise implies that the repeatability and reproducibility SDs of standard assays establish de facto guidelines for acceptability. The survey comprised papers where the SDs could be extracted directly or where they could be calculated from accessible data. Papers describing suspension tests as well as hard surface tests were included. For the standard antimicrobial assays reviewed, repeatability SDs ranged from 0.25 to 1.21 and the reproducibility SDs ranged from 0.31 to 1.54.

Checking the Validity of the Harvesting and Disaggregating Steps in Laboratory Tests of Surface Disinfectants

A chemical disinfectant against surface-associated bacteria typically uses carriers (e.g., glass disks) that are purposely contaminated with bacteria prior to disinfection. After disinfection, the bacteria are harvested by mechanically separating them from the carrier surface to form a suspension of cells in a dilution tube. Bacterial clumps in the tube are disaggregated using mechanical or chemical techniques, thereby creating a well-mixed suspension of single cells suitable for enumeration. Efficacy is quantified by comparing the viable cell count for a disinfected carrier to the viable cell count for sham-disinfected (control) carrier. A test is said to be biased (invalid) if the observed efficacy measure is systematically higher or lower than the true efficacy. It is shown here for the first time that the bias attributable to the harvesting and disaggregating steps of a disinfectant test can be measured. For some conventional biofilm harvesting and disaggregating techniques, laboratory checks showed either negligible bias or important bias, depending on the disinfectant. Quantitative bias checks on the harvesting and disaggregating steps are prudent for each combination of carrier material, microorganism, and disinfectant. The quantitative results should be augmented by microscopic examination of harvested disinfected and control carriers and of the disaggregated suspensions.

Determining the Efficacy of Liquid Sporicides Against Spores of Bacillus subtilis on a Hard Nonporous Surface Using the Quantitative Three Step Method: Collaborative Study

A collaborative study was conducted to validate the quantitative Three Step Method (TSM), a method designed to measure the performance of liquid sporicides on a hard nonporous surface. Ten laboratories agreed to participate in the collaborative study; data from 8 of 10 participating laboratories were used in the final statistical analysis. The TSM uses 5 5 1 mm glass coupons (carriers) upon which spores have been inoculated and which are introduced into liquid sporicidal agent contained in a microcentrifuge tube. Following exposure to a test chemical and a neutralization agent, spores are removed from carriers in 3 fractions: passive removal (Fraction A), sonication (Fraction B), and gentle agitation (Fraction C). Liquid from each fraction is serially diluted and plated on a recovery medium for spore enumeration. Control counts are compared to the treated counts, and the level of efficacy is determined by calculating the log10 reduction (LR) of spores. The main statistical goals were to evaluate the repeatability and reproducibility of the LR values, to estimate the components of variance for LR, and to assess method responsiveness. AOAC Method 966.04Method II was used as a reference method. The scope of the validation was limited to testing liquid formulations against spores of Bacillus subtilis, a surrogate for virulent strains of B. anthracis, on a hard nonporous surface (glass). The test chemicals used in the study were sodium hypochlorite, a combination of peracetic acid and hydrogen peroxide, and glutaraldehyde. Each test chemical was evaluated at 3 levels of presumed efficacy: high, medium, and low. Three replications were required. The TSM was validated as it successfully met the statistical parameters for quantitative test methods. Satisfactory validation parameters, such as the repeatability standard deviation (Sr) and reproducibility standard deviation (SR), were obtained for control carrier counts and LR values. Both the TSM and the reference method were responsive to the efficacy levels of the test chemicals. For the 72 total TSM tests conducted, the mean ( standard error of the mean) log density of spores per control carrier was 6.86 ( 0.08); the Sr and SR were low at 0.15 and 0.27, respectively. Across the range of test chemicals, the Sr and SR estimates associated with LR were also acceptably low. The Sr rangedfrom 0.17 to 0.72 and the SR ranged from 0.34 to 1.43. Overall, the Sr and SR estimates associated with the efficacy data were within the ranges published for other quantitative methods and meet the performance characteristics necessary for validation.

Use of Alternative Carrier Materials in AOAC Official MethodSM 2008.05, Efficacy of Liquid Sporicides Against Spores of Bacillus subtilis on a Hard, Nonporous Surface, Quantitative Three-Step Method

The quantitative Three-Step Method (TSM) for testing the efficacy of liquid sporicides against spores of Bacillus subtilis on a hard, nonporous surface (glass) was adopted as AOAC Official MethodSM 2008.05 in May 2008. The TSM uses 5 5 1 mm coupons (carriers) upon which spores have been inoculated and which are introduced into liquid sporicidal agent contained in a microcentrifuge tube. Following exposure of inoculated carriers and neutralization, spores are removed from carriers in three fractions (gentle washing, fraction A; sonication, fraction B; and gentle agitation, fraction C). Liquid from each fraction is serially diluted and plated on a recovery medium for spore enumeration. The counts are summed over the three fractions to provide the density (viable spores per carrier), which is log10-transformed to arrive at the log density. The log reduction is calculated by subtracting the mean log density for treated carriers from the mean log density for control carriers. This paper presents a single-laboratory investigation conducted to evaluate the applicability of using two porous carrier materials (ceramic tile and untreated pine wood) and one alternative nonporous material (stainless steel). Glass carriers were included in the study as the reference material. Inoculated carriers were evaluated against three commercially available liquid sporicides (sodium hypochlorite, a combination of peracetic acid and hydrogen peroxide, and glutaraldehyde), each at two levels of presumed efficacy (medium and high) to provide data for assessing the responsiveness of the TSM. Three coupons of each material were evaluated across three replications at each level; three replications of a control were required. Even though all carriers were inoculated with approximately the same number of spores, the observed counts of recovered spores were consistently higher for the nonporous carriers. For control carriers, the mean log densities for the four materials ranged from 6.63 for wood to 7.14 for steel. The pairwise differences between mean log densities, except for glass minus steel, were statistically significant (P < 0.001). The repeatability standard deviations (Sr) for the mean control log density per test were similar for the four materials, ranging from 0.08 for wood to 0.13 for tile. Spore recovery from the carrier materials ranged from approximately 20 to 70: 20 (pine wood), 40 (ceramic tile), 55 (glass), and 70 (steel). Although the percent spore recovery from pine wood was significantly lower than that from other materials, the performance data indicate that the TSM provides a repeatable and responsive test for determining the efficacy of liquid sporicides on both porous and nonporous materials.

Comparative Evaluation of Two Quantitative Test Methods for Determining the Efficacy of Liquid Sporicides and Sterilants on a Hard Surface: A Precollaborative Study

Two quantitative carrier-based test methods for determining the efficacy of liquid sporicides and sterilants on a hard surface, the Standard Quantitative Carrier Test MethodASTM E 2111-00 and an adaptation of a quantitative micro-method as reported by Sagripanti and Bonifacino, were compared in this study. The methods were selected based on their desirable characteristics (e.g., well-developed protocol, previous use with spores, fully quantitative, and use of readily available equipment) for testing liquid sporicides and sterilants on a hard surface. In this paper, the Sagripanti-Bonifacino procedure is referred to as the Three Step Method (TSM). AOAC Official Method 966.04 was included in this study as a reference method. Three laboratories participated in the evaluation. Three chemical treatments were tested: (1) 3000 ppm sodium hypochlorite with pH adjusted to 7.0, (2) a hydrogen peroxide/peroxyacetic acid product, and (3) 3000 ppm sodium hypochlorite with pH unadjusted (pH of approximately 10.0). A fourth treatment, 6000 ppm sodium hypochlorite solution with pH adjusted to 7.0, was included only for Method 966.04 as a positive control (high level of efficacy). The contact time was 10 min for all chemical treatments except the 6000 ppm sodium hypochlorite treatment which was tested at 30 min. Each chemical treatment was tested 3 times using each of the methods. Only 2 of the laboratories performed the AOAC method. Method performance was assessed by the within-laboratory variance, between-laboratory variance, and total variance associated with the log reduction (LR) estimates generated by each quantitative method. The quantitative methods performed similarly, and the LR values generated by each method were not statistically different for the 3 treatments evaluated. Based on feedback from the participating laboratories, compared to the TSM, ASTM E 2111-00 was more resource demanding and required more set-up time. The logistical and resource concerns identified for ASTM E 2111-00 were largely associated with the filtration process and counting bacterial colonies on filters. Thus, the TSM was determined to be the most suitable method.

Modification to the AOAC Sporicidal Activity of Disinfectants Test (Method 966.04): Collaborative Study

In an effort to improve AOAC Method 966.04, the Sporicidal Activity of Disinfectants Test, selected modifications to the procedure were evaluated in a collaborative study. Method 966.04 is used to generate efficacy data to support the product registration of sporicides and sterilants. The method is a carrier-based test that provides a qualitative measure of product efficacy against spores of Bacillus subtilis and Clostridium sporogenes. The use of garden soil extract and the lack of standard procedures for the enumeration of spores and neutralization of the test chemicals have been considered problematic for many years. The proposed modifications were limited to the B. subtilis and hard surface carrier (porcelain penicylinder) components of the method. The study included the evaluation of a replacement for soil extract nutrient broth and an establishment of a minimum spore titer per carrier, both considered crucial for the improvement and utilization of the method. Additionally, an alternative hard surface material and a neutralization confirmation procedure were evaluated. To determine the equivalence of the proposed alternatives to the standard method, 3 medium/carrier combinations, (1) soil extract nutrient broth/porcelain carrier (current method), (2) nutrient agar amended with 5 g/mL manganese sulfate/porcelain carrier, and (3) nutrient agar amended with 5 g/mL manganese sulfate/stainless steel carrier were analyzed for carrier counts, HCl resistance, efficacy, quantitative efficacy, and spore wash-off. The test chemicals used in the study represent 3 chemical classes and are commercially available antimicrobial liquid products: sodium hypochlorite (bleach), glutaraldehyde, and a combination of peracetic acid and hydrogen peroxide. Four laboratories participated in the study. The results of the spore titer per carrier, HCl resistance, efficacy, and wash-off studies demonstrate that amended nutrient agar in conjunction with the porcelain is comparable to the current method, soil extract nutrient broth/porcelain. The nutrient agar method is simple, inexpensive, reproducible, and provides an ample supply of high quality spores. Due to the current use of porcelain carriers for testing C. sporogenes, it is advisable to retain the use of porcelain carriers until stainless steel can be evaluated as a replacement carrier material for Clostridium. The evaluation of stainless steel for Clostridium has been initiated by the Study Director. Study Director recommendations for First Action revisions are provided in a modified method.

Reproducibility of antimicrobial test methods

We review reproducibility results for methods that test antimicrobial efficacy against biofilms, spores and bacteria dried onto a surface. Our review, that included test results for Pseudomonas aeruginosa, Salmonella choleraesuis and Bacillus subtilis, suggests that the level of reproducibility depends on the efficacy of the antimicrobial agent being tested for each microbe and microbial environment. To determine the reproducibility of a method, several laboratories must independently test the same antimicrobial agent using the method. Little variability among the efficacy results suggests good reproducibility. Such reproducibility assessments currently are hampered by the absence of an objective process for deciding whether the variability is sufficiently small. We present a quantitative decision process that objectively determines whether any method that assesses antimicrobial efficacy is reproducible. Because the perception of acceptable reproducibility may differ among stakeholders, the decision process is governed by a stakeholder's specifications that necessarily includes the efficacy of the agents to be tested.

Developing Horticultural Protocols for Threatened Plants from the UK Overseas Territories

The UK Overseas Territories (UKOTs) Programme based at the Royal Botanic Garden, Kew (RBG, Kew) has an active training and seed collection programme with local partners in most of the UK’s 16 Overseas Territories. Seeds are banked at the Millennium Seed Bank (MSB) for long-term storage, with a particular focus on endemic and threatened species, contributing to Target 8 of the Global Strategy for Plant Conservation (GSPC). Many of these threatened species have never been in cultivation so horticulture protocols are being developed for each species. Drawing on examples of threatened species from parts of the Caribbean and the Falkland Islands, this paper describes the components of horticulture protocols, from collection through to germination and growth in the first year. It outlines their role and value in the conservation of threatened species. These written protocols together with a short nursery guide are shared with local partners, thereby contributing to Target 3 of the GSPC.

Guidelines for the statistical analysis of a collaborative study of a laboratory method for testing disinfectant product performance

This paper presents statistical techniques suitable for analyzing a collaborative study (multilaboratory study or ring trial) of a laboratory disinfectant product performance test (DPPT) method. Emphasis is on the assessment of the repeatability, reproducibility, resemblance, and responsiveness of the DPPT method. The suggested statistical techniques are easily modified for application to a single laboratory study. The presentation includes descriptions of the plots and tables that should be constructed during initial examination of the data, including a discussion of outliers and QA checks. The statistical recommendations deal with evaluations of prevailing types of DPPTs, including both quantitative and semiquantitative tests. The presentation emphasizes tests in which the disinfectant treatment is applied to surface-associated microbes and the outcome is a viable cell count; however, the statistical guidelines are appropriate for suspension tests and other test systems. The recommendations also are suitable for disinfectant tests using any microbe (vegetative bacteria, virus, spores, etc.) or any disinfectant treatment. The descriptions of the statistical techniques include either examples of calculations based on published data or citations to published calculations. Computer code is provided in an appendix.

Cardiac complications associated with goal-directed therapy in high-risk surgical patients: a meta-analysis

Patients with limited cardiopulmonary reserve are at risk of mortality and morbidity after major surgery. Augmentation of oxygen delivery index (DO2I) with i.v. fluids and inotropes (goal-directed therapy, GDT) has been shown to reduce postoperative mortality and morbidity in high-risk patients. Concerns regarding cardiac complications associated with fluid challenges and inotropes may prevent clinicians from performing GDT in patients who need it most. We hypothesized that GDT is not associated with an increased risk of cardiac complications in high-risk, non-cardiac surgical patients. We performed a systematic search of Medline, Embase, and CENTRAL databases for randomized controlled trials (RCTs) of GDT in high-risk surgical patients. Studies including cardiac surgery, trauma, and paediatric surgery were excluded. We reviewed the rates of all cardiac complications, arrhythmias, myocardial ischaemia, and acute pulmonary oedema. Meta-analyses were performed using RevMan software. Data are presented as odds ratios (ORs), [95% confidence intervals (CIs)], and P-values. Twenty-two RCTs including 2129 patients reported cardiac complications. GDT was associated with a reduction in total cardiovascular (CVS) complications [OR=0.54, (0.38-0.76), P=0.0005] and arrhythmias [OR=0.54, (0.35-0.85), P=0.007]. GDT was not associated with an increase in acute pulmonary oedema [OR=0.69, (0.43-1.10), P=0.12] or myocardial ischaemia [OR=0.70, (0.38-1.28), P=0.25]. Subgroup analysis revealed the benefit is most pronounced in patients receiving fluid and inotrope therapy to achieve a supranormal DO2I, with the use of minimally invasive cardiac output monitors. Treatment of high-risk surgical patients GDT is not associated with an increased risk of cardiac complications; GDT with fluids and inotropes to optimize DO2I during early GDT reduces postoperative CVS complications.

Perioperative increase in global blood flow to explicit defined goals and outcomes after surgery: a Cochrane Systematic Review

This systematic review and meta-analysis summarizes the clinical effects of increasing perioperative blood flow using fluids with or without inotropes/vasoactive drugs to explicit defined goals in adults. We included randomized controlled trials of adult patients (aged 16 years or older) undergoing surgery. We included 31 studies of 5292 participants. There was no difference in mortality at the longest follow-up: 282/2615 (10.8%) died in the control group and 238/2677 (8.9%) in the treatment group, RR of 0.89 (95% CI: 0.76-1.05; P=0.18). However, the results were sensitive to analytical methods and withdrawal of studies with methodological limitations. The intervention reduced the rate of three morbidities (renal failure, respiratory failure, and wound infections) but not the rates of arrhythmia, myocardial infarction, congestive cardiac failure, venous thrombosis, and other types of infections. The number of patients with complications was also reduced by the intervention. Hospital length of stay was reduced in the treatment group by 1.16 days. There was no difference in critical care length of stay. The primary analysis of this review showed no difference between groups but this result was sensitive to the method of analysis, withdrawal of studies with methodological limitations, and was dominated by a single large study. Patients receiving this intervention stayed in hospital 1 day less with fewer complications. It is unlikely that the intervention causes harm. The balance of current evidence does not support widespread implementation of this approach to reduce mortality but does suggest that complications and duration of hospital stay are reduced.

Troponin in critically ill patients

Assays of cardiac troponin have become a cornerstone in the diagnosis of myocardial infarction across a broad range of clinical settings. In critically ill patients, cardiac troponin is detectable in the plasma in up to 60% of cases, and this incidence may increase further as assays become more sensitive. Troponin rises in critical care are commonly unrelated to pathology in the coronary arteries, but are frequently associated with conditions such as sepsis and respiratory failure. Such non-coronary troponin release is a significant, independent predictor of poor patient outcomes, and can be incorporated into risk scoring systems. Despite adding prognostic value, treatment for non-coronary troponin rises remains limited to management of the underlying cause, and restoration of a favourable balance between myocardial oxygen demand and supply. Conversely, troponin rises secondary to myocardial infarctions are amenable to the same interventions as in any other setting, albeit with additional diagnostic and therapeutic challenges. In this review, we will explore the utility of troponin as a biomarker in critical care, and we will outline a pragmatic management strategy for this patient population.

Raised serum cardiac troponin I concentrations predict hospital mortality in intensive care unit patients

BACKGROUND

Recent work suggests that increased plasma concentrations of cardiac troponin I (cTnI) are common in critically ill patients and are associated with poor outcome. We measured the frequency of increased plasma cTnI concentrations during patients' stay in a mixed medical/surgical intensive care unit (ICU) and compared our findings with hospital mortality.

METHODS

Basic details, organ support, and hospital mortality were recorded for all patients treated in ICU during a 6 month period. cTnI concentrations were sampled daily for all patients, using 0.04 µg litre(-1) as the upper limit of normal, and 0.12 µg litre(-1) as an additional stratification point.

RESULTS

Of 663 patients, 54% were male, with a mean (sd) age of 60 (18) yr, 65% were surgical patients, and the median Acute Physiology and Chronic Ill Health II (APACHE II) score was 15 (inter-quartile range 12-20). Increased cTnI concentrations were found in 345 patients (52%) while in ICU. One hundred and twenty patients (18%) died in hospital. cTnI concentration >0.04 µg litre(-1) was associated with reduced odds of hospital survival, independent of age, medical admission, unplanned admission, APACHE II score, mechanical ventilation, and haemofiltration (adjusted odds ratio 0.25, 95% confidence interval 0.08-0.75, P=0.014). Stratification by the degree of cTnI increase revealed an incremental trend towards a lower odds of hospital survival, including for patients with 'minor' elevations of cTnI (0.05-0.12 µg litre(-1)).

CONCLUSIONS

Increased serum cTnI concentrations during ICU stay independently predicts hospital mortality, even when the threshold is low. We found a trend towards an association between 'minor' elevations in cTnI and higher in-hospital mortality.

Efficacy of functional hemodynamic parameters in predicting fluid responsiveness with pulse power analysis in surgical patients

BACKGROUND

In this study we quantify the ability of dynamic cardiovascular parameters measured by the PulseCO™ algorithm of the LiDCO™plus monitor to predict the response to a fluid challenge in post-operative patients.

METHODS

Surgical patients, admitted to the Intensive Care Unit from the operating theatre were monitored with the LiDCO™plus system. A number of static and dynamic cardiovascular measurements were recorded before and after a fluid challenge. Receiver Operator Characteristic (ROC) curve analysis was used to identify the baseline values, with optimum sensitivity and specificity, to predict responsiveness to a fluid challenge.

RESULTS

Thirty-one patients were enrolled, and received protocol-based fluid challenges. Twelve (38%) responded by demonstrating an increase in stroke volume of >15%. Heart rate (HR) and central venous pressure (CVP) were not statistically different between responders and non-responders. Mean arterial pressure (mAP), systolic pressure variation (SPV), pulse pressure variation (PPV) and stroke volume variation (SVV) were statistically different between responders and non-responders. Parameters with a ROC area under the curve (AUC) significantly >0.5 included SPV 0.70 (0.52-0.88) P=0.046, PPV 0.87 (0.76-0.99) P<0.0002 and SVV 0.84 (0.71-0.96) P=0.0005. The best cut-off values (sensitivity and specificity) to predict fluid were SPV >9 mmHg (73%, 76%), PPV >13% (83%, 74%) and SVV >12.5% (75%, 83%). ROC analysis did not show the AUC to be significantly >0.5 for HR, mAP and CVP CONCLUSION: Dynamic indices measured by PulseCO™ (LiDCO) have a high sensitivity and specificity in predicting fluid responsiveness in sedated and mechanically ventilated patients. A cut-off value for PPV of 13% is the most sensitive and specific indicator of fluid responsiveness.

Use of alternative carrier materials in AOAC Official Method 2008.05, efficacy of liquid sporicides against spores of Bacillus subtilis on a hard, nonporous surface, quantitative three-step method

The quantitative Three-Step Method (TSM) for testing the efficacy of liquid sporicides against spores of Bacillus subtilis on a hard, nonporous surface (glass) was adopted as AOAC Official Method 2008.05 in May 2008. The TSM uses 5 x 5 x 1 mm coupons (carriers) upon which spores have been inoculated and which are introduced into liquid sporicidal agent contained in a microcentrifuge tube. Following exposure of inoculated carriers and neutralization, spores are removed from carriers in three fractions (gentle washing, fraction A; sonication, fraction B; and gentle agitation, fraction C). Liquid from each fraction is serially diluted and plated on a recovery medium for spore enumeration. The counts are summed over the three fractions to provide the density (viable spores per carrier), which is log10-transformed to arrive at the log density. The log reduction is calculated by subtracting the mean log density for treated carriers from the mean log density for control carriers. This paper presents a single-laboratory investigation conducted to evaluate the applicability of using two porous carrier materials (ceramic tile and untreated pine wood) and one alternative nonporous material (stainless steel). Glass carriers were included in the study as the reference material. Inoculated carriers were evaluated against three commercially available liquid sporicides (sodium hypochlorite, a combination of peracetic acid and hydrogen peroxide, and glutaraldehyde), each at two levels of presumed efficacy (medium and high) to provide data for assessing the responsiveness of the TSM. Three coupons of each material were evaluated across three replications at each level; three replications of a control were required. Even though all carriers were inoculated with approximately the same number of spores, the observed counts of recovered spores were consistently higher for the nonporous carriers. For control carriers, the mean log densities for the four materials ranged from 6.63 for wood to 7.14 for steel. The pairwise differences between mean log densities, except for glass minus steel, were statistically significant (P < 0.001). The repeatability standard deviations (Sr) for the mean control log density per test were similar for the four materials, ranging from 0.08 for wood to 0.13 for tile. Spore recovery from the carrier materials ranged from approximately 20 to 70%: 20% (pine wood), 40% (ceramic tile), 55% (glass), and 70% (steel). Although the percent spore recovery from pine wood was significantly lower than that from other materials, the performance data indicate that the TSM provides a repeatable and responsive test for determining the efficacy of liquid sporicides on both porous and nonporous materials.

Checking the validity of the harvesting and disaggregating steps in laboratory tests of surface disinfectants

A chemical disinfectant against surface-associated bacteria typically uses carriers (e.g., glass disks) that are purposely contaminated with bacteria prior to disinfection. After disinfection, the bacteria are harvested by mechanically separating them from the carrier surface to form a suspension of cells in a dilution tube. Bacterial clumps in the tube are disaggregated using mechanical or chemical techniques, thereby creating a well-mixed suspension of single cells suitable for enumeration. Efficacy is quantified by comparing the viable cell count for a disinfected carrier to the viable cell count for sham-disinfected (control) carrier. A test is said to be biased (invalid) if the observed efficacy measure is systematically higher or lower than the true efficacy. It is shown here for the first time that the bias attributable to the harvesting and disaggregating steps of a disinfectant test can be measured. For some conventional biofilm harvesting and disaggregating techniques, laboratory checks showed either negligible bias or important bias, depending on the disinfectant. Quantitative bias checks on the harvesting and disaggregating steps are prudent for each combination of carrier material, microorganism, and disinfectant. The quantitative results should be augmented by microscopic examination of harvested disinfected and control carriers and of the disaggregated suspensions.

Improving the AOAC use-dilution method by establishing a minimum log density value for test microbes on inoculated carriers

The AOAC Use-Dilution methods, 955.14 (Salmonella enterica), 955.15 (Staphylococcus aureus), and 964.02 (Pseudomonas aeruginosa), are used to measure the efficacy of disinfectants on hard inanimate surfaces. The methods do not provide procedures to assess log density of the test microbe on inoculated penicylinders (carrier counts). Without a method to measure and monitor carrier counts, the associated efficacy data may not be reliable and repeatable. This report provides a standardized procedure to address this method deficiency. Based on carrier count data collected by four laboratories over an 8 year period, a minimum log density value is proposed to qualify the test results. Carrier count data were collected concurrently with 242 Use-Dilution tests. The tests were conducted on products bearing claims against P. aeruginosa and S. aureus with and without an organic soil load (OSL) added to the inoculum (as specified on the product label claim). Six carriers were assayed per test for a total of 1452 carriers. All 242 mean log densities were at least 6.0 (geometric mean of 1.0 x 10(6) CFU/carrier). The mean log densities did not exceed 7.5 (geometric mean of 3.2 x 10(7) CFU/carrier). For all microbes and OSL treatments, the mean log density (+/- SEM) was 6.7 (+/- 0.07) per carrier (a geometric mean of 5.39 x 10(6) CFU/carrier). The mean log density for six carriers per test showed good repeatability (0.29) and reproducibility (0.32). A minimum mean log density of 6.0 is proposed as a validity requirement for S. aureus and P. aeruginosa. The minimum level provides for the potential inherent variability that may be experienced by a wide range of laboratories and the slight effect due to the addition of an OSL. A follow-up report is planned to present data to support the carrier count procedure and carrier counts for S. enterica.

Improving the AOAC Use-Dilution Method by Establishing a Minimum Log Density Value for Test Microbes on Inoculated Carriers

The AOAC Use-Dilution methods, 955.14 (Salmonella enterica), 955.15 (Staphylococcus aureus), and 964.02 (Pseudomonas aeruginosa), are used to measure the efficacy of disinfectants on hard inanimate surfaces. The methods do not provide procedures to assess log density of the test microbe on inoculated penicylinders (carrier counts). Without a method to measure and monitor carrier counts, the associated efficacy data may not be reliable and repeatable. This report provides a standardized procedure to address this method deficiency. Based on carrier count data collected by four laboratories over an 8 year period, a minimum log density value is proposed to qualify the test results. Carrier count data were collected concurrently with 242 Use-Dilution tests. The tests were conducted on products bearing claims against P. aeruginosa and S. aureus with and without an organic soil load (OSL) added to the inoculum (as specified on the product label claim). Six carriers were assayed per test for a total of 1452 carriers. All 242 mean log densities were at least 6.0 (geometric mean of 1.0 106 CFU/carrier). The mean log densities did not exceed 7.5 (geometric mean of 3.2 107 CFU/carrier). For all microbes and OSL treatments, the mean log density (SEM) was 6.7 (0.07) per carrier (a geometric mean of 5.39 106 CFU/carrier). The mean log density for six carriers per test showed good repeatability (0.29) and reproducibility (0.32). A minimum mean log density of 6.0 is proposed as a validity requirement for S. aureus and P. aeruginosa. The minimum level provides for the potential inherent variability that may be experienced by a wide range of laboratories and the slight effect due to the addition of an OSL. A follow-up report is planned to present data to support the carrier count procedure and carrier counts for S. enterica.

Women and alcohol: Current Australian research

Over the past decade research on women and alcohol has been gaining momentum with evidence of an accumulating data base and a growing section of the drug and alcohol literature specifically addressing this area of interest. Despite the gains made in gender sensitive research on substance use, a review of the literature reveals that many of the articulated concerns are similar to those identified over the preceding 20 years.This paper reports on the findings of an Australian wide survey investigating the current level of research on women and alcohol. The survey was used in conjunction with a critical analysis of the literature to identify gaps in research activity in the area of women and alcohol. Identified research gaps result, in part, from the disproportionate focus on women with severe alcohol problems within treatment facilities. There is a lack of qualitative and quantitative research on women's drinking, whether it be usual use or problematic use, within the general population as a way of bridging the gap between population surveys and clinical studies. In addition, there is a need for longitudinal research to provide information on the context of women's drinking over a several year period, giving insight into the many factors which could be influencing women's drinking behaviour. Finally, the relative lack of commitment to prevention as a research agenda for women needs to be addressed.

Determining the efficacy of liquid sporicides against spores of Bacillus subtilis on a hard nonporous surface using the quantitative three step method: collaborative study

A collaborative study was conducted to validate the quantitative Three Step Method (TSM), a method designed to measure the performance of liquid sporicides on a hard nonporous surface. Ten laboratories agreed to participate in the collaborative study; data from 8 of 10 participating laboratories were used in the final statistical analysis. The TSM uses 5 x 5 x 1 mm glass coupons (carriers) upon which spores have been inoculated and which are introduced into liquid sporicidal agent contained in a microcentrifuge tube. Following exposure to a test chemical and a neutralization agent, spores are removed from carriers in 3 fractions: passive removal (Fraction A), sonication (Fraction B), and gentle agitation (Fraction C). Liquid from each fraction is serially diluted and plated on a recovery medium for spore enumeration. Control counts are compared to the treated counts, and the level of efficacy is determined by calculating the log10 reduction (LR) of spores. The main statistical goals were to evaluate the repeatability and reproducibility of the LR values, to estimate the components of variance for LR, and to assess method responsiveness. AOAC Method 966.04-Method II was used as a reference method. The scope of the validation was limited to testing liquid formulations against spores of Bacillus subtilis, a surrogate for virulent strains of B. anthracis, on a hard nonporous surface (glass). The test chemicals used in the study were sodium hypochlorite, a combination of peracetic acid and hydrogen peroxide, and glutaraldehyde. Each test chemical was evaluated at 3 levels of presumed efficacy: high, medium, and low. Three replications were required. The TSM was validated as it successfully met the statistical parameters for quantitative test methods. Satisfactory validation parameters, such as the repeatability standard deviation (Sr) and reproducibility standard deviation (SR), were obtained for control carrier counts and LR values. Both the TSM and the reference method were responsive to the efficacy levels of the test chemicals. For the 72 total TSM tests conducted, the mean (+/- standard error of the mean) log density of spores per control carrier was 6.86 (+/- 0.08); the Sr and SR were low at 0.15 and 0.27, respectively. Across the range of test chemicals, the Sr and SR estimates associated with LR were also acceptably low. The Sr ranged from 0.17 to 0.72 and the SR ranged from 0.34 to 1.43. Overall, the Sr and SR estimates associated with the efficacy data were within the ranges published for other quantitative methods and meet the performance characteristics necessary for validation.

Comparative evaluation of biofilm disinfectant efficacy tests

Regulatory agencies are receiving registration applications for unprecedented, antibiofilm label claims for disinfectants. Reliable, practical, and relevant laboratory biofilm test methods are required to support such claims. This investigation describes the influence of fluid dynamics on the relevancy of a laboratory test. Several disinfectant formulations were tested using three different biofilm testing systems run side-by-side: the CDC biofilm reactor system that created turbulent flow (Reynolds number between 800 and 1850), the drip flow biofilm reactor system that created slow laminar flow (Reynolds number between 12 and 20), and the static biofilm system that involved no fluid flow. Each comparative experiment also included a dried surface carrier test and a dried biofilm test. All five disinfectant tests used glass coupons and followed the same steps for treatment, neutralization, viable cell counting, and calculating the log reduction (LR). Three different disinfectants, chlorine, a quaternary ammonium compound, and a phenolic, were each applied at two concentrations. Experiments were conducted separately with Pseudomonas aeruginosa and Staphylococcus aureus and every experiment was independently repeated. The results showed that biofilm grown in the CDC reactor produced the smallest LR, the static biofilm produced the largest LR, and biofilm grown in the drip flow reactor produced an intermediate LR. The differences were large enough to be of practical importance. The dried surface test often produced a significantly higher LR than the tests against hydrated or dried biofilm. The dried biofilm test produced LR values similar to those for the corresponding hydrated biofilm test. These results show that the efficacy of a disinfectant must be measured by using a laboratory method where biofilm is grown under fluid flow conditions similar to the environment where the disinfectant will be applied.

The Postoperative Morbidity Survey was validated and used to describe morbidity after major surgery

OBJECTIVES

To describe the reliability and validity of the Postoperative Morbidity Survey (POMS). To describe the level and pattern of short-term postoperative morbidity after major elective surgery using the POMS.

STUDY DESIGN AND SETTING

This was a prospective cohort study of 439 adults undergoing major elective surgery in a UK teaching hospital. The POMS, an 18-item survey that address nine domains of postoperative morbidity, was recorded on postoperative days 3, 5, 8, and 15.

RESULTS

Inter-rater reliability was perfect for 11/18 items (Kappa=1.0), with Kappa=0.94 for 6/18 items. A priori hypotheses that the POMS would discriminate between patients with known measures of morbidity risk, and predict length of stay were generally supported through observation of data trends, and there was statistically significant evidence of construct validity for all but the wound and neurological domains. POMS-defined morbidity was present in 325 of 433 patients (75.1%) remaining in hospital on postoperative day 3 after surgery, 231 of 407 patients (56.8%) on day 5, 138 of 299 patients (46.2%) on day 8, and 70 of 111 patients (63.1%) on day 15. Gastrointestinal (47.4%), infectious (46.5%), pain-related (40.3%), pulmonary (39.4%), and renal problems (33.3%) were the most common forms of morbidity.

CONCLUSION

The POMS is a reliable and valid survey of short-term postoperative morbidity in major elective surgery. Many patients remain in hospital without any morbidity as recorded by the POMS.

Asiatic acid and corosolic acid enhance the susceptibility of Pseudomonas aeruginosa biofilms to tobramycin

Asiatic acid and corosolic acid are two natural products identified as biofilm inhibitors in a biofilm inhibition assay. We evaluated the activities of these two compounds on Pseudomonas aeruginosa biofilms grown in rotating disk reactors (RDRs) in combination with tobramycin and ciprofloxacin. To determine the ruggedness of our systems, the antibiotic susceptibilities of these biofilms were assessed with tobramycin and ciprofloxacin. The biofilm bacteria produced in the RDR were shown to display remarkable tolerance to 10 mug/ml of ciprofloxacin, thus mimicking the tolerance observed in recalcitrant bacterial infections. These studies further demonstrate that a nonmucoid strain of P. aeruginosa can form a biofilm that tolerates ciprofloxacin at clinically relevant concentrations. Neither asiatic acid nor corosolic acid reduced the viable cell density of P. aeruginosa biofilms. However, both compounds increased the susceptibility of biofilm bacteria to subsequent treatment with tobramycin, suggesting asiatic acid and corosolic acid to be compounds that potentiate the activity of antibiotics. A similar statistical interaction was observed between ciprofloxacin and subsequent treatment with tobramycin.

Comparative evaluation of two quantitative test methods for determining the efficacy of liquid sporicides and sterilants on a hard surface: a precollaborative study

Two quantitative carrier-based test methods for determining the efficacy of liquid sporicides and sterilants on a hard surface, the Standard Quantitative Carrier Test Method-ASTM E 2111-00 and an adaptation of a quantitative micro-method as reported by Sagripanti and Bonifacino, were compared in this study. The methods were selected based on their desirable characteristics (e.g., well-developed protocol, previous use with spores, fully quantitative, and use of readily available equipment) for testing liquid sporicides and sterilants on a hard surface. In this paper, the Sagripanti-Bonifacino procedure is referred to as the Three Step Method (TSM). AOAC Official Method 966.04 was included in this study as a reference method. Three laboratories participated in the evaluation. Three chemical treatments were tested: (1) 3000 ppm sodium hypochlorite with pH adjusted to 7.0, (2) a hydrogen peroxide/peroxyacetic acid product, and (3) 3000 ppm sodium hypochlorite with pH unadjusted (pH of approximately 10.0). A fourth treatment, 6000 ppm sodium hypochlorite solution with pH adjusted to 7.0, was included only for Method 966.04 as a positive control (high level of efficacy). The contact time was 10 min for all chemical treatments except the 6000 ppm sodium hypochlorite treatment which was tested at 30 min. Each chemical treatment was tested 3 times using each of the methods. Only 2 of the laboratories performed the AOAC method. Method performance was assessed by the within-laboratory variance, between-laboratory variance, and total variance associated with the log reduction (LR) estimates generated by each quantitative method. The quantitative methods performed similarly, and the LR values generated by each method were not statistically different for the 3 treatments evaluated. Based on feedback from the participating laboratories, compared to the TSM, ASTM E 2111-00 was more resource demanding and required more set-up time. The logistical and resource concerns identified for ASTM E 2111-00 were largely associated with the filtration process and counting bacterial colonies on filters. Thus, the TSM was determined to be the most suitable method.

Interventions for 'poor responders' to controlled ovarian hyperstimulation (COH) in in-vitro fertilisation (IVF)

BACKGROUND

The success of in-vitro fertilisation (IVF) treatment depends on adequate follicle recruitment by using controlled ovarian stimulation with gonadotrophins. Failure to recruit adequate follicles is called 'poor response'. Various treatment protocols have been proposed that are targeted at this cohort of women, aiming to increase their ovarian response.

OBJECTIVES

To compare the effectiveness of different treatment interventions in women who have poor response to controlled ovarian hyperstimulation (are poor responders) in the context of in vitro fertilisation.

SEARCH STRATEGY

We searched the Cochrane Menstrual Disorders and Subfertility Group Specialised Register of controlled trials (MDSG), the Cochrane Central Register of Controlled trials (CENTRAL) (The Cochrane Library 2003, Issue 1), MEDLINE (1966 to August 2006), EMBASE (1980 to August 2006) and The National Research Register (NRR). The citation lists of relevant publications, review articles, abstracts of scientific meetings and included studies were also searched. The authors were contacted to identify or clarify data that were unclear from the trial reports.

SELECTION CRITERIA

Only randomised controlled trials (RCTs) comparing one type of intervention versus another for controlled ovarian stimulation of poor responders to a previous IVF treatment, using a standard long protocol were included.

DATA COLLECTION AND ANALYSIS

Two review authors independently scanned the abstracts, identified relevant papers, assessed inclusion and trial quality and extracted relevant data. Validity was assessed in terms of method of randomisation, completeness of treatment cycle and co-intervention. Where possible, data were pooled for analysis.

MAIN RESULTS

Nine trials involving six different comparison groups have been included in this review. Only one trial reported live birth rates. Four groups compared the long protocol with another intervention. Only one comparison group (bromocryptine versus long protocol) reported a higher clinical pregnancy rate per cycle, in the bromocryptine arm (OR 5.60, 95% CI 1.40 to 22.47). Two comparison groups showed a lower number of oocytes in the long protocol group (versus stop and gonadotrophin releasing hormone (GnRH) antagonist protocols). However, two comparison groups also showed lower cancellation rates in the long protocol treatment group (versus stop and GnRHa flare-up protocols). None reported any evident difference in the adverse effects.

AUTHORS' CONCLUSIONS

There is insufficient evidence to support the routine use of any particular intervention either for pituitary downregulation, ovarian stimulation or adjuvant therapy in the management of poor responders to controlled ovarian stimulation in IVF. More robust data from good quality RCTs with relevant outcomes are needed.

A laboratory hot tub model for disinfectant efficacy evaluation

This paper describes a novel laboratory hot tub (LHT) apparatus and associated standard operating procedure (SOP) designed to reproduce the key biological, chemical, and engineering parameters associated with recreational and therapeutic hot tubs. Efficacy, as measured quantitatively by log reduction values, was determined against both biofilm and planktonic bacteria. When the LHT was run according to the SOP, with no antimicrobial treatment, a consistent level of bacterial contamination occurred. The means of log10 viable cell densities (+/- the repeatability standard deviation of log densities) were 7.2 (+/-0.31) for the bulk water (density in units of cfu ml-1), 5.3 (+/-0.56) for the coupons (density in units of cfu cm-2), and 6.6 (+/-0.50) for the filters (density in units of cfu cm-2). When control and chlorine treated LHTs were run in parallel, the log reduction increased significantly with chlorine concentration for samples of planktonic bacteria in the bulk water (p=0.016), biofilm bacteria on the coupons (p=0.09) and biofilm bacteria on the filter (p=0.005), indicating that the method was sensitive to chlorine concentration. The method also displayed sensitivity by differentiating between chlorine and bromine treatments; in every case, chlorine produced a greater log reduction than did the same concentration of bromine. The model and SOP were shown to be rugged with respect to slight changes in fluid mixing intensity, water chemistry (saturation index), inoculum size, and organic loading. The LHT and associated SOP provide a reliable second tier in a three-tiered testing process, in which the first tier is a suspension test and the final tier is a field test.

Modification to the AOAC Sporicidal Activity of Disinfectants Test (Method 966.04): collaborative study

In an effort to improve AOAC Method 966.04, the Sporicidal Activity of Disinfectants Test, selected modifications to the procedure were evaluated in a collaborative study. Method 966.04 is used to generate efficacy data to support the product registration of sporicides and sterilants. The method is a carrier-based test that provides a qualitative measure of product efficacy against spores of Bacillus subtilis and Clostridium sporogenes. The use of garden soil extract and the lack of standard procedures for the enumeration of spores and neutralization of the test chemicals have been considered problematic for many years. The proposed modifications were limited to the B. subtilis and hard surface carrier (porcelain penicylinder) components of the method. The study included the evaluation of a replacement for soil extract nutrient broth and an establishment of a minimum spore titer per carrier, both considered crucial for the improvement and utilization of the method. Additionally, an alternative hard surface material and a neutralization confirmation procedure were evaluated. To determine the equivalence of the proposed alternatives to the standard method, 3 medium/carrier combinations, (1) soil extract nutrient broth/porcelain carrier (current method), (2) nutrient agar amended with 5 microg/mL manganese sulfate/porcelain carrier, and (3) nutrient agar amended with 5 microg/mL manganese sulfate/stainless steel carrier were analyzed for carrier counts, HCI resistance, efficacy, quantitative efficacy, and spore wash-off. The test chemicals used in the study represent 3 chemical classes and are commercially available antimicrobial liquid products: sodium hypochlorite (bleach), glutaraldehyde, and a combination of peracetic acid and hydrogen peroxide. Four laboratories participated in the study. The results of the spore titer per carrier, HCI resistance, efficacy, and wash-off studies demonstrate that amended nutrient agar in conjunction with the porcelain is comparable to the current method, soil extract nutrient broth/porcelain. The nutrient agar method is simple, inexpensive, reproducible, and provides an ample supply of high quality spores. Due to the current use of porcelain carriers for testing C. sporogenes, it is advisable to retain the use of porcelain carriers until stainless steel can be evaluated as a replacement carrier material for Clostridium. The evaluation of stainless steel for Clostridium has been initiated by the Study Director. Study Director recommendations for First Action revisions are provided in a modified method.

Statistical assessment of a laboratory method for growing biofilms

Microbial biofilms have been grown in laboratories using a variety of different approaches. A laboratory biofilm reactor system, called the CDC biofilm reactor (CBR) system, has been devised for growing biofilms under moderate to high fluid shear stress. The reactor incorporates 24 removable biofilm growth surfaces (coupons) for sampling and analysing the biofilm. Following preliminary experiments to verify the utility of the CBR system for growing biofilms of several clinically relevant organisms, a standard operating procedure for growing a Pseudomonas aeruginosa biofilm was created. This paper presents the results of a rigorous, intra-laboratory, statistical evaluation of the repeatability and ruggedness of that procedure as well as the results of the experiments with clinically relevant organisms. For the statistical evaluations, the outcome of interest was the density (c.f.u. cm(-2)) of viable P. aeruginosa. Replicate experiments were conducted to assess the repeatability of the log density outcome. The mean P. aeruginosa log10 density was 7.1, independent of the coupon position within the reactor. The repeatability standard deviation of the log density based on one coupon per experiment was 0.59. Analysis of variance showed that the variability of the log density was 53 % attributable to within-experiment sources and 47 % attributable to between-experiments sources. The ruggedness evaluation applied response-surface design and regression analysis techniques, similar to those often used for sensitivity analyses in other fields of science and engineering. This approach provided a quantitative description of ruggedness; specifically, the amount the log density was altered by small adjustments to four key operational factors--time allowed for initial surface colonization, temperature, nutrient concentration, and fluid shear stress on the biofilm. The small size of the regression coefficient associated with each operational factor showed that the method was rugged; that is, relatively insensitive to minor perturbations of the four factors. These results demonstrate that the CBR system is a reliable experimental tool for growing a standard biofilm in the laboratory and that it can be adapted to study several different micro-organisms.

Hypothesis for the role of nutrient starvation in biofilm detachment

A combination of experimental and theoretical approaches was used to investigate the role of nutrient starvation as a potential trigger for biofilm detachment. Experimental observations of detachment in a variety of biofilm systems were made with pure cultures of Pseudomonas aeruginosa. These observations indicated that biofilms grown under continuous-flow conditions detached after flow was stopped, that hollow cell clusters were sometimes observed in biofilms grown in flow cells, and that lysed cells were apparent in the internal strata of colony biofilms. When biofilms were nutrient starved under continuous-flow conditions, detachment still occurred, suggesting that starvation and not the accumulation of a metabolic product was responsible for triggering detachment in this particular system. A cellular automata computer model of biofilm dynamics was used to explore the starvation-dependent detachment mechanism. The model predicted biofilm structures and dynamics that were qualitatively similar to those observed experimentally. The predicted features included centrally located voids appearing in sufficiently large cell clusters, gradients in growth rate within these clusters, and the release of most of the biofilm with simulated stopped-flow conditions. The model was also able to predict biofilm sloughing resulting solely from this detachment mechanism. These results support the conjecture that nutrient starvation is an environmental cue for the release of microbes from a biofilm.

Statistical quantification of detachment rates and size distributions of cell clumps from wild-type (PAO1) and cell signaling mutant (JP1) Pseudomonas aeruginosa biofilms

The detachment of cells from bacterial biofilms is an important, yet poorly understood and largely unquantified phenomenon. Detached cell clumps from medical devices may form microemboli and lead to metastasis, especially if they are resistant to host defenses and antibiotics. In manufacturing plants detached clumps entering a process stream decrease product quality. Two strains of Pseudomonas aeruginosa, a wild type (PAO1) and a cell signaling mutant (JP1), were studied to (i) quantify and model detachment patterns and (ii) determine the influence of cell signaling on detachment. We collected effluent from a biofilm flowthrough reactor and determined the size distribution for cell detachment events by microscopic examination and image analysis. The two strains were similar in terms of both biofilm structure and detachment patterns. Most of the detachment events were single-cell events; however, multiple-cell detachment events contributed a large fraction of the total detached cells. The rates at which events containing multiple cells detached from the biofilm were estimated by fitting a statistical model to the size distribution data. For events consisting of at least 1,000 cells, the estimated rates were 4.5 events mm(-2) min(-1) for PAO1 and 4.3 events mm(-2) min(-1) for JP1. These rates may be significant when they are scaled up to the total area of a real biofilm-contaminated medical device surface and to the hours or days of patient exposure.

Comparison of fluorescence microscopy and solid-phase cytometry methods for counting bacteria in water

Total direct counts of bacterial abundance are central in assessing the biomass and bacteriological quality of water in ecological and industrial applications. Several factors have been identified that contribute to the variability in bacterial abundance counts when using fluorescent microscopy, the most significant of which is retaining an adequate number of cells per filter to ensure an acceptable level of statistical confidence in the resulting data. Previous studies that have assessed the components of total-direct-count methods that contribute to this variance have attempted to maintain a bacterial cell abundance value per filter of approximately 10(6) cells filter(-1). In this study we have established the lower limit for the number of bacterial cells per filter at which the statistical reliability of the abundance estimate is no longer acceptable. Our results indicate that when the numbers of bacterial cells per filter were progressively reduced below 10(5), the microscopic methods increasingly overestimated the true bacterial abundance (range, 15.0 to 99.3%). The solid-phase cytometer only slightly overestimated the true bacterial abundances and was more consistent over the same range of bacterial abundances per filter (range, 8.9 to 12.5%). The solid-phase cytometer method for conducting total direct counts of bacteria was less biased and performed significantly better than any of the microscope methods. It was also found that microscopic count data from counting 5 fields on three separate filters were statistically equivalent to data from counting 20 fields on a single filter.

A microtiter-plate screening method for biofilm disinfection and removal

A quantitative spectrophotometric method was developed to measure the removal and killing efficacy of antibiofilm agents. Biofilms of Pseudomonas aeruginosa or Staphylococcus epidermidis were grown in 96-well plates, treated with an agent, then stained with either the biomass indicator crystal violet or the respiratory indicator 5-cyano-2,3-ditolyl tetrazolium chloride. This rapid screening method is sensitive enough to elucidate concentration-response relationships as well as differences between species responses to treatments. Using these assays, agents can be ranked by their ability to remove or kill biofilm.

A computer investigation of chemically mediated detachment in bacterial biofilms

A three-dimensional computer model was used to evaluate the effect of chemically mediated detachment on biofilm development in a negligible-shear environment. The model, BacLAB, combines conventional diffusion-reaction equations for chemicals with a cellular automata algorithm to simulate bacterial growth, movement and detachment. BacLAB simulates the life cycle of a bacterial biofilm from its initial colonization of a surface to the development of a mature biofilm with cell areal densities comparable to those in the laboratory. A base model founded on well established transport equations that are easily adaptable to investigate conjectures at the biological level has been created. In this study, the conjecture of a detachment mechanism involving a bacterially produced chemical detachment factor in which high local concentrations of this detachment factor cause the bacteria to detach from the biofilm was examined. The results show that the often observed 'mushroom'-shaped structure can occur if detachment events create voids so that the remaining attached cells look like mushrooms.

A focusing crystal analyser for the rejection of inelastic X-ray scattering

A focusing crystal analyser has been constructed that allows the rejection of inelastic X-ray scattering during diffuse scattering measurements close to an absorption edge. A Johann geometry was obtained by cylindrical bending of perfect silicon and germanium crystals. The choice of reflection, the effect of bending and the contribution of the source size are discussed in relation to the energy resolution. Measurements at the As K-edge (11.867 keV) and at the Cs K-edge (35.985 keV) are presented to demonstrate that the focusing analyser can be used over a wide energy range. A direct comparison with a flat perfect crystal with comparable energy resolution shows a gain in intensity by a factor of 50.

Assessing technician effects when extracting quantities from microscope images

Consider an experiment where the response is based on an image; e.g., an image captured to a computer file by a digital camera mounted on a microscope. Suppose relevant quantitative measures are extracted from the images so that results can be analyzed by conventional statistical methods. The steps involved in extracting the measures may require that the technicians, who are processing the images, perform some subjective manipulations. In this case, it is important to determine the bias and variability, if any, attributable to the technicians' decisions. This paper describes the experimental design and statistical analyses that are useful for those determinations. The design and analysis are illustrated by application to two biofilm research projects that involved quantitative image analysis. In one investigation, the technician was required to choose a threshold level, then the image analysis program automatically extracted relevant measures from the resulting black and white image. In the other investigation, the technician was required to choose fiducial points in each of two images collected on different microscopes; then the image analysis program registered the images by stretching, rotating, and overlaying them, so that their quantitative features could be correlated. These investigations elucidated the effects of the technicians' decisions, thereby helping us to assess properly the statistical uncertainties in the conclusions for the primary experiments.

Movement, replication, and emigration rates of individual bacteria in a biofilm

Single-cell behavior within a biofilm was observed over a period of several hours. The observations were converted into quantitative stochastic rules governing the behavior of individual cells within a biofilm. Such a quantitative summary provides not only a concise description of the results but also information helpful when constructing computer models of dynamic biofilm systems. The time to division, emigration, and rate of motility of individual green fluorescent protein labeled Pseudomonas aeruginosa PAO1 cells in a 3-10 microm thick biofilm containing predominantly non-GFP labeled cells were calculated based on images of individual cells collected at 15-min time intervals. The biofilms were grown in flow cells and the images captured with a confocal laser microscope. Cells destined to emigrate are more active than those that remain; the geometric means for velocities in the biofilm are 1.0 microm/h for remaining cells and 1.5 microm/h for emigrating cells. The median time to emigration was 2.0 h. During the experimental observation period, the estimated probability for emigration is 0.44, illustrating that a substantial number of bacteria leave the field of view. Cells emigrate at a median time one-third that of the median time to replication. Specifically, the median time for cells to divide was 6.9 h, and it was estimated that 10% of the cells had a time to division greater than 10 h.

What are you going to do about the base deficit?

The management of elevated blood acid (metabolic acidosis) is poorly understood and standard therapies are often initiated without consideration of the underlying pathophysiology.

Production of bacterial cellulose from alternate feedstocks

Production of bacterial cellulose by Acetobacter xylinum ATCC 10821 and 23770 in static cultures was tested from unamended food process effluents. Effluents included low-solids (LS) and high-solids (HS) potato effluents, cheese whey permeate (CW), or sugar beet raffinate (CSB). Strain 23770 produced 10% less cellulose from glucose than did strain 10821 and diverted more glucose to gluconate. Unamended HS, CW, and CSB were unsuitable for cellulose production by either strain, and LS was unsuitable for production by strain 10821. However, strain 23770 produced 17% more cellulose from LS than from glucose, indicating that unamended LS could serve as a feedstock for bacterial cellulose.