The role of epidemiological cutoff values (ECVs/ECOFFs) in antifungal susceptibility testing and interpretation for uncommon yeasts and moulds

The role of antimicrobial susceptibility testing is to aid in selecting the best agent for the treatment of bacterial and fungal diseases. This has been best achieved by the setting of breakpoints by Clinical Laboratory Standards Institute (CLSI) for prevalent Candida spp. versus anidulafungin, caspofungin, micafungin, fluconazole, and voriconazole. The European Committee on Antimicrobial Susceptibility Testing (EUCAST) also has set breakpoints for prevalent and common Candida and Aspergillus species versus amphotericin B, itraconazole, and posaconazole. Recently, another interpretive category, the epidemiological cut off value, could aid in the early identification of strains with acquired resistance mechanisms. CLSI has postulated that epidemiological cut off values may, with due caution, aid physicians in managing mycosis by species where breakpoints are not available. This review provides (1) the criteria and statistical approach to establishing and estimating epidemiological cut off values (ECVs), (2) the role of the epidemiological cut off value in establishing breakpoints, (3) the potential role of epidemiological cut off values in clinical practice, (4) and the wide range of CLSI-based epidemiological cut off values reported in the literature as well as EUCAST and Sensititre Yeast One-ECVs. Additionally, we provide MIC/MEC (minimal inhibitory concentrations/minimum effective concentrations) ranges/modes of each pooled distribution used for epidemiological cut off value calculation. We focus on the epidemiological cut off value, the new interpretive endpoint that will identify the non-wild type strains (defined as potentially harboring resistance mechanisms). However, we emphasize that epidemiological cut off values will not categorize a fungal isolate as susceptible or resistant as breakpoints do, because the former do not account for the pharmacology of the antifungal agent or the findings from clinical outcome studies.

Determination of disk diffusion susceptibility testing interpretive criteria using model-based analysis: development and implementation

The determination of diffusion test breakpoints has become a challenging issue due to the increasing resistance of microorganisms to antibiotics. Currently, the most commonly-used method for determining these breakpoints is the modified error-rate bounded method. Its use has remained widespread despite the introduction of several model-based methods that have been shown superior in terms of precision and accuracy. However, the computational complexities associated with these new approaches has been a significant barrier for clinicians. To remedy this, we developed and examine the utility of a free online software package designed for the determination of diffusion test breakpoints: dBETS (diffusion Breakpoint Estimation Testing Software). This software package allows clinicians to easily analyze data from susceptibility experiments through visualization, error-rate bounded, and model-based approaches. We analyze four publicly available data sets from the Clinical and Laboratory Standards Institute using dBETS.

SaMpling Antibiotics in Renal Replacement Therapy (SMARRT): an observational pharmacokinetic study in critically ill patients

Background

Optimal antibiotic dosing is key to maximising patient survival, and minimising the emergence of bacterial resistance. Evidence-based antibiotic dosing guidelines for critically ill patients receiving RRT are currently not available, as RRT techniques and settings vary greatly between ICUs and even individual patients. We aim to develop a robust, evidence-based antibiotic dosing guideline for critically ill patients receiving various forms of RRT. We further aim to observe whether therapeutic antibiotic concentrations are associated with reduced 28-day mortality.

Methods/Design

We designed a multi-national, observational pharmacokinetic study in critically ill patients requiring RRT. The study antibiotics will be vancomycin, linezolid, piperacillin/tazobactam and meropenem. Pharmacokinetic sampling of each patient’s blood, RRT effluent and urine will take place during two separate dosing intervals. In addition, a comprehensive data set, which includes the patients’ demographic and clinical parameters, as well as modality, technique and settings of RRT, will be collected. Pharmacokinetic data will be analysed using a population pharmacokinetic approach to identify covariates associated with changes in pharmacokinetic parameters in critically ill patients with AKI who are undergoing RRT for the five commonly prescribed antibiotics.

Discussion

Using the comprehensive data set collected, the pharmacokinetic profile of the five antibiotics will be constructed, including identification of RRT and other factors indicative of the need for altered antibiotic dosing requirements. This will enable us to develop a dosing guideline for each individual antibiotic that is likely to be relevant to any critically ill patient with acute kidney injury receiving any of the included forms of RRT.

Trial registration

Australian New Zealand Clinical Trial Registry (ACTRN12613000241730) registered 28 February 2013

Antimicrobial stewardship: what is it, and how does it work?

Antimicrobial stewardship is emerging as a vital management tool in the efforts to contain antimicrobial resistance and retain the efficacy of available agents. It is based on a set of concepts about antimicrobial use and resistance that have been developed over the past 70 years. There are seven basic requirements for a stewardship program to function at a local level, including (1) ‘executive’ ownership of the issue, (2) consensus prescribing guidelines, (3) a local formulary with various levels of restricted access, (4) a local champion (or champions) who is a trusted peer, (5) authority to intervene in prescribing and/or dispensing, (6) authority for measurement of use, audit and feedback, and (7) access to reliable laboratory services and their cumulative resistance data. Stewardship programs are most advanced in larger public hospitals, but there is considerable interest and need for developing programs tailored to a wide range of settings in human and animal health, each with their own particular characteristics of access to antimicrobials and potential controls. The potential value of stewardship in food animal production is now recognised globally, and Australia has taken the first steps towards surveillance and stewardship in this sector, supported by a recently released national One Health strategy on the containment of antimicrobial resistance.

Quality control ranges for cefoperazone 30 μg disks for Staphylococcus aureus ATCC® 25923 and Escherichia coli ATCC® 25922

The third generation cephalosporin cefoperazone is commonly used for bovine mastitis therapy. So far, the cefoperazone susceptibility testing using 30 μg disks was hampered by the lack of quality control (QC) ranges and the respective interpretive criteria. The aim of this study was to develop CLSI-approved QC ranges for Staphylococcus aureus ATCC(®) 25923 and Escherichia coli ATCC(®) 25922. An interlaboratory trial including eight laboratories was conducted. Each laboratory tested both QC reference strains ten times using two lots of cefoperazone 30 μg disks and three lots of Mueller-Hinton agar. The results were analysed by using the published statistical analysis method. Based on the data, zone diameters of 23-34 mm and 24-33 mm were established as QC ranges for the 30 μg disk and S. aureus ATCC(®) 25923 and E. coli ATCC(®) 25922, respectively. These new QC ranges have been recently approved by the Clinical and Laboratory Standards Institute and will help diagnostic laboratories to validate their cefoperazone testing results using 30 μg disks.

Forgotten antibiotics: an inventory in Europe, the United States, Canada, and Australia

In view of the alarming spread of antimicrobial resistance in the absence of new antibiotics, this study aimed at assessing the availability of potentially useful older antibiotics. A survey was performed in 38 countries among experts including hospital pharmacists, microbiologists, and infectious disease specialists in Europe, the United States, Canada, and Australia. An international expert panel selected systemic antibacterial drugs for their potential to treat infections caused by resistant bacteria or their unique value for specific criteria. Twenty-two of the 33 selected antibiotics were available in fewer than 20 of 38 countries. Economic motives were the major cause for discontinuation of marketing of these antibiotics. Fourteen of 33 antibiotics are potentially active against either resistant Gram-positive or Gram-negative bacteria. Urgent measures are then needed to ensure better availability of these antibiotics on a global scale.

Carbapenemase-producing bacteria in companion animals: a public health concern on the horizon

Clinical infections attributed to carbapenemase-producing bacteria are a pressing public health concern owing to limited therapeutic options and linked antimicrobial resistance. In recent years, studies have reported the emergence and spread of carbapenemase-producing Enterobacteriaceae and their public health impact. This has been closely followed by the global dissemination of highly resistant and virulent zooanthroponotic extraintestinal pathogenic Escherichia coli (ExPEC) ST131 clones. It has also been hypothesized that companion animals may act as a reservoir for Gram-negative multidrug-resistant pathogens in the community. Two recent reports have documented the emergence of carbapenemase-producing bacteria in companion animals. This phenomenon is of great concern because of the close contact between humans and their pets, and the potential for cross-species transmission. This scenario suggests a role for multifaceted control of Gram-negative multidrug-resistant infections in companion animals. This short article addresses this issue and identifies steps that could facilitate this process.

MDRO Beijing Consensus Meeting Report: Global burden of multidrug-resistant organisms' current antimicrobial resistance problems in Asia-Pacific

The International Society of Chemotherapy's Working Groups on Antibiotic Resistance and Antibiotic Stewardship convened a half-day workshop on the burden of multidrug-resistant organisms in the Asia-Pacific. This short review is a summary of their discussion and conclusions.

Control of fluoroquinolone resistance through successful regulation, Australia

Fluoroquinolone antimicrobial drugs are highly bioavailable, broad-spectrum agents with activity against gram-negative pathogens, especially those resistant to other classes of antimicrobial drugs. Australia has restricted the use of quinolones in humans through its national pharmaceutical subsidy scheme; and, through regulation, has not permitted the use of quinolones in food-producing animals. As a consequence, resistance to fluoroquinolones in the community has been slow to emerge and has remained at low levels in key pathogens, such as Escherichia coli. In contrast to policies in most other countries, this policy has successfully preserved the utility of this class of antimicrobial drugs for treatment of most infections.

Use of empiric antimicrobial therapy in neutropenic fever. Australian Consensus Guidelines 2011 Steering Committee

Administration of empiric antimicrobial therapy is standard practice in the management of neutropenic fever, but there remains considerable debate about the selection of an optimal regimen. In view of emerging evidence regarding efficacy and toxicity differences between empiric treatment regimens, and strong evidence of heterogeneity in clinical practice, the current guidelines were developed to provide Australian clinicians with comprehensive guidance for selecting an appropriate empiric strategy in the setting of neutropenic fever. Beta-lactam monotherapy is presented as the treatment of choice for all clinically stable patients while early treatment with combination antibiotic therapy is considered for patients at higher risk. Due consideration is given to the appropriate use of glycopeptides in this setting. Several clinical caveats, accounting for institution- and patient-specific risk factors, are provided to help guide the judicious use of the agents described. Detailed recommendations are also provided regarding time to first dose, timing of blood cultures, selection of a first-line antibiotic regimen, subsequent modification of antibiotic choice and cessation of therapy.

Vertical Transmission, May 2011

Since my last bulletin, we, the Executive, have made considerable progress in ?steadying the ship?. We now have arrangements with ICMS to manage our annual conference and run our national office until the end of August next year. This has resulted in a great deal of stability for our immediate future, and we expect next year?s budget (April to March) to be back in surplus. The Executive and Council also have agreed that we will go out to tender for conference and national office management in the next few months for a fixed period from September 2012.

Steadying the ship

The last nine months have been an interesting and challenging time for the Executive of the ASM. I am taking this opportunity to describe the problems and what we are proposing to do about them, and have done so far. You may know that we have had a series of resignations from the office staff: our Conference Manager in May, our Office Manager in August and our Events Manager in November. At this time the ASM is no longer an employer. We have had to consider a number of things as these resignations have accumulated. You?d be aware already that we brought in a professional conference organiser (ICMS) to manage the annual meeting in July at short notice. Given the circumstances, ICMS did a great job, and the meeting went ahead smoothly and did not suffer financially.

Wild-type MIC distributions and epidemiological cutoff values for the echinocandins and Candida spp

We tested a global collection of Candida sp. strains against anidulafungin, caspofungin, and micafungin, using CLSI M27-A3 broth microdilution (BMD) methods, in order to define wild-type (WT) populations and epidemiological cutoff values (ECVs). From 2003 to 2007, 8,271 isolates of Candida spp. (4,283 C. albicans, 1,236 C. glabrata, 1,238 C. parapsilosis, 996 C. tropicalis, 270 C. krusei, 99 C. lusitaniae, 88 C. guilliermondii, and 61 C. kefyr isolates) were obtained from over 100 centers worldwide. The modal MICs (in microg/ml) for anidulafungin, caspofungin, and micafungin, respectively, for each species were as follows: C. albicans, 0.03, 0.03, 0.015; C. glabrata, 0.06, 0.03, 0.015; C. tropicalis, 0.03, 0.03, 0.015; C. kefyr, 0.06, 0.015, 0.06; C. krusei, 0.03, 0.06, 0.06; C. lusitaniae, 0.05, 0.25, 0.12; C. parapsilosis, 2, 0.25, 1; and C. guilliermondii, 2, 0.5. 05. The ECVs, expressed in microg/ml (percentage of isolates that had MICs that were less than or equal to the ECV is shown in parentheses) for anidulafungin, caspofungin, and micafungin, respectively, were as follows: 0.12 (99.7%), 0.12 (99.8%), and 0.03 (97.7%) for C. albicans; 0.25 (99.4%), 0.12 (98.5%), and 0.03 (98.2%) for C. glabrata; 0.12 (98.9%), 0.12 (99.4%), and 0.12 (99.1%) for C. tropicalis; 0.25(100%), 0.03 (100%), and 0.12 (100%) for C. kefyr; 0.12 (99.3%), 0.25 (96.3%), and 0.12 (97.8%) for C. krusei; 2 (100%), 0.5 (98.0%), and 0.5 (99.0%) for C. lusitaniae; 4 (100%), 1 (98.6%), and 4 (100%) for C. parapsilosis; 16 (100%), 4 (95.5%), and 4 (98.9%) for C. guilliermondii. These WT MIC distributions and ECVs will be useful in surveillance for emerging reduced echinocandin susceptibility among Candida spp. and for determining the importance of various FKS1 or other mutations.

Vertical Transmission, November 2010

Many of you would have heard about the difficulties the Society has been experiencing in the National Office over recent months. We have had a number of resignations; first our executive officer, then our conference manager and most recently our office manager. As I outlined in the last Vertical Transmission, in order to cope with the resignation of our conference manager in May (two months before the Sydney meeting), we were required to call in an experienced professional conference organiser (ICMS) to ensure that the Sydney meeting did not suffer in terms of organisation over such a crucial period. Hopefully, you will agree that the meeting ran successfully given these circumstances.

Vertical Transmission, September 2010

After a very successful scientific meeting in Sydney, it is good to reflect that the world of microbes is anything but dull and boring! The quality and diversity of the speakers and the material presented is a credit to the National Scientific Advisory Committee and the Local Organising Committee. You may have noticed (in a way we hope you didn?t) but we went into the meeting without our in-house conference organiser, Janette Sofronidis. Sadly for us, Janette left the ASM in May after 10 years of outstanding service. The Society would like to thank her for the great contribution she made to our meetings over this period and wish her well in her future endeavours. Because the professional conference organiser (PCO) industry in Australia is now mature and highly competitive, the Executive has elected not to replace Janette, but rather to outsource the organisational aspects of our annual meeting to a PCO, and in the not too distant future, through a tendering process.

Staphylococcus aureus bacteraemia: The Australia New Zealand Cooperative on Outcomes in Staphylococcal Sepsis (ANZCOSS)

Staphylococcus aureus is such a common organism, both as a coloniser and cause of infection in humans, that it is easy to take it for granted. Microbiologists, infectious diseases specialists and infection control practitioners deal with the organism on a regular basis, from screening for methicillin-resistant strains (MRSA) in asymptomatic carriers to treating patients with life-threatening sepsis syndrome in intensive care units.

Setting and revising antibacterial susceptibility breakpoints

Clinical microbiology laboratories need to communicate results of antibacterial susceptibility testing to prescribers. Sophisticated prescribers who are knowledgeable of the pharmacokinetics and pharmacodynamics of antibacterials may desire no more information than the MIC of the drug in question. However, most prescribers require interpretation of antibacterial susceptibility testing results. Breakpoints can assist in determining if an antibacterial is potentially useful in the treatment of a bacterial infection. Breakpoints should be set prior to an antibacterial being used clinically. Breakpoint setting requires integration of knowledge of the wild-type distribution of MICs, assessment of the pharmacokinetics/pharmacodynamics of the antibacterial, and study of the clinical outcome of infections when the antibacterial is used. It is mandatory that breakpoints be reviewed when antibacterial agents have been in clinical use for some time, particularly if mechanisms of bacterial resistance to the drug have been described. In general, greater amounts of information on the pharmacokinetics and pharmacodynamics of an antibacterial are available when breakpoints need to be revised. However, the opportunity to conduct randomized clinical studies of an antibacterial declines after the drug has been released commercially. Well-designed observational clinical studies are therefore necessary in order to provide reliable data to inform those reevaluating breakpoints. Breakpoint-setting organizations may also play a role in developing phenotypic tests for detection of resistance mechanisms, as this information may complement use of the breakpoint in some circumstances.

Statistical methods for establishing quality control ranges for antibacterial agents in Clinical and Laboratory Standards Institute susceptibility testing

Quality control (QC) ranges for antimicrobial agents against QC strains for both dilution and disk diffusion testing are currently set by the Clinical and Laboratory Standards Institute (CLSI), using data gathered in predefined structured multilaboratory studies, so-called tier 2 studies. The ranges are finally selected by the relevant CLSI subcommittee, based largely on visual inspection and a few simple rules. We have developed statistical methods for analyzing the data from tier 2 studies and applied them to QC strain-antimicrobial agent combinations from 178 dilution testing data sets and 48 disk diffusion data sets, including a method for identifying possible outlier data from individual laboratories. The methods are based on the fact that dilution testing MIC data were log normally distributed and disk diffusion zone diameter data were normally distributed. For dilution testing, compared to QC ranges actually set by CLSI, calculated ranges were identical in 68% of cases, narrower in 7% of cases, and wider in 14% of cases. For disk diffusion testing, calculated ranges were identical to CLSI ranges in 33% of cases, narrower in 8% of cases, and 1 to 2 mm wider in 58% of cases. Possible outliers were detected in 8% of diffusion test data but none of the disk diffusion data. Application of statistical techniques to the analysis of QC tier 2 data and the setting of QC ranges is relatively simple to perform on spreadsheets, and the output enhances the current CLSI methods for setting of QC ranges.