Estimation of epidemiological cut-off values for eight antibiotics used for treatment of bovine mastitis caused by Streptococcus uberis and Streptococcus dysgalactiae subsp. dysgalactiae

Interpretive criteria for antimicrobial susceptibility testing are lacking for most antimicrobials used for bovine streptococcal mastitis. The objectives of this study were to determine (tentative) epidemiological cut-off ((T)ECOFF) values for clinically relevant antibiotics used for treatment of bovine mastitis, and to estimate the proportion of acquired resistance (non-wild-types) in Streptococcus dysgalactiae subsp. dysgalactiae and Streptococcus uberis. A total of 255 S. uberis and 231 S. dysgalactiae subsp. dysgalactiae isolates were obtained in Denmark and Norway from bovine mastitis. The isolates were tested for susceptibility to 10 antibiotics using broth microdilution. In accordance with the European Committee on Antimicrobial Susceptibility Testing (EUCAST) standard operating procedure, additional published MIC distributions were included for the estimation of ECOFFs for cloxacillin, cephapirin, lincomycin and tylosin, and TECOFFs for amoxicillin, benzylpenicillin, cephapirin and oxytetracycline. The proportion of non-wild-type (NWT) isolates for the beta-lactams was significantly higher in the Danish S. uberis (45-55%) compared to the Norwegian isolates (10-13%). For oxytetracycline, the proportion of NWT was significantly higher in the Danish isolates, both for S. uberis (28% vs. 3%) and S. dysgalactiae (22% vs. 0%). A bridging study testing in parallel MICs in a subset of isolates (n = 83) with the CLSI-specified and the EUCAST-specified broths showed excellent correlation between the MICs obtained with the two methods. The new ECOFFs and TECOFFs proposed in this study can be used for surveillance of antimicrobial resistance, and - for antimicrobials licensed for streptococcal bovine mastitis - as surrogate clinical breakpoints for predicting their clinical efficacy for this indication.

Wild-type distributions of minimum inhibitory concentrations and epidemiological cut-off values-laboratory and clinical utility

The characterization of wild-type minimum inhibitory concentration (MIC) and zone diameter distributions with the setting of epidemiological cut-off values (ECOFFs or ECVs) provides a reference for the otherwise relative MIC values in the international system for antimicrobial susceptibility testing. Distributions of MIC values for a species and an agent follow a log-normal distribution, which in the absence of resistance mechanisms is monomodal and designated wild type (WT). The upper end of the WT distribution, the ECOFF, can be identified with statistical methods. In the presence of phenotypically detectable resistance, the distribution has at least one more mode (the non-WT), but despite this, the WT is most often identifiable using the same methods. The ECOFF provides the most sensitive measure of resistance development in a species against an agent. The WT and non-WT modes are independent of the organism´s response to treatment, but when the European Committee on Antimicrobial Susceptibility Testing (EUCAST) determines the clinical breakpoints, the committee avoids breakpoints that split WT distributions of target species. This is to avoid the poorer reproducibility of susceptibility categorization when breakpoints split major populations but also because the EUCAST has failed to identify different clinical outcomes for isolates with different MIC values inside the wild-type distribution. In laboratory practice, the ECOFF is used to screen for and exclude resistance and allows the comparison of resistance between systems with different breakpoints from different breakpoint organizations, breakpoints evolving over time, and different breakpoints between human and animal medicine. The EUCAST actively encourages colleagues to question MIC distributions as presented on the website (https://www.eucast.org/mic_and_zone_distributions_and_ecoffs) and to contribute MIC and inhibition zone diameter data.

The scope of antimicrobial resistance in residential aged care facilities determined through analysis of Escherichia coli and the total wastewater resistome

IMPORTANCE

Antimicrobial resistance (AMR) is a global threat that imposes a heavy burden on our health and economy. Residential aged care facilities (RACFs), where frequent inappropriate antibiotic use creates a selective environment that promotes the development of bacterial resistance, significantly contribute to this problem. We used wastewater-based epidemiology to provide a holistic whole-facility assessment and comparison of antimicrobial resistance in two RACFs and a retirement village. Resistant Escherichia coli, a common and oftentimes problematic pathogen within RACFs, was isolated from the wastewater, and the phenotypic and genotypic AMR was determined for all isolates. We observed a high prevalence of an international high-risk clone, carrying an extended-spectrum beta-lactamase in one facility. Analysis of the entire resistome also revealed a greater number of mobile resistance genes in this facility. Finally, both facilities displayed high fluoroquinolone resistance rates-a worrying trend seen globally despite measures in place aimed at limiting their use.

Towards clinical breakpoints for non-tuberculous mycobacteria - Determination of epidemiological cut off values for the Mycobacterium avium complex and Mycobacterium abscessus using broth microdilution

OBJECTIVE

For non-tuberculous mycobacteria (NTM), minimum inhibitory concentration (MIC) distributions of wild-type isolates have not been systematically evaluated despite their importance for establishing antimicrobial susceptibility testing (AST) breakpoints.

METHODS

We gathered MIC distributions for drugs used against the Mycobacterium avium complex (MAC) and Mycobacterium abscessus (MAB) obtained by commercial broth microdilution (SLOMYCOI and RAPMYCOI) from 12 laboratories. Epidemiological cut-off values (ECOFFs) and tentative ECOFFs (TECOFFs) were determined by EUCAST methodology including quality control (QC) strains.

RESULTS

The clarithromycin ECOFF was 16 mg/L for M. avium (n = 1271) whereas TECOFFs were 8 mg/L for M. intracellulare (n = 415) and 1 mg/L for MAB (n = 1014) confirmed by analysing MAB subspecies without inducible macrolide resistance (n = 235). For amikacin, the ECOFFs were 64 mg/L for MAC and MAB. For moxifloxacin, the WT spanned >8 mg/L for both MAC and MAB. For linezolid, the ECOFF and TECOFF were 64 mg/L for M. avium and M. intracellulare, respectively. Current CLSI breakpoints for amikacin (16 mg/L), moxifloxacin (1 mg/L) and linezolid (8 mg/L) divided the corresponding WT distributions. For QC M. avium and M. peregrinum, ≥95% of MIC values were well within recommended QC ranges.

CONCLUSION

As a first step towards clinical breakpoints for NTM, (T)ECOFFs were defined for several antimicrobials against MAC and MAB. Broad wild-type MIC distributions indicate a need for further method refinement which is now under development within the EUCAST subcommittee for anti-mycobacterial drug susceptibility testing. In addition, we showed that several CLSI NTM breakpoints are not consistent in relation to the (T)ECOFFs.

Establishment of RCPA national guidelines for selective reporting of antimicrobials: processes, challenges and measuring the impact

OBJECTIVES

In 2016, The Royal College of Pathologists of Australasia (RCPA) initiated the formation of a working group comprising medical microbiologists to establish guidelines to assist Australian laboratories to implement selective and cascade reporting of antimicrobials-the first guidelines of this type in the world.

METHODS

A 2017 audit of antimicrobial reporting in Australian and New Zealand laboratories identified significant opportunities for improvement and standardization of selective reporting.

RESULTS

The first draft of the RCPA Selective Reporting Guidelines was circulated to all RCPA Microbiology fellows for feedback in August 2018 and the first version was published in February 2019. Subsequently, version two of the guidelines has recently been published in Australia, and New Zealand adapted these guidelines for formulation of their own national guidelines to accommodate local needs.

CONCLUSIONS

Here we describe the processes, acceptance and challenges associated with the establishment of these guidelines and measurement of their impact.

Modelling the Future Clinical and Economic Burden of Antimicrobial Resistance: The Feasibility and Value of Models to Inform Policy

Due to the increasing threat to public health and the economy, governments internationally are interested in models to estimate the future clinical and economic burden of antimicrobial resistance (AMR) and to evaluate the cost-effectiveness of interventions to prevent or control resistance and to inform resource-allocation decision making. A widely cited UK report estimated that 10 million additional deaths will occur globally per annum due to AMR by 2050; however, the utility and accuracy of this prediction has been challenged. The precision of models predicting the future economic burden of AMR is dependent upon the accuracy of predicting future resistance rates. This paper reviews the feasibility and value of modelling to inform policy and resource allocation to manage and curb AMR. Here we describe methods used to estimate future resistance in published burden-of-disease models; the sources of uncertainty are highlighted, which could potentially mislead policy decision-making. While broad assumptions can be made regarding some predictable factors contributing to future resistance rates, the unexpected emergence, establishment and spread of new resistance genes introduces substantial uncertainty into estimates of future economic burden, and in models evaluating the effectiveness of interventions or policies to address AMR. Existing reporting standards for best practice in modelling should be adapted to guide the reporting of AMR economic models, to ensure model transparency and validation for interpretation by policymakers.

How To: ECOFFs - the why, the how and the don´ts of EUCAST epidemiological cutoff values

BACKGROUND

Identifying the MIC wild type distribution and its delineation of species targeted for receiving antimicrobial agent breakpoints is an important first step for determining clinical breakpoints. Having the main responsibility in EUCAST for characterizing the wild-type distributions and the setting of epidemiological cutoff values (ECOFFs), we explain the why, the how and frequent misconceptions of wild-type MIC distributions and ECOFFs.

OBJECTIVES

To clarify how wild type MIC distributions and ECOFFs for agents and important target organisms are defined and determined and why these are important tools in microbiology, as well as to point to common misunderstandings and inappropriate use.

SOURCES

The EUCAST database of >40 000 MIC distributions, publications addressing the definition of wild-type MIC distributions and ECOFFs in bacteria and fungi. The EUCAST Standard Operating Procedure 10. Documents published by the European Centre for Disease Control and the European Food Safety Agency.

CONTENT

The rationale for defining wild-type distributions and ECOFFs is explained. Setting breakpoints that bisect wild-type MIC distributions lead to poor methodological reproducibility and poor correlation between clinical outcome and susceptibility testing results. The methods applied by the European Committee on Antimicrobial Susceptibility Testing (EUCAST) to selecting distributions for aggregation and website display are described, highlighting the importance of incorporation of data from multiple sources and methods. The methods used by EUCAST to estimate ECOFFs are outlined. Finally, the common misunderstandings of these processes are addressed.

IMPLICATIONS

The international community needs to agree on the phenotypic definitions of wild-type distributions. Systematic methods for developing and applying ECOFFs are essential to the conduct of phenotypic antimicrobial susceptibility testing and interpretation, which will remain the dominant laboratory method for the foreseeable future.

Development of Quality Control Ranges for Biocide Susceptibility Testing

Every laboratory test needs validation by quality controls. For biocide susceptibility testing (BST), neither quality control (QC) strains nor QC ranges applicable to these strains are currently available. As QC strains, four well-defined laboratory reference strains (Staphylococcus aureus ATCC® 6538, Enterococcus hirae ATCC® 10541, Escherichia coli ATCC® 10536 and Pseudomonas aeruginosa ATCC® 15442), which have been used previously for biocide efficacy testing, were selected. In an interlaboratory trial with eleven participating laboratories, BST QC ranges should be developed for the aforementioned four strains and the four biocides benzalkonium chloride, chlorhexidine, octenidine and polyhexanide. The performance of three different lots of tryptic soy broth was explored using the broth microdilution method and the data were subsequently evaluated using the RangeFinder software. As a result, QC ranges were defined for all reference strain–biocide combinations, except for P. aeruginosa ATCC® 15442 with the two biocides chlorhexidine and polyhexanide. The development of the latter two QC ranges was not possible, due to the limited solubility of the biocides in the test range required for P. aeruginosa ATCC® 15442. The newly developed QC ranges comprise three to five dilution steps. The establishment of QC ranges will contribute to the validation of BST in the future.

Worldwide distribution and environmental origin of the Adelaide imipenemase (AIM-1), a potent carbapenemase in Pseudomonas aeruginosa

Carbapenems are potent broad-spectrum β-lactam antibiotics reserved for the treatment of serious infections caused by multidrug-resistant bacteria such as Pseudomonas aeruginosa. The surge in P. aeruginosa resistant to carbapenems is an urgent threat, as very few treatment options remain. Resistance to carbapenems is predominantly due to the presence of carbapenemase enzymes. The assessment of 147 P. aeruginosa isolates revealed that 32 isolates were carbapenem non-wild-type. These isolates were screened for carbapenem resistance genes using PCR. One isolate from wastewater contained the Adelaide imipenemase gene (bla _AIM-1) and was compared phenotypically with a highly carbapenem-resistant clinical isolate containing the bla _AIM-1 gene. A further investigation of wastewater samples from various local healthcare and non-healthcare sources as well as river water, using probe-based qPCR, revealed the presence of the bla _AIM-1 gene in all the samples analysed. The widespread occurrence of bla _AIM-1 throughout Adelaide hinted at the possibility of more generally extensive spread of this gene than originally thought. A blast search revealed the presence of the bla _AIM-1 gene in Asia, North America and Europe. To elucidate the identity of the organism(s) carrying the bla _AIM-1 gene, shotgun metagenomic sequencing was conducted on three wastewater samples from different locations. Comparison of these nucleotide sequences with a whole-genome sequence of a P. aeruginosa isolate revealed that, unlike the genetic environment and arrangement in P. aeruginosa, the bla _AIM-1 gene was not carried as part of any mobile genetic elements. A phylogenetic tree constructed with the deduced amino acid sequences of AIM-1 suggested that the potential origin of the bla _AIM-1 gene in P. aeruginosa might be the non-pathogenic environmental organism, Pseudoxanthomonas mexicana.

Comparative macrolide use in humans and animals: should macrolides be moved off the World Health Organisation's critically important antimicrobial list?

Macrolide antibiotics are categorized by the WHO as Highest Priority, Critically Important Antimicrobials due to their recommendation as treatment for severe cases of campylobacteriosis in humans; a self-limiting, rarely life-threatening, zoonotic foodborne infection. Low rates of macrolide resistance in Campylobacter jejuni and the availability of alternative treatments have prompted some regulatory schemes to assign macrolides to a lower importance category. Apart from rare, specific infections, macrolides largely play a supportive role to other drug classes in human medicine. By contrast, although the advent of alternative control methods has seen significant reductions in macrolide use in intensive livestock, they still have a crucial role in the treatment/control of respiratory infections and liver abscesses in cattle. Whilst acknowledging that ongoing surveillance is required to reduce the spread of recently emerged, transferable macrolide resistance among Campylobacter, this article recommends that macrolides should be moved to the WHO Highly Important category.

Inactivation, removal, and regrowth potential of opportunistic pathogens and antimicrobial resistance genes in recycled water systems

With two thirds of the global population living in areas affected by water scarcity, wastewater reuse is actively being implemented or explored by many nations. There is a need to better understand the efficacy of recycled water treatment plants (RWTPs) for removal of human opportunistic pathogens and antimicrobial resistant microorganisms. Here, we used a suite of probe-based multiplex and SYBR green real-time PCR assays to monitor enteric opportunistic pathogens (EOPs; Acinetobacter baumannii, Arcobacter butzlieri, Escherichia coli, Enterococcus faecalis, Klebsiella pneumoniae, Legionella spp., Listeria monocytogenes, Pseudomonas aeruginosa, Salmonella Enteritidis, Streptococcus spp.) and antimicrobial resistance genes (ARGs; qnrS, bla_SHV, bla_TEM, bla_GES, bla_KPC, bla_IMI, bla_SME, bla_NDM, bla_VIM, bla_IMP, bla_OXA-48-like, mcr-1 and mcr-3) of key concern from an antimicrobial resistance (AMR), waterborne and foodborne disease perspective. The class 1 integron-integrase gene (intl1) was quantified as a proxy for multi-drug resistance. EOPs, intl1 and ARGs absolute abundance (DNA and RNA) and metabolic activity (RNA) was assessed through three RWTPs with differing treatment trains. Our results indicate that RWTPs produced high quality recycled water for non-potable reuse by removing >95% of EOPs and ARGs, however, subpopulations of EOPs and ARGs survived disinfection and demonstrated potential to become actively growing members of the recycled water and distribution system microbiomes. The persistence of functional intl1 suggests that significant genetic recombination capacity remains in the recycled water, along with the likely presence of multi-drug resistant bacteria. Results provide new insights into the persistence and growth of EOPs, and prevalence and removal of ARGs in recycled water systems. These data will contribute towards the emerging evidence base of AMR risks in recycled water to inform quantitative risk-based policy development regarding water recycling schemes.

Robotic Antimicrobial Susceptibility Platform (RASP): a next-generation approach to One Health surveillance of antimicrobial resistance

Background

Surveillance of antimicrobial resistance (AMR) is critical to reducing its wide-reaching impact. Its reliance on sample size invites solutions to longstanding constraints regarding scalability. A robotic platform (RASP) was developed for high-throughput AMR surveillance in accordance with internationally recognized standards (CLSI and ISO 20776-1:2019) and validated through a series of experiments.

Methods

Experiment A compared RASP’s ability to achieve consistent MICs with that of a human technician across eight replicates for four Escherichia coli isolates. Experiment B assessed RASP’s agreement with human-performed MICs across 91 E. coli isolates with a diverse range of AMR profiles. Additionally, to demonstrate its real-world applicability, the RASP workflow was then applied to five faecal samples where a minimum of 47 E. coli per animal (239 total) were evaluated using an AMR indexing framework.

Results

For each drug–rater–isolate combination in Experiment A, there was a clear consensus of the MIC and deviation from the consensus remained within one doubling dilution (the exception being gentamicin at two dilutions). Experiment B revealed a concordance correlation coefficient of 0.9670 (95% CI: 0.9670–0.9670) between the robot- and human-performed MICs. RASP’s application to the five faecal samples highlighted the intra-animal diversity of gut commensal E. coli, identifying between five and nine unique isolate AMR phenotypes per sample.

Conclusions

While adhering to internationally accepted guidelines, RASP was superior in throughput, cost and data resolution when compared with an experienced human technician. Integration of robotics platforms in the microbiology laboratory is a necessary advancement for future One Health AMR endeavours.

Determination of norvancomycin epidemiological cut-off values (ECOFFs) for Staphylococcus aureus, Staphylococcus epidermidis, Staphylococcus haemolyticus and Staphylococcus hominis

OBJECTIVES

To determine the epidemiological cut-off values (ECOFFs) of norvancomycin for Staphylococcus aureus, Staphylococcus epidermidis, Staphylococcus haemolyticus and Staphylococcus hominis.

METHODS

We collected 1199 clinical isolates of Staphylococcus species from five laboratories located in four cities in China. MICs and inhibitory zone diameters of norvancomycin were determined by broth microdilution and the disc diffusion method, separately. ECOFFs of norvancomycin for four species were calculated by ECOFFinder software following EUCAST principles. Methicillin and vancomycin resistance genes (mecA/mecC and vanA/vanB/vanC/vanD/vanE) were screened for by PCR in all isolates. Pearson correlation and χ2 test were used to calculate the correlation of MICs and inhibition zone diameters, and MICs and resistance genes, respectively.

RESULTS

MICs of norvancomycin for all strains from five laboratories fell in the range of 0.12-2 mg/L. ECOFFs of norvancomycin were determined to be 2 mg/L for S. epidermidis and S. haemolyticus and 1 mg/L for S. aureus and S. hominis. A weak correlation was observed between MIC values and zone diameters for S. haemolyticus (r = -0.36) and S. hominis (r = -0.26), while no correlation was found for S. epidermidis and S. aureus. The mecA gene was detected in 63.1% of Staphylococcus, whereas no isolate carried mecC, vanA, vanB, vanC, vanD or vanE. ECOFFs of norvancomycin were not correlated with mecA gene carriage in Staphylococcus species.

CONCLUSIONS

ECOFFs of norvancomycin for four Staphylococcus species were determined, which will be helpful to differentiate WT strains. The correlation of MICs and zone diameters of norvancomycin was weak in Staphylococcus species.

Probenecid effects on cephalexin pharmacokinetics and pharmacodynamics in healthy volunteers

OBJECTIVES

We evaluated the effects of probenecid on the Pharmaco Kinetics (PK) and pharmacodynamics (PD) of oral cephalexin in healthy volunteers.

METHODS

Cephalexin 1000 mg was administered orally to 11 healthy volunteers following a standardized meal, with and without probenecid 500 mg orally, on two separate days one week apart. Total plasma concentrations of cephalexin and probenecid over a 12 h period were measured by liquid chromatography tandem mass spectrometry. Standard pharmacokinetic measures and contemporary PK/PD targets were compared.

RESULTS

Probenecid increased the mean (95% CI) cephalexin area under the concentration-time curve (AUC_0-∞) 1.73-fold (1.61-1.85, p < 0.0001), peak concentration 1.37-fold (1.16-1.58, p < 0.01), time to peak concentration 1.45-fold (1.1-1.8, p < 0.01)_, and half-life 1.33-fold (1.03-1.62, p < 0.05). The effects resulted in clinically meaningful increases in the probability of PK/PD target attainment (PTA). As an example, the PTA of total concentrations above the minimum inhibitory concentration required to inhibit methicillin-susceptible Staphylococcus aureus isolates (MIC ≤ 8 mg/L) for 70% of a 6 h dose interval approached 100% for cephalexin + probenecid while for cephalexin alone it was <15%.

CONCLUSIONS

Probenecid prolonged and flattened the plasma concentration-time curve, enhancing the probability of attaining PK/PD targets. Co-administration of probenecid may expand the clinical benefits of oral cephalexin.

The Effect of Renal Replacement Therapy and Antibiotic Dose on Antibiotic Concentrations in Critically Ill Patients: Data From the Multinational Sampling Antibiotics in Renal Replacement Therapy Study

BACKGROUND

The optimal dosing of antibiotics in critically ill patients receiving renal replacement therapy (RRT) remains unclear. In this study, we describe the variability in RRT techniques and antibiotic dosing in critically ill patients receiving RRT and relate observed trough antibiotic concentrations to optimal targets.

METHODS

We performed a prospective, observational, multinational, pharmacokinetic study in 29 intensive care units from 14 countries. We collected demographic, clinical, and RRT data. We measured trough antibiotic concentrations of meropenem, piperacillin-tazobactam, and vancomycin and related them to high- and low-target trough concentrations.

RESULTS

We studied 381 patients and obtained 508 trough antibiotic concentrations. There was wide variability (4-8-fold) in antibiotic dosing regimens, RRT prescription, and estimated endogenous renal function. The overall median estimated total renal clearance (eTRCL) was 50 mL/minute (interquartile range [IQR], 35-65) and higher eTRCL was associated with lower trough concentrations for all antibiotics (P < .05). The median (IQR) trough concentration for meropenem was 12.1 mg/L (7.9-18.8), piperacillin was 78.6 mg/L (49.5-127.3), tazobactam was 9.5 mg/L (6.3-14.2), and vancomycin was 14.3 mg/L (11.6-21.8). Trough concentrations failed to meet optimal higher limits in 26%, 36%, and 72% and optimal lower limits in 4%, 4%, and 55% of patients for meropenem, piperacillin, and vancomycin, respectively.

CONCLUSIONS

In critically ill patients treated with RRT, antibiotic dosing regimens, RRT prescription, and eTRCL varied markedly and resulted in highly variable antibiotic concentrations that failed to meet therapeutic targets in many patients.

Clinical and Laboratory Standards Institute and European Committee on Antimicrobial Susceptibility Testing Position Statements on Polymyxin B and Colistin Clinical Breakpoints

Recent data on polymyxin pharmacokinetics, pharmacodynamics, toxicity, and clinical outcomes suggest these agents have limited clinical utility. Pharmacokinetics-pharmacodynamics data show a steady-state concentration of 2 μg/mL is required for killing bacteria with colistin minimum inhibitory concentrations of 2 μg/mL. Less than 50% of patients with normal renal function achieve this exposure, and it is associated with high risk of nephrotoxicity. This exposure does not achieve bacterial stasis in pneumonia models. Randomized and observational studies consistently demonstrate increased mortality for polymyxins compared with alternative agents. The Clinical and Laboratory Standards Institute (CLSI) and European Committee on Antimicrobial Susceptibility Testing (EUCAST) are 2 global organizations that establish interpretive criteria for in vitro susceptibility data. CLSI has recently taken the step to eliminate the "susceptible" interpretive category for the polymyxins, whereas EUCAST maintains this interpretive category. This viewpoint describes the opinions of these organizations and the data that were used to inform their perspectives.

Utilising sigmoid models to predict the spread of antimicrobial resistance at the country level

BackgroundThe spread of antimicrobial resistance (AMR) is of worldwide concern. Public health policymakers and pharmaceutical companies pursuing antibiotic development require accurate predictions about the future spread of AMR.AimWe aimed to identify and model temporal and geographical patterns of AMR spread and to predict future trends based on a slow, intermediate or rapid rise in resistance.MethodsWe obtained data from five antibiotic resistance surveillance projects spanning the years 1997 to 2015. We aggregated the isolate-level or country-level data by country and year to produce country-bacterium-antibiotic class triads. We fitted both linear and sigmoid models to these triads and chose the one with the better fit. For triads that conformed to a sigmoid model, we classified AMR progression into one of three characterising paces: slow, intermediate or fast, based on the sigmoid slope. Within each pace category, average sigmoid models were calculated and validated.ResultsWe constructed a database with 51,670 country-year-bacterium-antibiotic observations, grouped into 7,440 country-bacterium-antibiotic triads. A total of 1,037 triads (14%) met the inclusion criteria. Of these, 326 (31.4%) followed a sigmoid (logistic) pattern over time. Among 107 triads for which both sigmoid and linear models could be fit, the sigmoid model was a better fit in 84%. The sigmoid model deviated from observed data by a median of 6.5%; the degree of deviation was related to the pace of spread.ConclusionWe present a novel method of describing and predicting the spread of antibiotic-resistant organisms.

Feasibility of de-linking reimbursement of antimicrobials from sales: the Australian perspective as a qualitative case study

Background

There is a disparity in the economic return achievable for antimicrobials compared with other drugs because of the need for stewardship. This has led to a decline in pharmaceutical companies’ willingness to invest in the development of these drugs and a consequent global interest in funding models where reimbursement is de-linked from sales.

Objectives

To explore the perspective of stakeholders regarding the feasibility of de-linked reimbursement of antimicrobials in Australia.

Methods

Semi-structured interviews were conducted with 18 participants sourced from the pharmaceutical industry and individuals representing public-sector payers or regulators. Interviews were transcribed verbatim, coded and thematically analysed using the framework method.

Results

Five key themes were identified in the interviews: funding silos are a barrier to de-linking reimbursement; varying levels of supporting evidence are (currently) required for funding depending upon setting; funding status or cost is used as a stewardship tool; a de-linked model may cost more; and concerns regarding governance and access to antimicrobials exist in the private sector.

Conclusions

Australia’s current multi-tiered funding of medicines across different levels of government was perceived as a barrier to de-linked reimbursement. Participants felt that the responsibility for antimicrobial funding and stewardship should be integrated and centralized. Implementing a nationally funded de-linked reimbursement model for new antimicrobials would require a review of funding decision-making criteria, given that most MDR infections are off-label indications and could not then be funded through the Australian Pharmaceutical Benefits Scheme. Findings from this study could be applicable to other countries with reimbursement frameworks similar to Australia.

Daptomycin in the treatment of enterococcal bloodstream infections and endocarditis: a EUCAST position paper

SCOPE

This position paper describes the view adopted by EUCAST on the role of daptomycin in the treatment of serious infections caused by Enterococcus species.

BACKGROUND

High-dose daptomycin is considered effective in the treatment of enterococcal bloodstream infection (BSI) and endocarditis, although published clinical experience with the latter condition is limited.

METHODS

EUCAST reviewed the available published data on pharmacokinetics-pharmacodynamics (PK-PD), resistance selection, clinical efficacy and safety for the use of 10-12 mg/kg/day of daptomycin for these conditions, noting that the doses licensed by the European Medicines Agency are only 4-6 mg/kg/day, and only for infections caused by Staphylococcus aureus.

FINDINGS AND RECOMMENDATIONS

The PK-PD evidence shows that, even with doses of 10-12 mg/kg/day, it is not possible to treat infections caused by isolates at the upper end of the wild-type distributions of Enterococcus faecalis (with MICs of 4 mg/L) and E. faecium (with MICs of 4 or 8 mg/L). For this reason, and because there are ongoing issues with the reliability of laboratory testing, EUCAST lists daptomycin breakpoints for Enterococcus species as "IE"-insufficient evidence. EUCAST advises increased vigilance in the use of high-dose of daptomycin to treat enterococcal BSI and endocarditis. Additional PK-PD studies and prospective efficacy and safety studies of serious Enterococcal infections treated with high-dose daptomycin may permit the setting of breakpoints in the future.

Estimating the utilisation of unregistered antimicrobials in Australia

OBJECTIVE

To identify and estimate the usage of unregistered antimicrobial drugs in Australian clinical practice.

METHODS

A descriptive pharmaco-epidemiological study, utilising three data sources: analysis of Special Access Scheme (SAS) applications for unregistered antimicrobials included in clinical guidelines over a five year period, analysis of antimicrobials dispensed from South Australian public hospital pharmacy departments over a two year period and analysis of National Antimicrobial Utilisation Surveillance Program (NAUSP) data for reported inpatient usage of unregistered antimicrobials in Australian hospitals over the last 5 years.

RESULTS

59 unregistered antimicrobials were identified using the mixed methods. 18,362 Special Access Scheme applications were submitted between May 2012 and April 2017 to access the 20 unregistered antimicrobials identified in the Therapeutic Guidelines® (eTG complete); 51.4% were determined by the prescriber to be for life-threatening indications. Annual applications more than doubled over the five years. 34 unregistered antimicrobials were dispensed from South Australian public hospitals between July 2015 and June 2017. On average, 1.1% of total antimicrobial usage (Defined Daily Doses) per month was accessed via the SAS, of which 87.7% were for outpatients or discharged patients. 34 unregistered antimicrobials for systemic use identified in the NAUSP database were used in Australian hospitals between 2013 and 2018.

CONCLUSION

The use of unregistered antimicrobials in Australian clinical practice is not uncommon. With increasing antimicrobial resistance, there will be a continued reliance on older less-used antimicrobial agents and an increasing need for novel drugs, therefore regulatory pathways need to facilitate security of supply and assurance of medicine quality and safety.

Clinical indications treated with unregistered antimicrobials: regulatory challenges of antimicrobial resistance and access to effective treatment for patients

Objective Increasing antimicrobial resistance and a concurrent paucity of new antimicrobials marketed increases the risk that patients will develop infections resistant to currently available drugs. This study aimed to determine the range of clinical indications for which unregistered antimicrobials are prescribed at two tertiary hospitals in South Australia to identify any trends over a 2-year period. The effects of recent regulatory changes to the Special Access Scheme (SAS) were assessed. Methods Data were extracted from application forms submitted to the Therapeutic Goods Administration to access unregistered antimicrobials via the SAS pathway at two Australian tertiary hospitals for the period July 2015–June 2017. Average weighted antimicrobial prices were retrieved from the hospital iPharmacy (DXC Technology, Macquarie Park, NSW, Australia) dispensing system. To estimate the effect of a new access pathway (Category C), the SAS classification for each application was retrospectively assessed over time with each regulatory change. Results Between July 2015 and June 2017, 477 SAS applications for 29 different antimicrobials were submitted for 353 patients at the two hospitals. The most common indications were tuberculosis (43.6%) and refractory Helicobacter pylori (10%). Regulatory changes reduced the proportion of applications requiring preapproval for access. Conclusions Although the introduction of a new pathway has decreased the administrative burden when accessing unregistered antimicrobials, this study highlights the range of clinical conditions for which there are no registered drugs available in Australia. What is known about the topic? With increasing antimicrobial resistance and a paucity of novel antimicrobials entering the market, access to older, previously less-used antimicrobials is increasingly important in clinical practice. Accessing unregistered antimicrobials is common practice in Australian hospitals, but the range of clinical indications for which they are used is unclear. What does this paper add? Increasing antimicrobial resistance and a concurrent paucity of new antimicrobials being marketed globally is increasing the risk that patients may develop infections that cannot be treated with registered products. This study describes the range of clinical conditions for which registered antimicrobials are not available or appropriate, illustrating the challenges associated with sustainable access to effective treatments. What are the implications for practitioners? Access to effective antimicrobials in a timely manner is essential for optimal patient outcomes. Reliance on unregistered products is associated with increased risks regarding timely access to safe, quality-assured, effective medicines.

Variation of MIC measurements: the contribution of strain and laboratory variability to measurement precision

Objectives

Although testing of antimicrobial agents for susceptibility has inherent variability like any assay, it is generally held that there are also real differences in susceptibility between strains. In the routine laboratory, variability of the MIC measurement may be sufficient to mask real strain differences. We determined which factors contributed to the variability, using linezolid against Staphylococcus aureus as one example.

Methods

Twenty-five S. aureus strains were sent to five different laboratories in quadruplicate in a blinded fashion. Laboratories determined MICs of linezolid using Etest. Results of 22 strains corresponding to 440 observations were available for analysis. Sources of variability were explored and quantified using an ANOVA approach.

Results

The overall geometric mean MIC was 1.8 mg/L, comparable to that of the published WT distribution of 1.7 mg/L (www.eucast.org). The total variation amounted to ∼1.3 2-fold dilutions for a one-sided CI of 95% and two 2-fold dilutions for a CI of 99%. Variation between laboratories and variation between strains contributed 10% and 48%, and in a subset analysis averaging 17% and 26%, respectively. Strain-to-strain variation (biological variation) could not be reliably determined, even with four replicates.

Conclusions

This analysis serves as an example of an approach to discerning various sources of MIC variation. Here, at best, a single measurement of an MIC may provide an indication of whether it likely belongs to the WT distribution. Only repeated measurements of MICs for individual strains within one laboratory may provide an indication of differences in susceptibility between strains.

Polymyxin Susceptibility Testing and Breakpoint Setting

Susceptibility testing of polymyxins has been subject to intensive review and revision in recent years. A joint working group was established by the Clinical and Laboratory Standards Institute and the European Committee on Antimicrobial Susceptibility Testing to establish a reference method. Issues examined included the effects of divalent cations, binding to laboratory materials, and addition of polysorbate 80. The working group recommended the use of broth microdilution without the addition of polysorbate 80 as the reference method. Published studies have shown that other testing methods, including agar dilution, disk diffusion and gradient diffusion, have unacceptably high levels of very major errors compared to the reference method, and are not recommended for routine laboratory use. Most data were for the testing of colistin; less information was available for polymyxin B. The joint working group was also asked to consider the setting of clinical breakpoints for relevant pathogens. This task involved examination of the available pharmacokinetic-pharmacodynamic, pharmacokinetic-toxicodynamic and population clinical pharmacokinetic data. All current pharmacokinetic-pharmacodynamic targets are based on MICs generated using the reference broth dilution procedure.

Probenecid and food effects on flucloxacillin pharmacokinetics and pharmacodynamics in healthy volunteers

OBJECTIVES

To measure the effect of probenecid, fasting and fed, on flucloxacillin pharmacokinetic and pharmacodynamic endpoints.

METHODS

Flucloxacillin 1000 mg orally was given to 11 volunteers alone while fasting ('flucloxacillin alone'), and with probenecid 500 mg orally while fasting ('probenecid fasting') and with food ('probenecid fed'). Flucloxacillin pharmacokinetic and pharmacodynamic endpoints were compared.

RESULTS

Probenecid, fasting and fed, increased free plasma flucloxacillin area under the concentration-time curve (zero to infinity) ∼1.65-fold (p < 0.01) versus flucloxacillin alone. Probenecid fed prolonged time to peak flucloxacillin concentrations ∼2-fold versus the other two regimens (p < 0.01). Probenecid fasting or fed increased free flucloxacillin concentrations exceeding 30%, 50% and 70% of the first 6, 8 and 12 h post-dose by 1.58- to 5.48-fold compared with flucloxacillin alone. As an example of this pharmacodynamic improvement, the probability of target attainment of free concentrations above the minimum inhibitory concentration for Staphylococcus aureus (0.5 mg/L) for 50% of a 6-hour dose interval was > 80% for flucloxacillin plus probenecid (fasting or fed) and < 20% for flucloxacillin alone.

CONCLUSIONS

Probenecid increased flucloxacillin exposure, with predicted pharmacodynamic effects greater than pharmacokinetic effects because of the altered shape of the concentration-time curve. Probenecid may improve the applicability of oral flucloxacillin regimens.

Benzylpenicillin versus flucloxacillin for penicillin-susceptible Staphylococcus aureus bloodstream infections from a large retrospective cohort study

In clinical practice, differing opinions exists regarding the optimal management of patients with penicillin-susceptible Staphylococcus aureus (PSSA) bloodstream infection (BSI). The aim of this study was to compare the 30-day mortality of patients treated with benzylpenicillin or flucloxacillin for PSSA BSI from a large prospectively collected data set from Australia and New Zealand. A logistic regression model and propensity score treatment analysis using inverse probability of treatment weighting were used. A total of 915 patients were included in the study, with an overall mortality rate of 12.9% (118/915) [benzylpenicillin 10.5% (33/315) and flucloxacillin 14.2% (85/600)]. Endocarditis was associated with benzylpenicillin treatment choice, whereas skin and soft-tissue infection was associated with flucloxacillin treatment choice. In the multivariate analysis, increased 30-day mortality was associated with flucloxacillin compared with benzylpenicillin [odds ratio (OR) = 1.6, 95% confidence interval (CI) 1.0-2.5; P = 0.05). When adjusted for treatment choice in the propensity score analysis, flucloxacillin was again associated with increased 30-day mortality (OR = 1.06, 95% CI 1.01-1.1; P = 0.03). An increase in 30-day mortality associated with flucloxacillin use suggests a potential benefit for benzylpenicillin therapy in patients with PSSA BSI.

MIC-based dose adjustment: facts and fables

Over recent decades, several publications have described optimization procedures for antibiotic therapy in the individual patient based on antimicrobial MIC values. Most methods include therapeutic drug monitoring and use a single MIC determination plus the relevant pharmacokinetics/pharmacodynamics to adjust the dose to optimize antimicrobial drug exposure and antibacterial effects. However, the use of an MIC obtained by a single MIC determination is inappropriate. First, routine clinical laboratories cannot determine MICs with sufficient accuracy to guide dosage owing to the inherent assay variation in the MIC test. Second, the variation in any MIC determination, whatever method is used, must be accounted for. If dose adjustments are made based on therapeutic drug monitoring and include MIC determinations, MIC variation must be considered to prevent potential underdosing of patients. We present the problems and some approaches that could be used in clinical practice.

Antimicrobial resistance in clinical Escherichia coli isolated from companion animals in Australia

Multidrug-resistant (MDR) Escherichia coli have become a major public health concern to both humans and animal health. While the frequency of antimicrobial resistance (AMR) in clinical E. coli is monitored regularly in human medicine, current frequency of AMR in companion animals remains unknown in Australia. In this study we conducted antimicrobial susceptibility testing (AST) and where possible, determined potential risk factors for MDR infection among 883 clinical Escherichia coli isolated from dogs (n=514), cats (n=341) and horses (n=28). AST was undertaken for 15 antimicrobial agents according to the Clinical Laboratory Standards Institute (CLSI) guidelines and interpreted using epidemiological cut-off values (ECOFFs) as well as CLSI veterinary and human clinical breakpoints. The AST revealed complete absence of resistance to carbapenems while resistance to amikacin was observed at a low level in isolates from dogs (1.6%) and cats (1.5%) compared to horses (10.7%). Among dog isolates, resistance to fluoroquinolones ranged from 9.1%-9.3% whereas among cat isolates, it ranged from 3.2%-5%. Among dog isolates, the proportion showing a 3rd generation cephalosporin (3GC) non-wild type phenotype was significantly higher (P<0.05) in skin and soft tissue infection (SSTI, n=122) isolates (17.2%-20.5%) compared to urinary tract infection (UTI, n=392) isolates (9.9%-10.2%). The frequency of multidrug resistance was 18.1%, 11.7% and 42.9% in dog, cat and horse isolates, respectively. Risk factor analysis revealed that MDR E. coli isolated from UTI were positively associated with chronicity of infection and previous antimicrobial treatment. Dogs and cats with chronic UTI that had been previously treated with antimicrobials were eight times and six times more likely to be infected with MDR E. coli compared to dogs and cats with non-chronic UTI, and no history of antimicrobial treatment, respectively. This study revealed that pre-existing disease condition and prior antimicrobial use were the major risks associated with UTI with MDR E. coli in companion animals.

Antimicrobial use Guidelines for Treatment of Respiratory Tract Disease in Dogs and Cats: Antimicrobial Guidelines Working Group of the International Society for Companion Animal Infectious Diseases

Respiratory tract disease can be associated with primary or secondary bacterial infections in dogs and cats and is a common reason for use and potential misuse, improper use, and overuse of antimicrobials. There is a lack of comprehensive treatment guidelines such as those that are available for human medicine. Accordingly, the International Society for Companion Animal Infectious Diseases convened a Working Group of clinical microbiologists, pharmacologists, and internists to share experiences, examine scientific data, review clinical trials, and develop these guidelines to assist veterinarians in making antimicrobial treatment choices for use in the management of bacterial respiratory diseases in dogs and cats.

Epidemiology and Mortality of Staphylococcus aureus Bacteremia in Australian and New Zealand Children

IMPORTANCE

Staphylococcus aureus bacteremia (SAB) in children causes significant morbidity and mortality, but the epidemiology in children is not well characterized.

OBJECTIVE

To describe the epidemiology of SAB in children and adolescents younger than 18 years from Australia and New Zealand.

DESIGN, SETTING, AND PARTICIPANTS

A prospective cohort study, using data from the Australian New Zealand Cooperative on Outcomes in Staphylococcal Sepsis cohort for 1153 children with SAB from birth to less than 18 years in pediatric and general hospitals across Australia and New Zealand, collected between January 1, 2007, and December 31, 2012. Multivariate analysis was performed to identify risk factors for mortality. Incidence calculations were calculated separately for Australasian children younger than 15 years using postcode population denominator data from Australian and New Zealand census data.

MAIN OUTCOMES AND MEASURES

Demographic data, hospital length of stay, principal diagnosis, place of SAB onset (community or hospital), antibiotic susceptibility and principal antibiotic treatment, and 7- and 30-day mortality.

RESULTS

Of the 1153 children with SAB, complete outcome data were available for 1073 children (93.1%); of these, males accounted for 684 episodes (63.7%) of SAB. The median age was 57 months (interquartile range, 2 months to 12 years). The annual incidence of SAB for Australian children was 8.3 per 100 000 population and was higher in indigenous children (incident rate ratio, 3.0 [95% CI, 2.4-3.7]), and the incidence for New Zealand children was 14.4 per 100 000 population and was higher in Māori children (incident rate ratio, 5.4 [95% CI, 4.1-7.0]). Community-onset SAB occurred in 761 cases (70.9%), and 142 cases (13.2%) of the infections were methicillin-resistant S aureus (MRSA). Bone or joint infection was most common with 348 cases (32.4%), and endocarditis was uncommon with 30 cases (2.8%). Seven- and 30-day mortality rates were 2.6% (n = 28) and 4.7% (n = 50), respectively. Risk factors for mortality were age younger than 1 year; Māori or Pacific ethnicity; endocarditis, pneumonia, or sepsis; and receiving no treatment or treatment with vancomycin. Mortality was 14.0% (6 of 43) in children with methicillin-susceptible S aureus (MSSA) treated with vancomycin compared with 2.6% (22 of 851) in children treated with alternative agents (OR, 6.1 [95% CI, 1.9-16.7]). MRSA infection was associated with increased length of stay but not mortality.

CONCLUSIONS AND RELEVANCE

In this large cohort study of the epidemiology of SAB in children, death was uncommon, but the incidence was higher for infants and varied by treatment, ethnicity, and clinical presentation. This study provides important information on the epidemiology of SAB in children and risk factors for mortality.