Guiding antimicrobial stewardship through thoughtful antimicrobial susceptibility testing and reporting strategies: an updated approach in 2023

Antimicrobial susceptibility test and report guidelines are an important tool for antimicrobial stewardship programs. Since 1972, Tables 1 within the Clinical and Laboratory Standards Institute (CLSI) M100 document have provided a general framework upon which clinical microbiologists and antimicrobial stewardship teams can build algorithms for susceptibility testing and reporting that meet the specific needs of their institution. Many changes were made to Tables 1 in M100-Ed33 to modernize the content to reflect the landscape of current clinical practice, including the growing armamentarium of antimicrobial agents, the emergence of new mechanisms of antimicrobial resistance, the increasing prevalence of infections caused by multidrug-resistant organisms, and updated consensus recommendations for first-choice and alternative agents for treatment. With these items in mind, the CLSI Table 1 ad hoc working group revised Tables 1 with the ultimate goal of supporting institutions in the creation of individualized test and report strategies that support local antimicrobial stewardship program initiatives. These strategies are built on the concepts of selective and cascade reporting. This minireview introduces the concept of CLSI M100-Ed33 Tables 1, describes the changes to Tables 1 introduced in 2023, and provides clinical vignettes that demonstrate how Tables 1 can be used in various scenarios to devise antimicrobial susceptibility test and report strategies.

Vitamin D in human serum and adipose tissue after supplementation

BACKGROUND

Serum 25-hydroxyvitamin D [25(OH)D] concentration is an indicator of vitamin D exposure, but it is also influenced by clinical characteristics that affect 25(OH)D production and clearance. Vitamin D is the precursor to 25(OH)D but is analytically challenging to measure in biological specimens.

OBJECTIVES

We aimed to develop and validate a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for quantification of vitamins D3 and D2 in serum and to explore the potential of circulating vitamin D as a biomarker of exposure in supplementation trials.

METHODS

The method was validated using guideline C62-A from the Clinical and Laboratory Standards Institute and was applied in 2 pilot clinical trials of oral vitamin D3 supplementation. Pilot study 1 included 22 adults randomly assigned to placebo or 2000 IU/d. Blood was collected at baseline, 1, 3, 6, and 12 mo. Pilot study 2 included 15 adults randomly assigned to 2000 or 4000 IU/d. Blood and subcutaneous (SUBQ) adipose tissue were collected at baseline and 3 mo.

RESULTS

In study 1, mean change (baseline to 3 mo) in serum vitamin D3 was -0.1 ng/mL in the placebo group and 6.8 ng/mL in the 2000 IU/d group (absolute difference: 6.9; 95% CI: 4.5, 9.3 ng/mL). In study 2, mean change (baseline to 3 mo) in serum vitamin D3 was 10.4 ng/mL in the 2000 IU/d group and 22.2 ng/mL in the 4000 IU/d group (fold difference: 2.15; 95% CI: 1.40, 3.37). Serum and adipose tissue vitamin D3 concentrations were correlated, and the dose-response of vitamin D3 in adipose mirrored that in serum.

CONCLUSIONS

We validated a sensitive, robust, and high-throughput LC-MS/MS method to quantify vitamins D3 and D2 in serum. Serum and SUBQ adipose tissue vitamin D3 concentrations increased proportionally to dose with 3 mo of daily supplementation.These trials were registered at clinicaltrials.gov as NCT00552409 (pilot study 1) and NCT01477034 (pilot study 2).

Clinical and laboratory standards institute versus European committee for antimicrobial susceptibility testing guidelines for interpretation of carbapenem antimicrobial susceptibility results for Escherichia coli in urinary tract infection (UTI)

BACKGROUND

Carbapenems show excellent activity against resistant uropathogens, and they are the antibiotics of choice for urinary tract infections (UTIs). The choice of carbapenem prescription is strongly influenced by antimicrobial susceptibility testing (AST) report. With the publication of recent AST guidelines by the European Committee on AST (EUCAST), we were curious to evaluate the difference in results between Clinical and Laboratory Standards Institute (CLSI) and the EUCAST guidelines for the interpretation of carbapenems.

METHODS

During a period of 1 year, midstream urine specimens received in the laboratory were cultured by conventional techniques and 2932 of them grew significant colony counts of Escherichia coli. Out of them, 501 E. coli isolates which were resistant to at least six first-line antibiotics were further subjected to second-line antimicrobials imipenem and meropenem, reported by E-tests (bioMerieux, France). The E-test results were interpreted by both CLSI 2016 and EUCAST 6.0 (2016) guidelines. Weighted kappa was used to determine absolute agreement, and McNemar's Chi-square test was used to test the difference in proportions of susceptibility between two methods, respectively.

RESULTS

Taking CLSI guidelines as a gold standard, there was 100% sensitivity in a susceptible category by the EUCAST guidelines for both the carbapenems. Weighted kappa showed good and moderate agreement between them for imipenem and meropenem, respectively. However, McNemar Chi-square test in the nonsusceptible category between the two tests was 9.38% and 33.03% for imipenem and meropenem, respectively, and they were highly significant (P < 0.001).

CONCLUSIONS

A laboratory can follow EUCAST guidelines as well and the guidelines are more useful in urinary concentrated antibiotics such as carbapenems. Further other antibiotics need to be evaluated by both these guidelines.

From CLSI to EUCAST, a necessary step in Spanish laboratories

The Spanish Antibiogram Committee (Comité Español del Antibiograma, COESANT) presents in this document a simple "roadmap" or decalogue of recommendations, with a view to facilitating the transition from the Clinical and Laboratory Standards Institute (CLSI) to the European Committee on Antimicrobial Susceptibility Testing (EUCAST) antimicrobial susceptibility testing regulations to the Clinical Microbiology Spanish laboratories that still use the CLSI guidelines. The objectives are to adapt the closer European regulations to the Spanish clinical and epidemiological reality and to fully implement the EUCAST recommendations in all microbiology laboratories in Spain.

Colistin susceptibility testing of gram-negative bacilli: Better performance of vitek2 system than E-test compared to broth microdilution method as the gold standard test

Introduction

Unavailability of optimal susceptibility testing (ST) challenges the clinical use of colistin. Broth microdilution (BMD), which is the reference for colistin ST, is inconvenient for diagnostics. Vitek2 and E-test although technically easier, are no longer recommended.

Materials and Methods

For the evaluation of Vitek2 and E-test in reference with BMD, a total of 138 Gram-negative bacilli (GNB) especially carbapenem-resistant isolates from Tata Medical Center, Kolkata, India, were included during 2017-2018. The evaluation was performed only for Enterobacteriaceae (n = 102), but not for non-fermentative GNB (n = 36) due to lack of colistin-resistant (COLR) isolates.

Results and Conclusion

Of 138 isolates, meropenem, colistin and dual resistance were detected in 110 (79.7%), 31 (22.5%) and 21 (15.2%) of isolates, respectively. Using the European Committee on Antimicrobial Susceptibility Testing guidelines (susceptible, ≤2 μg/ml), Vitek2 performed better than E-test (essential agreement, 92.2% vs. 63.7%; categorical agreement, 94.1% vs. 93.1%; very major error [VME], 10% vs. 23.3%). However, Vitek2 overcalled resistance than E-test (major error, 4.2% vs. 0%). Considering Chew et al. proposed breakpoints (susceptible, ≤1 μg/ml), VMEs declined for both test (6.7% vs. 10%), but still remained unacceptable. Of eight colistin-heteroresistant isolates, two VME were categorised by Vitek2, one VME was by E-test, and two were uninterpretable. Both Vitek2 and E-test are unreliable. Further studies correlating minimum inhibitory concentrations with clinical outcome are needed to determine the accurate breakpoints for better patient management.

Impact of 21st Century Cures Act on Breakpoints and Commercial Antimicrobial Susceptibility Test Systems: Progress and Pitfalls

Antimicrobial resistance is the most pressing medical challenge of the past decade. At the front line are clinical laboratories, which are responsible for accurately reporting antimicrobial susceptibility test (AST) results to clinicians and public health authorities. The ability of the laboratory to detect resistance has been hampered by several factors. In 2016, the 21st Century Cures Act was signed into law, marking an important step toward resolving many regulatory dilemmas that hampered development and updates to commercial AST systems (cASTs). We describe the pathway and history of U.S. regulation of cASTs and outline both the rewards and unmet needs possible from the 21st Century Cures Act.

Comparison of Clinical & Laboratory Standards Institute standards in antimicrobial susceptibility among the carbapenemase producing Enterobacteriaceae

Aim

Carbapenems are antibiotics reserved for treatment of severe infections. Carbapenem antimicrobial susceptibility testing profiles were determined in a population of Klebsiella pneumoniae, and their resistance assessed based on previous and current Clinical and Laboratory Standards Institute criteria.

Materials & methods

Isolates were examined using an automated antimicrobial susceptibility testing method, and real time polymerase chain reaction to detect the resistance (blaKPC) gene.

Results

The prevalence of blaKPC gene was 45/54 (83.3%). Five isolates that were susceptible under the previous criteria changed to nonsusceptible with the current standards. The overall difference in susceptibility between the standards was 8%.

Conclusion

This study shows that the current Clinical and Laboratory Standards Institute criteria may not offer additional benefits in the fight against carbapenem-resistant Enterobacteriaceae.

New interpretive criteria for danofloxacin antibacterial susceptibility testing against Mannheimia haemolytica and Pasteurella multocida associated with bovine respiratory disease

Danofloxacin is a fluoroquinolone antibacterial agent approved for use in veterinary medicine to treat and control bovine respiratory disease caused by Mannheimia haemolytica or Pasteurella multocida. Susceptible minimal inhibitory concentration (MIC) breakpoint (≤0.25 µg/mL) and disk diffusion interpretive criteria (≥22 mm) values for danofloxacin against M. haemolytica and P. multocida were first approved by the Clinical and Laboratory Standards Institute (CLSI) in 2003. However, intermediate and resistant breakpoint values were not established because only susceptible wild-type populations were evident at the time of breakpoint approvals. Since then, nonsusceptible isolates of M. haemolytica and P. multocida have been identified. We report danofloxacin intermediate MIC breakpoint (0.5 µg/mL) and disk diffusion interpretive criteria (18-21 mm), as well as danofloxacin-resistant MIC breakpoint (≥1 µg/mL) and disk diffusion interpretive criteria (≤17 mm), based on scattergram plots of MIC values versus disk zone diameters and calculated error-bound rates using M. haemolytica and P. multocida isolates recovered from bovine respiratory disease in North America in 2004-2014. These newly established intermediate and resistant clinical breakpoint values have been endorsed by CLSI and can be used for interpreting results from antibacterial susceptibility testing of danofloxacin against M. haemolytica and P. multocida isolated from bovine respiratory disease.

Empirical third-generation cephalosporin therapy for adults with community-onset Enterobacteriaceae bacteraemia: Impact of revised CLSI breakpoints

Third-generation cephalosporins (3GCs) [ceftriaxone (CRO) and cefotaxime (CTX)] have remarkable potency against Enterobacteriaceae and are commonly prescribed for the treatment of community-onset bacteraemia. However, clinical evidence supporting the updated interpretive criteria of the Clinical and Laboratory Standards Institute (CLSI) is limited. Adults with community-onset monomicrobial Enterobacteriaceae bacteraemia treated empirically with CRO or CTX were recruited. Clinical information was collected from medical records and CTX MICs were determined using the broth microdilution method. Eligible patients (n=409) were categorised into de-escalation (260; 63.6%), no switch (115; 28.1%) and escalation (34; 8.3%) groups according to the type of definitive antibiotics. Multivariate regression revealed five independent predictors of 28-day mortality: fatal co-morbidities based on McCabe classification [odds ratio (OR)=19.96; P<0.001]; high Pitt bacteraemia score (≥4) at bacteraemia onset (OR=13.91; P<0.001); bacteraemia because of pneumonia (OR=5.45; P=0.007); de-escalation after empirical therapy (OR=0.28; P=0.03); and isolates with a CTX MIC≤1mg/L (OR=0.17; P=0.02). Of note, isolates with a CTX MIC≤8mg/L (indicated as susceptible by previous CLSI breakpoints) were not associated with mortality. Furthermore, clinical failure and 28-day mortality rates had a tendency to increase with increasing CTX MIC (γ=1.00; P=0.01). Conclusively, focusing on patients with community-onset Enterobacteriaceae bacteraemia receiving empirical 3GC therapy, the present study provides clinically critical evidence to validate the proposed reduction in the susceptibility breakpoint of CTX to MIC≤1mg/L.

Candida species distribution and antifungal susceptibility testing according to European Committee on Antimicrobial Susceptibility Testing and new vs. old Clinical and Laboratory Standards Institute clinical breakpoints: a 6-year prospective candidaemia survey from the fungal infection network of Switzerland

We analyzed the species distribution of Candida blood isolates (CBIs), prospectively collected between 2004 and 2009 within FUNGINOS, and compared their antifungal susceptibility according to clinical breakpoints defined by the European Committee on Antimicrobial Susceptibility Testing (EUCAST) in 2013, and the Clinical and Laboratory Standards Institute (CLSI) in 2008 (old CLSI breakpoints) and 2012 (new CLSI breakpoints). CBIs were tested for susceptiblity to fluconazole, voriconazole and caspofungin by microtitre broth dilution (Sensititre® YeastOne™ test panel). Of 1090 CBIs, 675 (61.9%) were C. albicans, 191 (17.5%) C. glabrata, 64 (5.9%) C. tropicalis, 59 (5.4%) C. parapsilosis, 33 (3%) C. dubliniensis, 22 (2%) C. krusei and 46 (4.2%) rare Candida species. Independently of the breakpoints applied, C. albicans was almost uniformly (>98%) susceptible to all three antifungal agents. In contrast, the proportions of fluconazole- and voriconazole-susceptible C. tropicalis and F-susceptible C. parapsilosis were lower according to EUCAST/new CLSI breakpoints than to the old CLSI breakpoints. For caspofungin, non-susceptibility occurred mainly in C. krusei (63.3%) and C. glabrata (9.4%). Nine isolates (five C. tropicalis, three C. albicans and one C. parapsilosis) were cross-resistant to azoles according to EUCAST breakpoints, compared with three isolates (two C. albicans and one C. tropicalis) according to new and two (2 C. albicans) according to old CLSI breakpoints. Four species (C. albicans, C. glabrata, C. tropicalis and C. parapsilosis) represented >90% of all CBIs. In vitro resistance to fluconazole, voriconazole and caspofungin was rare among C. albicans, but an increase of non-susceptibile isolates was observed among C. tropicalis/C. parapsilosis for the azoles and C. glabrata/C. krusei for caspofungin according to EUCAST and new CLSI breakpoints compared with old CLSI breakpoints.

Synthesis and antimicrobial activity of cysteine-free coprisin nonapeptides

Coprisin is a 43-mer defensin-like peptide from the dung beetle, Copris tripartitus. CopA3 (LLCIALRKK-NH₂), a 9-mer peptide containing a single free cysteine residue at position 3 of its sequence, was derived from the α-helical region of coprisin and exhibits potent antibacterial and anti-inflammatory activities. The single cysteine implies a tendency for dimerization; however, it remains unknown whether this cysteine residue is indispensible for CopA3's antimicrobial activity. To address this issue, in the present study we synthesized eight cysteine-substituted monomeric CopA3 analogs and two dimeric analogs, CopA3 (Dimer) and CopIK (Dimer), and evaluated their antimicrobial effects against bacteria and fungi, as well as their hemolytic activity toward human erythrocytes. Under physiological conditions, CopA3 (Mono) exhibits a 6/4 (monomer/dimer) molar ratio in HPLC area percent, indicating that its effects on bacterial strains likely reflect a CopA3 (Mono)/CopA3 (Dimer) mixture. We also report the identification of CopW, a new cysteine-free nonapeptide derived from CopA3 that has potent antimicrobial activity with virtually no hemolytic activity. Apparently, the cysteine residue in CopA3 is not essential for its antimicrobial function. Notably, CopW also exhibited significant synergistic activity with ampicillin and showed more potent antifungal activity than either wild-type coprisin or melittin.

Evaluation of the performance of four methods for detection of hepatitis B surface antigen and their application for testing 116,455 specimens

Hepatitis B surface antigen (HBsAg) is a crucial serum marker for the diagnosis of hepatitis B virus (HBV) infection. It is imperative to compare test results from different detection methods based on different principles. Four methods, chemiluminescent microparticle immunoassay (CMIA), electrochemiluminescent immunoassay (ECLIA), enzyme-linked immunosorbent assay (ELISA) and golden immunochromato-graphic assay (GICA) were applied to test the HBsAg level in 250 specimens. According to the EP12-A2 and EP15-A2 documents from Clinical and Laboratory Standards Institute (CLSI), the concentration at which repeated results are 50% positive (C50) of HBsAg detected by CMIA, ECLIA, ELISA and GICA was 0.05, 0.08, 0.15 and 15.0IU/ml, respectively. When the detection concentration of HBsAg was 0.5IU/ml, the imprecision degree of CMIA, ECLIA and ELISA was 8.1%, 5.9% and 14.9% respectively. When detecting high HBsAg level (≥20.0IU/ml) and HBsAg negative specimens, the consistency of the four methods was high, while for the low level (0.05-20.0IU/ml), the consistency was poor (except for the CMIA and ECLIA, P<0.05). When evaluation of the four methods in qualitative diagnosis of HBsAg level in the 116,455 specimens, there was no significant discrepancy among CMIA, CMIA and ECLIA, however, GICA was significantly different from the other 3 methods. Compared with CMIA, the false negative rate of ECLIA, ELISA and GICA was 0.2%, 1.3% and 12.3% respectively. In conclusion, GICA was only suitable for the preliminary screening of HBsAg positive individuals and ELISA can be applied to the qualitative diagnosis of HBsAg. Both CMIA and ECLIA were suitable for the quantitative determination of HBsAg.

PNA-FISH assays for early targeted bacteraemia treatment

PNA-FISH S. aureus/CNS and GNR Traffic Light assays were compared with standard culture methods for identifying bacteraemia in 156 blood cultures from 131 patients. Results correlated with final culture results in 153 cultures. Retrospective case note review revealed that earlier targeted treatment would have occurred in 10.7% of cases.

Antifungal effect of CopA3 monomer peptide via membrane-active mechanism and stability to proteolysis of enantiomeric D-CopA3

In our previous study, coprisin, a 43-mer defensin-like peptide, was derived from the dung beetle, Copris tripartitus, and a 9-mer CopA3 (monomer), truncated coprisin analog peptide, was designed. However, the antifungal effects of CopA3 are not known yet. In this study, the antifungal activity and mechanism of CopA3 were investigated and to develop a more effective antimicrobial peptide under physiological conditions, the enantiomeric d-CopA3 was designed. l- and d-CopA3 had a similar antifungal activity without chiral selectivity, and their activity was more potent than that of melittin used as a positive control. Furthermore, l- and d-CopA3 did not even show any hemolysis against human erythrocytes. Membrane studies using propidium iodide and bis-(1,3-dibutylbarbituric acid) trimethine oxonol [DiBAC4(3)], suggested that the antifungal effect of l- and d-CopA3 was due to the membrane-active mechanism, by contrast with coprisin possessing apoptotic mechanism without membrane permeabilization. Finally, the proteolytic resistance and antifungal activity of l- and d-CopA3 against trypsin was analyzed by HPLC and colony count assay. The results showed that only d-CopA3 maintained a potent antifungal activity despite the proteolytic condition. Therefore, this study suggests that d-CopA3 has potential as a novel antimicrobial agent.

Comparative evaluation of the Bio-Rad Geenius HIV-1/2 Confirmatory Assay and the Bio-Rad Multispot HIV-1/2 Rapid Test as an alternative differentiation assay for CLSI M53 algorithm-I

INTRODUCTION

The CLSI-M53-A, Criteria for Laboratory Testing and Diagnosis of Human Immunodeficiency Virus (HIV) Infection; Approved Guideline includes an algorithm in which samples that are reactive on a 4th generation EIA screen proceed to a supplemental assay that is able to confirm and differentiate between antibodies to HIV-1 and HIV-2. The recently CE-marked Bio-Rad Geenius HIV-1/2 Confirmatory Assay was evaluated as an alternative to the FDA-approved Bio-Rad Multispot HIV-1/HIV-2 Rapid Test which has been previously validated for use in this new algorithm.

METHODS

This study used reference samples submitted to the Canadian - NLHRS and samples from commercial sources. Data was tabulated in 2×2 tables for statistical analysis; sensitivity, specificity, predictive values, kappa and likelihood ratios.

RESULTS

The overall performance of the Geenius and Multispot was very high; sensitivity (100%, 100%), specificity (96.3%, 99.1%), positive (45.3, 181) and negative (0, 0) likelihood ratios respectively, high kappa (0.96) and low bias index (0.0068). The ability to differentiate HIV-1 (99.2%, 100%) and HIV-2 (98.1%, 98.1%) Ab was also very high.

CONCLUSION

The Bio-Rad Geenius HIV-1/2 Confirmatory Assay is a suitable alternative to the validated Multispot for use in the second stage of CLSI M53 algorithm-I. The Geenius has additional features including traceability and sample and cassette barcoding that improve the quality management/assurance of HIV testing. It is anticipated that the CLSI M53 guideline and assays such as the Geenius will reduce the number of indeterminate test results previously associated with the HIV-1 WB and improve the ability to differentiate HIV-2 infections.

Heterogeneity of manufacturers' declarations for lipemia interference--an urgent call for standardization

INTRODUCTION

Due to the budget limitations, laboratories mostly rely on the manufacturers' information about the influence of interfering substances on laboratory results. However, some manufacturers do not follow the recommended procedures for testing interferences (CLSI standard) and there is a great variability in the presentation of data regarding lipemia interference.

MATERIALS AND METHODS

We aimed to verify the manufacturers' specifications for lipemia interference for clinical chemistry reagents provided by Beckman Coulter, Roche and Siemens. Bias was determined using the Intralipid® simulated lipemic samples. Furthermore, we aimed to compare obtained data with the manufacturers' claims and desirable specification for imprecision derived from biological variation.

RESULTS

i) Manufacturers' declarations were not confirmed for all three manufacturers; ii) the magnitude and direction of the effect of lipemia on laboratory results differ substantially between the three tested analytical systems; and iii) manufacturers are using arbitrary limits in declaring the expected effect of interference on laboratory results.

CONCLUSIONS

There is an urgent need to standardize the way manufacturers test and report their data on the lipemia interference. We propose that, instead of arbitrary limits, manufacturers use evidence based quality specifications for assessing the allowable biases. Moreover, laboratories should be aware of the possible lack of replicability of manufacturers' declarations.

Analytical characterization and clinical evaluation of an enzyme-linked immunosorbent assay for measurement of afamin in human plasma

Background

Comparative proteomics has recently identified afamin, the newest member of the albumin gene family, as a potential biomarker for ovarian cancer. The aim of this study was the analytical and clinical evaluation of a sandwich enzyme-linked immunosorbent assay for the determination of afamin in human plasma.

Methods

We evaluated precision, linearity, and detection limit of the assay, analyte stability and biological variability, determined reference values and quantified afamin concentrations in various diseases.

Results

Within-run and total coefficients of variation were < 10%. The method was linear across the tested measurement range. Detection limit was 7 mg/L for the assay. The analyte was stable for 24 h at room temperature, for 48 h at 4 °C, and for at least one year at − 20 °C and − 80 °C. The reference change value for healthy individuals was 24%. Age- and sex-independent reference values in healthy blood donors were 45–99 mg/L (median 68 mg/L). In the clinical assay evaluation afamin plasma concentrations were modestly decreased in patients with heart failure. Patients with pneumonia or sepsis exhibited markedly decreased afamin plasma concentrations. However, patients with chronic renal disease or chronic obstructive pulmonary disease showed no difference in afamin plasma concentrations as compared to healthy individuals. Correlation analyses revealed an inverse association between afamin and inflammatory biomarkers.

Conclusions

The afamin assay meets quality specifications for laboratory medicine. The results of the clinical assay evaluation revealed novel insights with respect to afamin as a potential negative acute phase protein and should encourage further studies.

•

The aim of this study was the analytical and clinical evaluation of a human afamin ELISA.

•

The afamin assay meets the needs of quality specifications of laboratory medicine.

•

Afamin exerts a good in vitro stability which is important of preanalytical issues.

•

The RCV was 24% and reference values in healthy blood donors were 45–99 mg/L.

•

We revealed novel insights with respect to afamin as a potential negative acute phase protein.

Relationship between the distribution of cefepime minimum inhibitory concentrations and detection of extended-spectrum β-lactamase production among clinically important Enterobacteriaceae isolates obtained from patients in intensive care units in Taiwan: results from the Surveillance of Multicenter Antimicrobial Resistance in Taiwan (SMART) in 2007

BACKGROUND

The data on susceptibility of important cephalosporins against four Enterobacteriaceae members producing potential extended-spectrum β-lactamase (ESBL) collected from Taiwanese intensive care units are lacking.

METHODS

Minimum inhibitory concentrations (MICs) of cefotaxime, ceftazidime, and cefepime were determined using agar dilution method, against Escherichia coli (n = 344), Klebsiella pneumoniae (n = 359), Enterobacter cloacae (n = 103), and Proteus mirabilis (n = 78). Susceptibilities of these isolates to three cephalosporins were assessed according to MIC breakpoints recommended by the Clinical and Laboratory Standards Institute (CLSI) and the European Committee on Antimicrobial Susceptibility Testing (EUCAST) in 2013. The double-disk synergy test using disks containing cefepime (30 μg) with or without clavulanate (10 μg) was applied to confirm production of ESBL for isolates with cephalosporin MIC ≥ 2 μg/mL.

RESULTS

A total of 175 isolates were verified as ESBL producers. The rates of cefepime susceptibility among the ESBL-producing isolates, according to CLSI (EUCAST) criteria, were 56.7% (22.4%) for E. coli, 61.3% (12.0%) for K. pneumoniae, 57.9% (31.6%) for E. cloacae, and 71.4% (7.1%) for P. mirabilis. Using different cefepime MIC breakpoints (MICs ≥ 16 μg/mL recommended by CLSI criteria and ≥ 2 μg/mL by EUCAST criteria) to define nonsusceptibility, we found that both criteria were poorer at predicting ESBL producers among K. pneumoniae and E. cloacae than among the other two species. In addition, we also found that the cefepime MIC level of 1.0 μg/mL best distinguished non-ESBL- from ESBL-producing K. pneumoniae and E. cloacae.

CONCLUSION

To detect ESBLs, CLSI should revise the cefepime MIC breakpoint against Enterobacteriaceae.

Would CLSI M53-A have helped in the diagnosis of HIV in Canada? Results of the performance of Canadian laboratories participating in a recent NLHRS proficiency testing panel containing HIV-1 antigen positive (antibody negative) and HIV-2 samples

INTRODUCTION

The Clinical and Laboratory Standards Institute recently published M53-A, Criteria for Laboratory Testing and Diagnosis of Human Immunodeficiency Virus (HIV) Infection; Approved Guideline (2011), which includes a state of the art algorithm for identifying HIV-1 acute and HIV-2 infections. To assess the ability of Canadian laboratories to detect these sample types and the impact of M53-A, the National Laboratory for HIV Reference Services distributed a special proficiency testing panel.

METHODS

HIVS425-2012Nov22 was sent to 42 laboratories across Canada. It contained one HIV negative sample (B), two HIV-1 positive samples (A and E), one HIV-2 positive sample (C) and one HIV-1/2 antibody negative-HIV-1 antigen positive sample (D). Data was collected and analyzed using DigitalPT; a standardized on-line tool.

RESULTS

Forty-one laboratories returned results. Sample B (HIV negative) was identified by 95% of laboratories (39/41) and samples A and E (HIV-1 positive) by 98% (40/41). No laboratory identified sample C as HIV-2 positive, although 85% (35/41) detected reactivity prompting a referral for further testing. The remaining laboratories identified sample C as HIV-1 positive (4), indeterminate (1) or gave no final status (1). Sample D (HIV antibody negative-antigen positive) was correctly identified by two laboratories as HIV-1 antigen positive while 78% (32/41) detected reactivity, recommending further testing. One laboratory did not provide a final status. Alarmingly, six laboratories called this sample HIV negative.

CONCLUSION

Although there is a high quality of HIV testing across Canada, introduction of the M53-A guideline would further improve the ability of laboratories to diagnose HIV-1 acute and HIV-2 infection.

Qualification of cardiac troponins for nonclinical use: a regulatory perspective

The US Food and Drug Administration (FDA) Biomarker Qualification Review Team presents its perspective on the recent qualification of cardiac troponins for use in nonclinical safety assessment studies. The goal of this manuscript is to provide greater transparency into the qualification process and factors that were considered in reaching a regulatory decision. This manuscript includes an overview of the data that were submitted and a discussion of the strengths and shortcomings of these data supporting the qualification decision. The cardiac troponin submission is the first literature-based biomarker application to be reviewed by the FDA and insights gained from this experience may aid future submissions and help streamline the characterization and qualification of future biomarkers.

A new pentacyclic triterpene with potent antibacterial activity from Limnophila indica Linn. (Druce)

A new pentacyclic triterpenoid constituent, characterized as 3-oxo-olean-12(13),18(19)-dien-29α-carboxylic acid (1) on the basis of detailed spectral studies, was isolated from the aerial parts and roots of Limnophila indica (Scrophulariaceae). Compound 1 exhibited considerable antibacterial activity against three Gram-positive bacteria viz. Bacillus subtilis, Staphylococcus aureus and Listeria monocytogenes (MICs within a range of 25-30 μg/ml) and moderate activity against four Gram-negative bacteria Salmonella typhimurium, Escherichia coli, Pseudomonas aeruginosa, and Pantoea ananatis (MICs within a range of 30-100 μg/ml). The plant pathogenic bacterium P. ananatis and human pathogenic S. typhimurium responded at comparatively higher concentrations of the compound 1, which were 75 and 100 μg/ml respectively. The compound inhibited the growth of Gram-positive B. subtilis and Gram-negative P. aeruginosa completely with a clear bactericidal mode of action at their MIC values. The compound upon treatment on both B. subtilis and P. aeruginosa released substantial amount of nucleic acid in the external medium and also effected the change of morphology towards pleomorphicity, thereby indicating its probable action on cell membrane. Furthermore, the triterpenoid 1 was found not to inhibit a probiotic lactic acid bacterium Lactococcus lactis subsp. lactis LABW4 under in vitro condition and to possess no toxicity in Swiss albino mice.

Characterization of ciprofloxacin resistant Escherichia coli isolates among men undergoing evaluation for transrectal ultrasound guided prostate biopsy

PURPOSE

We determine the prevalence of ciprofloxacin resistant gram-negative bacilli in patients scheduled for transrectal ultrasound guided prostate biopsy, characterize the Escherichia coli strains recovered from this patient population, and characterize the mechanisms responsible for β-lactam and ciprofloxacin resistance.

MATERIALS AND METHODS

Rectal swabs from 991 patients were cultured for ciprofloxacin resistant gram-negative bacilli with a selective medium. Recovered E. coli isolates were further analyzed with susceptibility testing, pulsed field gel electrophoresis, plasmid isolation and sequencing.

RESULTS

A total of 193 ciprofloxacin resistant gram-negative bacilli were recovered and of these isolates 167 (87%) were E. coli. The prevalence of ciprofloxacin resistant E. coli in the study population was 17%. Only 38 (26%) of the 149 E. coli isolates that received susceptibility testing were susceptible to ampicillin and ampicillin-sulbactam. In select isolates transferrable plasmids carrying β-lactamase were responsible for the resistance to the β-lactam agents and other nonβ-lactam antimicrobials. Diverse combinations of gyrA and parC mutations associated with fluoroquinolone resistance were identified. Strain typing and plasmid typing indicated that the E. coli isolates did not share a common origin.

CONCLUSIONS

Of the patients in our study 17% carried ciprofloxacin resistant E. coli. Analysis of resistance mechanisms and plasmid analysis along with strain typing demonstrated that this patient population harbored organisms with heterogeneous phenotypic susceptibility, indicating that universal prophylaxis would not provide optimal coverage for patients undergoing transrectal ultrasound guided prostate biopsy.

Multiplex newborn screening for Pompe, Fabry, Hunter, Gaucher, and Hurler diseases using a digital microfluidic platform

PURPOSE

New therapies for lysosomal storage diseases (LSDs) have generated interest in screening newborns for these conditions. We present performance validation data on a digital microfluidic platform that performs multiplex enzymatic assays for Pompe, Fabry, Hunter, Gaucher, and Hurler diseases.

METHODS

We developed an investigational disposable digital microfluidic cartridge that uses a single dried blood spot (DBS) punch for performing a 5-plex fluorometric enzymatic assay on up to 44 DBS samples. Precision and linearity of the assays were determined by analyzing quality control DBS samples; clinical performance was determined by analyzing 600 presumed normal and known affected samples (12 for Pompe, 7 for Fabry and 10 each for Hunter, Gaucher and Hurler).

RESULTS

Overall coefficient of variation (CV) values between cartridges, days, instruments, and operators ranged from 2 to 21%; linearity correlation coefficients were ≥0.98 for all assays. The multiplex enzymatic assay performed from a single DBS punch was able to discriminate presumed normal from known affected samples for 5 LSDs.

CONCLUSIONS

Digital microfluidic technology shows potential for rapid, high-throughput screening for 5 LSDs in a newborn screening laboratory environment. Sample preparation to enzymatic activity on each cartridge is less than 3h.

New guideline supports the development and evaluation of continuous interstitial glucose monitoring devices

For the millions of patients who are managing diabetes, daily self-monitoring of blood glucose is a fact of life. However, the cost and inconvenience of self-monitoring have led to noncompliance by many patients.Continuous interstitial glucose monitoring (CGM) has emerged as a promising and welcome alternative to traditional glucose monitoring, which requires the patient to endure repeated finger sticks. The Clinical and Laboratory Standards Institute (CLSI) (Wayne, PA) has been working cooperatively with the Diabetes Technology Society on the development of a consensus guideline for CGM. CLSI has recently released document POCT5-P-Performance Metrics for Continuous Interstitial Glucose Monitoring; Proposed Guideline. This document specifies requirements and recommendations for methods determining analytical and clinical metrics of CGM. This guideline will support and streamline the further development and evaluation of CGM devices.