Colistin and polymyxin B remain part of the last line of antibiotics for multidrug-resistant Gram-negative bacteria, such as carbapenem-resistant Enterobacteriaceae. Current joint EUCAST-CLSI recommendations are for broth microdilution (BMD) to be performed for MIC testing of colistin. Commercial susceptibility testing methods were evaluated and compared against the reference BMD, using a susceptibility breakpoint of Յ2 mg/liter for both colistin and polymyxin B. Seventy-six Enterobacteriaceae were included, of which 21 were mcr-1 positive (18 Escherichia coli isolates, 2 Klebsiella pneumoniae isolates, and 1 Enterobacter aerogenes isolate). Rates of essential agreement (EA) of colistin test results between BMD and Vitek 2, Sensititre, and Etest were 93.4%, 89.5%, and 75.0%, respectively. Rates of EA of polymyxin B test results between BMD and Vitek 2, Sensititre, and Etest were 96.1%, 96.1%, and 48.7%, respectively. A positive MIC correlation with a categorical agreement of Ͼ90% was achieved for Sensititre (colistin Spearman's ϭ 0.863, and polymyxin B Spearman's ϭ 0.877) and Vitek 2 (polymyxin B [only] Spearman's ϭ 0.8917). Although a positive MIC correlation (Spearman's ϭ 0.873) with the reference method was achieved for colistin testing with Vitek 2, categorical agreement was Ͻ90%, with very major error rates of 36%. Correlation with the Etest MIC was lower, with very major error rates of 12% (colistin) and 26.1% (polymyxin B). MicroScan (colistin) categorical agreement was 88.2%, with a very major error rate of 4%. Colistin MICs for 15 of the 21 mcr-1-positive isolates were Ͼ2 mg/liter, and polymyxin MICs for 17 of them were Ͼ2 mg/liter by broth microdilution. The use of a lower breakpoint of Յ1 mg/liter further improves detection of mcr-1 for all testing methods. However, further data on the correlation between MICs and clinical outcome are required to determine the most suitable breakpoint to guide clinical management.KEYWORDS colistin, polymyxin B, susceptibility testing, mcr-1 M ultidrug-resistant organisms (MDROs) represent a progressive burden on health care systems globally. Carbapenem-resistant Enterobacteriaceae (CRE) are now reported worldwide. CRE infections are difficult to treat, and there are limited options available. The polymyxins (colistin and polymyxin B) are antibiotics which are used for treating infections with CRE. Polymyxins initially fell out of favor among clinicians due to concerns over high rates of nephrotoxicity and neurotoxicity (1). In recent years, the use of polymyxins has been on the rise, with increasing rates of CRE infection.

IgG assay in COVID-19 patients. Methods: Residual sera from 177 symptomatic SARS-CoV-2-positive patients and 163 non-COVID-19 patients were tested for antibody with the Abbott SARS-CoV-2 IgG assay (Abbott Diagnostics, Chicago, USA). Clinical records for COVID-19 patients were reviewed to determine the time from onset of clinical illness to testing. Results: Specificity of the assay was 100.0% (95%CI: 97.1e100.0%). The clinical sensitivity of the assay varied depending on time from onset of symptoms, increasing with longer periods from the onset of clinical illness. The clinical sensitivity at 6 days was 8.6% (7/81; 95%CI: 3.8e17.5%), at 7e13 days 43.6% (17/39; 95%CI: 28.2e60.2%), at 14e20 days 84.0% (21/25; 95%CI: 63.1e94.7%), and at 21 days 84.4% (27/ 32; 95%CI: 66.5e94.1%). Clinical sensitivity was higher in the 14-day group compared to <14 days. There were no differences between the 14e20-day and 21-days groups; the combined clinical sensitivity for these groups (14 days) was 84.2% (49/57; 71.6e92.1%). Conclusion:The Abbott SARS-CoV-2 IgG test has high specificity. Clinical sensitivity was limited in the early stages of disease but improved from 14 days after the onset of clinical symptoms.

Introduction This study aims to assess the association of piperacillin/tazobactam and meropenem minimum inhibitory concentration (MIC) and beta-lactam resistance genes with mortality in the MERINO trial. Methods Blood culture isolates from enrolled patients were tested by broth microdilution and whole genome sequencing at a central laboratory. Multivariate logistic regression was performed to account for confounders. Absolute risk increase for 30-day mortality between treatment groups was calculated for the primary analysis (PA) and the microbiologic assessable (MA) populations. Results 320 isolates from 379 enrolled patients were available with susceptibility to piperacillin/tazobactam 94% and meropenem 100%. The piperacillin/tazobactam non-susceptible breakpoint (MIC &gt; 16 mg/L) best predicted 30-day mortality after accounting for confounders (odds ratio 14.9, 95% CI 2.8 – 87.2). The absolute risk increase for 30-day mortality for patients treated with piperacillin/tazobactam compared with meropenem was 9% (95% CI 3% – 15%) and 8% (95% CI 2% – 15%) for the original PA population and the post-hoc MA populations, which reduced to 5% (95% CI -1% – 10%) after excluding strains with piperacillin/tazobactam MIC values &gt; 16 mg/L. Isolates co-harboring ESBL and OXA-1 genes were associated with elevated piperacillin/tazobactam MICs and the highest risk increase in 30-mortality of 14% (95% CI 2% – 28%). Conclusion After excluding non-susceptible strains, the 30-day mortality difference was from the MERINO trial was less pronounced for piperacillin/tazobactam. Poor reliability in susceptibility testing performance for piperacillin/tazobactam and the high prevalence of OXA co-harboring ESBLs suggests meropenem remains the preferred choice for definitive treatment of ceftriaxone non-susceptible E. coli and Klebsiella.

Citation Chew KL, Cheng B, Lin RTP, Teo JWP. 2018. Elizabethkingia anophelis is the dominant Elizabethkingia species found in blood cultures in Singapore. J Clin Microbiol 56:e01445-17.

In this study, we evaluated and compared six SARS-CoV-2 serology kits including the Abbott SARS-CoV-2 IgG assay, Beckman Access SARS-CoV-2 IgG assay, OCD Vitros OCD Anti-SARS-CoV-2 Total antibody assay, Roche Elecsys Anti SARS-CoV-2 assay, Siemens SARS-CoV-2 Total assay, and cPass surrogate viral neutralising antibody assay. A total of 336 non-duplicated residual serum samples that were obtained from COVID-19 confirmed patients (n=173) on PCR and negative controls (n=163) obtained pre-December 2019 before the COVID-19 pandemic were used for the study. These were concurrently analysed on the different immunoassay platforms and correlated with clinical characteristics. Our results showed all assays had specificity ranging from 99.3% to 100.0%. Overall sensitivity across all days of symptoms, in descending order were OCD (49.1%, 95% CI 41.8-56.5%), cPass (44.8%, 95% CI 37.5-52.3%), Roche (41.6%, 95% CI 34.5-49.0%), Siemens (39.9%, 95% CI 32.9-47.3%), Abbott (39.8%, 95% CI 32.9-47.3%) and Beckman (39.6%, 95% CI 32.5-47.3%). Testing after at least 14 days from symptom onset is required to achieve AUCs greater than 0.80. OCD and cPass performed the best in terms of sensitivity for >21 days symptoms with 93.3% (95% CI, 73.5-99.2%) and 96.7% (95% CI, 82.8-99.9%), respectively. Both also shared the greatest concordance, kappa 0.963 (95% CI 0.885-1.0), p<0.001, and had the lowest false negative rates. Serology results should be interpreted with caution in certain cases. False negatives were observed in a small number of individuals with COVID-19 on immunosuppressive therapy, paucisymptomatic or who received antiretroviral therapy. In conclusion, all assays exhibited excellent specificity and total antibody assays with spike protein configurations generally outperformed nucleocapsid configurations and IgG assays in terms of diagnostic sensitivity.

Klebsiella pneumoniae remains a major pathogen responsible for localized infections such as cystitis and pneumonia, and disseminated infections that may result in severe sepsis and death. Invasive disease such as liver abscesses and endogenous endophthalmitis are associated with capsular serotypes K1 and K2. These infections require a prolonged course of antimicrobial treatment which has evolved over the years from inpatient treatment to outpatient parenteral antibiotic therapy. The emergence of plasmid-mediated resistance began with extended-spectrum β-lactamases (ESBLs) and AmpC β-lactamases. This was followed by carbapenemase genes and now plasmid transmissible colistin resistance (mcr), thus limiting viable treatment options. Plasmid-mediated carbapenemase production in Singapore was first reported in 1996. Carbapenemase production has since become the predominant mechanism of carbapenem resistance and incidence rates continue to increase over time. Although carbapenemases can occur in all Enterobacteriaceae, K. pneumoniae are the most common carrier of carbapenemase genes. Alternative treatment options are urgently required before the simplest infections, let alone invasive infections are left potentially untreatable. Clinical management requires guidance from robust laboratory testing methods to optimize patient outcomes. We explore past and present trends in treatment of K. pneumoniae infections, and discuss future treatment options and gaps in knowledge for further study.

Context: The use of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) serological tests detect antibodies in the host, contributing to the identification of individuals who have been exposed to Coronavirus Disease 2019 (COVID-19). Objective: To critically evaluate two commercially available SARS-CoV-2 serology tests. Design: A total of 333 unique, non-duplicated serum samples obtained from COVID-19 patients (n=170) and negative controls (n=163) obtained pre-December 2019 were used in the study. Samples were tested on the Roche E411 and Abbott Architect i4000SR platforms and results were correlated to reverse transcription polymerase chain reaction (PCR) results and clinical symptoms. Results: There was a strong level of agreement in the qualitative results between both assays with a Cohen's kappa value of 0.840, P&lt;.001. The specificity for both Roche and Abbott were excellent at 100%. Roche exhibited marginally better performance in the ≥21 days group with a sensitivity of 90.6% (95% CI 75.8–96.8%) versus Abbott's sensitivity 84.4% (95% CI 68.3 – 93.1%) as well as the 14–20 days group with a sensitivity of 85.7% (95% CI 65.4 – 95.0%) versus Abbott sensitivity 81.0% (95% CI 60.0 – 92.3%). Less than 14 days of symptoms groups exhibited poor sensitivity at &lt;50% for both assays. The area under curve (AUC ± standard error) for Roche (0.894 ± 0.025, P&lt; .001) and Abbott (0.884 ± 0.026, P &lt;.001) were very similar. Potential confounders for negative serological results include antiretroviral medication use and pauci-symptomatic patients. Conclusions: Specificities for high throughput Roche and Abbott immunoassays are excellent but users need to be cautious to interpret serological test results after 14 days of symptoms to avoid false negatives

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