• Clinical Evaluation of Sofia Rapid Antigen Assay for Detection of Severe Acute Respiratory Syndrome Coronavirus 2 among Emergency Department to Hospital Admissions

      Smith, Richard D; Johnson, J Kristie; Clay, Colleen; Girio-Herrera, Leo; Stevens, Diane; Abraham, Michael; Zimand, Paul; Ahlman, Mark; Gimigliano, Sheri; Zhao, Richard; et al. (Cambridge University Press, 2021-06-24)
      Objective: To determine the utility of the Sofia® SARS rapid antigen fluorescent immunoassay (FIA) to guide hospital bed placement of patients being admitted through the emergency department (ED). Design: Cross-sectional analysis of a clinical quality improvement study. Setting: Two community hospitals in Maryland. From 9/21/2020 to 12/3/2020, 2887 patients simultaneously received the Sofia® SARS rapid antigen FIA and SARS-CoV-2 RT-PCR assays on admission through the ED. Methods: Rapid antigen results and symptom assessment guided initial patient placement while confirmatory RT-PCR was pending. The sensitivity, specificity, positive and negative predictive values of the rapid antigen assay were calculated relative to RT-PCR, overall and separately for symptomatic and asymptomatic patients. Assay sensitivity was compared to RT-PCR cycle threshold (Ct) values. Assay turnaround times were compared. Clinical characteristics of RT-PCR positive patients and potential exposures from false-negative antigen assays were evaluated. Results: Overall agreement, sensitivity, and specificity for all patients was 97.9%, 76.6% (95% confidence interval (CI): 71%, 82%), and 99.7% (95% CI: 99%, 100%), respectively. No differences in performance were seen between asymptomatic and symptomatic individuals. As RT-PCR Ct increased, sensitivity of the antigen assay decreased. Mean turnaround time for the antigen assay and RT-PCR was 1.2 (95% CI: 1.0, 1.3) and 20.1 (95% CI: 18.9, 40.3) hours, respectively (p<0.001). No transmission from antigen-negative/RT-PCR-positive patients was identified. Conclusions: While not a replacement for RT-PCR for detection of all SARS-CoV-2 infections, the Sofia® SARS antigen FIA has clinical utility for potential initial timely patient placement.
    • MgrB-Dependent Colistin Resistance in Klebsiella pneumoniae Is Associated with an Increase in Host-to-Host Transmission.

      Bray, Andrew S; Smith, Richard D; Hudson, Andrew W; Hernandez, Giovanna E; Young, Taylor M; George, Hannah E; Ernst, Robert K; Zafar, M Ammar (American Society for Microbiology, 2022-03-21)
      Due to its high transmissibility, Klebsiella pneumoniae is one of the leading causes of nosocomial infections. Here, we studied the biological cost of colistin resistance, an antibiotic of last resort, in this opportunistic pathogen using a murine model of gut colonization and transmission. Colistin resistance in K. pneumoniae is commonly the result of the inactivation of the small regulatory protein MgrB. Without a functional MgrB, the two-component system PhoPQ is constitutively active, leading to an increase in lipid A modifications and subsequent colistin resistance. Using an isogenic mgrB deletion mutant (MgrB-), we demonstrate that the mutant's colistin resistance is not associated with a fitness defect under in vitro growth conditions. However, in our murine model of K. pneumoniae gastrointestinal (GI) colonization, the MgrB- colonizes the gut poorly, allowing us to identify a fitness cost. Moreover, the MgrB- mutant has higher survival outside the host compared with the parental strain. We attribute this enhanced survivability to dysregulation of the PhoPQ two-component system and accumulation of the master stress regulator RpoS. The enhanced survival of MgrB- may be critical for its rapid host-to-host transmission observed in our model. Together, our data using multiple clinical isolates demonstrate that MgrB-dependent colistin resistance in K. pneumoniae comes with a biological cost in gut colonization. However, this cost is mitigated by enhanced survival outside the host and consequently increases its host-to-host transmission. Additionally, it underscores the importance of considering the entire life cycle of a pathogen to determine the actual biological cost associated with antibiotic resistance. IMPORTANCE The biological cost associated with colistin resistance in Klebsiella pneumoniae was examined using a murine model of K. pneumoniae gut colonization and fecal-oral transmission. A common mutation resulting in colistin resistance in K. pneumoniae is a loss-of-function mutation of the small regulatory protein MgrB that regulates the two-component system PhoPQ. Even though colistin resistance in K. pneumoniae comes with a fitness defect in gut colonization, it increases bacterial survival outside the host enabling it to transmit more effectively to a new host. The enhanced survival is dependent upon the accumulation of RpoS and dysregulation of the PhoPQ. Hence, our study expands our understanding of the underlying molecular mechanism contributing to the transmission of colistin-resistant K. pneumoniae.
    • A Novel Lipid-Based MALDI-TOF Assay for the Rapid Detection of Colistin-Resistant Species.

      Smith, Richard D; McElheny, Christi L; Izac, Jerilyn R; Gardner, Francesca M; Chandler, Courtney E; Goodlett, David R; Doi, Yohei; Johnson, J Kristie; Ernst, Robert K (American Society for Microbiology, 2022-02-02)
      Enterobacter species are classified as high-priority pathogens due to high prevalence of multidrug resistance from persistent antibiotic use. For Enterobacter infections caused by multidrug-resistant isolates, colistin (polymyxin E), a last-resort antibiotic, is a potential treatment option. Treatment with colistin has been shown to lead to emergence of polymyxin resistance. The primary mechanism for colistin resistance is modification of terminal phosphate moieties of lipid A, leading to decreased membrane electronegativity and reducing colistin binding affinity. Detection of these modifications, including the addition of phosphoethanolamine and 4-amino-4-deoxy-l-arabinose (Ara4N), can be used for prediction of colistin resistance using matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS). The objective of this study was to identify lipid A markers for colistin resistance in Enterobacter species and Klebsiella aerogenes (formerly Enterobacter aerogenes). Using a collection of Enterobacter and Klebsiella aerogenes clinical isolates, broth MICs for colistin were determined initially. Subsequently, killing assays were carried out to determine how the concentration of colistin at which there is approximately 50% survival (kill50) equates to their MICs. Finally, lipid A analysis was conducted via MALDI-TOF MS using the novel rapid extraction method, termed fast lipid analysis technique (FLAT), to correlate MIC and killing efficacy with predictive lipid A modifications. Sensitivity and specificity of the MS assay compared to MIC interpretation were 100% and 53.4%, respectively. A receiver operator characteristic (ROC) demonstrated that MS was highly correlated with killing, with area under the curve of 0.97. This analysis demonstrated the potential utility of MALDI-TOF MS as a rapid diagnostic platform of colistin resistance in Enterobacter species. IMPORTANCE In this study, we develop a novel method for identifying colistin resistance in Enterobacter species and Klebsiella aerogenes without performing antimicrobial susceptibility testing. Typically, susceptibility testing requires an additional 24 to 48 h, while the MS assay described in this study allows for resistant identifications in under 1 h after initial culture. Identification using MALDI-TOF MS would save time and prevent inappropriate use of colistin. MALDI-TOF MS is an easy-to-use, readily available, robust diagnostic tool in clinical laboratories. Furthermore, this study highlights limitations of polymyxin susceptibility testing. Use of a killing assay best captures how colistin treats infection and is shown to be highly correlated with our MS assay; thus, the MS assay in this study effectively predicts how colistin would treat a patient's infection. Use of MALDI-TOF MS for accurate and early identification of antimicrobial resistance can improve antimicrobial stewardship and patient outcomes.
    • Rapid identification of 1-positive from patient urine using a novel lipid-based MALDI-TOF-MS assay.

      Smith, Richard D; Izac, Jerilyn R; Ha, Michael; Yang, Hyojik; Johnson, J Kristie; Ernst, Robert K (American Society for Microbiology, 2021-12-17)
      Mobilized colistin resistance (mcr) genes confer resistance to colistin, a last-resort antibiotic for multidrug-resistant Gram-negative infections. In this case report, we describe a novel lipid-based matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) diagnostic used to rapidly identify an mcr-1-positive Escherichia coli directly from a patient with a urinary tract infection without the need for ex vivo growth.