Citations

ABSTRACT Achromobacter species can cause opportunistic infections which are difficult to treat due to a variety of antimicrobial resistance (AMR) mechanisms. As such, antimicrobial susceptibility testing (AST) is a cornerstone to successful treatment for these organisms. Currently, there are no specific Clinical and Laboratory Standards Institute (CLSI) AST guidelines for Achromobacter species. The purpose of this study was to (i) establish tentative CLSI M45 MIC and disk diffusion (DD) breakpoints (BPs), (ii) evaluate the modified carbapenem inactivation method (mCIM), and (iii) understand the mechanisms mediating AMR among Achromobacter species. Contemporary MIC data from multiple sources were collated to define the tentative epidemiological cutoff values (tECVs), and the MIC distributions were used to inform the establishment of MIC BPs for various agents. A disk-to-MIC correlate study with 91 isolates from across the United States was completed by testing reference broth microdilution and DD from the same inoculum and applying the dBETS software to establish DD BPs. Lastly, the mCIM and whole-genome sequencing (WGS) were pursued. The tECVs for piperacillin-tazobactam, imipenem, and meropenem were 1, 2, and 0.5 µg/mL, respectively. Disk correlates met CLSI M23 acceptance criteria with a few exceptions related to a small number of isolates, resulting in high minor errors. WGS revealed that 82 (90.1%) isolates harbored a bla OXA variant with bla OXA-114 predominating (90.2%). Nineteen isolates harbored acquired beta-lactamase genes, including 16 bla AXC , 2 bla VIM-4 , and 1 bla AZM-1. The mCIM had a sensitivity of 100% and specificity of 87%. Upon review, the CLSI M45 committee set tentative MIC and DD BPs for piperacillin-tazobactam, imipenem, meropenem, and trimethoprim-sulfamethoxazole. IMPORTANCE Achromobacter species can cause opportunistic infections which may be difficult to treat due to a variety of antimicrobial resistance mechanisms. Antimicrobial susceptibility testing is a critical component of patient treatment for these infections. Currently, the Clinical and Laboratory Standards Institute M100 non-Enterobacterales susceptibility test interpretive criteria and methodology are utilized for Achromobacter by clinical laboratories and likely do not accurately predict susceptibility results for Achromobacter species. This study was designed to establish tentative MIC and disk diffusion breakpoints specific to Achromobacter species.

Abstract Background Antibiograms are an important stewardship tool that can inform optimal empiric therapy; most antibiograms are hospital-wide. Unit-specific antibiogram data for unique patient populations including intensive care unit and pediatrics is robust; however, published experience with unit-specific antibiograms in the hematology-oncology (heme-onc) population is limited. These patients are unique because of the common use of antimicrobial prophylaxis, prolonged broad-spectrum antibiotics, and an immunocompromised state. We sought to examine the trends in antibiogram antimicrobial susceptibility over time. Methods This retrospective quality initiative included microbiology results (first isolates per patient per timeframe) from Mayo Clinic Rochester from 2012 to 2022. Eligible cultures were those identified as being obtained from one of 8 hematology, oncology, or bone marrow transplant inpatient units. Agar dilution susceptibility testing and Clinical and Laboratory Standards Institute (CLSI) breakpoints were used. Screening PCRs (eg, VRE PCR) were excluded. Culture and susceptibilities were identified by an EMR based report, compiled annually, and reported for two-year periods. Susceptibility rates were compared using the Chi-square test and Chi-square analysis for trends. Results There were 4 gram-negative and 5 gram-positive organism groups that met CLSI antibiogram criteria of ≥ 30 isolates and were included (tables 1-4). There were several significant differences in comparison to the hospital-wide antibiogram, with lower antibiotic susceptibility rates in the heme-onc units for multiple organisms, notably fluoroquinolones to E.coli and P. aeruginosa and several cephalosporins to Enterobacterales as well as penicillin and levofloxacin to Viridans group Streptococcus and vancomycin to E. faecium (tables 1&2). Over the period of 2012-2013 to 2021-2022, susceptibility rates remained stable among the heme-onc antibiogram, with few significant changes (tables 3&4). Conclusion Heme-onc antibiograms illustrated susceptibility rate differences compared to our hospital-wide antibiograms, particularly for antimicrobials used as prophylaxis. Through population-specific antibiograms, providers may be able to improve empiric antibiotic selection. Disclosures Christina G. Rivera (O'Connor), Pharm.D, Gilead Sciences: Board Member

ABSTRACT The Burkholderia cepacia complex (BCC) is a group of Gram-negative bacteria that cause opportunistic infections, most notably in people with cystic fibrosis (CF), and have been associated with outbreaks caused by contaminated medical products. Antimicrobial susceptibility testing (AST) is often used to guide treatment for BCC infections, perhaps most importantly in people with CF who are being considered for lung transplant. However, recent studies have highlighted problems with AST methods. Here, we address limitations from previous studies to further evaluate BCC AST methods. We assessed the performance of reference broth microdilution (BMD), disk diffusion (DD) using Mueller-Hinton agar (MHA) from three manufacturers, agar dilution (AD), and gradient diffusion (ETEST) for ceftazidime (CAZ), levofloxacin (LVX), meropenem (MEM), minocycline (MIN), and trimethoprim-sulfamethoxazole (TMP-SMX) on a set of 205 BCC isolates. The isolate set included 100 isolates from people with CF and 105 isolates from people without CF from a variety of sources, which enabled us to systematically evaluate whether specimen source impacts AST performance. For all BCC isolates, BMD reproducibility was 93%, 98%, 99%, 98%, and 96% for CAZ, LVX, MEM, MIN, and TMP-SMX, respectively. Using BMD as the comparator method, we show that DD, AD, and ETEST perform poorly, with neither MHA manufacturer nor specimen source significantly impacting method performance. Based on our data, we recommend that routine AST should not be performed for BCC isolates. If a provider requests AST, clinical microbiology laboratories should perform Clinical and Laboratory Standards Institute reference methodology for BMD (stored frozen) and report MIC only. IMPORTANCE Antimicrobial susceptibility testing for the Burkholderia cepacia complex (BCC) is often used to determine eligibility for lung transplant in people with cystic fibrosis. However, problems with method performance have been reported. Here, we systematically evaluate the performance of reference broth microdilution, disk diffusion, agar dilution, and gradient diffusion (ETEST) for BCC organisms isolated from people with and without cystic fibrosis. We show that broth microdilution reproducibility is acceptable for levofloxacin, meropenem, minocycline, and trimethoprim-sulfamethoxazole, while ceftazidime was just below the acceptability cut-off. Regardless of specimen source, the results from disk diffusion, agar dilution, and ETEST do not correlate with broth microdilution. Based on these findings, we recommend that antimicrobial susceptibility testing should not be routinely performed for BCC, and if requested by the provider, only broth microdilution following Clinical and Laboratory Standards Institute guidelines should be used. Providers should be aware of the significant limitations of antimicrobial susceptibility testing methods for BCC.

Routine antimicrobial susceptibility testing (AST) of Helicobacter pylori by agar dilution is difficult to perform and not practical in most clinical microbiology laboratories. The Etest gradient diffusion method can be a reliable alternative for H. pylori AST with the advantage of being a less laborious quantitative method. This work reveals that an optimized Etest method can provide acceptable performance for H. pylori AST and describes the challenges associated with this methodology.

Abstract Background Rapid blood culture diagnostics are of unclear benefit for patients with gram-negative bacilli (GNB) bloodstream infections (BSIs). We conducted a multicenter, randomized, controlled trial comparing outcomes of patients with GNB BSIs who had blood culture testing with standard-of-care (SOC) culture and antimicrobial susceptibility testing (AST) vs rapid organism identification (ID) and phenotypic AST using the Accelerate Pheno System (RAPID). Methods Patients with positive blood cultures with Gram stains showing GNB were randomized to SOC testing with antimicrobial stewardship (AS) review or RAPID with AS. The primary outcome was time to first antibiotic modification within 72 hours of randomization. Results Of 500 randomized patients, 448 were included (226 SOC, 222 RAPID). Mean (standard deviation) time to results was faster for RAPID than SOC for organism ID (2.7 [1.2] vs 11.7 [10.5] hours; P < .001) and AST (13.5 [56] vs 44.9 [12.1] hours; P < .001). Median (interquartile range [IQR]) time to first antibiotic modification was faster in the RAPID arm vs the SOC arm for overall antibiotics (8.6 [2.6–27.6] vs 14.9 [3.3–41.1] hours; P = .02) and gram-negative antibiotics (17.3 [4.9–72] vs 42.1 [10.1–72] hours; P < .001). Median (IQR) time to antibiotic escalation was faster in the RAPID arm vs the SOC arm for antimicrobial-resistant BSIs (18.4 [5.8–72] vs 61.7 [30.4–72] hours; P = .01). There were no differences between the arms in patient outcomes. Conclusions Rapid organism ID and phenotypic AST led to faster changes in antibiotic therapy for gram-negative BSIs. Clinical Trials Registration NCT03218397.

Plasmid-mediated colistin resistance (PMCR) is a global public health concern, given its ease of transmissibility. The purpose of this study was to evaluate two methods for the detection of PMCR from bacterial colonies: (i) the NG-Test MCR-1 lateral flow immunoassay (LFA; NG Biotech, Guipry, France) and (ii) the EDTA-colistin broth disk elution (EDTA-CBDE) screening test method. These methods were evaluated using a cohort of contemporary, clinical Gram-negative bacillus isolates from 3 U.S. academic medical centers (126 isolates of the Enterobacterales , 50 Pseudomonas aeruginosa isolates, and 50 Acinetobacter species isolates; 1 isolate was mcr positive) and 12 mcr -positive CDC-FDA Antibiotic Resistance (AR) Isolate Bank isolates for which reference broth microdilution colistin susceptibility results were available.

Abstract Background Rapid blood culture diagnostics increase cost and have unclear benefit for patients with Gram-negative bacilli (GNB) bloodstream infections (BSIs). We conducted a multicenter, prospective randomized controlled trial (RAPIDS-GN), comparing outcomes of patients with GNB BSI who had blood culture testing with standard of care (SOC) culture and antibiotic susceptibility testing (AST) vs. rapid organism identification (ID) and phenotypic AST using the Accelerate Pheno System (AXDX). Methods Subjects with blood culture Gram stain showing GNB were randomized to receive SOC testing with antimicrobial stewardship review (AS) or AXDX plus SOC testing with AS, at two academic medical centers between October 2017 and October 2018. SOC testing included rapid MALDI-TOF mass spectrometry ID and agar dilution or broth microdilution AST. In a modified intention to treat analysis, subjects were excluded if: Gram stain was erroneous, culture was positive during off-hours, blood culture in the prior week had GNB, they were deceased/on comfort care, or admitted to a nonparticipating hospital. The primary outcome was time to first antibiotic modification within 72 hours after randomization. Subjects without antibiotic modifications were assigned a time of 72 hours. No censoring was observed. T-tests and Wilcoxon rank-sum tests were used for statistical analyses. Results Of 500 randomized subjects, 448 were included (226 SOC, 222 AXDX). Groups did not differ in baseline characteristics (Table 1). Median (IQR) hours to first antibiotic modification was faster in the AXDX vs. SOC group [8.6 (2.6, 27.6) vs. 14.9 (3.3, 41.1)], P = 0.02 (Figure 1). Median (IQR) hours to first Gram-negative antibiotic modification (including escalation and de-escalation) was faster in the AXDX than SOC group [17.4 (4.9, 72) vs. 42.1 (10.1, 72)], P < 0.001 (Figure 2). Groups did not differ in clinical outcomes (Table 2). Mean (S.D.) time to results was faster for AXDX than SOC for organism ID [2.7 (1.2) h vs. 15.6 (20.3) h, P < 0.001] and AST [13 (55.7) h vs. 54.6 (45.5) h, P < 0.001]. Conclusion In the largest trial to evaluate the clinical impact of a blood culture diagnostic for GNB BSI, we found that rapid organism ID and phenotypic AST led to faster changes in antibiotic therapy for Gram-negative bacteremia. Disclosures Ritu Banerjee, MD, PhD, Accelerate Diagnostics: Grant/Research Support; BioFire: Research Grant; Biomerieux: Research Grant; Roche: Research Grant Robin Patel, MD, ASM and IDSA: Other Financial or Material Support, Travel reimbursement, editor’s stipends; CD Diagnostics, Merck, Hutchison Biofilm Medical Solutions, Accelerate Diagnostics, ContraFect, TenNor Therapeutics Limited, Shionogi: Grant/Research Support; Curetis, Specific Technologies, NextGen Diagnostics, PathoQuest, Qvella: Consultant; NBME, Up-to-Date, the Infectious Diseases Board Review Course: Honorarium recipient, Other Financial or Material Support; Patent on Bordetella pertussis/parapertussis PCR issued, a patent on a device/method for sonication with royalties paid by Samsung to Mayo Clinic, and a patent on an anti-biofilm substance issued: Other Financial or Material Support, Patents.

Susceptibility testing of the polymyxins (colistin and polymyxin B) is challenging for clinical laboratories. The Clinical and Laboratory Standards Institute (CLSI) Antimicrobial Susceptibility Testing Subcommittee evaluated two methods to enable accurate testing of these agents. These methods were a colistin broth disk elution (CBDE) and a colistin agar test (CAT), the latter of which was evaluated using two inoculum volumes, 1 μl (CAT-1) and 10 μl (CAT-10).