Citations

Despite the increasing reliance on polymyxin antibiotics (polymyxin B and colistin) for treatment of multidrug-resistant Gram-negative infections, many clinical laboratories are unable to perform susceptibility testing due to the lack of accurate and reliable methods. Although gradient agar diffusion is commonly performed for other antimicrobials, its use for polymyxins is discouraged due to poor performance characteristics.

Abstract Background Polymerase chain reaction (PCR)/sequencing targeting the 16S ribosomal RNA (rRNA) gene to detect bacteria in normally sterile tissues and fluids has become increasingly popular in clinical medicine. This culture-independent technique can detect bacteria that are nonviable or difficult to cultivate using conventional methods. The clinical value of this type of testing is not well defined. We aimed to assess the diagnostic value of 16S rRNA PCR/Sanger sequencing as a clinical diagnostic assay at Mayo Clinic. Methods This is an interim analysis of the first 173 of 478 patients who had 16S rRNA PCR/Sanger sequencing done on sterile tissues or fluids at our institution from April, 2017 to November, 2018 as part of routine clinical practice. Medical records are being retrospectively reviewed, with results compared with those of culture. Results We reviewed 207 specimens from 173 patients (musculoskeletal 79%, cardiovascular 7%, central nervous system 4%, other 9%) that underwent 16S rRNA PCR/Sanger sequencing by clinical request (Table 1). In 90% of these specimens, the test was pre-planned rather than added-on. Nine specimens were excluded from analysis, as cultures were not performed. Overall concordance of culture with PCR/sequencing was 81% (160/197; P < 0.0001). Of 44 culture-positive specimens, PCR detected the same bacterium in 21 (48%) (Table 2). 45% (20/44) of those with positive cultures and 46% of those with positive PCR/sequencing results had received prior antimicrobial therapy (Table 3). PCR was negative in 139/144 specimens that were culture-negative (97%). PCR/sequencing was helpful in detecting a putative bacterial pathogen in 4 patients with negative cultures (Table 4). Conclusion Overall, 16S rRNA PCR/Sanger sequencing improved diagnostic yield compared with culture in a minority of cases. The described assay is limited by its inability to detect polymicrobial infections, a technical limitation that could possibly be addressed using massive parallel sequencing. Careful selection of cases and a save and add-on approach may be more cost-effective than upfront testing, although this was requested in a minority of cases. Disclosures 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.

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).

Introduction Cutibacterium acnes is a recognized culprit for implant-associated infections, but positive cultures do not always indicate clinically relevant infection. Studies have shown a correlation between the β-hemolytic phenotype of C. acnes and its infectious capacity, but correlation with genetic phylotype has not been performed in literature. The purpose of this study is to evaluate β-hemolysis phenotype, genetic phylotype, and mid-term clinical outcomes of C. acnes isolated from orthopedic surgical sites. Methods Fifty-four C. acnes isolates previously obtained from surgical wounds of patients undergoing hip, knee, shoulder, or spine implant removal were re-cultured. There were 21 females and 33 males with an average age of 59 years (range, 18–84). Twenty-four were from clinically infected sites whereas 30 were considered contaminants. De novo β-hemolysis was analyzed and a retrospective chart review was performed to evaluate clinical outcomes at 7.1 years (range, 0.1–12.8). Results On Brucella agar with 5% rabbit blood, 46% of contaminant and 43% of infectious isolates were hemolytic. Type II phylotype was significantly more nonhemolytic regardless of infectious or contaminant status (p < 0.05). Type 1B correlated with a hemolytic-infectious phenotype and Type 1A with a hemolytic-contaminant phenotype but was not statistically significant. Conclusion The β-hemolytic profile of C. acnes did not correlate with phylotype or clinically relevant orthopedic infection.

Respiratory viral infections are associated with a wide range of acute syndromes and infectious disease processes in children and adults worldwide. Many viruses are implicated in these infections, and these viruses are spread largely via respiratory means between humans but also occasionally from animals to humans.