Clinical Significance of Staphylococcus aureus in a Single Positive Blood Culture Bottle

Clinical significance of a single positive blood culture bottle (SPBCB) with Staphylococcus aureus is unclear. We aimed to assess the significance of a SPBCB by looking at the associated outcomes. We performed a retrospective, multicenter study of patients with a SPBCB with S. aureus using data collected from both electronic health records and the clinical microbiology laboratory. Overall, 534 patients with S. aureus bacteremia were identified and 118 (22.1%) had a SPBCB. Among cases with a SPBCB, 106 (89.8%) were classified as clinically significant while 12 (10.2%) were considered contaminated or of unclear significance. A majority (92.4%) of patients received antibiotic therapy but patients with clinically significant bacteremia were treated with longer courses (25.9 vs 5.7 days, P<0.001). Significant differences in both frequency of echocardiography (65.1% vs 84.6%, P<0.001), and infective endocarditis diagnosis (3.8% vs 14.2%, P=0.002) were seen in those with a single positive blood culture bottle compared to those with multiple positive bottles. A longer hospital length of stay, and higher 90-day, 6-month, and 1-year mortality rates were seen in patients with multiple positive blood culture bottles. A SPBCB with S. aureus was common among our patients. While this syndrome has a more favorable prognosis as compared to those with multiple positive blood cultures, clinicians should remain concerned as it portends a risk of infective endocarditis and mortality.

6. Staphylococcus aureus in a Single Blood Culture Bottle: Should We be Concerned?

Background Staphylococcus aureus bacteremia (SAB) is common and is characterized by high rates of morbidity and mortality. The clinical importance of a single positive blood culture bottle (SPBCB), however, is poorly defined despite it being a frequent laboratory finding. We therefore examined patients with SPBCB to determine its clinical significance and to understand the rationale of current practice. Methods We performed a retrospective, multicenter study of patients with a SPBCB for S. aureus in initial cultures from January 2019 to December 2019 using data collected from both electronic health records and the clinical microbiology laboratory. Results Overall, 534 patients with SAB were identified, and 118 (22.1%) had a SPBCB. Among SPBCB cases, 106 (89.3%) were classified as clinically significant while 12 were considered contaminated or of unclear clinical significance. Baseline characteristics were similar between the groups (Table 1). A majority (92.4%) received antibiotic therapy, but patients with clinically significant bacteremia were treated with a longer antibiotic course (25.9 vs 5.7 days, p< 0.001). Outcomes between those with SPBCB (contaminant vs clinically significant) were similar (Table 2). Of note, while there was no difference in use of echocardiography based on PREDICT criteria between the clinically significant SPBCB vs. the multiple positive blood culture bottles (MPBC) cohorts (Table 3), significant differences were seen in both frequency of echocardiography (65.1% vs. 84.6%, P< 0.001) and IE diagnosis (3.8% vs. 14.2%, P=0.002) for patients in the SPBCB vs. MPBC groups, respectively. In addition, those with MPBC had higher 90-day, 6-month and 1-year mortality rates. Conclusion SPBCB was documented in almost one-quarter of SAB cases and should trigger a thorough investigation as its associated mortality was high and complications, including IE, occurred. Although some SPBCB cases may represent contamination, antibiotic treatment of SPBCB was commonplace. Patients with clinically significant SPBCB were less likely to undergo echocardiography and had a reduced prevalence of an IE diagnosis as compared to those with MPBC. Patients with SPBCB may have a more favorable long-term prognosis as compared to that in patients with MPBC. Disclosures Muhammad R. Sohail, MD, Medtronic (Consultant)Philips (Consultant) Larry M. Baddour, MD, Boston Scientific (Individual(s) Involved: Self): Consultant; Botanix Pharmaceuticals (Individual(s) Involved: Self): Consultant; Roivant Sciences (Individual(s) Involved: Self): Consultant

Lysinibacillus massiliensis Isolated from the Synovial Fluid: A Case Report

Lysinibacillus massiliensis is an aerobic, endospore-forming, gram-negative staining bacterium with peritrichous flagella belonging to the Bacillaceae family. A few cases of L. massiliensis isolated from the cerebrospinal fluid and tissue have been reported. In this study, we aimed to describe a case of L. massiliensis isolated from the synovial fluid. The synovial fluid from a 74-year-old female patient was inoculated into blood culture bottle. Gram-negative rods were observed in a gram-stained smear from a positive blood culture bottle. The bacterium was identified as Lysinibacillus sphaericus/Lysinibacillus fusiformis, with a probability of 89% using an automated bacterial identification system (VITEK2; Biomerieux, France). Subsequently, 16S rRNA gene sequencing was performed, and the sequence was analyzed using the Basic Local Alignment Search Tool. The sequence had 99.9% (1426/1427) identity with the strain L. massiliensis (GenBank ID: NR_043092.1). To our knowledge, this is the first reported case of L. massiliensis isolated from the synovial fluid. When an endospore-forming gram-negative staining bacterium can not be identified by phenotypic characterization, L. massiliensis should be considered, and different microbiological methods should be used for identification.

Proof of Concept of Culturomics Use of Time of Care

Culturomics, a high throughput culture method with rapid identification of the colonies by Matrix Assisted Laser Desorption Ionization/Time Of Flight Mass Spectrometry (MALDI-TOF MS), has demonstrated its contribution to the exploration of the gut microbiota over the past 10 years. However, the cost, work time and workload, considerably limit its use on a large scale or emergency context. Here, by testing two different stool samples, including a stool sample from a patient requiring rapid immunotherapy treatment, we tested a new fast culturomic protocol using two pre-incubation media, blood culture bottle and YCFA modified medium. Both media were supplemented with 2 ml of rumen fluid filtered at 0.2 μm and 2 ml of defibrinated and sterile sheep blood. Unlike the standard culturomics, subculturing of blood culture bottle were performed at reduced incubation time (3 h, 6 h, 9 h, 24 h) and at a longer incubation time (3 days, 7 days, and 10 days) at 37°C. By testing 5,200 colonies per MALDI-TOF MS and obtaining a comparable number of cultured bacterial species (131 to 143) in a stool sample, this new protocol reduced the number of colonies tested by 57%, working time by 78.6% and cost by 72.2%. In addition, we highlighted that the proportion of strict anaerobic species has increased by 24%, known to be the preferential targets for biotherapy, including Faecalibacterium prausnitzii, Akkermansia muciniphila, Christensenella minuta, and Phascolarctobacterium faecium. Finally, this work showed that some bacterial species grew earlier but disappeared with prolonged incubation times.