RESUMEN
A 45-year-old woman was admitted with severe pain in the right leg and dyspnea. Her medical history included previous Staphylococcus aureus endocarditis, biological aortic valve replacement, and intravenous drug abuse. She was febrile but did not have any focal signs of infection. Blood tests showed raised infectious markers and troponin levels. Electrocardiogram showed sinus rhythm without signs of ischemia. Ultrasound revealed thrombosis of the right popliteal artery. The leg was not critically ischemic, and therefore, treatment with dalteparin was chosen. Transesophageal echocardiography showed an excrescence on the biological aortic valve. Empiric treatment for endocarditis was started with intravenous vancomycin, gentamicin, and oral rifampicin. Blood cultures subsequently grew Staphylococcus pasteuri. On day 2, treatment was changed to intravenous cloxacillin. Due to the comorbidity, the patient was not a candidate for the surgical treatment. On day 10, the patient developed moderate expressive aphasia and weakness in the right upper limb. Magnetic resonance imaging showed micro-embolic lesions scattered across both hemispheres of the brain. Treatment was changed from cloxacillin to cefuroxime. On day 42, infectious markers were normal, and echocardiography showed regression of the excrescence. Antibiotic treatment was stopped. Follow-up on day 52 did not show any signs of active infection. However, on day 143, the patient was readmitted with cardiogenic shock due to aortic root fistulation to the left atrium. She quickly deteriorated and died.
RESUMEN
Cable bacteria are multicellular filamentous bacteria within the Desulfobulbaceae that couple the oxidation of sulfide to the reduction of oxygen over centimeter distances via long distance electron transport (LDET). So far, none of the freshwater or marine cable bacteria species have been isolated into pure culture. Here we describe a method for establishing a stable single-strain cable bacterium culture in partially sterilized sediment. By repeated transfers of a single cable bacterium filament from freshwater pond sediment into autoclaved sediment, we obtained strain GS, identified by its 16S rRNA gene as a member of Ca. Electronema. This strain was further propagated by transferring sediment clumps, and has now been stable within its semi-natural microbial community for several years. Its metagenome-assembled genome was 93% complete, had a size of 2.76 Mbp, and a DNA Gâ¯+â¯C content of 52%. Average Nucleotide Identity (ANI) and Average Amino Acid Identity (AAI) suggest the affiliation of strain GS to Ca. Electronema as a novel species. Cell size, number of outer ridges, and detection of LDET in the GS culture are likewise consistent with Ca. Electronema. Based on these combined features, we therefore describe strain GS as a new cable bacterium species of the candidate genus Electronema, for which we propose the name Candidatus Electronema aureum sp.nov. Although not a pure culture, this stable single-strain culture will be useful for physiological and omics-based studies; similar approaches with single-cell or single-filament transfers into natural medium may also aid the characterization of other difficult-to-culture microbes.