An unexpected case of Cardiobacterium valvarum prosthetic arthritis without cardiac lesions: Case report and literature review

We report a case of prosthetic arthritis caused by Cardiobacterium valvarum, which has been exclusively reported to cause intravascular infections. A 81-year-old Japanese female complained prosthetic knee joint pain. Arthrocentesis cultured no pathogen, and surgical replacement of the implant surface was performed. Modified Levinthal medium culture and 16S rRNA sequencing has finally led to diagnosis of C. valvarum prosthetic knee arthritis without cardiac lesions.Fastidious bacteria such as C. valvarum can be candidate pathogens of orthopedic infections whose causative agents are sometimes unidentified. Further development of molecular diagnostics is expected, but also the importance of conventional methods should be noted.     

Membrane voltage-dependent activation mechanism of the bacterial flagellar protein export apparatus

The proton motive force (PMF) consists of the electric potential difference (Δψ), which is measured as membrane voltage, and the proton concentration difference (ΔpH) across the cytoplasmic membrane. The flagellar protein export machinery is composed of a PMF-driven transmembrane export gate complex and a cytoplasmic ATPase ring complex consisting of FliH, FliI, and FliJ. ATP hydrolysis by the FliI ATPase activates the export gate complex to become an active protein transporter utilizing Δψ to drive proton-coupled protein export. An interaction between FliJ and a transmembrane ion channel protein, FlhA, is a critical step for Δψ-driven protein export. To clarify how Δψ is utilized for flagellar protein export, we analyzed the export properties of the export gate complex in the absence of FliH and FliI. The protein transport activity of the export gate complex was very low at external pH 7.0 but increased significantly with an increase in Δψ by an upward shift of external pH from 7.0 to 8.5. This observation suggests that the export gate complex is equipped with a voltage-gated mechanism. An increase in the cytoplasmic level of FliJ and a gain-of-function mutation in FlhA significantly reduced the Δψ dependency of flagellar protein export by the export gate complex. However, deletion of FliJ decreased Δψ-dependent protein export significantly. We propose that Δψ is required for efficient interaction between FliJ and FlhA to open the FlhA ion channel to conduct protons to drive flagellar protein export in a Δψ-dependent manner.

The ion motive force (IMF) across the cell membrane is one of the most important sources of biological energy in any cell. The IMF is utilized for many essential biological activities, such as ATP synthesis, solute transport, nutrient uptake, protein secretion, flagella-driven motility, and so on (1). The IMF is the sum of the electrical (Δψ) and chemical (ΔpI) potential differences of ions such as protons (H⁺) (the proton motive force [PMF]) and sodium ions (Na⁺) (the sodium motive force [SMF]) across the membrane and is defined by Eq. 1:IMF=Vm+kBTq ln[ion]in[ion]ex,[1]where V_m is Δψ; [ion]_in and [ion]_ex are the internal and external ion concentrations, respectively; k_B is Boltzmann’s constant; T is the absolute temperature (in kelvins); and q is the charge of the ion. The Δψ corresponds to the membrane voltage (2).The flagellum of the enteric bacterium Salmonella enterica serovar Typhimurium (hereafter referred to as Salmonella) is a supramolecular motility machine consisting of the basal body, which acts as a bidirectional rotary motor; the hook, which functions as a universal joint; and the filament, which works as a helical propeller. The Salmonella flagellar motor is powered by a PMF across the cytoplasmic membrane. The motor consists of a rotor and multiple stator units, each of which acts as a transmembrane proton channel complex. The stator unit converts the proton influx through the channel into the force for high-speed rotation of the long helical filament (3, 4).For construction of the hook and filament structures at the cell exterior, a specialized protein transporter utilizes the PMF to transport flagellar building blocks to the distal end of the growing flagellar structure. The flagellar protein transporter consists of a PMF-driven export gate complex made of five transmembrane proteins, FlhA, FlhB, FliP, FliQ, and FliR, and an ATPase ring complex consisting of three cytoplasmic proteins, FliH, FliI, and FliJ (SI Appendix, Fig. S1) (5, 6). These proteins are evolutionarily related to those of the virulence-associated type III secretion systems of pathogenic bacteria, which inject effector proteins into eukaryotic host cells for invasion (7). Furthermore, the entire structure of the ATPase ring complex is structurally similar to the cytoplasmic F₁ part of F_OF₁-ATP synthase, which utilizes the PMF for ATP synthesis (8–10).FliI forms a homo-hexamer that hydrolyzes ATP at an interface between neighboring FliI subunits (10–12). FliJ binds to the central pore of the FliI ring (9). ATP hydrolysis by the FliI ATPase not only activates the transmembrane export gate complex through an interaction between FliJ and the C-terminal cytoplasmic domain of FlhA (FlhA_C) (13, 14) but also opens the entrance gate of the polypeptide channel through an interaction between FliI and the C-terminal cytoplasmic domain of FlhB (FlhB_C) (15). As a result, the export gate complex becomes an active proton/protein antiporter that couples an inward-directed H⁺ flow with an outward-directed protein export (SI Appendix, Fig. S1) (16). When the cytoplasmic ATPase complex becomes nonfunctional, the FlgN chaperone activates the Na⁺-driven export engine of the export gate complex over a wide range of external pH, allowing the export gate complex to drive Na⁺-coupled protein export (17, 18). The transmembrane domain of FlhA (FlhA_TM) acts as a transmembrane ion channel for the transit of both H⁺ and Na⁺ across the cytoplasmic membrane (17).A chemical potential gradient of either H⁺ (ΔpH) or Na⁺ (ΔpNa) is required for efficient inward-directed translocation of H⁺ or Na⁺ when FliH and FliI are absent (13, 17). Although the Δψ component is critical for flagellar protein export by the wild-type export gate complex (19), it remains unknown when and how Δψ is used for the flagellar protein export process. To clarify this question, we used the Salmonella MMHI0117 [ΔfliH-fliI flhB(P28T)] strain (hereafter referred to as ΔHI B*; Table 1) (20), in which the export gate complex uses both Δψ and ΔpNa at different steps of the flagellar protein export process (13, 17). We show that an increase in Δψ generated by an upward shift of the external pH from 7.0 to 8.5 activates flagellar protein export by this mutant even in the absence of ΔpNa, suggesting the presence of a Δψ-dependent activation mechanism for proton-coupled protein secretion by the export gate complex. We also show that an increased Δψ facilitates efficient docking of FliJ to FlhA_C.Table 1.Summary for flagellar protein export properties of Salmonella strains used in this study

Low T3 Syndrome Is Associated With High Mortality in Hospitalized Patients With Heart Failure

Background

We aimed to clarify the prognosis and pathophysiological parameters of low T3 syndrome in patients with heart failure (HF).

Squamous Cell Carcinoma after Endoscopic Injection Sclerotherapy for Esophageal Varices

We report two cases of squamous cell carcinoma of the esophagus following endoscopic injection sclerotherapy for esophageal varices. The interval between sclerotherapy and the development of carcinoma was 24 months in case 1 and 21 months in case 2. The sclerosant was 5% sodium morrhuate in case 1 (total dose, 10 ml) and 5% ethanolamine oleate in case 2 (45.5 ml). Although no recurrent variceal bleeding occurred after sclerotherapy, we could not perform any curative surgical treatment for esophageal cancer because of the advanced stage of the cancer and the severity of the accompanying liver dysfunction. It is difficult to determine the relationship between sclerotherapy and carcinoma; however, long-term surveillance is essential to avoid overlooking a neoplasm in the esophagus after endoscopic injection sclerotherapy.