Choon-Mee Kim

Ferrophilic Characteristics of Vibrio vulnificus and Potential Usefulness of Iron Chelation Therapy

We determined the ferrophilic characteristics of Vibrio vulnificus to evaluate the potential usefulness of iron chelation therapy for the prevention of V. vulnificus infection. Readily available non-transferrin-bound iron (NTBI) is required for the initiation of V. vulnificus growth under in vitro iron-limited conditions and human ex vivo conditions. NTBI aided efficient transferrin-bound iron (TBI) use by V. vulnificus, and the vulnibactin-mediated iron-uptake system was expressed after bacterial growth had been started by NTBI. V. vulnificus required higher NTBI levels for the initiation of growth, produced siderophores at lower levels, and used TBI less efficiently than other bacteria. In addition, the growth of V. vulnificus was inhibited by deferiprone, a clinically available iron chelator. These results show that V. vulnificus is a ferrophilic bacterium that requires higher NTBI levels than other pathogens and that iron chelation therapy might be an effective means of preventing the in vivo growth of V. vulnificus in susceptible patients.

Iron Differentially Regulates Gene Expression and Extracellular Secretion of Vibrio vulnificus Cytolysin-Hemolysin

In a previous study, we showed that Vibrio vulnificus is a ferrophilic bacterium that requires high levels of available iron for growth. In the present study, we show that iron stimulates, in an unusual manner, the production of cytolysin-hemolysin (VvhA), the most potent exotoxin produced by V. vulnificus. The vvhA gene possesses a putative ferric uptake regulator (Fur)-binding box in the regulatory region, andvvhA transcription was repressed by iron and de-repressed by fur mutation. However, extracellular secretion of VvhA was conversely increased by iron. Iron increased transcription of pilD, which encodes PilD, a component of the type II general secretion system responsible for extracellular VvhA secretion. These results indicate that iron increases extracellular VvhA secretion via the type II general secretion system, although it can repress vvhA transcription via Fur.

Regulation of the Vibrio vulnificus vvpE expression by cyclic AMP-receptor protein and quorum-sensing regulator SmcR.

In Vibrio vulnificus, cAMP-receptor protein (CRP) and the quorum-sensing regulator SmcR are simultaneously and cooperatively required for the metalloprotease vvpE gene expression, rather than sequentially in a regulatory cascade. However, this study shows a new temporal and functional sequence between the two factors in regulating vvpE expression. A crp mutation inhibited vvpE expression with growth impairment from early stage. In contrast, a smcR mutation inhibited vvpE expression only at the late stage with no effect on growth. A crp-smcR double mutation severely inhibited vvpE expression with growth impairment from early stage. The inhibited vvpE expression was restored only at the early stage by a crp single complementation, but not at all by a smcR complementation. These results indicate that CRP functions as an essential activator, whereas SmcR functions in the presence of CRP for full vvpE expression.

Two forms of Vibrio vulnificus metalloprotease VvpE are secreted via the type II general secretion system.

Vibrio vulnificus has been known to secrete one form of metalloprotease VvpE (45 kDa) that is cleaved to 34 kDa-VvpE and 11 kDa-C-terminal propeptide via extracellular autoproteolysis. However, we found that extracellular secretion of both the 34 and 45 kDa forms of VvpE began in the early growth phase; moreover, 34 kDa-VvpE existed as the major form in V. vulnificus cell lysates and culture supernatants. In addition, extracellular secretion of both 34 and 45 kDa-VvpE was blocked by mutation of the pilD gene, which encodes for the type IV leader peptidase/N-methyltransferase of the type II general secretion system, and the blocked VvpE secretion was recovered by in trans-complementation of the wild-type pilD gene. These results indicate that 34 kDa-VvpE is the major form secreted along with 45 kDa-VvpE from the early growth phase via the PilD-mediated type II general secretion system.

Cyclic AMP-receptor protein activates aerobactin receptor IutA expression in Vibrio vulnificus

The ferrophilic bacterium Vibrio vulnificus can utilize the siderophore aerobactin of Escherichia coli for iron acquisition via its specific receptor IutA. This siderophore piracy by V. vulnificus may contribute to its survival and proliferation, especially in mixed bacterial environments. In this study, we examined the effects of glucose, cyclic AMP (cAMP), and cAMP-receptor protein (Crp) on iutA expression in V. vulnificus. Glucose dose-dependently repressed iutA expression. A mutation in cya encoding adenylate cyclase required for cAMP synthesis severely repressed iutA expression, and this change was recovered by in trans complementing cya or the addition of exogenous cAMP. Furthermore, a mutation in crp encoding Crp severely repressed iutA expression, and this change was recovered by complementing crp. Accordingly, glucose deprivation under iron-limited conditions is an environmental signal for iutA expression, and Crp functions as an activator that regulates iutA expression in response to glucose availability.

Effect of Latitude and Seasonal Variation on Scrub Typhus, South Korea, 2001–2013

In South Korea, scrub typhus is one of the most common rickettsial diseases. The number of scrub typhus patients has increased in South Korea, a total of 69,210 cases were reported from 2001 to 2013. The seasonality and relation of scrub typhus cases to latitude were analyzed in this article using data obtained from the National Notifiable Diseases Surveillance System website of the Korea Centers for Disease Control and Prevention. The incidence of scrub typhus tended to increase in the later months of the year, especially in October-December. In general, lower latitudes were associated with a later peak incidence. Our results suggest for the first time that the monthly observed incidence tended to increase in the later months of the year as the latitude decreased, and on a yearly basis in Korea.

Scrub typhus hepatitis confirmed by immunohistochemical staining

Scrub typhus is an acute febrile disease caused by Orientia tsutsugamushi (O. tsutsugamushi). We report herein the case of a woman who presented with fever and elevated serum levels of liver enzymes and who was definitively diagnosed with scrub typhus by histopathological examination of liver biopsy specimens, serological tests and nested polymerase chain reaction. Immunohistochemical staining using a monoclonal anti-O. tsutsugamushi antibody showed focally scattered positive immunoreactions in the cytoplasm of some hepatocytes. This case suggests that scrub typhus hepatitis causes mild focal inflammation due to direct liver damage without causing piecemeal necrosis or interface hepatitis. Thus, scrub typhus hepatitis differs from acute viral hepatitis secondary to liver damage due to host immune responses, which causes severe lobular disarray with diffuse hepatocytic degeneration, necrosis and apoptosis as well as findings indicative of hepatic cholestasis, such as hepatic bile plugs or brown pigmentation of hepatocytes.

Effects of Pyrogallol on Growth and Cytotoxicity of Wild-Type and katG Mutant Strains of Vibrio vulnificus.

Vibrio vulnificus is a causative agent of fatal septicemia and necrotic wound infection and the pathogen infection became an important public health problem in many counties. Vibrio vulnificus causes RtxA1 toxin-induced acute cell death. We tried to identify natural products that inhibit the acute cytotoxicity of V. vulnificus using a lactate hydrogenase assay. A polyphenol pyrogallol protected HeLa cells from V. vulnificus-induced cytotoxicity. Pyrogallol also decreased the growth of V. vulnificus; this inhibitory effect was more significant during log phase than stationary phase. To further elucidate the inhibitory mechanism, pyrogallol-induced toxicity was compared between a V. vulnificus catalase-peroxidase mutant (katG−) and the isogenic wild-type MO6-24/O strains. No growth was observed for the katG− mutant in the presence of pyrogallol (50 μg/mL) even after 24 h, whereas the wild-type strain demonstrated growth recovery following a prolonged lag phase. Pyrogallol-mediated growth inhibition of the katG− mutant strain was partially rescued by exogenous catalase treatment. These results indicate that the mechanism by which pyrogallol inhibits the growth and cytotoxicity of V. vulnificus likely involves polyphenol-induced prooxidant damage. Taken together, these results suggest that pyrogallol has potential for development as a new paradigm drug to treat infectious diseases.

Accuracy of Conventional PCR Targeting the 16S rRNA Gene with the Ot-16sRF1 and Ot-16sRR1 Primers for Diagnosis of Scrub Typhus: a Case-Control Study

ABSTRACT We retrospectively evaluated the accuracy of conventional PCR targeting the 16S rRNA gene (16S C-PCR) using the Ot-16sRF1/Ot-16sRR1 primers for diagnosing scrub typhus. The diagnosis of Orientia tsutsugamushi infection by 16S C-PCR presented an increased sensitivity of 87.0% and specificity of 100% compared with those obtained with other targets and is thus a simple and clinically useful method with good diagnostic accuracy.

Hemorrhagic fever with renal syndrome accompanied by panhypopituitarism and central diabetes insipidus: a case report

Central diabetes insipidus (DI) was detected in a patient with hemorrhagic fever with renal syndrome (HFRS) who had been molecularly and serologically diagnosed with Hantaan virus infection. We recommend that clinicians differentiate central DI in HFRS patients with a persistent diuretic phase even when pituitary MRI findings are normal.