Jong Sook Jin

Acinetobacter baumannii Secretes Cytotoxic Outer Membrane Protein A via Outer Membrane Vesicles

Acinetobacter baumannii is an important nosocomial pathogen that causes a high morbidity and mortality rate in infected patients, but pathogenic mechanisms of this microorganism regarding the secretion and delivery of virulence factors to host cells have not been characterized. Gram-negative bacteria naturally secrete outer membrane vesicles (OMVs) that play a role in the delivery of virulence factors to host cells. A. baumannii has been shown to secrete OMVs when cultured in vitro, but the role of OMVs in A. baumannii pathogenesis is not well elucidated. In the present study, we evaluated the secretion and delivery of virulence factors of A. baumannii to host cells via the OMVs and assessed the cytotoxic activity of outer membrane protein A (AbOmpA) packaged in the OMVs. A. baumannii ATCC 19606T secreted OMVs during in vivo infection as well as in vitro cultures. Potential virulence factors, including AbOmpA and tissue-degrading enzymes, were associated with A. baumannii OMVs. A. baumannii OMVs interacted with lipid rafts in the plasma membranes and then delivered virulence factors to host cells. The OMVs from A. baumannii ATCC 19606T induced apoptosis of host cells, whereas this effect was not detected in the OMVs from the ΔompA mutant, thereby reflecting AbOmpA-dependent host cell death. The N-terminal region of AbOmpA22-170 was responsible for host cell death. In conclusion, the OMV-mediated delivery of virulence factors to host cells may well contribute to pathogenesis during A. baumannii infection.

Serum resistance of Acinetobacter baumannii through the binding of factor H to outer membrane proteins

Bacteremia is a common systemic disease caused by Acinetobacter baumannii, an important hospital-acquired pathogen among critically ill patients. The complement system is central to innate immune defense against invading bacteria in the blood. The present study investigated the susceptibility of clinical A. baumannii isolates to normal human sera (NHS), and determined the resistance mechanism of A. baumannii against complement-mediated lysis. The survival of A. baumannii isolates from bacteremic patients was significantly decreased in undiluted NHS, but they were resistant to 40% NHS. The alternative complement pathway was responsible for the direct killing of bacteria. The main regulator of the alternative complement pathway, factor H, bound to the surface of live A. baumannii treated with NHS. Factor H interacted with the outer membrane proteins with molecular sizes of 38 (AbOmpA), 32, and 24 kDa. The isogenic AbOmpA(-) mutant was highly susceptible to NHS in comparison with the wild-type A. baumannii strain, suggesting that AbOmpA was an important complement regulator-acquiring surface protein. These results indicate that A. baumannii evades complement attack through the acquisition of factor H to their surface.

Hospital outbreak of Burkholderia stabilis bacteraemia related to contaminated chlorhexidine in haematological malignancy patients with indwelling catheters

Burkholderia cepacia complex (BCC) is an opportunistic pathogen that occasionally causes hospital outbreaks. This paper describes an outbreak of BCC bacteraemia in haematological malignancy patients related to a contaminated chlorhexidine gluconate solution. Eight BCC isolates were obtained from patients hospitalised in the same ward of a cancer centre in a Korean hospital. A further three BCC isolates were obtained from 0.5% chlorhexidine gluconate used in the same ward. The isolates were identified as B. stabilis and exhibited identical pulsed-field gel electrophoresis profiles. All patients with B. stabilis bacteraemia had indwelling intravenous catheters, which were treated with chlorhexidine to disinfect the catheters. Following identification of the source of contamination, strict controls regarding surveillance cultures for disinfectants have been enforced. No further B. stabilis infections have been found in the hospital.

Characterization of Acinetobacter baumannii carrying blaOXA.23blaPER-1 and armA in a Korean hospital

Forty-two multidrug-resistant (MDR) Acinetobacter baumannii isolates were obtained during outbreaks in a Korean hospital. The co-carriage of bla(OXA-23), bla(OXA-51), bla(PER-1) and armA was observed in 23 isolates, and they were susceptible only to colistin and minocycline. The MDR A. baumannii isolates were found to belong to sequence group 1 using sequence-based typing.

Emergence of a new mutation and its accumulation in the topoisomerase IV gene confers high levels of resistance to fluoroquinolones in Escherichia coli isolates

Mutations in DNA gyrase and topoisomerase IV genes are the main mechanisms of resistance to quinolones. In this study, we determined mutations in gyrA, gyrB, parC and parE among 57 ciprofloxacin-resistant Escherichia coli isolates from a South Korean hospital and analysed the relationship between the minimal inhibitory concentrations (MICs) of fluoroquinolones and mutations in the topoisomerase IV gene. All ciprofloxacin-resistant E. coli isolates carried double mutations in gyrA and at least a single mutation in parC; some isolates also carried a single mutation in parE. The most common mutations were S83L and D87N in gyrA, S80I in parC and S458A in parE, which accounted for 25% of isolates. Single mutations in parE at L445I, S458P and S458W were identified for the first time. Double mutations in parC and a combination of single mutations in parC and parE significantly increased the MIC values of fluoroquinolones. In vitro induction of resistance to ciprofloxacin showed that double mutations in gyrA were a prerequisite to conferring a resistant phenotype to fluoroquinolones, and an additional mutation in the topoisomerase IV gene increased the MIC values of ciprofloxacin. In conclusion, emergence of a new mutation in parC and parE and its accumulation induces high levels of resistance to fluoroquinolones in E. coli.

Dissemination of the blaIMP-1 and blaVIM-2 metallo-β-lactamase genes among genetically unrelated Pseudomonas aeruginosa isolates in a South Korean hospital

f miltefosine resistance, and involvement of a member of he ATP-binding cassette (ABC) subfamily, the Leishmania -glycoprotein-like transporter, has been postulated [1]. Translation initiation in eukaryotes is regulated by eukarytic initiation factors (eIFs). eIF4A of Leishmania was riginally described as a Th1-type natural adjuvant and as n antigen that induces a Th1 response [5,8]. Characterisaion of eIF4A in Leishmania infantum has shown it in vitro o be an RNA-dependent ATPase and an ATP-dependent NA helicase [9]. Expression of recombinant eIF4A of L. nfantum in a yeast deletion mutant did not complement deleion of the essential TIF1 and TIF2 genes encoding yeast IF4A [9]. Instead, its expression resulted in inhibition of east growth. The protein species (SSP 6607 and 6608) dentified in our study could be new isoforms of eIF4A r a variant of the isoform in the wild-type strain. eIF4A verexpression was previously reported to confer lithium esistance in Saccharomyces cerevisiae [10]. To date, milefosine resistance in L. donovani has been believed to be perational through specific membranous pumps resulting n altered drug uptake [1], However, our data highlight he possible multifactorial mechanism of miltefosine resisance in Leishmania. Although biochemical evidence is arranted to ascertain the exact role of eIF4A, the presnce of unique eIF4A in Ld-M80 points towards a direct r indirect effect of miltefosine pressure and its involveent in the acquisition and/or maintenance of miltefosine esistance. Funding: HDC was supported by a NIPER Fellowship. S was supported by a Senior Research Fellowship from the ouncil for Scientific and Industrial Research, New Delhi, ovt. of India. CSD, being a faculty member of NIPER, is unded by NIPER and for this particular work from the source s obtained for GS, as indicated above. Competing interests: None declared. Ethical approval: Not required.