Effect of Copper(II) Ion Binding by Porin P1 Precursor Fragments from Fusobacterium nucleatum on DNA Degradation

Fusobacterium nucleatum is one of the most notorious species involved in colorectal cancer. It was reported that numerous outer membrane proteins (OMP) are actively involved in carcinogenesis. In this paper, the structure and stability of certain complexes, as well as DNA cleavage and ROS generation by fragments of OMP, were investigated using experimental and theoretical methods. Mass spectrometry, potentiometry, UV-Vis, CD, EPR, gel electrophoresis and calculations at the density functional theory (DFT) level were applied. Two consecutive model peptides, Ac-AKGHEHQLE-NH₂ and Ac-FGEHEHGRD-NH₂, were studied. Both of these were rendered to form a variety of thermodynamically stable complexes with copper(II) ions. All of the complexes were stabilized, mainly due to interactions of metal with nitrogen and oxygen donor atoms, as well as rich hydrogen bond networks. It was also concluded that these complexes in the presence of hydrogen peroxide or ascorbic acid can effectively produce hydroxyl radicals and have an ability to cleave the DNA strands. Surprisingly, the second studied ligand at the micromolar concentration range causes overall DNA degradation.

Backbone and side-chain (1)H, (13)C, and (15)N NMR assignments of the N-terminal domain of Escherichia coli LpoA

The peptidoglycan is a major component of the bacterial cell wall and is essential to maintain cellular integrity and cell shape. Penicillin-Binding Proteins (PBPs) catalyze the final biosynthetic steps of peptidoglycan synthesis from lipid II precursor and are the main targets of β-lactam antibiotics. The molecular details of peptidoglycan growth and its regulation are poorly understood. Presumably, PBPs are active in peptidoglycan synthesizing multi-enzyme complexes that are controlled from inside the cell by cytoskeletal elements. Recently, two outer-membrane lipoproteins, LpoA and LpoB, were shown to be required in Escherichia coli for the function of the main peptidoglycan synthases, PBP1A and PBP1B, by stimulating their transpeptidase activity. However, the mechanism of PBP-activation by Lpo proteins is not known, and the Lpo proteins await structural characterization at atomic resolution. Here we present the backbone and side-chain (1)H, (13)C, (15)N NMR assignments of the N-terminal domain of LpoA from E. coli for structural and functional studies.

Targeting the mycobacterial envelope for tuberculosis drug development

The bacterium that causes tuberculosis, Mycobacterium tuberculosis, possesses a rather unique outer membrane composed largely of lipids that possess long-chain and branched fatty acids, called mycolic acids. These lipids form a permeability barrier that prevents entry of many environmental solutes, thereby making these bacteria acid-fast and able to survive extremely hostile surroundings. Antitubercular drugs must penetrate this layer to reach their target. This review highlights drug development efforts that have added to the slowly growing tuberculosis drug pipeline, identified new enzyme activities to target with drugs and increased the understanding of important biosynthetic pathways for mycobacterial outer membrane and cell wall core assembly. In addition, a portion of this review looks at discovery efforts aimed at weakening this barrier to decrease mycobacterial virulence, decrease fitness in the host or enhance the efficacy of the current drug repertoire by disrupting the permeability barrier.

First insights on organic cosolvent effects on FhuA wildtype and FhuA Δ1-159

Circular dichroism (CD) and deconvolution were used to study the structural integrity of a "plugged" and an "open" FhuA transmembrane channel protein in the presence of varied concentrations of tetrahydrofuran (THF), ethanol (EtOH) and chloroform/methanol (C/M). FhuA is an Escherichia coli outer membrane protein (78.9 kDa) consisting of 22 β-sheets and an internal globular cork domain which acts as an iron transporter. FhuA and the deletion variant FhuA Δ1-159 showed comparable and remarkable resistance in the presence of THF (≤40 vol%) and EtOH (≤10 vol%). In C/M, significant differences in structural resistance were observed (FhuA stable ≤10 vol%; FhuA Δ1-159 ≤1 vol%). Deconvolution of CD-spectra for FhuA and FhuA Δ1-159 yielded β-sheet contents of 61 % (FhuA) and 58% (FhuA Δ1-159). Interestingly, FhuA and FhuA Δ1-159 had comparable β-sheet contents in the presence and absence of all three organic cosolvents. Additionally, precipitated FhuA and FhuA Δ1-159 (in 40 vol% C/M or 65 vol% THF) redissolved by supplementing the detergent n-octyl-oligo-oxyethylene (oPOE).

Synergistic anti-bacterial and proteomic effects of epigallocatechin gallate on clinical isolates of imipenem-resistant Klebsiella pneumoniae

Imipenem-resistant Klebsiella pneumoniae (IRKP) were used to explore the synergistic anti-bacterial and proteomic effects of imipenem alone or in combination with epigallocatechin gallate (EGCg). The minimal inhibitory concentrations (MICs) of EGCG for 12 clinically isolated IRKP strains ranged from 300 to 650 μg/ml. Each of the 12 IRKP strains experienced a 4- to 64-fold reduction in the MIC of imipenem upon co-incubation with 0.25 × MIC level of EGCg. The time-kill method was used on the 12 IRKP clinical isolates to evaluate the bactericidal activities of imipenem alone or with EGCg. Compared to imipenem alone, EGCg with imipenem demonstrated enhanced bactericidal activity. Two-dimensional polyacrylamide gel electrophoresis identified eight down-regulated and four up-regulated proteins in the IRKP strain upon exposure to 1 × MIC of EGCg. Analysis of the outer membrane protein profiles of IRKP cultures treated with EGCg revealed unique changes in outer membrane proteins. In addition, scanning electron microscopic analysis demonstrated the presence of cells with wrinkled surfaces containing perforations and irregular rod-shaped forms after treatment with EGCg or imipenem. These studies demonstrate that EGCg can synergize the bacterial activity of imipenem and differentially stimulate the expression of various proteins in IRKP.

Iron regulated outer membrane proteins (IROMPs) as potential targets against carbapenem-resistant Acinetobacter spp. isolated from a Medical Centre in Malaysia

BACKGROUND & OBJECTIVES

Carbapenem-resistant Acinetobacter spp. have gained increasing significance as opportunistic pathogens in hospitalized patients. Carbapenem resistance is often associated with the loss and/or decrease in outer membrane proteins (OMP) and overexpression of multidrug efflux systems. However, carbapenem-hydrolysing beta-lactamases of Ambler Class B (metallo-enzymes) and Ambler Class D (oxacillinases) have also been detected in Acinetobacter spp. In this study we have investigated the role of the iron regulated outer membrane protein (IROMPs) and the loss of a 29-kDa OMP in carbapenem resistance of Acinetobacter calcoaceticus.

METHODS

Carbapenem resistant clinical isolates (n=39) of Acinetobacter baumannii / calcoaceticus were used. Identification of Acinetobacter spp. at species level was done by amplified ribosomal DNA restriction analysis (ARDRA). MIC was evaluated using agar dilution method according to CLSI standards. Presence of outer membrane proteins were determined by SDS-PAGE. A representative strain of A. calcoaceticus, S26 with the loss of 29-kDa OMP was selected for further analysis as strain S26 had unique resistance mechanism, that is, the presence of IMP-4 metallo-beta-lactamases. IROMPs were expressed under iron deficit conditions. Bands corresponding to IROMPs were excised from SDS-PAGE and used to immunize rabbits for the production of polyclonal antibodies. The antibodies raised against IROMPs were detected by an in-house ELISA and then used for bactericidal activity against carbapenem resistant A. baumannii / calcoaceticus.

RESULTS

All isolates were resistant to all antibiotics including imipenem and meropenem and had loss of a 29-kDa OMP. The polyclonal antibodies showed bactericidal effect against the organism tested and it specifically killed the bacteria grown in iron deficit medium.

INTERPRETATION & CONCLUSIONS

In this study, a 29-kDa OMP has been identified to be the major outer membrane protein in A. baumannii / calcoaceticus and loss of this porin and overexpression of IROMPs have contributed to carbapenem resistance. Polyclonal antibodies raised against IROMPs may have a role in antimicrobial therapy in these isolates.

Outer membrane permeability for nonpolar antimicrobial agents underlies extreme susceptibility of Pasteurella multocida to the hydrophobic biocide triclosan

Pasteurella multocida exhibits nonspecific susceptibility to nonpolar antimicrobial agents such as triclosan, despite possessing an ultrastructurally typical gram-negative cell envelope. Capsulated and noncapsulated cell surface variants were examined to investigate the role outer membrane permeability plays in triclosan susceptibility. Test strains were unable to initiate growth in the presence of bile salts and were susceptible to triclosan with minimal inhibitory concentrations (MICs) ranging from 0.06 to 0.25 microg/ml. Disk agar diffusion bioassays revealed triclosan susceptibility to be dose dependent and all strains were susceptible to the hydrophobic antibiotics novobiocin, rifamycin SV, and chloramphenicol. Triclosan minimal bactericidal concentrations were greater than MICs, thereby suggesting that dose dependency reflected both bacteriostatic and bactericidal effects. Total and viable cell density growth kinetic determinations revealed a triclosan concentration of 2.0 microg/ml resulted in loss of batch culture viability within 4-24 h. Concentrations of 0.02 and 0.2 microg/ml exerted either a bacteriostatic or bactericidal effect depending on the strain. Uptake of the hydrophobic probe 1-N-phenylnaphthylamine was greater in P. multocida strains than refractory control organisms Pseudomonas aeruginosa and Escherichia coli thereby suggesting the presence of phospholipid bilayer regions in the outer membrane. Because triclosan inhibits a conserved enoyl-ACP reductase necessary for bacterial fatty acid biosynthesis, these data support the notion that extreme susceptibility in P. multocida is due to the general inability of the outer membrane to exclude nonpolar compounds. Moreover, susceptibility is independent of the presence of capsular material and the biocide is bactericidal in a concentration dependent manner.

Deoxycholic Acid Blocks Vibrio cholerae OmpT but Not OmpU Porin

OmpT and OmpU are general diffusion porins of the human intestinal pathogen Vibrio cholerae. The sole presence of OmpT in the outer membrane sensitizes cells to the bile component deoxycholic acid, and the repression of OmpT in the intestine may play an important role in the adaptation of cells to the host environment. Here we report a novel important functional difference between the two porins, namely the sensitivity to deoxycholic acid. Single channel recordings show that submicellar concentrations of sodium deoxycholate induce time-resolved blocking events of OmpT but are devoid of any effect on OmpU. The effects are dose-, voltage-, and pH-dependent. They are elicited by deoxycholate applied to either side of the membrane, with some asymmetry in the sensitivity. The voltage dependence remains even when deoxycholate is applied symmetrically, indicating that it is intrinsic to the binding site. The pH dependence suggests that the active form is the neutral deoxycholic acid and not the negatively charged species. The results are interpreted as deoxycholic acid acting as an open-channel blocker, which may relate to deoxycholic acid permeation.

Identifying the components in eggshell membrane responsible for reducing the heat resistance of bacterial pathogens

The biological activity (D-value determination) of eggshell membrane (ESM) was examined to determine the membrane components and mechanisms responsible for antibacterial activity. Biological and enzymatic activities (i.e., beta-N-acetylglucosaminidase [beta-NAGase], lysozyme, and ovotransferrin) of ESM denatured with trypsin, lipases, or heat were compared with those of untreated ESM. Trypsin-treated ESM lost all biological activity (D-values at 54 degrees C were 5.12 and 5.38 min for immobilized and solubilized trypsin, respectively) but showed no significant loss of enzymatic activities. Treatments with porcine lipase and a lipase cocktail did not impact biological or enzymatic activities. Heat denaturation of ESM (at 80 and 100 degrees C for 15 min) resulted in significant decreases in biological activity (D-values of 3.99 and 4.43 min, respectively) and loss of beta-NAGase activity. Lysozyme and ovotransferrin activities remained but were significantly reduced. Purified ESM and hen egg white components (i.e., beta-NAGase, lysozyme, and ovotransferrin) were added to Salmonella Typhimurium suspensions (in 0.1% peptone water) at varying concentrations to evaluate their biological activity. D-values at 54 degrees C were 4.50 and 3.68 min for treatment with lysozyme or beta-NAGase alone, respectively, and 2.44 min for ovotransferrin but 1.47 min for a combination of all three components (similar to values for ESM). Exposure of Salmonella Typhimurium cells to a mixture of ovotransferrin, lysozyme, and beta-NAGase or ESM resulted in significant increases in extracellular concentrations of Ca2+, Mg2+, and K+. Transmission electron microscopic examination of Salmonella Typhimurium cells treated with a combination of ovotransferrin, lysozyme, and beta-NAGase revealed membrane disruption and cell lysis. The findings of this study demonstrate that ovotransferrin, lysozyme, and beta-NAGase are the primary components responsible for ESM antibacterial activity. The combination of these proteins and perhaps other ESM components interferes with interactions between bacterial lipopolysaccharides, sensitizing the outer bacterial membrane to the lethal affects of heat and possibly pressure and osmotic stressors.

Effect of outer membrane permeabilisation on intrinsic resistance to low triclosan levels in Pseudomonas aeruginosa

The present study was undertaken to investigate the possibility that outer cell envelope impermeability might be involved in the intrinsic resistance of Pseudomonas aeruginosa to low levels of the hydrophobic biocide triclosan. Macrobroth dilution and batch cultural turbidimetric assays were employed to assess the ability of compounds that render the Gram-negative outer membrane permeable to non-polar molecules to sensitise cell envelope variants to triclosan. Pseudomonas aeruginosa strains possessing highly refractory (PAO1) and atypically permeable (Z61) outer cell envelopes as well as a PAO1 derivative lacking four multidrug efflux pumps (YM64) were examined. Whilst the triclosan minimal inhibitory concentrations (MICs) differed dramatically for both PAO1 and Z61, significant decreases were seen for both strains in the presence of the outer membrane permeabiliser polymyxin B-nonapeptide. Strain YM64 was as resistant to triclosan as strain PAO1. Turbidimetric assessments of batch cultural growth kinetics revealed that the three chemically unrelated outer membrane permeabilisers polymyxin B-nonapeptide, compound 48/80 and ethylenediaminetetraacetate (EDTA) sensitised all strains to a sub-MIC concentration of triclosan (2.0 microg/mL). These data support the notion that the outer membrane exclusionary properties of P. aeruginosa for non-polar molecules confer intrinsic resistance to low concentrations of triclosan such as might be expected to occur in environmental residues. Moreover, a role for outer cell envelope impermeability is suggested for resistance to high triclosan concentrations in vitro.

Azithromycin exhibits bactericidal effects on Pseudomonas aeruginosa through interaction with the outer membrane

The aim of the present study was to elucidate the effect of the macrolide antibiotic azithromycin on Pseudomonas aeruginosa. We studied the susceptibility to azithromycin in P. aeruginosa PAO1 using a killing assay. PAO1 cells at the exponential growth phase were resistant to azithromycin. In contrast, PAO1 cells at the stationary growth phase were sensitive to azithromycin. The divalent cations Mg2+ and Ca2+ inhibited this activity, suggesting that the action of azithromycin is mediated by interaction with the outer membranes of the cells, since the divalent cations exist between adjacent lipopolysaccharides (LPSs) and stabilize the outer membrane. The divalent cation chelator EDTA behaved in a manner resembling that of azithromycin; EDTA killed more PAO1 in the stationary growth phase than in the exponential growth phase. A 1-N-phenylnaphthylamine assay showed that azithromycin interacted with the outer membrane of P. aeruginosa PAO1 and increased its permeability while Mg2+ and Ca2+ antagonized this action. Our results indicate that azithromycin directly interacts with the outer membrane of P. aeruginosa PAO1 by displacement of divalent cations from their binding sites on LPS. This action explains, at least in part, the effectiveness of sub-MICs of macrolide antibiotics in pseudomonal chronic airway infection.

Differences in heat resistance among pathogenic Yersinia enterocolitica depended on growth temperature and serotype

To gain a better understanding about the effect of growth temperature on heat resistance of Yersinia enterocolitica, we determined decimal reduction times at 60 degrees C (D60-values) for O:3; O:5,27; O:8; and O:9 strains harboring virulence plasmid coding for Yersinia outer membrane protein and experimentally virulence plasmid-deleted strains after they were grown to stationary phase at 7, 25, or 37 degrees C. Bacteria were inoculated into Trypticase soy broth and were incubated at several temperatures. D60-values of O:3; O:5,27; and O:8 strains were larger when they were grown at 37 degrees C than at 7 or 25 degrees C, despite the presence or absence of virulence plasmids. However, similar D60-values were observed in O:9 strains, despite growth at 7, 25, or 37 degrees C. The results indicate two types of Y. enterocolitica strains, growth temperature-dependent and -independent, and a Yersinia outer membrane protein that is not directly involved in growth temperature-dependent heat resistance.

[Properties of the Burkholderia pseudomallei insertional mutants deficient in membrane proteins production]

Transposon-induced B. pseudomallei mutants deficient in membrane proteins production were obtained for evaluation of the functional role of these cell components. In comparison with the wild type strain B. pseudomallei 57576, mutant clones TTM6, TTM7 and TTM9 carrying Tn5 chromosome insertions were characterized by lost or decreased production of outer membrane proteins 27, 48, 52, 150, 200 kDa. Alterations in outer membrane protein spectra were accompanied by twofold increase in susceptibility of bacteria to fluoroquinolones (pefloxacin, ofloxacin) and cephalosporins (ceftazidime) and noticeable reduction of virulence for white mice and guinea pigs in contrast to the initial strain, the obtained mutants were also less resistant in in vitro phagocyte killing.

Effects of sub-minimum inhibitory concentration antibiotic levels and temperature on growth kinetics and outer membrane protein expression in Mannheimia haemolytica and Haemophilus somnus

The objective of this study was to determine the effects of sub-minimum inhibitory concentrations (sub-MICs) of 2 veterinary antibiotic preparations, chlortetracycline (CTC) and chlortetracycline-sulfamethazine (CTC + SMZ), on growth kinetics and outer membrane protein expression in Mannheimia haemolytica and Haemophilus somnus at normal and febrile body temperatures. Sub-minimum inhibitory concentrations of both antibiotics reduced the growth rates of M. haemolytica and H. somnus. Growth of both species was not inhibited when grown at 41 degrees C compared to 37 degrees C. There was no detectable consistent effect of antibiotic or temperature on outer membrane protein expression for either species. Our study indicates that sub-MIC levels of CTC and CTC + SMZ markedly impair growth of clinical M. haemolytica and H. somnus isolates, potentially allowing more effective host clearance during infection.

Chitosan kills bacteria through cell membrane damage

The bactericidal activity of chitosan (CS) acetate solution against Escherichia coli and Staphylococcus aureus was evaluated by the enumeration of viable organisms at different incubation times. Morphologies of bacteria treated with CS were observed by transmission electron microscopy (TEM). The integrity of the cell membranes of both species and the permeabilities of the outer membrane (OM) and inner membrane (IM) of E. coli were investigated by determining the release from cells of materials that absorb at 260 nm, changes in the fluorescence of cells treated with the fluorescent probe 1-N-phenylnaphthylamine (NPN) and release of cytoplasmic beta-galactosidase activity. In addition, the interaction of CS with synthetic phospholipid membranes was studied using gel permeation chromatography (GPC), UV-VIS spectrophotometery, Fourier-transform infrared spectroscopy (FT-IR) and thermal analysis. Results showed that CS increased the permeability of the OM and IM and ultimately disrupted bacterial cell membranes, with the release of cellular contents. This damage was likely caused by the electrostatic interaction between NH(3)(+) groups of CS acetate and phosphoryl groups of phospholipid components of cell membranes.

RamA is an alternate activator of the multidrug resistance cascade in Enterobacter aerogenes

Multidrug resistance (MDR) in Enterobacter aerogenes can be mediated by induction of MarA, which is triggered by certain antibiotics and phenolic compounds. In this study, we identified the gene encoding RamA, a 113-amino-acid regulatory protein belonging to the AraC-XylS transcriptional activator family, in the Enterobacter aerogenes ATCC 13048 type strain and in a clinical multiresistant isolate. Overexpression of RamA induced an MDR phenotype in drug-susceptible Escherichia coli JM109 and E. aerogenes ATCC 13048, as demonstrated by 2- to 16-fold-increased resistance to beta-lactams, tetracycline, chloramphenicol, and quinolones, a decrease in porin production, and increased production of AcrA, a component of the AcrAB-TolC drug efflux pump. We show that RamA enhances the transcription of the marRAB operon but is also able to induce an MDR phenotype in a mar-deleted strain. We demonstrate here that RamA is a transcriptional activator of the Mar regulon and is also a self-governing activator of the MDR cascade.

[Drug screening model acting on out-membrane protein OprM in pseudomonas aeruginosa efflux pump system]

OBJECTIVE

To establish an efflux pump inhibitor screening model with the out-membrane protein OprM in Pseudomonas aeruginosa efflux pump system as the target point.

METHODS

Efflux pump out-membrane protein gene oprM was obtained from standard Pseudomonas aeruginosa PA01 strain. Expression of OprM protein was induced in E. coli strain HS151 with T-easy vector as the cloning vector, and pMMB67EH as the expression vector. In order to evaluate the function of OprM protein, we measured intracellular tetracycline concentrations with liquid scintillation counter, measured the diameters of bacteriostatic circles with paper disc, and then established a screening model accordingly.

RESULTS

OprM protein was highly expressed. Using Pseudomonas aeruginosa as the main detecting bacteria, we established a drug screening model acting on OprM. A total of 1 600 microbial fermentation samples were screened with this model, among which 56 positive strains were found, with a positive rate of 3.5%.

CONCLUSION

OprM plays an important role in drug efflux. The established model has good specificity and maneuverability.

Tolerance of Pseudomonas aeruginosa to Melaleuca alternifolia (tea tree) oil is associated with the outer membrane and energy-dependent cellular processes

OBJECTIVES

The essential oil of Melaleuca alternifolia (tea tree oil) and its components have antimicrobial activity against a wide range of Gram-positive and Gram-negative bacteria, fungi and viruses. The mechanism(s) by which Pseudomonas aeruginosa NCTC 10662 maintains a decreased susceptibility to tea tree oil and components was investigated.

RESULTS

Ethylene diamine tetraacetic acid enhanced the antimicrobial activity of tea tree oil and terpinen-4-ol against stationary phase P. aeruginosa while polymyxin B nonapeptide enhanced the activity of tea tree oil and gamma-terpinene. Pre-treatment with the protonophore carbonyl cyanide m-chlorophenylhydrazone increased the susceptibility of exponential phase cells to sub-inhibitory concentrations of tea tree oil, terpinen-4-ol and gamma-terpinene, indicating that intrinsic tolerance to tea tree oil and components is substantially energy dependent.

CONCLUSIONS

Increased tolerance to tea tree oil in P. aeruginosa is directly related to the barrier and energy functions of the outer membrane, and may involve efflux systems.

Macrophage L-type Ca2+ channel antagonists alter Chlamydia pneumoniae MOMP and HSP-60 mRNA gene expression, and improve antibiotic susceptibility

Recent data have shown a unique relationship between Ca2+ signaling in macrophages through L-type channels and the outcome of C. pneumoniae infection of such cells. The present investigation seeks to provide insights into the manner in which macrophage L-type Ca2+ channel operation affects major outer membrane protein (MOMP) and heat shock protein-60 (HSP-60) mRNA gene expression (factors associated with Chlamydia chronicity), and the possible effect of this on antibiotic susceptibility. Intracellular calcium ([Ca2+]i) chelation using varying doses of 1,2-bis (o-aminophenoxy) ethane-N,N,N'N'--tetra acetic acid (acetoxymethyl) ester (BAPTA-AM) induced an increase in MOMP and a decrease in HSP-60 mRNA gene expression. L-type Ca2+ channel antagonists produced an identical but enhanced effect. Since these findings associate specialized Ca2+ channels to Chlamydia chronicity, it was important to determine Ca2+ channel effect on the usual antibiotic refractory form of C. pneumoniae in macrophages. Inhibition of macrophage L-type Ca2+ channel operation improved C. pneumoniae antibiotic susceptibility assessed by decreased inclusion counts or down-regulated MOMP and HSP-60 mRNA gene expression. These findings provide molecular insights into how specialized Ca2+ channels influence Chlamydia chronic course in macrophages and demonstrates a role for L-type Ca2+ channel inhibitors in enhanced C. pneumoniae susceptibility to antibiotic therapy.

Cross-resistance to antibiotics of Escherichia coli adapted to benzalkonium chloride or exposed to stress-inducers

AIMS

To study the effects of adaptation and stress on the resistance to benzalkonium chloride (BC) and cross-resistance to antibiotics in Escherichia coli.

METHODS AND RESULTS

Precultivation of E. coli ATCC 11775 and E. coli DSM 682 in the presence of subinhibitory concentrations of BC or stress inducers (salicylate, chenodeoxycholate and methyl viologen) resulted in higher minimum inhibitory concentration (MIC) of BC and chloramphenicol (CHL). Adaptation to growth in sixfold of the initial MIC of BC resulted in stable BC resistance and enhanced tolerance to several antibiotics and ethidium bromide (EtBr). The MIC of CHL increased more than 10-fold for both strains. Enhanced efflux of EtBr in adapted E. coli ATCC 11775 indicated that the observed resistance was due to efflux. Changes in outer membrane protein profiles were detected in the BC-adapted cells. There were no indications of lower membrane permeability to BC.

CONCLUSIONS

Induction of stress response or gradual adaptation to BC or CHL results in acquired cross-tolerance between BC and antibiotics in E. coli. Enhanced efflux was one of the observed differences in adapted cells.

SIGNIFICANCE AND IMPACT OF THE STUDY

Provided not taking due precautions, extensive use of disinfectants could lead to emergence of antibiotic-resistant isolates.

Internalization of OspA in rsCD14 complex and aggregated forms

Although the spirochetal protein OspA is capable of stimulating immune cells in a CD14- and TLR2-dependent manner, little is known about how TLR2 receptor complex ligands, such as OspA, are handled by the cell once delivered. We examine here the internalization of the fluorescently derivatized forms of both the full length OspA lipoprotein delivered as a recombinant soluble CD14 (rsCD14) complex and the corresponding lipohexapeptide given to the cells as an aggregate. Both forms of OspA are internalized in a similar manner to acetylated low density lipoprotein (AcLDL), a scavenger receptor ligand. Acetylated low density lipoprotein is capable of competing for internalization with OspA even when OspA is delivered as a rsCD14 complex. We observe co-localization of OspA with lysosomes but not with the Golgi complex. These phenomena are similar between RAW264.7 macrophages and endothelial cells but change drastically when the cells are deprived of serum. Upon serum starvation, OspA shows some localization to the Golgi apparatus whereas the lipohexapeptide remains on the cell surface. Inhibition of internalization of OspA via treatment with cytochalasin D or of the lipohexapeptide via serum starvation does not interfere with TNF induction activity, consistent with signalling from the cell surface.

Membrane proteome of Acinetobacter radioresistens S13 during aromatic exposure

Study of the bacterial membrane proteome, though in its early stages, is a field of growing interest in the search for information about nutrient transport and processing. We tested different strategies and chemical compounds to extract proteins from the membranes (inner and outer) of Acinetobacter radioresistens S13, a Gram-negative bacterium selected for its ability to degrade aromatics. A. radioresistens S13 was monitored under different growth substrate conditions, using acetate, benzoate or phenol as sole carbon source. Two-dimensional gel electrophoresis map analysis of membrane extracts from benzoate- and phenol-grown cells reveals differences versus controls (acetate-grown cultures). Primarily, a different pattern of spots was observed and, in particular, some proteins were only expressed in the presence of aromatic substrate. Among these, we detected a Na(+)/H(+) antiporter, whose function is likely to be regulation of intracellular pH, and an ABC type sugar transport system, probably involved in capsular polysaccharide translocation. We also identified other proteins, detectable in acetate-grown but over-expressed in aromatic-grown cells. These include: (1) an outer membrane protein ascribable to an OmpA-like protein, recently described in the literature as "alasan", a bioemulsifying agent involved in solubilizing and enhancing bioavailability of hydrocarbons; (2) a trimeric porin of the PhoE family also belonging to the outer membrane and involved in facilitating the transport of anions (especially phosphate); and (3) two glycosyl transferases probably involved in capsules and/or lipopolysaccharide biosynthesis. Study of the bacterial membrane proteome helps to elucidate the role of the membrane as modulable site enabling communication between internal and external environments.

[Impact of non-target gene mutations and reduced permeability of outer membrane on quinolone resistance and multiple antibiotic resistance in Escherichia coli]

OBJECTIVE

To investigate the impact of non-target gene mutations and reduced permeability of the outer membrane on quinolone resistance and multiple antibiotic resistance (mar) in Escherichia coli.

METHODS

Several high-level quinolone resistant isolates whose strains were accompanied by concurrent resistant to several antibiotics were selected. The PCR products of marOR region were sequenced to detect the possible gene changes and then the strains' outer membrane proteins (Omps) were extracted to analyze on the constitutive profiles.

RESULTS

We found two site mutations in R410 isolate: 1,870(T-->C, Val-->Ala) and 1,879(A-->C, terminator-->Ser). The OmpF deficiency was found in all 3 resistant strains.

CONCLUSION

The increased expression of MarA induced by gene mutations in marOR and the constitutive profile changes of the Omps (OmpF deficient strains) may play some role in the quinolone resistance and multiple antibiotic resistance of Escherichia coli.

The surface-associated and secreted MopE protein of Methylococcus capsulatus (Bath) responds to changes in the concentration of copper in the growth medium

Expression of surface-associated and secreted protein MopE of the methanotrophic bacterium Methylococcus capsulatus (Bath) in response to the concentration of copper ions in the growth medium was investigated. The level of protein associated with the cells and secreted to the medium changed when the copper concentration in the medium varied and was highest in cells exposed to copper stress.

Differential expression of the Escherichia coli autoaggregation factor antigen 43

Antigen 43 (Ag43) is a self-recognizing surface adhesin found in most Escherichia coli strains. Due to its excellent cell-to-cell aggregation characteristics, Ag43 expression confers clumping and fluffing of cells and promotes biofilm formation. Ag43 expression is repressed by the cellular redox sensor OxyR. Here we used mutant versions of OxyR that are locked in either the reduced or the oxidized form as well as the addition of a simple redox-changing chemical to show that the redox state of OxyR influences Ag43 expression. Furthermore, the redox state of OxyR influences the biofilm-forming potential of E. coli. Finally, we demonstrated that Ag43-mediated cell aggregation confers significant protection against hydrogen peroxide killing.

Phase variation of Ag43 is independent of the oxidation state of OxyR

OxyR is a DNA binding protein that differentially regulates a cell's response to hydrogen peroxide-mediated oxidative stress. We previously reported that the reduced form of OxyR is sufficient for repression of transcription of agn43 from unmethylated template DNA, which is essential for deoxyadenosine methylase (Dam)- and OxyR-dependent phase variation of agn43. Here we provide evidence that the oxidized form of OxyR [OxyR(ox)] also represses agn43 transcription. In vivo, we found that exogenous addition of hydrogen peroxide, sufficient to oxidize OxyR, did not affect the expression of agn43. OxyR(ox) repressed in vitro transcription but only from an unmethylated agn43 template. The -10 sequence of the promoter and three Dam target sequences were protected in an in vitro DNase I footprint assay by OxyR(ox). Furthermore, OxyR(ox) bound to the agn43 regulatory region DNA with an affinity similar to that for the regulatory regions of katG and oxyS, which are activated by OxyR(ox), indicating that binding at agn43 can occur at biologically relevant concentrations. OxyR-dependent regulation of Ag43 expression is therefore unusual in firstly that OxyR binding at agn43 is dependent on the methylation state of Dam target sequences in its binding site and secondly that OxyR-dependent repression appears to be independent of hydrogen-peroxide mediated oxidative stress and the oxidation state of OxyR.

Bacterial outer membrane and cell wall penetration and cell destruction by polluting chemical agents and physical conditions

In the environment, bacteria and other microorganisms are subjected to a variety of constantly changing chemical and physical agencies. Chemical ones include antimicrobial compounds (both biocides and antibiotics), pollutants, drugs, cosmetic and pharmaceutical ingredients and pesticides. The physical agents include desiccation and drying, osmotic pressure, hydrostatic pressure, temperature and pH changes and radiations (ultraviolet, sunlight, ionizing). Bacteria must thus adapt to survive these inimicable conditions. Organisms such as bacterial spores usually survive, whereas other types of microorganisms may be much more susceptible. Depending on the type of organism, the bacterial cell wall, outer membrane or the spore outer layers may act as permeability barriers to the intracellular uptake of antibiotics and biocides. Some antibacterial agents interact with, and damage or modify, the outer components. Physical agencies are known to damage the cytoplasmic membrane or to produce alterations in DNA or proteins or enzymes. Nevertheless, significant damage to the cell wall or outer membrane may also occur. Four types of organisms are considered: cocci, mycobactria, Gram-negative bacteria and bacterial spores. The nature of the damage inflicted on, or in some cases prevented by, their outer cell layers is discussed for each type of organism.

Contributions of MexAB-OprM and an EmrE homolog to intrinsic resistance of Pseudomonas aeruginosa to aminoglycosides and dyes

Of the six putative small multidrug resistance (SMR) family proteins of Pseudomonas aeruginosa, a protein encoded by the PA4990 gene (emrE(Pae)) shows the highest identity to the well-characterized EmrE efflux transporter of Escherichia coli. Reverse transcription-PCR confirmed the expression of emrE(Pae) in the wild-type strain of P. aeruginosa. Using isogenic emrE(Pae), mexAB-oprM, and/or mexB deletion mutants, the contributions of the EmrE protein and the MexAB-OprM efflux system to drug resistance in P. aeruginosa were assessed by a drug susceptibility test carried out in a low-ionic-strength medium, Difco nutrient broth. We found that EmrE(Pae) contributed to intrinsic resistance not only to ethidium bromide and acriflavine but also to aminoglycosides. In this low-ionic-strength medium, MexAB-OprM was also shown to contribute to aminoglycoside resistance, presumably via active efflux. Aminoglycoside resistance caused by these two pumps could not be demonstrated in high-ionic-strength media, such as Luria broth or Mueller-Hinton broth. The EmrE-dependent efflux of ethidium bromide was confirmed by a continuous fluorescence assay.

Mechanisms of beta-lactam resistance in Pseudomonas aeruginosa: prevalence of OprM-overproducing strains in a French multicentre study (1997)

One hundred and forty-three non-repetitive strains of Pseudomonas aeruginosa were collected in 13 French hospitals in 1997. A decreased susceptibility or resistance to ticarcillin (MIC > 16 mg/L) was found in 61 isolates (43%) and this was attributed to three major mechanisms: (i) overexpression of OprM and hence related efflux components such as MexAB or MexXY (42.6%), (ii) production of acquired beta-lactamase (29.5%) and (iii) overexpression of chromosomally encoded AmpC cephalosporinase (21.3%). Four of seven 'intrinsically' resistant strains (11.5%) with normal amounts of OprM were shown to produce low levels of AmpC, whereas in three isolates no resistance mechanism to beta-lactams could be identified. Overproduction of OprM thus appears as an important mechanism of ticarcillin resistance in French isolates of P. aeruginosa.

TonB of Escherichia coli activates FhuA through interaction with the beta-barrel

FhuA is a multifunctional protein in the outer membrane of Escherichia coli that actively transports Fe(3+)-ferrichrome and the antibiotics albomycin and rifamycin CGP 4832, and serves as a receptor for the unrelated phages T5, T1, phi80 and UC-1, colicin M and microcin J25. The energy source for active transport is the proton-motive force of the cytoplasmic membrane, which is required for all FhuA functions except infection by phage T5, and is thought to be mediated to the outer-membrane receptor FhuA by the TonB protein. The crystal structure of FhuA consists of a beta-barrel that is closed by a globular domain. The proximal region carries the TonB box (residues 7-11), for which genetic evidence exists that it interacts with the region around residue 160 of TonB. However, deletion of the TonB box along with the globular domain results in a protein, FhuAdelta5-160, that still displays TonB-dependent active ferrichrome transport across the outer membrane and confers sensitivity to the FhuA ligands. In this study synthetic nonapeptides identical in sequence to amino acids 150-158, 151-159, 152-160, 153-161 and 158-166 of TonB were shown to reduce ferrichrome transport of cells via wild-type FhuA and the corkless derivative FhuAdelta5-160, which suggests that this TonB region is involved in the interaction of TonB with the beta-barrel of FhuA. TonB missense mutants reduced the activity of FhuA and FhuAdelta5-160. TonB proteins of different Enterobacteriaceae activated FhuA and FhuAdelta5-160 to a similar degree. TonB of Pantoea agglomerans displayed low activity in an E. coli tonB mutant. Sequencing of the tonB gene of P. agglomerans revealed differences from E. coli TonB in the region around residue 160 of the deduced protein; these differences might contribute to the lower activity of the P. agglomerans TonB protein when coupled to the E. coli FhuA protein. The data support the theory that the beta-barrel receives the energy from the cytoplasmic membrane via TonB and responds to the energy input and thus represents the transporting domain of FhuA.

Cellular and molecular aspects of drugs of the future: meropenem

Meropenem, first synthesized in the late eighties, has become one of the most important beta-lactam antibiotics of the carbapenem subclass used for the treatment of a variety of life-threatening infections. Due to its unique chemical structure, meropenem is not inactivated by the kidney dehydropeptidase I and the majority of microbial beta-lactamases. Its antimicrobial activity is based on its high affinity for the majority of cell wall-synthesizing enzymes, the so-called penicillin-binding proteins, of Gram-positive and -negative bacteria. However, bacteria have evolved several approaches to resist meropenem: (i) by reducing the affinity of the penicillin-binding proteins for the antibiotics, (ii) by decreasing the permeability of the outer membrane of Gram-negative bacteria, (iii) by using efflux pumps, and (iv) by activating zinc-dependent carbapenemases. Meropenem has a low toxicity profile and, in contrast to imipenem, no central nervous system toxicity.

Identification and analysis of amino acid mutations in porin IB that mediate intermediate-level resistance to penicillin and tetracycline in Neisseria gonorrhoeae

PenB is the third resistance determinant in the stepwise acquisition of multiple resistance genes in chromosomally mediated resistant Neisseria gonorrhoeae (CMRNG). Alterations in por(IB), one of two alleles at the por locus that encodes the outer membrane protein porin IB (PIB), were recently reported to be responsible for the increased resistance to penicillin and tetracycline conferred by penB, but the specific mutations conferring antibiotic resistance were not identified experimentally. To determine which amino acids in PIB confer increased resistance, we transformed a recipient strain with chimeras of the por(IB) genes from strains FA1090 and FA140 (penB2). These studies revealed that two amino acid changes, G120D and A121D, were both necessary and sufficient to confer increased resistance to penicillin and tetracycline. Site-saturation and site-directed mutagenesis of Gly-120 and Ala-121 revealed that both a single mutation, G120K, and the double mutations G120R A121H and G120P A121P also conferred antibiotic resistance to the recipient strain. The identical mutations in PIA increased penicillin and tetracycline resistance either moderately or not at all. Analysis of por(IB) genes present in the GenBank database from 51 clinical isolates demonstrated that lysine and aspartate mutations at positions 120 and/or 121 also occur in nature. These studies demonstrate that charged amino acids at positions 120 and 121 in PIB are highly preferential for conferring resistance to penicillin and tetracycline in N. gonorrhoeae.

Stress-based identification and classification of antibacterial agents: second-generation Escherichia coli reporter strains and optimization of detection

Escherichia coli strains bearing single-copy fusions between the lacZ reporter gene and the cspA, ibp, or P3rpoH stress promoters offer a simple means to detect sublethal concentrations of antibacterial agents interfering with prokaryotic translation or cell envelope integrity while simultaneously providing information on the mechanism of action of the test compound (A. A. Bianchi and F. Baneyx, Appl. Environ. Microbiol. 65:5023-5027, 1999). Here, we expand the usefulness of this system by (i) demonstrating that a fusion between the SOS-inducible sulA promoter and lacZ is a highly specific probe for the detection of antimicrobial agents that ultimately interfere with DNA replication, (ii) showing that inactivation of the tolC gene allows efficient detection of very low concentrations of model antibiotics (including aminoglycosides) whereas polymyxin B-mediated outer membrane permeabilization facilitates the identification of intermediate concentrations of hydrophobic compounds, and (iii) validating the potential of detector strains and sensitization strategies for high-throughput screening using a reproducible and internally consistent 96-well microplate assay.

Activities of polymyxin B and cecropin A-,melittin peptide CA(1-8)M(1-18) against a multiresistant strain of Acinetobacter baumannii

Polymyxin B (PXB) and the cecropin A-melittin hybrid CA(1-8)M(1-18) (KWKLFKKIGIGAVLKVLTTGLPALIS-NH2) were compared for antibiotic activity on reference and multiresistant Acinetobacter baumannii strains. Significant differences for both peptides were observed on their inner membrane interaction and inhibition by environmental factors, supporting the use of CA(1-8)M(1-18) as a potential alternative to PXB against ACINETOBACTER:

Inhibition of bacterial ice nucleation by polyglycerol polymers

The simple linear polymer polyglycerol (PGL) was found to apparently bind and inhibit the ice nucleating activity of proteins from the ice nucleating bacterium Pseudomonas syringae. PGL of molecular mass 750 Da was added to a solution consisting of 1 ppm freeze-dried P. syringae 31A in water. Differential ice nucleator spectra were determined by measuring the distribution of freezing temperatures in a population of 98 drops of 1 microL volume. The mean freezing temperature was lowered from -6.8 degrees C (control) to -8.0,-9.4,-12.5, and -13.4 degrees C for 0.001, 0.01, 0.1, and 1% w/w PGL concentrations, respectively (SE < 0.2 degrees C). PGL was found to be an ineffective inhibitor of seven defined organic ice nucleating agents, whereas the general ice nucleation inhibitor polyvinyl alcohol (PVA) was found to be effective against five of the seven. The activity of PGL therefore seems to be specific against bacterial ice nucleating protein. PGL alone was an ineffective inhibitor of ice nucleation in small volumes of environmental or laboratory water samples, suggesting that the numerical majority of ice nucleating contaminants in nature may be of nonbacterial origin. However, PGL was more effective than PVA at suppressing initial ice nucleation events in large volumes, suggesting a ubiquitous sparse background of bacterial ice nucleating proteins with high nucleation efficiency. The combination of PGL and PVA was particularly effective for reducing ice formation in solutions used for cryopreservation by vitrification.

Synthesis and antibacterial activity of novel 4-pyrrolidinylthio carbapenems Part IV. 2-Alkyl substituents containing cationic heteroaromatics linked via a C–C bond

The synthesis and biological activity of a novel series of 2-alkyl-4-pyrrolidinylthio-beta-methylcarbapenems containing a variety of cationic heteroaromatic substituents linked via a C-C bond is described. As a result of these studies, we selected FR21818 (In) as a candidate compound for development. FR21818 exhibited a well balanced spectrum of antibacterial activity, including Pseudomonas aeruginosa and methicillin-resistant Staphylococcus aureus (MRSA), excellent urinary recovery, good stability against renal dehydropeptidase-I (DHP-I). no antigenicity and mutagenicity, weak toxicities, and good efficacy and therapeutic effect on mice systemic infections. Affinities to PBP's, permeability of outer membrane, and plasma levels in mice, dog, and cynomolgous monkey of FR21818 are also reported.

Iron influences the expression of Helicobacter pylori outer membrane vesicle-associated virulence factors

BACKGROUND

Helicobacter pylori shed outer membrane vesicles (OMV) in vitro and in vivo. These OMV, which contain active VacA, provide a potential vehicle for the delivery of H. pylori virulence factors to the gastric mucosa.

OBJECTIVE

To assess the influence of environmental iron levels on H. pylori OMV VacA and protease expression in vitro.

METHODS

Three well-characterized H. pylori type-strains were grown for 72 h under normal (Brucella broth, 5% fetal calf serum) and iron-limiting (Brucella broth, 5% fetal calf serum, 50 micromol/l deferoxamine) conditions. Following harvesting by differential centrifugation, the ratio of whole cells to OMV was determined. OMV VacA levels in response to iron availability were determined by ELISA and immunolabelling of washed bacteria. Protease activity was detected by zymography of OMV in the presence and absence of enzyme inhibitors and activators. HEp-2 cells were used to assay for OMV-associated cytopathogenic toxins.

RESULTS

Decreased iron availability, which limited bacterial growth but not OMV release, also influenced the expression of OMV-associated virulence factors. VacA levels were reduced, whereas two new proteolytic enzymes were expressed on these OMV. When an iron salt was added to counteract the effect of the deferoxamine, VacA levels were restored in the outer membrane and the proteolytic activity disappeared.

CONCLUSIONS

These results suggest that OMV release by H. pylori is influenced by environmental iron levels, and that the qualitative changes that occur in outer membrane composition may contribute to the clinical patterns of H. pylori-associated disease.

Salicylate induction of phenotypic resistance to quinolones in Serratia marcescens

The influence of salicylic acid on the permeability and susceptibility of Serratia marcescens to both nalidixic acid and ciprofloxacin was studied, as well as the effect of salicylate on outer membrane proteins and lipopolysaccharide. As salicylic acid concentration increased, ciprofloxacin accumulation decreased with a concomitant, previously observed, reduction in the porin content of the outer membrane. Resistance to ciprofloxacin and nalidixic acid was enhanced when bacteria grew in the presence of salicylic acid.

Relationship between outer membrane alterations and susceptibility to antimicrobial agents in isogenic strains of Klebsiella pneumoniae

The activities of beta-lactams, chloramphenicol, tetracycline, fluoroquinolones and aminoglycosides against Klebsiella pneumoniae C3 (O1:K66, producing porins OmpK35 and OmpK36) and a set of isogenic mutants derived from it lacking the O antigen of lipopolysaccharide (LPS), capsular K antigen, or one or both porins were determined. MICs remained within one dilution step in mutants deficient in antigen O, in capsule or in one of the two porins. No increases in the MICs of aminoglycosides, fluoroquinolones, tetracycline and chloramphenicol were observed for strains deficient in the two porins, but the MICs of ampicillin, cephalothin, cefoxitin, cefotaxime and ceftazidime for this type of mutant increased four- to >256-fold. The highest MICs of beta-lactams were obtained in a porin-deficient mutant expressing increased beta-lactamase activity. It is concluded that isolated outer membrane alterations in K. pneumoniae are not decisive factors in increasing resistance to antimicrobial agents, but porin loss co-operates with beta-actamase production to increase resistance to beta-lactams.

In vitro selected fluoroquinolone-resistant mutants of Citrobacter freundii: analysis of the quinolone resistance acquisition

Ten quinolone-resistant mutants of Citrobacter freundii, which were selected in vitro with fluoroquinolones from two clinical isolates, were studied. The parent isolates were susceptible to quinolones in spite of showing a single substitution in the GyrB (His-417 --> Leu). No change was observed in the outer membrane proteins or in the lipopolysaccharide in any of the ten mutants studied with respect to their parent isolates. The development of quinolone resistance in selected mutants was associated with the appearance of a substitution in the GyrA (Thr-83 --> Ile) in nine of the ten mutants plus enhanced active efflux in all of them.

Insulin-like growth factor-1 affects expressions of cyclin-dependent kinase 5 and its activator p35 in reperfused rat brain

Insulin-like growth factor-1 (IGF-1) was applied topically on the brain surface of reperfused rat brain after 60 min of transient middle cerebral artery (MCA) occlusion. In contrast to the cases treated with vehicle, the infarct volume was greatly reduced at 24 h of reperfusion by the treatment with IGF-1. Immunohistochemical analysis in the MCA territory showed that the increase of cyclin-dependent kinase 5 (cdk5) was greatly reduced, and that the decrease of the critical regulatory subunit of cdk5, p35, was preserved with treatment of IGF-1. The present results suggest that IGF-1 has a significant effect on ameliorating brain injury after transient focal brain ischemia with affecting the expressions of cdk5 and its activator p35.

Presence of Na+-stimulated P-type ATPase in the membrane of a facultatively anaerobic alkaliphile, Exiguobacterium aurantiacum

It was found that a facultatively anaerobic alkaliphile, Exiguobacterium aurantiacum, possesses a membrane-bound ATPase, which was activated specifically by Na+. The Na+-stimulated ATPase activity reached a maximum value at 200 mM NaCl. In the presence of 200 mM NaCl, the activity was drastically reduced by vanadate, a potent inhibitor of P-type ATPase, with a half-maximal inhibition at 1 microM. Incubation of the membranes with [gamma-32P]ATP followed by acidic lithium dodecyl sulfate-polyacrylamide gel electrophoresis demonstrated the existence of two phosphorylated intermediates with apparent molecular masses of 60 and 100 kDa. Only phosphorylation of the 100-kDa polypeptide was inhibited by vanadate. The membrane extract containing Na+-stimulated ATPase, when reconstituted into soybean phospholipid vesicles, exhibited 22Na+ transport by the addition of ATP, which was inhibited by vanadate and gramicidin. It is likely that the Na+-stimulated ATPase belongs to P-type and is involved in Na+ transport.

Elevated temperature treatment as a novel method for decreasing p57 on the cell surface of Renibacterium salmoninarum

Renibacterium salmoninarum is a Gram-positive diplo-bacillus and the causative agent of bacterial kidney disease, a prevalent disease of salmonid fish. Virulent isolates of R. salmoninarum have a hydrophobic cell surface and express the 57-58 kDa protein (p57). Here we have investigated parameters which effect cell hydrophobicity and p57 degradation. Incubation of R. salmoninarum cells at 37 degrees C for > 4 h decreased cell surface hydrophobicity as measured by the salt aggregation assay, and decreased the amount of cell associated p57. Incubation of cells at lower temperatures (22, 17, 4 or -20 degrees C) for up to 16 h did not reduce hydrophobicity or the amount of cell associated p57. Both the loss of cell surface hydrophobicity and the degradation of p57 were inhibited by pre-incubation with the serine protease inhibitor phenylmethylsulfonyl fluoride (PMSF). Cell surface hydrophobicity was specifically reconstituted by incubation with extracellular protein (ECP) concentrated from culture supernatant and was correlated with the reassociation of p57 onto the bacterial cell surface as determined by western blot and total protein stain analyses. The ability of p57 to reassociate suggests that the bacterial cell surface is not irreversibly modified by the 37 degrees C treatment and that p57 contributes to the hydrophobic nature of R. salmoninarum. In summary, we describe parameters effecting the removal of the p57 virulence factor and suggest the utility of this modification for generating a whole cell vaccine against bacterial kidney disease.

Apoptotic effect of outer-membrane proteins from Campylobacter jejuni on chicken lymphocytes

Campylobacter jejuni is a significant cause of food-borne diseases in humans. The bacterium is considered a commensal organism in chickens, and it can heavily colonize chickens without causing inflammation. Poultry may be the major reservoir for the human infection in developed countries. Here we show that an outer-membrane protein extract prepared from the bacteria caused apoptosis of chicken lymphocytes detected in vitro with the terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling assay that preferentially labels individual apoptotic cells. Blood- and spleen-lymphocytes from different-aged chickens displayed a significantly greater percentage of apoptotic cells after culture with the outer-membrane proteins from C. jejuni than controls treated with phosphate-buffered saline, chicken ovalbumin, or outer-membrane proteins prepared from E. coli strain BL21. The C. jejuni extract also produced apoptosis of chicken lymphoblastoid tumor cell lines. Apoptosis was blocked by pretreating the extract with proteinase K or antiserum against outer-membrane proteins. The results suggest that C. jejuni may be capable of achieving immune avoidance in chickens by causing apoptosis of lymphocytes.

Impaired imipenem uptake associated with alterations in outer membrane proteins and lipopolysaccharides in imipenem-resistant Shigella dysenteriae

Three imipenem-resistant mutants were obtained from a clinical isolate (C152) of Shigella dysenteriae by selection with increasing concentrations of imipenem. Resistance to imipenem was associated with resistance to several other beta-lactam antibiotics. The penicillin-binding protein (PBP) patterns of the resistant and the wild-type strains were comparable. The permeability of the outer membrane proteins (OMPs) of the most resistant mutant, IM16, was lower than that of the parent strain C152 when imipenem and arabinose were used as test solutes. This mutant had lower levels of both the major OMPs of M(r) 43,000 and 38,000. There were also differences in the patterns of lipopolysaccharide (LPS) of the mutants and the wild-type strain. The mutant IM16 had less short-chain LPS than the parent C152. Increasing imipenem resistance was also associated with a concomitant decrease in the level of 2-keto-3-deoxyoctonate, a component of the core region of LPS.

Decorin-binding protein of Borrelia burgdorferi is encoded within a two-gene operon and is protective in the murine model of Lyme borreliosis

Isolated outer membranes of Borrelia burgdorferi were used in immunoblotting experiments with sera from immune mice to identify new putative Lyme disease vaccine candidates. One immunoreactive polypeptide migrated on polyacrylamide gels just proximal to outer surface protein C and comigrated with [3H]palmitate-labeled polypeptides. A degenerate oligonucleotide primer based upon internal amino acid sequence information was used to detect the corresponding gene within a B. burgdorferi total genomic library. The relevant open reading frame (ORF) encoded a polypeptide comprised of a 24-amino-acid putative signal peptide terminated by LLISC, a probable consensus sequence for lipoprotein modification, and a mature protein of 163 amino acids. Immunoblots of a recombinant fusion protein corresponding to this ORF supported the idea that the encoded protein was a previously reported decorin-binding protein (DBP) of B. burgdorferi N40 (B. P. Guo, S. J. Norris, L. C. Rosenberg, and M. Höök, Infect. Immun. 63:3467-3472, 1995). However, further DNA sequencing revealed the presence of a second ORF, designated ORF-1, whose termination codon was 119 bp upstream of the dbp gene. ORF-1 also encoded a putative lipoprotein with a mature length of 167 amino acids. Northern blots, Southern blots, and primer extension analyses indicated that ORF-1 and dbp comprised a two-gene operon located on the 49-kb linear plasmid. Both proteins, which were 40% identical and 56% similar, partitioned into Triton X-114 detergent extracts of B. burgdorferi isolated outer membranes. Mice infected with B. burgdorferi produced high titers of antibodies against the ORF-1-encoded protein and DBP during both early and later stages of chronic infection. Both DBP and the ORF-1-encoded protein were sensitive to proteinase K treatment of intact borreliae, suggesting that they were surface exposed. In active immunization experiments, 78% of mice immunized with recombinant DBP were immune to challenge. While it is not clear whether the two lipoproteins encoded by the ORF-1-dbp operon have analogous decorin-binding functions in vivo, the combined studies implicate DBP as a new candidate for a human Lyme disease vaccine.

Outer membrane proteins of Klebsiella pneumoniae after exposure to ciprofloxacin

Suppression of bacterial growth of two Klebsiella pneumoniae strains after a short time exposure to ciprofloxacin at suprainhibitory concentrations was found (postantibiotic effect-PAE). PAEs induced by ciprofloxacin at 2 x MIC were 4.1 h and 5.3 h for the strains tested, the concentration of 4 x MIC manifested a suppression of the bacterial growth which lasted 5.9 h and 6.3 h. Delay of regrowth of K. pneumoniae strains exposed to suprainhibitory concentrations of quinolones was shown also by other authors. New information concerning the outer membrane protein profile of K. pneumoniae after PAE has been found. SDS-PAGE analysis revealed that outer membrane protein patterns isolated from K. pneumoniae strains treated with a suprainhibitory concentration of ciprofloxacin did not show apparent changes as compared to controls.