Enterobacter bacteremia: clinical features and emergence of antibiotic resistance during therapy

OBJECTIVES

To study the effect of previously administered antibiotics on the antibiotic susceptibility profile of Enterobacter, the factors affecting mortality, and the emergence of antibiotic resistance during therapy for Enterobacter bacteremia.

DESIGN

Prospective, observational study of consecutive patients with Enterobacter bacteremia.

SETTING

Three university tertiary care centers, one major university-affiliated hospital, and two university-affiliated Veterans Affairs medical centers.

PATIENTS

A total of 129 adult patients were studied.

MEASUREMENTS

The two main end points were emergence of resistance during antibiotic therapy and death.

MAIN RESULTS

Previous administration of third-generation cephalosporins was more likely to be associated with multiresistant Enterobacter isolates in an initial, positive blood culture (22 of 32, 69%) than was administration of antibiotics that did not include a third-generation cephalosporin (14 of 71, 20%; P less than 0.001). Isolation of multiresistant Enterobacter sp. in the initial blood culture was associated with a higher mortality rate (12 of 37, 32%) than was isolation of a more sensitive Enterobacter sp. (14 of 92, 15%; P = 0.03). Emergence of resistance to third-generation cephalosporin therapy (6 of 31, 19%) occurred more often than did emergence of resistance to aminoglycoside (1 of 89, 0.01%; P = 0.001) or other beta-lactam (0 of 50; P = 0.002) therapy.

CONCLUSIONS

More judicious use of third-generation cephalosporins may decrease the incidence of nosocomial multiresistant Enterobacter spp., which in turn may result in a lower mortality for Enterobacter bacteremia. When Enterobacter organisms are isolated from blood, it may be prudent to avoid third-generation cephalosporin therapy regardless of in-vitro susceptibility.

Uric acid, a natural scavenger of peroxynitrite, in experimental allergic encephalomyelitis and multiple sclerosis

Uric acid, the naturally occurring product of purine metabolism, is a strong peroxynitrite scavenger, as demonstrated by the capacity to bind peroxynitrite but not nitric oxide (NO) produced by lipopolysaccharide-stimulated cells of a mouse monocyte line. In this study, we used uric acid to treat experimental allergic encephalomyelitis (EAE) in the PLSJL strain of mice, which develop a chronic form of the disease with remissions and exacerbations. Uric acid administration was found to have strong therapeutic effects in a dose-dependent fashion. A regimen of four daily doses of 500 mg/kg uric acid was required to promote long-term survival regardless of whether treatment was initiated before or after the clinical symptoms of EAE had appeared. The requirement for multiple doses is likely to be caused by the rapid clearance of uric acid in mice which, unlike humans, metabolize uric acid a step further to allantoin. Uric acid treatment also was found to diminish clinical signs of a disease resembling EAE in interferon-gamma receptor knockout mice. A possible association between multiple sclerosis (MS), the disease on which EAE is modeled, and uric acid is supported by the finding that patients with MS have significantly lower levels of serum uric acid than controls. In addition, statistical evaluation of more than 20 million patient records for the incidence of MS and gout (hyperuricemic) revealed that the two diseases are almost mutually exclusive, raising the possibility that hyperuricemia may protect against MS.

qnr prevalence in ceftazidime-resistant Enterobacteriaceae isolates from the United States

We screened 313 ceftazidime-resistant Enterobacteriaceae isolates obtained in the United States from 1999 to 2004 for all three known qnr genes. A qnr gene was present in 20% of Klebsiella pneumoniae isolates, 31% of Enterobacter sp. isolates, and 4% of Escherichia coli isolates. qnrA and qnrB occurred with equivalent frequencies and, except for qnrB in enterobacters, were stable over time. qnrS was absent.

Fluoroquinolone antimicrobial agents

The fluoroquinolones, a new class of potent orally absorbed antimicrobial agents, are reviewed, considering structure, mechanisms of action and resistance, spectrum, variables affecting activity in vitro, pharmacokinetic properties, clinical efficacy, emergence of resistance, and tolerability. The primary bacterial target is the enzyme deoxyribonucleic acid gyrase. Bacterial resistance occurs by chromosomal mutations altering deoxyribonucleic acid gyrase and decreasing drug permeation. The drugs are bactericidal and potent in vitro against members of the family Enterobacteriaceae, Haemophilus spp., and Neisseria spp., have good activity against Pseudomonas aeruginosa and staphylococci, and (with several exceptions) are less potent against streptococci and have fair to poor activity against anaerobic species. Potency in vitro decreases in the presence of low pH, magnesium ions, or urine but is little affected by different media, increased inoculum, or serum. The effects of the drugs in combination with a beta-lactam or aminoglycoside are often additive, occasionally synergistic, and rarely antagonistic. The agents are orally absorbed, require at most twice-daily dosing, and achieve high concentrations in urine, feces, and kidney and good concentrations in lung, bone, prostate, and other tissues. The drugs are efficacious in treatment of a variety of bacterial infections, including uncomplicated and complicated urinary tract infections, bacterial gastroenteritis, and gonorrhea, and show promise for therapy of prostatitis, respiratory tract infections, osteomyelitis, and cutaneous infections, particularly when caused by aerobic gram-negative bacilli. Fluoroquinolones have also proved to be efficacious for prophylaxis against travelers' diarrhea and infection with gram-negative bacilli in neutropenic patients. The drugs are effective in eliminating carriage of Neisseria meningitidis. Patient tolerability appears acceptable, with gastrointestinal or central nervous system toxicities occurring most commonly, but only rarely necessitating discontinuance of therapy. In 17 of 18 prospective, randomized, double-blind comparisons with another agent or placebo, fluoroquinolones were tolerated as well as or better than the comparison regimen. Bacterial resistance has been uncommonly documented but occurs, most notably with P. aeruginosa and Staphylococcus aureus and occasionally other species for which the therapeutic ratio is less favorable. Fluoroquinolones offer an efficacious, well-tolerated, and cost-effective alternative to parenteral therapies of selected infections.

Emerging mechanisms of fluoroquinolone resistance

Broad use of fluoroquinolones has been followed by emergence of resistance, which has been due mainly to chromosomal mutations in genes encoding the subunits of the drugs' target enzymes, DNA gyrase and topoisomerase IV, and in genes that affect the expression of diffusion channels in the outer membrane and multidrug-resistance efflux systems. Resistance emerged first in species in which single mutations were sufficient to cause clinically important levels of resistance (e.g., Staphylococcus aureus and Pseudomonas aeruginosa). Subsequently, however, resistance has emerged in bacteria such as Campylobacter jejuni, Escherichia coli, and Neisseria gonorrhoeae, in which multiple mutations are required to generate clinically important resistance. In these circumstances, the additional epidemiologic factors of drug use in animals and human-to-human spread appear to have contributed. Resistance in Streptococcus pneumoniae, which is currently low, will require close monitoring as fluoroquinolones are used more extensively for treating respiratory tract infections.

Mechanisms of action of antimicrobials: focus on fluoroquinolones

Five bacterial targets have been exploited in the development of antimicrobial drugs: cell wall synthesis, protein synthesis, ribonucleic acid synthesis, deoxyribonucleic acid (DNA) synthesis, and intermediary metabolism. Because resistance to drugs that interact with these targets is widespread, new antimicrobials and an understanding of their mechanisms of action are vital. The fluoroquinolones are the only direct inhibitors of DNA synthesis; by binding to the enzyme-DNA complex, they stabilize DNA strand breaks created by DNA gyrase and topoisomerase IV. Ternary complexes of drug, enzyme, and DNA block progress of the replication fork. Cytotoxicity of fluoroquinolones is likely a 2-step process involving (1) conversion of the topoisomerase-quinolone-DNA complex to an irreversible form and (2) generation of a double-strand break by denaturation of the topoisomerase. The molecular factors necessary for the transition from step 1 to step 2 remain unclear, but downstream pathways for cell death may overlap with those used by other bactericidal antimicrobials. Studies of fluoroquinolone-resistant mutants and purified topoisomerases indicate that many quinolones have differing activities against the two targets. Drugs with similar activities against both targets may prove less likely to select de novo resistance.

Uric acid, a peroxynitrite scavenger, inhibits CNS inflammation, blood-CNS barrier permeability changes, and tissue damage in a mouse model of multiple sclerosis

Peroxynitrite (ONOO(-)), a toxic product of the free radicals nitric oxide and superoxide, has been implicated in the pathogenesis of CNS inflammatory diseases, including multiple sclerosis and its animal correlate experimental autoimmune encephalomyelitis (EAE). In this study we have assessed the mode of action of uric acid (UA), a purine metabolite and ONOO(-) scavenger, in the treatment of EAE. We show that if administered to mice before the onset of clinical EAE, UA interferes with the invasion of inflammatory cells into the CNS and prevents development of the disease. In mice with active EAE, exogenously administered UA penetrates the already compromised blood-CNS barrier, blocks ONOO(-)-mediated tyrosine nitration and apoptotic cell death in areas of inflammation in spinal cord tissues and promotes recovery of the animals. Moreover, UA treatment suppresses the enhanced blood-CNS barrier permeability characteristic of EAE. We postulate that UA acts at two levels in EAE: 1) by protecting the integrity of the blood-CNS barrier from ONOO(-)-induced permeability changes such that cell invasion and the resulting pathology is minimized; and 2) through a compromised blood-CNS barrier, by scavenging the ONOO(-) directly responsible for CNS tissue damage and death.

Prevention of experimental allergic encephalomyelitis by targeting nitric oxide and peroxynitrite: implications for the treatment of multiple sclerosis

In this study we provide further evidence associating activated cells of the monocyte lineage with the lesions of multiple sclerosis (MS). Using a combination of immunohistochemistry and reverse transcriptase-dependent in situ polymerase chain reaction analysis, we have identified monocytes expressing inducible nitric oxide synthase (iNOS) to be prevalent in the plaque areas of post mortem brain tissue from patients with MS. In addition, we have obtained evidence of the nitration of tyrosine residues in brain areas local to accumulations of iNOS-positive cells. In parallel studies we have assessed the effects of inhibitors of iNOS induction, as well as scavengers of nitric oxide and peroxynitrite in the experimental allergic encephalomyelitis model. Significant therapeutic effects were seen with the inhibitor of iNOS induction, tricyclodecan-9-xyl-xanthogenate, a nitric oxide scavenger, 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, and a peroxynitrite scavenger, uric acid. In particular, treatment with high doses of uric acid virtually prevented clinical symptoms of the disease. Together with our demonstration of the presence of activated macrophages expressing high levels of iNOS and evidence of peroxynitrite formation in brain tissue from patients with MS, these findings are of importance in the development of approaches to treat this disease.

Cross-resistance to fluoroquinolones in multiple-antibiotic-resistant (Mar) Escherichia coli selected by tetracycline or chloramphenicol: decreased drug accumulation associated with membrane changes in addition to OmpF reduction

Chromosomal multiple-antibiotic-resistant (Mar) mutants of Escherichia coli, selected on agar containing low concentrations of tetracycline or chloramphenicol, were 6- to 18-fold less susceptible to the fluoroquinolones than were their wild-type E. coli K-12 or E. coli C parental strains. The frequency of emergence of such mutants was at least 1,000-fold higher than that of those selected by the fluoroquinolone norfloxacin directly. When Mar mutants, but not wild-type cells, were plated on norfloxacin, mutants resistant to high levels of norfloxacin (2 micrograms/ml) appeared at a relatively high (approximately 10(-7] frequency. In addition to decreased amounts of OmpF, Mar mutants had other outer membrane protein changes and were four- to eightfold less susceptible to fluoroquinolones than was an ompF::Tn5 mutant lacking only OmpF. Accumulation of [3H]norfloxacin was more than threefold lower in the Mar mutants than in wild-type cells and twofold lower than in the OmpF-deficient derivative. These differences were not attributable to a change in the endogenous active efflux system for norfloxacin in E. coli. Norfloxacin-induced inhibition of DNA synthesis was threefold lower in intact cells of a Mar mutant than in susceptible cells, but this difference was not seen in toluene-permeabilized cells. Insertion of Tn5 into marA (min 34.05 on the chromosome) led to a return of the wild-type patterns of norfloxacin accumulation, fluoroquinolone and other antimicrobial agent susceptibilities, and outer membrane protein profile, including partial restoration of OmpF. These findings together suggest that marA-dependent fluoroquinolone resistance is linked to decreased cell permeability, only part of which can be accounted for by the reduction in OmpF. Once mutated to marA, cells can achieve high levels of quinolone resistance at a relatively high frequency.

Mechanisms of action and resistance of older and newer fluoroquinolones

The fluoroquinolones interact with 2 bacterial targets, the related enzymes DNA gyrase and topoisomerase IV, both of which are involved in DNA replication. Quinolones form complexes of these enzymes with DNA, complexes that block movement of the DNA-replication fork and thereby inhibit DNA replication. Many older quinolones differ in their relative activities against gyrase and topoisomerase IV in a bacterial cell, having greater potency against gyrase than against topoisomerase IV in many gram-negative bacteria and greater potency against topoisomerase IV than against gyrase in many gram-positive bacteria. Several newer quinolones appear to have more closely balanced activity against these enzymes. Resistance to fluoroquinolones occurs as a result of mutational amino acid substitutions in the subunits of the more sensitive (or primary-target) enzyme within the cell. If, however, both enzymes are similarly susceptible to a fluoroquinolone, then the level of resistance caused by a primary-target mutation may be low and may be limited by the sensitivity of the secondary target. Fluoroquinolones also differ in the extent to which common bacterial multidrug efflux pumps affect their activity, with some compounds being unaffected by resistance mechanisms because of overexpression of such pumps. Newer fluoroquinolone interaction with dual targets and avoidance of efflux-resistance mechanisms may each contribute to the lower frequencies of selection of resistant mutants in the laboratory.

MgrA is a multiple regulator of two new efflux pumps in Staphylococcus aureus

In an analysis of the resistance mechanisms of an mgrA mutant, we identified two genes encoding previously undescribed transporters, NorB and Tet38. norB was 1,392 bp and encoded a predicted 49-kDa protein. When overexpressed, NorB led to an increase in resistance to hydrophilic quinolones, ethidium bromide, and cetrimide and also to sparfloxacin, moxifloxacin, and tetracycline, a resistance phenotype of the mgrA mutant. NorA and NorB shared 30% similarity, and NorB shared 30 and 41% similarities with the Bmr and Blt transporters of Bacillus subtilis, respectively. The second efflux pump was a more selective transporter that we have called Tet38, which had 46% similarity with the plasmid-encoded TetK efflux transporter of S. aureus. tet38 was 1,353 bp and encoded a predicted 49-kDa protein. Overexpression of tet38 produced resistance to tetracycline but not to minocycline and other drugs. norB and tet38 transcription was negatively regulated by MgrA. Limited binding of MgrA to the promoter regions of norB and tet38 was demonstrated by gel shift assays, suggesting that MgrA was an indirect regulator of norB and tet38 expression. The mgrA norB double mutant was reproducibly twofold more susceptible to the tested quinolones than the mgrA mutant. The mgrA tet38 double mutant became more susceptible to tetracycline than the wild-type parent strain. These data demonstrate that overexpression of NorB and Tet38 contribute, respectively, to the hydrophobic quinolone resistance and the tetracycline resistance of the mgrA mutant and that MgrA regulates expression of norB and tet38 in addition to its role in regulation of norA expression.

Pathogenicity of different rabies virus variants inversely correlates with apoptosis and rabies virus glycoprotein expression in infected primary neuron cultures

The mouse-adapted rabies virus strain CVS-24 has stable variants, CVS-B2c and CVS-N2c, which differ greatly in their pathogenicity for normal adult mice and in their ability to infect nonneuronal cells. The glycoprotein (G protein), which has previously been implicated in rabies virus pathogenicity, shows substantial structural differences between these variants. Although prior studies have identified antigenic site III of the G protein as the major pathogenicity determinant, CVS-B2c and CVS-N2c do not vary at this site. The possibility that pathogenicity is inversely related to G protein expression levels is suggested by the finding that CVS-B2c, the less pathogenic variant, expresses at least fourfold-higher levels of G protein than CVS-N2c in infected neurons. Although there is some difference between CVS-B2c- and CVS-N2c-infected neurons in G protein mRNA expression levels, the differential expression of G protein appears to be largely determined by posttranslational mechanisms that affect G protein stability. Pulse-chase experiments indicated that the G protein of CVS-B2c is degraded more slowly than that of CVS-N2c. The accumulation of G protein correlated with the induction of programmed cell death in CVS-B2c-infected neurons. The extent of apoptosis was considerably lower in CVS-N2c-infected neurons, where G protein expression was minimal. While nucleoprotein (N protein) expression levels were similar in neurons infected with either variant, the transport of N protein into neuronal processes was strongly inhibited in CVS-B2c-infected cells. Thus, downregulation of G protein expression in neuronal cells evidently contributes to rabies virus pathogenesis by preventing apoptosis and the apparently associated failure of the axonal transport of N protein.

A new two-component regulatory system involved in adhesion, autolysis, and extracellular proteolytic activity of Staphylococcus aureus

A transposition mutant of Staphylococcus aureus was selected from the parent strain MT23142, a derivative of strain 8325. The site of transposition was near the 5' terminus of the gene arlS. ArlS exhibits strong similarities with histidine protein kinases. Sequence analysis suggested that arlS forms an operon with upstream gene arlR. The predicted product of arlR is a member of the OmpR-PhoB family of response regulators. The arlS mutant formed a biofilm on a polystyrene surface unlike the parent strain and the complemented mutant. Biofilm formation was associated with increased primary adherence to polystyrene, whereas cellular adhesion was only slightly decreased. In addition, the arlS mutant exhibited increased autolysis and altered peptidoglycan hydrolase activity compared to the parental strain and to the complemented mutant. As it has been shown for coagulase-negative staphylococci that some autolysins are able to bind polymer surfaces, these data suggest that the two-component regulatory system ArlS-ArlR may control attachment to polymer surfaces by affecting secreted peptidoglycan hydrolase activity. Finally, the arlS mutant showed a dramatic decrease of extracellular proteolytic activity, including serine protease activity, in comparison to the wild-type strain and the complemented mutant, and cells grown in the presence of phenylmethylsulfonyl fluoride (a serine protease inhibitor) showed an increased autolysin activity. Since the locus arlR-arlS strikingly modifies extracellular proteolytic activity, this locus might also be involved in the virulence of S. aureus.

Mode of action of fluoroquinolones

The mode of action of quinolones involves interactions with both DNA gyrase, the originally recognised drug target, and topoisomerase IV, a related type II topoisomerase. In a given bacterium these 2 enzymes often differ in their relative sensitivities to many quinolones, and commonly DNA gyrase is more sensitive in gram-negative bacteria and topoisomerase IV more sensitive in gram-positive bacteria. Usually the more sensitive enzyme represents the primary drug target determined by genetic tests, but poorly understood exceptions have been documented. The formation of the ternary complex of quinolone, DNA, and either DNA gyrase or topoisomerase IV occurs through interactions in which quinolone binding appears to induce changes in both DNA and the topoisomerase that occur separately from the DNA cleavage that is the hallmark of quinolone action. X-ray crystallographic studies of a fragment of the gyrase A subunit, as well as of yeast topoisomerase IV, which has homology to the subunits of both DNA gyrase and topoisomerase IV, have revealed domains that are likely to constitute quinolone binding sites, but no topoisomerase crystal structures that include DNA and quinolone have been reported to date. Inhibition of DNA synthesis by quinolones requires the targeted topoisomerase to have DNA cleavage capability, and collisions of the replication fork with reversible quinolone-DNA-topoisomerase complexes convert them to an irreversible form. However, the molecular factors that subsequently generate DNA double-strand breaks from the irreversible complexes and that probably initiate cell death have yet to be defined.

Quinolone resistance mutations in topoisomerase IV: relationship to the flqA locus and genetic evidence that topoisomerase IV is the primary target and DNA gyrase is the secondary target of fluoroquinolones in Staphylococcus aureus

Mutations in the flqA (formerly ofx/cfx) resistance locus of Staphylococcus aureus were previously shown to be common after first-step selections for resistance to ciprofloxacin and ofloxacin and to map on the S. aureus chromosome distinctly from gyrA, gyrB, and norA.grlA and grlB, the genes for the topoisomerase IV of S. aureus, were identified from a genomic lambda library on a common KpnI fragment, and grlB hybridized specifically with the chromosomal SmaI A fragment, which contains the flqA locus. Amplification of grlA sequences (codons 1 to 251) by PCRs from nine independent single-step flqA mutants, one multistep mutant, and the parent strain identified mutations encoding a change from Ser to Phe at position 80 in four mutants, a novel change from Ala to either Glu or Pro at position 116 in three mutants, and no change in three mutants. In the multistep mutant, another resistance locus, flqC, was mapped by transformation to the chromosomal SmaI G fragment by linkage to omega(ch::Tn551)1051 (58%) and nov (97.9%), which encodes resistance to novobiocin. This fragment contains the gyrA gene, and flqC mutants had a mutation in gyrA encoding a change from Ser to Leu at position 84, a change previously found in resistant clinical isolates. In genetic outcrosses, the flqC (gyrA) mutation expressed resistance only in flqA mutants, including those with both types of grla mutations. The silent mutant allele of gyrA was present in a flqA background and expressed resistance only upon introduction of a grlA mutation. At fourfold the MIC of ciprofloxacin, the bactericidal activity of ciprofloxacin was reduced in a grlA mutant and was abolished in gyrA grlA double mutants. These findings provide direct genetic evidence that topoisomerase IV is the primary target of current fluoroquinolones in S. aureus and that this effect may result from the greater sensitivity of topoisomerase IV relative to that of DNA gyrase to these agents. Furthermore, resistance from an altered DNA gyrase requires resistant topoisomerase IV for its expression.

Inosine to increase serum and cerebrospinal fluid urate in Parkinson disease: a randomized clinical trial

IMPORTANCE

Convergent biological, epidemiological, and clinical data identified urate elevation as a candidate strategy for slowing disability progression in Parkinson disease (PD).

OBJECTIVE

To determine the safety, tolerability, and urate-elevating capability of the urate precursor inosine in early PD and to assess its suitability and potential design features for a disease-modification trial.

DESIGN, SETTING, AND PARTICIPANTS

The Safety of Urate Elevation in PD (SURE-PD) study, a randomized, double-blind, placebo-controlled, dose-ranging trial of inosine, enrolled participants from 2009 to 2011 and followed them for up to 25 months at outpatient visits to 17 credentialed clinical study sites of the Parkinson Study Group across the United States. Seventy-five consenting adults (mean age, 62 years; 55% women) with early PD not yet requiring symptomatic treatment and a serum urate concentration less than 6 mg/dL (the approximate population median) were enrolled.

INTERVENTIONS

Participants were randomized to 1 of 3 treatment arms: placebo or inosine titrated to produce mild (6.1-7.0 mg/dL) or moderate (7.1-8.0 mg/dL) serum urate elevation using 500-mg capsules taken orally up to 2 capsules 3 times per day. They were followed for up to 24 months (median, 18 months) while receiving the study drug plus 1 washout month.

MAIN OUTCOMES AND MEASURES

The prespecified primary outcomes were absence of unacceptable serious adverse events (safety), continued treatment without adverse event requiring dose reduction (tolerability), and elevation of urate assessed serially in serum and once (at 3 months) in cerebrospinal fluid. RESULTS Serious adverse events (17), including infrequent cardiovascular events, occurred at the same or lower rates in the inosine groups relative to placebo. No participant developed gout and 3 receiving inosine developed symptomatic urolithiasis. Treatment was tolerated by 95% of participants at 6 months, and no participant withdrew because of an adverse event. Serum urate rose by 2.3 and 3.0 mg/dL in the 2 inosine groups (P < .001 for each) vs placebo, and cerebrospinal fluid urate level was greater in both inosine groups (P = .006 and <.001, respectively). Secondary analyses demonstrated nonfutility of inosine treatment for slowing disability.

CONCLUSIONS AND RELEVANCE

Inosine was generally safe, tolerable, and effective in raising serum and cerebrospinal fluid urate levels in early PD. The findings support advancing to more definitive development of inosine as a potential disease-modifying therapy for PD.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT00833690.

Genetic and biochemical characterization of norfloxacin resistance in Escherichia coli

In Escherichia coli the frequency of spontaneous single-step mutation to high levels of resistance to the newer 4-quinolone agent norfloxacin was confirmed to be over 300-fold lower than that to the older agent nalidixic acid. Serial passage on incremental concentrations of drug was necessary to produce mutants highly resistant to norfloxacin. Genetic analysis of one such highly resistant strain identified two mutations conferring drug resistance. One mutation, nfxA, mapped around 48 min on the E. coli genetic map and was shown to be an allele of gyrA by studies demonstrating an increased drug resistance of DNA gyrase reconstituted with the gyrase A subunit isolated from the mutant strain. These findings also identified the DNA gyrase A subunit as a target of norfloxacin. The second mutation, nfxB, mapped between 20 and 22 min was associated with additional resistances to tetracycline, chloramphenicol, and cefoxitin and with decreases in outer membrane porin protein OmpF. The nfxA and nfxB mutations together accounted for most, but not all, of the norfloxacin resistance phenotype of this strain.

Collaboration of antibody and inflammation in clearance of rabies virus from the central nervous system

To investigate the involvement of various cellular and humoral aspects of immunity in the clearance of rabies virus from the central nervous system, (CNS), we studied the development of clinical signs and virus clearance from the CNS in knockout mice lacking either B and T cells, CD8+ cytotoxic T cells, B cells, alpha/beta interferon (IFN-alpha/beta) receptors, IFN-gamma receptors, or complement components C3 and C4. Following intranasal infection with the attenuated rabies virus CVS-F3, normal adult mice of different genetic backgrounds developed a transient disease characterized by loss of body weight and appetite depression which peaked at 13 days postinfection (p.i.). While these animals had completely recovered by day 21 p.i., mice lacking either B and T cells or B cells alone developed a progressive disease and succumbed to infection. Mice lacking either CD8+ T cells, IFN receptors, or complement components C3 and C4 showed no significant differences in the development of clinical signs by comparison with intact counterparts having the same genetic background. However, while infectious virus and viral RNA could be detected in normal control mice only until day 8 p.i., in all of the gene knockout mice studied except those lacking C3 and C4, virus infection persisted through day 21 p.i. Analysis of rabies virus-specific antibody production together with histological assessment of brain inflammation in infected animals revealed that clearance of CVS-F3 by 21 days p.i. correlated with both a strong inflammatory response in the CNS early in the infection (day 8 p.i.), and the rapid (day 10 p.i.) production of significant levels of virus-neutralizing antibody (VNA). These studies confirm that rabies VNA is an absolute requirement for clearance of an established rabies virus infection. However, for the latter to occur in a timely fashion, collaboration between VNA and inflammatory mechanisms is necessary.

Expression in plants and immunogenicity of plant virus-based experimental rabies vaccine

A new approach to the production and delivery of vaccine antigens is the use of engineered amino virus-based vectors. A chimeric peptide containing antigenic determinants from rabies virus glycoprotein (G protein) (amino acids 253-275) and nucleoprotein (N protein) (amino acids 404-418) was PCR-amplified and cloned as a translational fusion product with the alfalfa mosaic virus (AlMV) coat protein (CP). This recombinant CP was expressed in two plant virus-based expression systems. The first one utilized transgenic Nicotiana tabacum cv. Samsun NN plants providing replicative functions in trans for full-length infectious RNA3 of AlMV (NF1-g24). The second one utilized Nicotiana benthamiana and spinach (Spinacia oleracea) plants using autonomously replicating tobacco mosaic virus (TMV) lacking native CP (Av/A4-g24). Recombinant virus containing the chimeric rabies virus epitope was isolated from infected transgenic N. tabacum cv. Samsun NN plants and used for parenteral immunization of mice. Mice immunized with recombinant virus were protected against challenge infection. Based on the previously demonstrated efficacy of this plant virus-based experimental rabies vaccine when orally administered to mice in virus-infected unprocessed raw spinach leaves, we assessed its efficacy in human volunteers. Three of five volunteers who had previously been immunized against rabies virus with a conventional vaccine specifically responded against the peptide antigen after ingesting spinach leaves infected with the recombinant virus. When rabies virus non-immune individuals were fed the same material, 5/9 demonstrated significant antibody responses to either rabies virus or AlMV. Following a single dose of conventional rabies virus vaccine, three of these individuals showed detectable levels of rabies virus-neutralizing antibodies, whereas none of five controls revealed these antibodies. These findings provide clear indication of the potential of the plant virus-based expression systems as supplementary oral booster for rabies vaccinations.

Characterization of a unique variant of bat rabies virus responsible for newly emerging human cases in North America

The silver-haired bat variant of rabies virus (SHBRV) has been identified as the etiological agent of a number of recent human rabies cases in the United States that are unusual in not having been associated with any known history of conventional exposure. Comparison of the different biological and biochemical properties of isolates of this virus with those of a coyote street rabies virus (COSRV) revealed that there are unique features associated with SHBRV. In vitro studies showed that, while the susceptibility of neuroblastoma cells to infection by both viruses was similar, the infectivity of SHBRV was much higher than that of COSRV in fibroblasts (BHK-21) and epithelial cells (MA-104), particularly when these cells were kept at 34 degrees C. At this temperature, low pH-dependent fusion and cell-to-cell spread of virus is seen in BHK-21 cells infected with SHBRV but not with COSRV. It appears that SHBRV may possess an unique cellular tropism and the ability to replicate at lower temperature, allowing a more effective local replication in the dermis. This hypothesis is supported by in vivo results which showed that while SHBRV is less neurovirulent than COSRV when administered via the intramuscular or intranasal routes, both viruses are equally neuroinvasive if injected intracranially or intradermally. Consistent with the above findings, the amino acid sequences of the glycoproteins of SHBRV and COSRV were found to have substantial differences, particularly in the region that contains the putative toxic loop, which are reflected in marked differences in their antigenic composition. Nevertheless, an experimental rabies vaccine based on the Pittman Moore vaccine strain protected mice equally well from lethal doses of SHBRV and COSRV, suggesting that currently used vaccines should be effective in the postexposure prophylaxis of rabies due to SHBRV.

Quinolone resistance mediated by norA: physiologic characterization and relationship to flqB, a quinolone resistance locus on the Staphylococcus aureus chromosome

We identified a quinolone resistance locus, flqB, linked to transposon insertion omega 1108 and fus on the SmaI D fragment of the Staphylococcus aureus NCTC 8325 chromosome, the same fragment that contains the norA gene. S. aureus norA cloned from flqB and flqB+ strains in Escherichia coli differed only in a single nucleotide in the putative promoter region. There was no detectable change in the number of copies of norA on the chromosomes of flqB strains, but they had increased levels of norA transcripts. Cloned norA produced resistance to norfloxacin and other hydrophilic quinolones and reduced norfloxacin accumulation in intact cells that was energy dependent, suggesting active drug efflux as the mechanism of resistance. Drug efflux was studied by measurement of norfloxacin uptake into everted inner membrane vesicles prepared from norA-containing E. coli cells. Vesicles exhibited norfloxacin uptake after the addition of lactate or NADH, and this uptake was abolished by carbonyl cyanide m-chlorophenylhydrazone and nigericin but not valinomycin, indicating that it was linked to the pH gradient across the cell membrane. Norfloxacin uptake into vesicles was also saturable, with an apparent Km of 6 microM, a concentration between those that inhibit the growth of flqB and flqB+ S. aureus cells, indicating that drug uptake is mediated by a carrier with a high apparent affinity for norfloxacin. Ciprofloxacin and ofloxacin competitively inhibited norfloxacin uptake into vesicles. Reserpine, which inhibits the multidrug efflux mediated by the bmr gene of bacillus subtilis, which is similar to norA, abolished norfloxacin uptake into vesicles as well as the norfloxacin resistance of an flqB mutant, suggesting a potential means for circumventing quinolone resistance as a result of drug efflux in S. aureus. These findings indicate that the chromosomal flqB resistance locus is associated with increased levels of expression of norA and strongly suggest that the NorA protein itself functions as a drug transporter that is coupled to the proton gradient across the cell membrane.

Glioma grade is associated with the accumulation and activity of cells bearing M2 monocyte markers

PURPOSE

This study is directed at identifying the cell source(s) of immunomodulatory cytokines in high-grade gliomas and establishing whether the analysis of associated markers has implications for tumor grading.

EXPERIMENTAL DESIGN

Glioma specimens classified as WHO grade II-IV by histopathology were assessed by gene expression analysis and immunohistochemistry to identify the cells producing interleukin (IL)-10, which was confirmed by flow cytometry and factor secretion in culture. Finally, principal component analysis (PCA) and mixture discriminant analysis (MDA) were used to investigate associations between expressed genes and glioma grade.

RESULTS

The principle source of glioma-associated IL-10 is a cell type that bears phenotype markers consistent with M2 monocytes but does not express all M2-associated genes. Measures of expression of the M2 cell markers CD14, CD68, CD163, and CD204, which are elevated in high-grade gliomas, and the neutrophil/myeloid-derived suppressor cell (MDSC) subset marker CD15, which is reduced, provide the best index of glioma grade.

CONCLUSIONS

Grade II and IV astrocytomas can be clearly differentiated on the basis of the expression of certain M2 markers in tumor tissues, whereas grade III astrocytomas exhibit a range of expression between the lower and higher grade specimens. The content of CD163(+) cells distinguishes grade III astrocytoma subsets with different prognosis.