A Type 1 Diabetes Genetic Risk Score Predicts Progression of Islet Autoimmunity and Development of Type 1 Diabetes in Individuals at Risk

OBJECTIVE

We tested the ability of a type 1 diabetes (T1D) genetic risk score (GRS) to predict progression of islet autoimmunity and T1D in at-risk individuals.

RESEARCH DESIGN AND METHODS

We studied the 1,244 TrialNet Pathway to Prevention study participants (T1D patients' relatives without diabetes and with one or more positive autoantibodies) who were genotyped with Illumina ImmunoChip (median [range] age at initial autoantibody determination 11.1 years [1.2-51.8], 48% male, 80.5% non-Hispanic white, median follow-up 5.4 years). Of 291 participants with a single positive autoantibody at screening, 157 converted to multiple autoantibody positivity and 55 developed diabetes. Of 953 participants with multiple positive autoantibodies at screening, 419 developed diabetes. We calculated the T1D GRS from 30 T1D-associated single nucleotide polymorphisms. We used multivariable Cox regression models, time-dependent receiver operating characteristic curves, and area under the curve (AUC) measures to evaluate prognostic utility of T1D GRS, age, sex, Diabetes Prevention Trial-Type 1 (DPT-1) Risk Score, positive autoantibody number or type, HLA DR3/DR4-DQ8 status, and race/ethnicity. We used recursive partitioning analyses to identify cut points in continuous variables.

RESULTS

Higher T1D GRS significantly increased the rate of progression to T1D adjusting for DPT-1 Risk Score, age, number of positive autoantibodies, sex, and ethnicity (hazard ratio [HR] 1.29 for a 0.05 increase, 95% CI 1.06-1.6; P = 0.011). Progression to T1D was best predicted by a combined model with GRS, number of positive autoantibodies, DPT-1 Risk Score, and age (7-year time-integrated AUC = 0.79, 5-year AUC = 0.73). Higher GRS was significantly associated with increased progression rate from single to multiple positive autoantibodies after adjusting for age, autoantibody type, ethnicity, and sex (HR 2.27 for GRS >0.295, 95% CI 1.47-3.51; P = 0.0002).

CONCLUSIONS

The T1D GRS independently predicts progression to T1D and improves prediction along T1D stages in autoantibody-positive relatives.

Selection and characterization of HIV-1 variants resistant to the (+) and (-) enantiomers of 2'-deoxy-3'-oxa-4'-thiocytidine (dOTC)

Human immunodeficiency virus type 1 (HIV-1) variants were selected for resistance against the (+) and (-) enantiomers of a novel nucleoside analogue, 2'-deoxy-3'-oxa-4'-thiocytidine (dOTC), using the infectious molecular clone HXB2D grown in the MT-4 line of human T cells. The variants selected with (+) dOTC were approximately 6-7-fold less sensitive than wild-type virus to this drug. Cloning and sequencing of the complete reverse transcriptase (RT) coding region of these variants identified the M1841 mutation and further selection with virus containing the M1841 substitution led to the appearance of an M184V mutation. In contrast, selection experiments performed with (-) dOTC yielded variants capable of growing in drug concentrations as high as 100 microM, but phenotypic analysis of these viruses revealed near wild-type 50% inhibitory concentration (IC50) values for this compound. Site-directed mutagenesis experiments in which the M1841 and M184V mutations were introduced into HXB2D confirmed the importance of these mutations when viruses were grown in MT4 cells. However, wild-type IC50 values in regard to both (-) and (+) dOTC were obtained when these recombinant viruses were grown in cord blood mononuclear cells (CBMC). Clinical isolates of HIV-1 resistant to lamivudine and containing the M184V substitution also displayed low-level resistance to both (-) and (+) dOTC when grown in CBMC. Finally, cell-free RT assays were performed in the presence of either (-) dOTC triphosphate, (+) dOTC triphosphate, or the triphosphate of a racemic mixture of (+) and (-) dOTC with wild-type and mutated M184V-containing recombinant RT. The data demonstrate chain termination effects of these compounds with regard to both wild-type and mutated enzyme and that the latter was approximately twofold less sensitive than the former to these drugs.

Drug resistance and drug combination features of the human immunodeficiency virus inhibitor, BCH-10652 [(+/-)-2'-deoxy-3'-oxa-4'-thiocytidine, dOTC]

The heterosubstituted nucleoside analogue dOTC [( )-2'-deoxy-3'-oxa-4'-thiocytidine, BCH-10652] is a racemic compound structurally related to 3TC (lamivudine), but has the oxygen and sulphur in the furanosyl ring transposed. Both the enantiomers (-)dOTC (BCH-10618) and (+)dOTC (BCH-10619) had equivalent activity against wild-type strains of HIV-1 in C8166 T-cells (EC50 1.0-10.0 microM) and in PBMCs (EC50 0.1-3.0 microM). Investigation of the activity of dOTC and its enantiomers against laboratory strains of HIV-1 with defined resistance to 3TC, AZT (zidovudine), ddl (didanosine), PMEA (adefovir), nevirapine and saquinavir indicated that sensitivity was maintained (<3-fold change in EC50) in all cases, with the exception of HIV-1RF 3TC-resistant viruses. The degree of resistance recorded for dOTC (four- to sevenfold), (-)dOTC (five- to eightfold) and (+)dOTC (five- to >18-fold) against these M1841 or M184V mutants, was significantly less than that recorded for 3TC (>100-fold). In addition, the inhibitory effect of the compounds against clinical isolates of HIV-1 recovered from patients with suspected resistance to 3TC and AZT was investigated. Clinical isolates were genotyped using the Murex Line Probe Assay (LiPA) and subgrouped into wild-type, 3TC-resistant and dual 3TC/AZT-resistant, as well as undefined or mixed genotype populations. Compared with the mean EC50 values obtained with genotypically and phenotypically wild-type clinical isolates, the mean EC50 values calculated for isolates phenotypically resistant to 3TC or 3TC and AZT were only 2.6-, 1.6- and 8.2-fold higher for dOTC, (-)dOTC and (+)dOTC, respectively. When the rate of emergence of virus resistant to dOTC and its enantiomers in vitro was investigated, virus resistant to (+)dOTC was readily selected for (<10 passages), and a methionine (ATG) to isoleucine (ATA) amino acid change at codon 184 was identified. In contrast, virus resistant to dOTC and (-)dOTC took longer to appear (15-20 passages), with a methionine (ATG) to valine (GTG) amino acid change at position 184 identified in both cases. In addition, virus passaged 20 times in the presence of dOTC also had a partial lysine (AAA) to arginine (AGA) exchange at position 65. These viruses showed only low-level resistance to dOTC and its enantiomers, but were highly resistant to 3TC. The antiviral effects of dOTC in combination with the nucleoside RT inhibitors AZT, 3TC, d4T (stavudine) and ddl, the non-nucleoside RT inhibitor nevirapine and the protease inhibitors saquinavir, ritonavir and indinavir was investigated. Two-way drug combination assays were carried out in peripheral blood mononuclear cell (PBMC) cultures by measuring the reduction in p24 viral antigen levels, and data was analysed using the MacSynergy II program. dOTC in combination with 3TC or d4T showed a moderate synergistic effect while all other combinations had an additive interaction.

A novel high throughput screening assay for HCV NS3 helicase activity

A novel assay for measurement of Hepatitis C virus (HCV) NS3 helicase activity was developed using Flashplate technology. This assay involves the use of a DNA duplex substrate and recombinant HCV NS3 produced in Escherichia coli. The DNA duplex consisted of a pair of oligonucleotides, one biotinylated, the other radiolabeled at their respective 5' termini. This DNA duplex was immobilized, via the biotin molecule, on the surface of a neutravidin-coated SMP103 Flashplate (NEN Life Science Products). Helicase activity results in the release of the radiolabeled oligonucleotide, which translates in signal reduction with respect to control wells. Biochemical characterization of the HCV NS3 helicase activity was performed using this assay. We demonstrated that the NS3-mediated unwinding is proportional to both the amount of DNA substrate in the well, and to the NS3 concentration in the reaction. Most of the NS3-mediated unwinding was achieved in the initial 60 min of incubation. As expected the reactions were ATP-dependent and found to be affected by the concentration of MgCl(2), MnCl(2), KCl, EDTA, and by pH. We found this assay to be highly reproducible since only slight variation was observed when a total of 68 helicase reactions were performed on one plate. Therefore, this Flashplate helicase assay is fast, convenient and reproducible. These criteria make it suitable for high throughput screening of potential NS3 helicase inhibitors.

Antiviral properties of a series of 1,6-naphthyridine and 7, 8-dihydroisoquinoline derivatives exhibiting potent activity against human cytomegalovirus

A series of 1,6-naphthyridine (L. Chan, H. Jin, T. Stefanac, J. F. Lavallee, G. Falardeau, W. Wang, J. Bedard, S. May, and L. Yuen, J. Med. Chem. 42:3023-3025, 1999) and isoquinoline (L. Chan, H. Jin, T. Stefanac, W. Wang, J. F. Lavallee, J. Bedard, and S. May, Bioorg. Med. Chem. Lett. 9:2583-2586, 1999) analogues exhibiting a high level of anti-human cytomegalovirus (HCMV) activity were investigated in a series of studies aimed at better understanding the mechanism of action of some representatives of this class of compounds. In vitro antiviral profiling revealed that these compounds were active against a narrow spectrum of viruses, essentially the human herpesviruses and type 2 rhinovirus. In HCMV assays, a 39- to 223-fold lower 50% inhibitory concentration was obtained for compound A1 than for ganciclovir against strains AD 169 and Towne. In addition, ganciclovir, foscarnet, cidofovir, and BDCRB (2-bromo-5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole)-resistant HCMV strains remained susceptible to 1,6-naphthyridines and 7, 8-dihydroisoquinolines tested in this study, supporting the view that a novel mechanism of action could be involved. Drug combination studies showed a small but significant synergistic antiviral effect between compound B2 and ganciclovir. Cytotoxicity profiling of representative compounds under various cell growth conditions indicated a generally similar cytotoxic effect, relative to ganciclovir, in log-phase growing cells. However, in stationary cells, a relatively higher level of toxicity was observed than that for control compound. Effect of time of drug addition showed that the anti-HCMV activity of compound A1, ganciclovir, and cidofovir was lost at approximately the same time (72 h postinfection), indicating that the compound was affecting events at the early and late stage of virus replication. This interpretation is also supported by reduction of de novo synthesis of pp65 tegument protein and lack of any effect of the compound on viral adsorption. A reduction of the HCMV enhancer-promoter-directed luciferase expression was also observed in a stably transfected cell line when compound A1 was present at relatively high concentrations.

Antiviral activity of 2'-deoxy-3'-oxa-4'-thiocytidine (BCH-10652) against lamivudine-resistant human immunodeficiency virus type 1 in SCID-hu Thy/Liv mice

Oral administration of 2'-deoxy-3'-oxa-4'-thiocytidine (BCH-10652), a nucleoside analog structurally similar to lamivudine (3TC), caused dose-dependent inhibition of viral replication in SCID-hu Thy/Liv mice infected with human immunodeficiency virus type 1 NL4-3 and with an NL4-3 clone containing the M184V mutation in reverse transcriptase that confers resistance to 3TC. These experiments demonstrate the utility of this mouse model for evaluating drug resistance and for performing direct comparisons between antiviral compounds in vivo.

Pyrido [1,2a] indole derivatives identified as novel non-nucleoside reverse transcriptase inhibitors of human immunodeficiency virus type 1

Pyrido [1,2a] indole derivatives were identified as potent inhibitors of human immunodeficiency virus type 1 (HIV-1) replication during a random screening programme. The compounds showed no antiviral activity against HIV-2 or in cells chronically infected with HIV-1, but had good inhibitory effect against purified HIV-1 reverse transcriptase (RT) in an in vitro assay. They were therefore classified as non-nucleoside RT inhibitors (NNRTI). The synthesis of additional compounds of the same class revealed a structure-activity relationship. The most potent compound of the series, BCH-1, had similar antiviral activity to the licensed NNRTI nevirapine against laboratory strains of HIV-1 cultured in cell lines and primary clinical isolates of HIV-1 cultured in peripheral blood mononuclear cells. However, BCH-1 showed greater cytotoxicity, providing a narrow selectivity index in the order of 35. BCH-1 had equivalent antiviral activity against viruses resistant to the nucleoside RT inhibitors zidovudine, didanosine and lamivudine and maintained better activity (less than threefold change in IC50) than nevirapine against viruses resistant to a range of NNRTIs with the single amino acid changes L100I, K103N, E138K or Y181C in the RT. Viruses with single V106A or Y188C amino acid changes showed five- and 10-fold resistance to BCH-1, respectively, in contrast to nevirapine, which had a > 100-fold change in IC50. However, virus with both V106A and Y188C amino acid changes showed higher level resistance (> 15-fold) to BCH-1. Virus with > 10-fold resistance to BCH-1 was rapidly selected for after growth in increasing concentrations of compound and was shown to be cross-resistant to nevirapine. Sequencing of this virus revealed two amino acid changes at positions 179 (V to D) and 181 (Y to C) in the RT. BCH-1 represents a new class of NNRTI, which may act as a lead to identify more selective compounds.

Comparative study of the anti-human cytomegalovirus activities and toxicities of a tetrahydrofuran phosphonate analogue of guanosine and cidofovir

Cidofovir is the first nucleoside monophosphate analogue currently being used for the treatment of human cytomegalovirus (HCMV) retinitis in individuals with AIDS. Unfortunately, the period of therapy with the use of this compound may be limited due to the possible emergence of serious irreversible nephrotoxic effects. New drugs with improved toxicity profiles are needed. The goal of this study was to investigate the anticytomegaloviral properties and drug-induced toxicity of a novel phosphonate analogue, namely, (-)-2-(R)-dihydroxyphosphinoyl-5-(S)-(guanin-9'-yl-methyl) tetrahydrofuran (compound 1), in comparison with those of cidofovir. The inhibitory activities of both compounds on HCMV propagation in vitro were similar against the AD 169 and Towne strains, with 50% inhibitory concentrations ranging from 0.02 to 0.17 microgram/ml for cidofovir and < 0.05 to 0.09 microgram/ml for compound 1. A clinical HCMV isolate that was resistant to ganciclovir and that had a known mutation within the UL54 DNA polymerase gene and a cidofovir-resistant laboratory strain derived from strain AD 169 remained sensitive to compound 1, whereas their susceptibilities to ganciclovir and cidofovir were reduced by 33- and 10-fold, respectively. Both compound 1 and cidofovir exhibited equal potencies in an experimentally induced murine cytomegalovirus (MCMV) infection in mice, with a prevention or prolongation of mean day to death at dosages of 1.0, 3.2, and 10.0 mg/kg of body weight/day. In cytotoxicity experiments, compound 1 was found to be generally more toxic than cidofovir in cell lines Hs68, HFF, and 3T3-L1 (which are permissive for HCMV or MCMV replication) but less toxic than cidofovir in MRC-5 cells (which are permissive for HCMV replication). Drug-induced toxic side effects were noticed for both compounds in rats and guinea pigs in a 5-day repeated-dose study. In guinea pigs, a greater weight loss was noticed with cidofovir than with compound 1 at dosages of 3.0 and 10.0 mg/kg/day. An opposite effect was detected in rats, which were treated with the compounds at relatively high dosages (up to 100 mg/kg/day). Compound 1 and cidofovir were nephrotoxic in both rats and guinea pigs, with the epithelium lining the proximal convoluted tubules in the renal cortex being the primary target site. The incidence and the severity of the lesions were found to be dose dependent. The lesions observed were characterized by cytoplasm degeneration and nuclear modifications such as karyomegaly, the presence of pseudoinclusions, apoptosis, and degenerative changes. In the guinea pig model, a greater incidence and severity of lesions were observed for cidofovir than for compound 1 (P < 0.001) with a drug regimen of 10 mg/kg/day.

A high throughput colorimetric cell proliferation assay for the identification of human cytomegalovirus inhibitors

A colorimetric assay based on the cleavage of the tetrazolium salt WST-1 has been developed for human cytomegalovirus (HCMV) antiviral susceptibility testing and adapted to a microtiter plate format. Optimal conditions were determined and the standard routine assay was calibrated with a viral input of 0.05-0.10 plaque forming unit (p.f.u.)/cell with a density of 2000 cells/well in a 96-well microtiter plate for an incubation period of 7 days. Ganciclovir (9-(2-hydroxy-1(hydroxymethyl) ethyoxymethyl) guanine; DHPG), and cidofovir ((S)-1-(3-hydroxy-2-phosphonylmethoxypropyl) cytosine; HPMPC) were used as positive control test compounds to validate the assay. The effective EC50 concentration values obtained with the two antiviral compounds in the present assay were in good agreement with plaque reduction assay results performed in parallel experiments. This method presents the advantage of being easy and rapid to perform, reliable, reproducible, and convenient for use in a high throughput screening capacity.

Preoperative physical therapy in primary total knee arthroplasty

In order to evaluate the efficacy of preoperative physical therapy for patients undergoing elective primary total knee arthroplasty, 10 patients completed 6 weeks of physical therapy before surgery (PT group). Ten patients served as controls (C group). Subjects were tested at baseline (PT only), before surgery, 6 weeks after surgery, and 3 months after surgery using the Hospital for Special Surgery knee rating scale, range of motion, thigh circumference, walking speed, Cybex II isokinetic knee flexion, and extension testing, and computed tomography scanning for cross-sectional muscle area. Hospital stay and need for physical therapy after inpatient rehabilitation were also compared. Physical therapy produced modest gains in isokinetic flexion strength in these severely arthritic knees but no difference in extension strength. The decrease in isokinetic strength after surgery was not affected by preoperative physical therapy. Muscle area did not decrease significantly for the PT group, but it did decrease for the C group after surgery. While postoperative strength differences could not be demonstrated, preoperative physical therapy preserved thigh muscle area after surgery. The clinical significance of this finding is uncertain. Consequently, this study failed to support the routine use of preoperative physical therapy in knee replacement surgery.

Design and synthesis of monocyclic beta-lactams as mechanism-based inhibitors of human cytomegalovirus protease

Mechanism based inhibitors of HCMV protease have been designed based on the monocyclic beta-lactam nucleus, which have been shown to acylate the viral enzyme in a time dependent manner. SAR in a series of monocyclic beta-lactam N-ureas, has defined the size and relative stereochemistry of the C-3 substituent producing a low micromolar inhibitor 17b with good aqueous stability and selectivity over the mammalian serine proteases.

Comparison of the short-term efficacy and tolerability of lovastatin and pravastatin in the management of primary hypercholesterolemia

Few data are available on the relative efficacy and tolerability of lovastatin and pravastatin, two 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors, currently available in North America for treatment of hypercholesterolemia. The recommended starting dose is 20 mg QD with the evening meal for lovastatin. The recommended starting dose is 10 mg or 20 mg once daily at bedtime for pravastatin. In a double blind, double placebo, multicenter, randomized study, we compared the changes in plasma lipids and apolipoproteins in 217 patients with primary hypercholesterolemia treated for eight weeks with lovastatin 20 mg QD to pravastatin 10 mg QD or pravastatin 20 mg QD. The reductions in total cholesterol (TC) (21%), low-density lipoprotein cholesterol (LDL-C) (28%), and apolipoprotein B (apo B) (22%) were comparable for the lovastatin 20-mg and pravastatin 20-mg groups. Lovastatin 20 mg QD was significantly more effective than pravastatin 10 mg QD in lowering TC and LDL-C after four weeks of therapy and in the reduction of apo B after four and eight weeks of therapy. At the end of eight weeks of therapy, the mean reductions in TC and LDL-C were numerically greater with lovastatin 20 mg QD compared with pravastatin 10 mg QD, but the differences were not statistically significant. At the end of eight weeks, there was no difference between pravastatin 20 mg and pravastatin 10 mg in lowering TC and LDL-C. The frequency of overall side effects, including central nervous system-related symptoms and headache, was similar and low in all groups.

Impermeability to quinolones in gram-positive and gram-negative bacteria

The initial step in the accumulation of fluoroquinolone antimicrobial agents is binding to cell surface components reduced by lowered pH and divalent cations. Uptake into gram-negative and gram-positive bacteria is by simple diffusion. Entry through the outer membrane occurs preferentially for most agents by the porin route but a second process using the self-promoted uptake pathway is active especially for more hydrophobic agents. Fluoroquinolones bind to vesicles of phospholipid which may be the initiating step in cross-cytoplasmic membrane diffusion. An active efflux system has been described in Escherichia coli with evidence supporting its presence in several other bacteria. Total upset is not altered by a resistant gyrase. Resistant isolates associated with reduced total quinolone accumulation due to lowered uptake have been described for laboratory mutants and clinical isolates. Most but not all of these have had alterations in outer membrane proteins. A functionally dominant resistance gene has been cloned from resistant Staphylococcus aureus and codes for a highly hydrophobic protein most likely membrane associated. This gene is expressed in Escherichia coli and specifies resistance especially to hydrophilic quinolones, possibly by altered accumulation.

Contribution of permeability and sensitivity to inhibition of DNA synthesis in determining susceptibilities of Escherichia coli, Pseudomonas aeruginosa, and Alcaligenes faecalis to ciprofloxacin

To examine the correlation between bacterial cell susceptibility to ciprofloxacin and the magnitude of uptake and cell target sensitivity, the relative contribution of ciprofloxacin accumulation in intact cells and its ability to inhibit DNA synthesis were investigated among strains of Escherichia coli, Pseudomonas aeruginosa, and Alcaligenes faecalis. Uptake studies of [14C]ciprofloxacin demonstrated diffusion kinetics for P. aeruginosa and E. coli. Ciprofloxacin was more readily removed from E. coli J53 and A. faecalis ATCC 19018 by washing than from P. aeruginosa PAO503. These results indicate that the process of cell accumulation is different for P. aeruginosa in that the drug is firmly bound at an extracellular site. Whatever the washing conditions, A. faecalis accumulated less drug than either of the other two bacteria. Magnesium chloride (10 mM) caused a substantial decrease of ciprofloxacin accumulated and an increase in the MIC, depending upon the nature of the medium. The addition of carbonyl cyanide m-chlorophenylhydrazone caused a variable increase in drug accumulated, depending on the medium and the bacterial strain. The concentration of ciprofloxacin required to obtain 50% inhibition (ID50) of DNA synthesis for P. aeruginosa PAO503 and A. faecalis ATCC 19018 did not correlate with their corresponding MICs but did for E. coli J53. Treatment with EDTA decreased the ID50 of ciprofloxacin for P. aeruginosa PAO503 and its gyrA derivative by 5- and 2-fold, respectively, and decreased the ID50 for E. coli JB5R, a strain with a known decrease in OmpF, by 1.4-fold but did not decrease the ID50 for the normally susceptible E. coli J53. The ID(50) for P. aeruginosa obtained after EDTA treatment or in ether-permeabilized cells was higher than that obtained for the other two strains. The protonophore carbonyl cyanide m-chlorophenylhydrazone prevented killing by low ciprofloxacin concentrtaions, but sodium azide did not. The latter compound did not enhance killing in association with inhibition of a previously described energy-dependent efflux of ciprofloxacin susceptibility being the susceptibility to inhibition of DNA synthesis in E. coli, poor premeability associated with the small pore size of A. faecalis, and a combination of low permeability and reduced susceptibility of DNA synthesis to inhibition for P. aeruginosa.

Interaction of the fluoroquinolone antimicrobial agents ciprofloxacin and enoxacin with liposomes

The interaction between ciprofloxacin and enoxacin and phospholipid-containing bilayers was examined as the initial step in transmembrane diffusion processes. By using cosedimentation, maximal association of liposomes and 14C-labeled enoxacin and ciprofloxacin was detected at acidic and neutral pHs. Aqueous solubility of ciprofloxacin, enoxacin, and norfloxacin was poorest at neutral pH and greater at alkaline or acidic pHs. These investigations suggest that the interaction occurs because of ionic and hydrophobic forces and is nonsaturable up to 20 micrograms/ml.

Quinolone antimicrobial agents: mechanism of action and resistance development

The primary target of fluoroquinolone antimicrobial agents is the A subunit of DNA gyrase. In several cases a close relationship to ID50 (inhibitory dose-50%) and minimum inhibitory concentration (MIC) has been shown for gram-negative bacteria, although this has not been regularly observed for gram-positive bacteria to date. Cellular entry is by means of diffusion and involves, at least in part, the porin pathway in the outer membrane of gram-negative bacteria. An energy dependent efflux occurs which is more active in brain heart infusion broth than nutrient broth and which, to date, has not been shown to contribute to inhibition of growth or bacterial lethality. The extent of uptake by different gram-negative bacteria varies and may contribute in some cases to determination of the MIC. Resistance to fluoroquinolones is by means of mutations affecting the gyrase gene coding for the A subunit and mutations which affect cell permeability particularly involving porin proteins of the outer membrane. Combined target and permeability resistance has been reported but involves two or more mutational steps. Resistance during clinical treatment has been observed, but is most likely to be of low magnitude and to be detected in patients with significantly compromised host defenses.

Accumulation of enoxacin by Escherichia coli and Bacillus subtilis

Several methods were used to determine enoxacin uptake in Escherichia coli strains because washing of cells removed all or most cell-associated enoxacin whereas no washing was associated with large amounts of cell-bound enoxacin. Washing after up to 40 to 45 min of exposure to enoxacin followed by suspension in drug-free medium prevented a significant effect of enoxacin on cell growth. Cell uptakes obtained with different methods showed no difference in the shape of the timed uptake curves but did show significant quantitative differences. These results are consistent with cell-associated enoxacin comprising a freely exchangeable pool of drug. Lineweaver-Burk plots of uptake were consistent with uptake of enoxacin by simple diffusion. No saturability and no competition with ciprofloxacin were observed. Low temperature (4 degrees C) was associated with decreased uptake. Arsenate, carbonyl cyanide m-chlorophenylhydrazone, sodium fluoride, sodium azide, and 2,4-dinitrophenol had no effect on uptake. We conclude that the mechanism of transport of enoxacin into cells is by simple diffusion. Mutants of E. coli with deficiency of outer membrane proteins F and C and an enoxacin-resistant mutant selected by serial passage with increasing enoxacin concentrations demonstrated that F porins play a significant role in enoxacin uptake and influence susceptibility to enoxacin. Uptake was shown to be similar in a strain of Bacillus subtilis.