New quinolones and gram-positive bacteria

In vitro activity and rodent efficacy of clinafloxacin for bovine and swine respiratory disease

Clinafloxacin is a broad-spectrum fluoroquinolone that was originally developed and subsequently abandoned in the late 1990s as a human health antibiotic for respiratory diseases. The purpose of this study was to investigate the activity of clinafloxacin as a possible treatment for respiratory disease in cattle and pigs. Minimum inhibitory concentration (MIC) values were determined using Clinical and Laboratory Standards Institute recommended procedures with recent strains from the Zoetis culture collection. Rodent efficacy was determined in CD-1 mice infected systemically or intranasally with bovine Mannheimia haemolytica or Pasteurella multocida, or swine Actinobacillus pleuropneumoniae, and administered clinafloxacin for determination of ED₅₀ (efficacious dose-50%) values. The MIC₉₀ values for clinafloxacin against bovine P. multocida, M. haemolytica, Histophilus somni, and M. bovis were 0.125, 0.5, 0.125, and 1 μg/ml, respectively, and the MIC₉₀ values against swine P. multocida, A. pleuropneumoniae, S. suis, and M. hyopneumoniae were í0.03, í0.03, 0.125, and í0.008 μg/ml, respectively. Efficacy in mouse models showed average ED₅₀ values of 0.019 mg/kg/dose in the bovine M. haemolytica systemic infection model, 0.55 mg/kg in the bovine P. multocida intranasal lung challenge model, 0.08 mg/kg/dose in the bovine P. multocida systemic infection model, and 0.7 mg/kg/dose in the swine A. pleuropneumoniae systemic infection model. Clinafloxacin shows good in vitro activity and efficacy in mouse models and may be a novel treatment alternative for the treatment of respiratory disease in cattle and pigs.

The management of infection and colonization due to methicillin-resistant Staphylococcus aureus: A CIDS/CAMM position paper

Methicillin-resistant Staphylococcus aureus (MRSA) is being seen with greater frequency in most hospitals and other health care facilities across Canada. The organism may cause life-threatening infections and has been associated with institutional outbreaks. Several studies have confirmed that MRSA infection is associated with increased morbidity and mortality compared with infections caused by susceptible strains, even when the presence of comorbidities is accounted for. Treatment of MRSA infection is complicated by the fact that these organisms are resistant to multiple antimicrobial agents, so treatment options are limited. The effectiveness of decolonization therapy (attempting to eradicate MRSA carriage) is also uncertain. This paper reviews the medical management of MRSA infections, discusses the potential role of decolonization and provides an overview of evidence to support recommended infection control practices.

Synthesis and in vitro antibacterial activity of 7-(3-alkoxyimino-5-amino/methylaminopiperidin-1-yl)fluoroquinolone derivatives

We report herein the design and synthesis of novel 7-(3-alkoxyimino-5-amino/methylaminopiperidin-1-yl)fluoroquinolone derivatives based on the structures of new fluoroquinolones IMB and DZH. The antibacterial activity of these newly synthesized compounds was also evaluated and compared with gemifloxacin, ciprofloxacin, and levofloxacin. Results revealed that all of the target compounds 10-27 have good potency in inhibiting the growth of Staphylococcus aureus including MSSA (MIC: 0.125-8 μg/mL), Staphylococcus epidermidis including MRSE (MIC: 0.25-16 μg/mL), Streptococcus pneumoniae (MIC: 0.125-4 μg/mL), and Escherichia coli (MIC: 0.25-0.5 μg/mL). In particular, some compounds showed useful activity against several fluoroquinolone-resistant strains, and the most active compound 15 was found to be 16-128, 2-32, and 4-8-fold more potent than the three reference drugs against fluoroquinolone-resistant MSSA, MRSA, and MRSE.

Pharmacologic characteristics of prulifloxacin

Prulifloxacin, the prodrug of ulifloxacin, is a broad-spectrum oral fluoroquinolone antibacterial agent. After absorption, prulifloxacin is metabolized by esterases to ulifloxacin. The drug has a long elimination half-life, allowing once-daily administration. In vitro, ulifloxacin is generally more active than other fluoroquinolones against a variety of clinical isolates of Gram-negative bacteria, including community and nosocomial isolates of Escherichia coli, Klebsiella spp., Proteus, Providencia and Morganella spp., Moraxella catarrhalis, Haemophilus spp., and Pseudomonas aeruginosa. Gram-positive organisms, including methicillin- or oxacillin-susceptible Staphylococcus aureus, Enterococcus spp. and Streptococcus pneumoniae, are susceptible to ulifloxacin. In well-designed clinical trials, prulifloxacin showed good clinical and bacteriological efficacy (similar to that of ciprofloxacin) and was generally well tolerated, demonstrating a similar tolerability profile to that of ciprofloxacin. In conclusion, the in vitro inhibitory and bactericidal activities exhibited by ulifloxacin and the favorable characteristics shown by its prodrug (prulifloxacin) in clinical trials, particularly indicate this drug for the treatment of lung and urinary infections.

Susceptibility and resistance genes to fluoroquinolones in methicillin-resistant Staphylococcus aureus isolated in 2002

The activity of six fluoroquinolones (FQs) was determined against 100 methicillin-resistant Staphylococcus aureus (MRSA) isolated in 2002 along with mutations in the grlA and gyrA genes and in the norA promoter of these isolates. Of the isolates tested, 97% had mutations in grlA and gyrA. A single mutation in grlA and gyrA resulted in a decrease of susceptibility to old generation FQs (norfloxacin, enoxacin, ciprofloxacin, fleroxacin, sparfloxacin and levofloxacin) but not to new generation FQs (gatifloxacin and moxifloxacin). Double mutations of both grlA and gyrA resulted in high-level resistance to all FQs tested. All norA mutants (15%) contained double mutations in grlA and gyrA and showed no decrease of MIC in the presence of reserpine, which is known to inhibit the drug-efflux pump. Our results showed that double mutations in grlA and gyrA were necessary for the expression of high-level resistance to new generation FQs. As different FQ-resistant mutants occur in the same PFGE type, FQ-resistant MRSA may well develop individually.

Antimicrobial drug susceptibility of Staphylococcus intermedius clinical isolates from canine pyoderma

A total of 50 Staphylococcus intermedius strains isolated in France from canine pyodermas in 2002 were investigated for their susceptibility to various antimicrobial drugs. Antimicrobial susceptibility was assessed using a 2-fold serial dilution method in Mueller-Hinton agar, and the minimal inhibitory concentrations (MICs) were determined. About 62% of the 50 strains tested were producers of beta-lactamase and categorized as penicillin-resistant. About 26% demonstrated resistance to sulphonamides, 46% to oxytetracycline, 30% to chloramphenicol, 28% to streptomycin, kanamycin, neomycin or erythromycin, 22% to clindamycin, 6% to doxycycline, 2% to gentamicin, enrofloxacin, marbofloxacin or pradofloxacin. Acquired resistance was not observed to a clavulanic acid-amoxicillin combination, oxacillin, cephalosporins (cephalexin, ceftiofur and cefquinome), trimethoprim, a sulphamethoxazole-trimethoprim combination and florfenicol. About 42% were simultaneously resistant to three or more antimicrobial classes (multiresistance). All isolates with acquired resistance to erythromycin were also resistant to streptomycin and neomycin/kanamycin. About 22% of isolates exhibited cross-resistance between erythromycin and clindamycin and all clindamycin-resistant isolates also exhibited resistance to erythromycin. Resistance to penicillin, oxytetracycline and chloramphenicol was also positively associated with resistance to erythromycin and streptomycin.

Isolation of E. coli from foam and effects of fluoroquinolones on E. coli and foam production in male Japanese quail

Sexually active male Japanese quail (Coturnix coutrnix Japonica) produce a foamy substance from their cloacal gland. It was postulated that bacteria played an important role in production of foam. The primary objective of this study was to isolate and identify bacteria present in the cloacal foam. The secondary objective was to evaluate the effect of fluoroquinolone treatment on bacterial counts and foam production. Healthy adult Japanese quail were maintained in individual cages under uniform husbandry conditions and allocated arbitrarily into three groups (each group consisted of 12 male and 12 female birds). Foam was collected from the cloacal gland of male birds of each group separately into sterile petri dishes and was cultured to isolate and identify bacteria and to determine their sensitivity to various antibiotics. Escherichia coli bacteria, sensitive to various antibacterials (including the fluoroquinolones ciprofloxacin and pefloxacin), were isolated. In the second part of the study, male quails of Group I (control) received I mL vehicle (normal saline 0.9% (w/v) NaCl) daily (via the intraperitoneal route) for 12 days. Male birds from groups II and III were treated intraperitoneally with ciprofloxacin or pefloxacin at the rate of 10 mg and 12 mg per/kg body weight respectively, for 12 days. In antibiotic-treated birds, there was a gradual reduction in foam production during treatment. At the end of treatment, the cloacal gland area was smaller (P < 0.05) in pefloxacin-treated birds compared to the other groups. Furthermore, a trend towards decreasing body weight and fertilizing ability was noted in the same group. A drastic reduction in bacterial counts of foam was recorded only in fluoroquinolone-treated groups during treatment period. After cessation of treatment, all end points were increasing back to pre-treatment levels. In conclusion, E. coli were present in the foam of the cloacal gland of Japanese quail and may have a role in foam production.

Minimal inhibitory concentrations and time-kill determination of moxifloxacin against aerobic and anaerobic isolates

Moxifloxacin is a new oral 8-methoxy-quinolone with a wide spectrum of activity against Gram-negative and anaerobic bacteria, atypical micro-organisms and multi-resistant Gram-positive bacteria. This study was designed to assess the in vitro activity of moxifloxacin against Gram-positive bacteria with different resistance patterns, anaerobes and atypical micro-organisms such as Chlamydia and Mycoplasma. Moxifloxacin had good activity against Streptococcus pneumoniae with all strains inhibited by < or =0.12 mg/l. The minimal inhibitory concentrations (MICs) of moxifloxacin for Streptococcus pyogenes and Streptococcus agalactiae ranged from 0.03 to 0.5 mg/l while those of ciprofloxacin were about two- to four-fold higher (MICs=0.12-1 mg/l). Moxifloxacin was poorly active against enterococci but its activity against Clostridium and Bacteroides spp. was in the same range as that of metronidazole and superior to that of clindamycin. Moxifloxacin was substantially more active than both ciprofloxacin and sparfloxacin against Chlamydia.

Cleavable-complex formation by wild-type and quinolone-resistant Streptococcus pneumoniae type II topoisomerases mediated by gemifloxacin and other fluoroquinolones

Gemifloxacin is a recently developed fluoroquinolone with potent activity against Streptococcus pneumoniae. We show that the drug is more active than moxifloxacin, gatifloxacin, levofloxacin, and ciprofloxacin against S. pneumoniae strain 7785 (MICs, 0.03 to 0.06 microg/ml versus 0.25, 0.25, 1, and 1 to 2 microg/ml, respectively) and against isogenic quinolone-resistant gyrA-parC mutants (MICs, 0.5 to 1 microg/ml versus 2 to 4, 2 to 4, 16 to 32, and 64 microg/ml, respectively). Gemifloxacin was also the most potent agent against purified S. pneumoniae DNA gyrase and topoisomerase IV in both catalytic inhibition and DNA cleavage assays. The drug concentrations that inhibited DNA supercoiling or DNA decatenation by 50% (IC(50)s) were 5 to 10 and 2.5 to 5.0 microM, respectively. Ciprofloxacin and levofloxacin were some four- to eightfold less active against either enzyme; moxifloxacin and gatifloxacin showed intermediate activities. In assays of drug-mediated DNA cleavage by gyrase and topoisomerase IV, the same order of potency was seen: gemifloxacin > moxifloxacin > gatifloxacin > levofloxacin approximately ciprofloxacin. For gemifloxacin, the drug concentrations that caused 25% linearization of the input DNA by gyrase and topoisomerase IV were 2.5 and 0.1 to 0.3 microM, respectively; these values were 4-fold and 8- to 25-fold lower than those for moxifloxacin, respectively. Each drug induced DNA cleavage by gyrase at the same spectrum of sites but with different patterns of intensity. Finally, for enzymes reconstituted with quinolone-resistant GyrA S81F or ParC S79F subunits, although cleavable-complex formation was reduced by at least 8- to 16-fold for all the quinolones tested, gemifloxacin was the most effective; e.g., it was 4- to 16-fold more active than the other drugs against toposiomerase IV with the ParC S79F mutation. It appears that the greater potency of gemifloxacin against both wild-type and quinolone-resistant S. pneumoniae strains arises from enhanced stabilization of gyrase and topoisomerase IV complexes on DNA.

In vitro antibacterial activities of AF 3013, the active metabolite of prulifloxacin, against nosocomial and community Italian isolates

AF 3013, the active metabolite of prulifloxacin, was tested to determine its inhibitory and bactericidal activities against 396 nosocomial and 258 community Italian isolates. Compared with that of ciprofloxacin, its activity (assessed in MIC and minimal bactericidal concentration tests) was generally similar or greater against gram-positive bacteria and greater against gram-negative bacteria. In time-kill assays using selected isolates, its bactericidal activity was comparable to that of ciprofloxacin.

Synthesis and antibacterial activity of 2-substituted 6-fluoro-1,4-dihydro-4-oxo-3-quinolinecarboxylic acids

A series of 2-substituted 6-fluoro-1,4-dihydro-4-oxo-3-quinolinecarboxylic acids was prepared and evaluated for antibacterial activity. The 6-fluoro-2-methyl-1-prenyl-1,4-dihydro-7-(3,5-dimethylpiperazinyl)-4-oxo-3-quinolinecarboxylic acid (14f) exhibited the most potent antibacterial activity against gram-positive bacteria among the total 32 derivatives. The synthetic strategies involve the use of well known keto ester condensation of benzoyl chloride and reductive cyclization of intermediates (4a-d) to afford 4-hydroxy-1,2-dihydro-2-oxo-quinoline derivatives (5a,b) or 1-hydroxy-1,4-dihydro-4-oxo-quinoline derivatives (6a,b).

Antimicrobial activity of enrofloxacin against Staphylococcus intermedius strains isolated from canine pyodermas

This study examined and compared the minimal inhibition concentrations (MICs) of enrofloxacin against 393 Staphylococcus intermedius strains isolated in France from canine pyodermas during three different years, 1995 (174 isolates), 1997 (101 isolates) and 1999 (118 isolates). The MICs of enrofloxacin against these strains ranged from 0.063 to 64 mg L-1, with MIC50 and MIC90 equal to 0.125 and 0.25 mg L-1, respectively. Two resistant strains were found, but only among isolates collected in 1999. The data show that resistance to enrofloxacin among S. intermedius strains is still rare in dogs, but the selection in vitro of variants in which the MICs were increased 4-16-fold after 10 serial passages in subinhibitory concentrations of enrofloxacin suggests that inappropriate use might favour the development of resistant strains in vivo.

Vancomycin-resistant enterococci

After they were first identified in the mid-1980s, vancomycin-resistant enterococci (VRE) spread rapidly and became a major problem in many institutions both in Europe and the United States. Since VRE have intrinsic resistance to most of the commonly used antibiotics and the ability to acquire resistance to most of the current available antibiotics, either by mutation or by receipt of foreign genetic material, they have a selective advantage over other microorganisms in the intestinal flora and pose a major therapeutic challenge. The possibility of transfer of vancomycin resistance genes to other gram-positive organisms raises significant concerns about the emergence of vancomycin-resistant Staphylococcus aureus. We review VRE, including their history, mechanisms of resistance, epidemiology, control measures, and treatment.

Recurrent penicillin-resistant pneumococcal sepsis after matched unrelated donor (MUD) transplantation for refractory T cell lymphoma

Patients who undergo splenectomy and recipients of allogeneic marrow (alloBMT) or peripheral stem cell transplantation are at increased risk of overwhelming infection from encapsulated organisms such as Streptococcus pneumoniae, Haemophilus influenzae and Neisseria meningitidis. As prophylaxis against these pathogens splenectomised patients are immunised and may also receive antibiotics for life. We report relapsing overwhelming sepsis caused by penicillin-resistant pneumococcus in a patient who was immunised and received prophylactic phenoxymethylpenicillin for 8 months following splenectomy and matched unrelated donor (MUD) marrow transplantation for refractory T cell lymphoma. No obvious focus of sepsis was found during any of the three episodes and S. pneumoniae serogroup 6, subtype 6B was isolated from blood cultures on each occasion. He was treated with i.v. cephalosporins, as the organisms were resistant to penicillin with a minimum inhibitory concentration (MIC) of 2.0, and there was complete resolution of symptoms each time. In the light of recurrent sepsis with this penicillin-resistant organism the decision was made to give prophylactic levofloxacin for the next 12 months. This case illustrates that the choice of prophylactic regimen and the treatment of sepsis in immunocompromised patients remain difficult and challenging issues.

Potent antipneumococcal activity of gemifloxacin is associated with dual targeting of gyrase and topoisomerase IV, an in vivo target preference for gyrase, and enhanced stabilization of cleavable complexes in vitro

We investigated the roles of DNA gyrase and topoisomerase IV in determining the susceptibility of Streptococcus pneumoniae to gemifloxacin, a novel fluoroquinolone which is under development as an antipneumococcal drug. Gemifloxacin displayed potent activity against S. pneumoniae 7785 (MIC, 0.06 microgram/ml) compared with ciprofloxacin (MIC, 1 to 2 microgram/ml). Complementary genetic and biochemical approaches revealed the following. (i) The gemifloxacin MICs for isogenic 7785 mutants bearing either parC or gyrA quinolone resistance mutations were marginally higher than wild type at 0.12 to 0.25 microgram/ml, whereas the presence of both mutations increased the MIC to 0.5 to 1 microgram/ml. These data suggest that both gyrase and topoisomerase IV contribute significantly as gemifloxacin targets in vivo. (ii) Gemifloxacin selected first-step gyrA mutants of S. pneumoniae 7785 (gemifloxacin MICs, 0.25 microgram/ml) encoding Ser-81 to Phe or Tyr, or Glu-85 to Lys mutations. These mutants were cross resistant to sparfloxacin (which targets gyrase) but not to ciprofloxacin (which targets topoisomerase IV). Second-step mutants (gemifloxacin MICs, 1 microgram/ml) exhibited an alteration in parC resulting in changes of ParC hot spot Ser-79 to Phe or Tyr. Thus, gyrase appears to be the preferential in vivo target. (iii) Gemifloxacin was at least 10- to 20-fold more effective than ciprofloxacin in stabilizing a cleavable complex (the cytotoxic lesion) with either S. pneumoniae gyrase or topoisomerase IV enzyme in vitro. These data suggest that gemifloxacin is an enhanced affinity fluoroquinolone that acts against gyrase and topoisomerase IV in S. pneumoniae, with gyrase the preferred in vivo target. The marked potency of gemifloxacin against wild type and quinolone-resistant mutants may accrue from greater stabilization of cleavable complexes with the target enzymes.

Vancomycin-resistant enterococci

After they were first identified in the mid-1980s, vancomycin-resistant enterococci (VRE) spread rapidly and became a major problem in many institutions both in Europe and the United States. Since VRE have intrinsic resistance to most of the commonly used antibiotics and the ability to acquire resistance to most of the current available antibiotics, either by mutation or by receipt of foreign genetic material, they have a selective advantage over other microorganisms in the intestinal flora and pose a major therapeutic challenge. The possibility of transfer of vancomycin resistance genes to other gram-positive organisms raises significant concerns about the emergence of vancomycin-resistant Staphylococcus aureus. We review VRE, including their history, mechanisms of resistance, epidemiology, control measures, and treatment.

Comparative activities of telithromycin (HMR 3647), levofloxacin, and other antimicrobial agents against human mycoplasmas

The activities of telithromycin and levofloxacin against 99 mycoplasma strains were compared to those of several macrolides, ofloxacin, and doxycycline. Telithromycin MICs of </=0.25 microgram/ml were found for all isolates, except for Mycoplasma hominis, while levofloxacin was active at concentrations of </=1 microgram/ml against all species studied.

Comparison of gyrA and parC mutations and resistance levels among fluoroquinolone-resistant isolates and laboratory-derived mutants of oral streptococci

Laboratory-derived fluoroquinolone-resistant mutants were obtained by serial passage of Streptococcus sanguis and Streptococcus anginosus isolates on agar containing increasing concentrations of old and new fluoroquinolones, ofloxacin and DU-6859a, respectively. Sequencing of an S. sanguis isolate exposed to DU-6859a showed that resistance was associated with two mutations in the quinolone resistance determining region (QRDR) of the gyrA gene (Ser83-->Phe; Glu87-->Lys), and with a mutation in the parC gene (Ser79-->Ile). However, different mutations in the gyrA gene (Ser83-->Tyr) and parC gene (Ser79-->Phe) were found in a S. sanguis isolate exposed to ofloxacin. A fluoroquinolone-resistant isolate, QR-95101, from a dental infection, had a single mutation in the gyrA gene (Ser83-->Phe) and in the parC gene (Ser79-->Phe). Two fluoroquinolone-resistant mutants, QS-701OFm and QS-701DUm, were obtained from S. anginosus QS-701, by exposure to ofloxacin and DU-6859a, respectively. These mutants showed a common substitution at codon 83 (Ser-->Phe) in the gyrA gene but had different substitutions at codon 87 (QS-701OFm, Glu-->Gln; QS-701DUm, Glu-->Lys). They also had different substitutions at codons 79 and 135 in the parC gene (QS-701OFm, Ser79-->Leu but no change at Glu135; QS-701DUm, Ser79-->Ile and Glu135-->Gln). The resistance levels of the DU-6859a-selected resistant S. sanguis mutant QS-951DUm to DU-6859a, ofloxacin, ciprofloxacin and norfloxacin were higher than those of the ofloxacin-selected resistant mutant QS-951OFm. However, ampicillin susceptibilities of these mutants were not different from the parental strains. In S. anginosus, the DU-6859a-selected fluoroquinolone-resistant mutant QS-701DUm was resistant to all the fluoroquinolones tested, while the ofloxacin-selected mutant QS-701OFm was resistant to three fluoroquinolones, but not DU-6859a. The results indicate that different fluoroquinolones select distinct mutations in the QRDR of the gyrA and parC genes in oral streptococci. The gyrA or parC mutation in oral streptococci may determine the levels of fluoroquinolone resistance.

Engineering the specificity of antibacterial fluoroquinolones: benzenesulfonamide modifications at C-7 of ciprofloxacin change its primary target in Streptococcus pneumoniae from topoisomerase IV to gyrase

We have examined the antipneumococcal mechanisms of a series of novel fluoroquinolones that are identical to ciprofloxacin except for the addition of a benzenesulfonylamido group to the C-7 piperazinyl ring. A number of these derivatives displayed enhanced activity against Streptococcus pneumoniae strain 7785, including compound NSFQ-105, bearing a 4-(4-aminophenylsulfonyl)-1-piperazinyl group at C-7, which exhibited an MIC of 0.06 to 0.125 microg/ml compared with a ciprofloxacin MIC of 1 microg/ml. Several complementary approaches established that unlike the case for ciprofloxacin (which targets topoisomerase IV), the increased potency of NSFQ-105 was associated with a target preference for gyrase: (i) parC mutants of strain 7785 that were resistant to ciprofloxacin remained susceptible to NSFQ-105, whereas by contrast, mutants bearing a quinolone resistance mutation in gyrA were four- to eightfold more resistant to NSFQ-105 (MIC of 0.5 microg/ml) but susceptible to ciprofloxacin; (ii) NSFQ-105 selected first-step gyrA mutants (MICs of 0.5 microg/ml) encoding Ser-81-to-Phe or -Tyr mutations, whereas ciprofloxacin selects parC mutants; and (iii) NSFQ-105 was at least eightfold more effective than ciprofloxacin at inhibiting DNA supercoiling by S. pneumoniae gyrase in vitro but was fourfold less active against topoisomerase IV. These data show unequivocally that the C-7 substituent determines not only the potency but also the target preference of fluoroquinolones. The importance of the C-7 substituent in drug-enzyme contacts demonstrated here supports one key postulate of the Shen model of quinolone action.

Efficacy of levofloxacin in the treatment of experimental endocarditis caused by viridans group streptococci

Levofloxacin was investigated against viridans group streptococci in vitro and in rats with experimental aortic endocarditis. The MIC(90)s of levofloxacin and ciprofloxacin for 20 independent isolates of such bacteria were 1 and 8 mg/L, respectively. Rats were infected with two types of organism: either fully susceptible to levofloxacin MIC < or = 0.5 mg/L) or borderline susceptible (MIC 1-2 mg/L). Fully levofloxacin-susceptible bacteria comprised one penicillin-susceptible (MIC 0.004 mg/L) Streptococcus gordonii, and one penicillin-tolerant as well as one intermediate penicillin-resistant (MIC 0.125 mg/L) isogenic strains. Borderline levofloxacin-susceptible bacteria comprised one penicillin-susceptible Streptococcus sanguis and one highly penicillin-resistant Streptococcus mitis (MIC 2 mg/L). Rats were treated for 5 days with drug dosages simulating the following treatments in humans: (i) levofloxacin 500 mg orally once a day (q24 h), (ii) levofloxacin 500 mg orally twice a day (q12 h), (iii) levofloxacin 1 g orally q24 h, (iv) ciprofloxacin 750 mg orally q12 h, and (v) ceftriaxone 2 g iv q24 h. Levofloxacin was equivalent or superior to ceftriaxone, and was successful in treating experimental endocarditis irrespective of penicillin resistance. Nevertheless, standard levofloxacin treatment equivalent to 500 mg q24 h in human was less effective than twice daily 500 mg or once daily 1 g doses against borderline-susceptible organisms. Ciprofloxacin, used as a negative control, was ineffective and selected for resistant isolates. This underlines the importance of MIC determinations when treating severe streptococcal infection with quinolones. In the case of borderline-susceptible pathogens, total daily doses of 1 g of levofloxacin should be considered.

Activity of gemifloxacin against penicillin- and ciprofloxacin-resistant Streptococcus pneumoniae displaying topoisomerase- and efflux-mediated resistance mechanisms

Nine penicillin-resistant Streptococcus pneumoniae clinical isolates from Northern Ireland, resistant to ciprofloxacin (MICs, 2 to 64 microg/ml) through topoisomerase- and/or reserpine-sensitive efflux mechanisms, were highly susceptible to gemifloxacin (MICs, 0.03 to 0. 12 microg/ml). Two strains (requiring a ciprofloxacin MIC of 64 microg/ml) carried known quinolone resistance mutations in parC, parE, and gyrB, resulting in S79F, D435V, and E474K changes, respectively. Thus, gemifloxacin is active against clinical strains exhibiting altered topoisomerase and efflux phenotypes.

Biochemical and molecular characterization of erthromycin-resistant avian Staphylococcus spp. isolated from chickens

The epidemiology of the two common erythromycin-resistant methylase (erm) genes ermC and ermA was analyzed in 12 coagulase-negative Staphylococcus spp. and 34 coagulase-positive Staphylococcus spp. isolated from chicken. Southern hybridization indicated that only 2 of the 12 coagulase-negative Staphylococcus spp. strains contained the ermC gene on the plasmid; 1 strain of Staphylococcus xylosus harbored the ermC gene on a 2.5-kb plasmid, and 1 strain of Staphylococcus cohnii harbored the gene on a 4.0-kb plasmid. Twelve of the 34 strains of Staphylococcus aureus contained the ermC gene. Eleven of these strains had the ermC gene on a 2.5-kb plasmid, and 1 strain had the gene on a 4.0-kb plasmid. Ten of the 12 coagulase-negative Staphylococcus spp. and 22 of the 34 coagulase-positive Staphylococcus spp. harbored the ermA gene exclusively on the chromosome. Two different ermA EcoRI restriction fragment length polymorphisms (RFLP) were identified. A majority of the isolates was found to have two chromosomal inserts (8.0- and 6.2-kb EcoRI fragments) of ermA. One strain of S. aureus had different chromosomal inserts (6.4- and 5.8-kb EcoRI fragments) of ermA. Our results indicate that either the ermC or ermA gene, homologous to those described in human isolates, was present in all avian Staphylococcus spp. and that ermA was the predominant gene in coagulase-negative and coagulase-positive avian Staphylococcus spp. The size and copy numbers of the ermA gene were different from its human counterpart.

In vitro development of resistance to five quinolones and amoxicillin-clavulanate in Streptococcus pneumoniae

The ability of 50 sequential subcultures in subinhibitory concentrations of ciprofloxacin, levofloxacin, grepafloxacin, sparfloxacin, trovafloxacin, and amoxicillin-clavulanate to select for resistance was studied for six penicillin-susceptible and four penicillin-intermediate pneumococci. Subculturing in ciprofloxacin, grepafloxacin, levofloxacin, and sparfloxacin led to selection of mutants requiring increased MICs for all 10 strains, with MICs rising from (i) 0.5 to 4.0 to (ii) 4.0 to 32.0 microgram/ml after 7 to 12 passages for ciprofloxacin, from (i) 0.06 to 0.25 to (ii) 0.5 to 8.0 microgram/ml after 5 to 23 passages for grepafloxacin, from (i) 0.5 to 1.0 to (ii) 4.0 to 64 microgram/ml after 14 to 49 passages for levofloxacin, and from (i) 0.125 to 0.25 to (ii) 1.0 to 16.0 microgram/ml after 8 to 26 passages for sparfloxacin. Subculturing in trovafloxacin led to increased MICs for eight strains, with MICs rising from (i) 0.06 to 0.125 to (ii) 0.5 to 8.0 microgram/ml after 6 to 28 passages. Subculturing in amoxicillin-clavulanate led to raised MICs for only one strain, with the MIC rising from 0.015 to 0. 125 microgram/ml after 24 passages. Double mutations in both ParC and GyrA led to high-level quinolone resistance when ParC mutations were at S79. Trovafloxacin MICs were 1 to 2 microgram/ml in double mutants with ParC mutations at positions other than S79 (e.g., D83). Mutations in ParE (at D435, R447, and E474) and GyrB (at S405, D406, and D435) were found in four and six mutants, respectively. In the presence of reserpine, 29 mutants had lower ciprofloxacin MICs (2 to 16 times lower), 8 mutants had lower levofloxacin MICs (2 times), and one mutant had a lower trovafloxacin MIC (2 times), suggesting the involvement of an efflux mechanism. In contrast to the case for quinolones, subculturing in the presence of amoxicillin-clavulanate did not select for resistance to this drug.

Streptococcus pneumoniae DNA gyrase and topoisomerase IV: overexpression, purification, and differential inhibition by fluoroquinolones

Streptococcus pneumoniae gyrA and gyrB genes specifying the DNA gyrase subunits have been cloned into pET plasmid vectors under the control of an inducible T7 promoter and have been separately expressed in Escherichia coli. Soluble 97-kDa GyrA and 72-kDa GyrB proteins bearing polyhistidine tags at their respective C-terminal and N-terminal ends were purified to apparent homogeneity by one-step nickel chelate column chromatography and were free of host E. coli topoisomerase activity. Equimolar amounts of the gyrase subunits reconstituted ATP-dependent DNA supercoiling with comparable activity to gyrase of E. coli and Staphylococcus aureus. In parallel, S. pneumoniae topoisomerase IV ParC and ParE subunits were similarly expressed in E. coli, purified to near homogeneity as 93- and 73-kDa proteins, and shown to generate efficient ATP-dependent DNA relaxation and DNA decatenation activities. Using the purified enzymes, we examined the inhibitory effects of three paradigm fluoroquinolones-ciprofloxacin, sparfloxacin, and clinafloxacin-which previous genetic studies with S. pneumoniae suggested act preferentially through topoisomerase IV, through gyrase, and through both enzymes, respectively. Surprisingly, all three quinolones were more active in inhibiting purified topoisomerase IV than gyrase, with clinafloxacin showing the greatest inhibitory potency. Moreover, the tested agents were at least 25-fold more effective in stabilizing a cleavable complex (the relevant cytotoxic lesion) with topoisomerase IV than with gyrase, with clinafloxacin some 10- to 32-fold more potent against either enzyme, in line with its superior activity against S. pneumoniae. The uniform target preference of the three fluoroquinolones for topoisomerase IV in vitro is in apparent contrast to the genetic data. We interpret these results in terms of a model for bacterial killing by quinolones in which cellular factors can modulate the effects of target affinity to determine the cytotoxic pathway.

Efficacy of trovafloxacin in treatment of experimental staphylococcal or streptococcal endocarditis

The efficacy of trovafloxacin against Staphylococcus aureus and viridans group streptococci was investigated in vitro and in an experimental model of endocarditis. The MICs at which trovafloxacin and ciprofloxacin inhibited 90% of clinical isolates of such bacteria (MIC90s) were (i) 0.03 and 2 mg/liter, respectively, for 30 ciprofloxacin-susceptible S. aureus isolates, (ii) 32 and 128 mg/liter, respectively, for 20 ciprofloxacin-resistant S. aureus isolates, and (iii) 0.25 and 8 mg/liter, respectively, for 28 viridans group streptococci. Rats with aortic vegetations were infected with either of two ciprofloxacin-susceptible but methicillin-resistant S. aureus strains (strains COL and P8), one penicillin-susceptible Streptococcus sanguis strain, or one penicillin-resistant Streptococcus mitis strain. Rats were treated for 3 or 5 days with doses that resulted in kinetics that simulated those achieved in humans with trovafloxacin (200 mg orally once a day), ciprofloxacin (750 mg orally twice a day), vancomycin (1 g intravenously twice a day), or ceftriaxone (2 g intravenously once a day). Against the staphylococci, the activities of both trovafloxacin and ciprofloxacin were equivalent to that of vancomycin, and treatment of endocarditis with these drugs was successful (P < 0.05). However, ciprofloxacin selected for resistant derivatives in vitro and in vivo, whereas trovafloxacin was 10 to 100 times less prone than ciprofloxacin to select for resistance in vitro and did not select for resistance in vivo. Against the two streptococcal isolates, trovafloxacin significantly (P < 0.05) decreased bacterial counts in the vegetations but was less effective than the control drug, ceftriaxone. Thus, a simulated oral dose of trovafloxacin (200 mg per day) was effective against ciprofloxacin-susceptible staphylococci and was less likely than ciprofloxacin to select for resistance. The simulated oral dose of trovafloxacin also had some activity against streptococcal endocarditis, but optimal treatment of infections caused by such organisms might require higher doses of the drug.

Comparative efficacy of trovafloxacin in experimental endocarditis caused by ciprofloxacin-sensitive, methicillin-resistant Staphylococcus aureus

The new fluoroquinolone trovafloxacin was tested against a ciprofloxacin-sensitive, methicillin-resistant Staphylococcus aureus strain in the rabbit model of endocarditis. Trovafloxacin was more effective than vancomycin (CFU/g of vegetation, 2.65 +/- 1.87 versus 4.54 +/- 2.80 [mean +/- standard deviation]; P < 0.05) or ampicillin-sulbactam plus rifampin (4.9 +/- 1.1 CFU/g). The addition of ampicillin-sulbactam to trovafloxacin tended to reduce titers further.

Antibiotic resistance in oral/respiratory bacteria

In the last 20 years, changes in world technology have occurred which have allowed for the rapid transport of people, food, and goods. Unfortunately, antibiotic residues and antibiotic-resistant bacteria have been transported as well. Over the past 20 years, the rise in antibiotic-resistant gene carriage in virtually every species of bacteria, not just oral/respiratory bacteria, has been documented. In this review, the main mechanisms of resistance to the important antibiotics used for treatment of disease caused by oral/respiratory bacteria--including beta-lactams, tetracycline, and metronidazole--are discussed in detail. Mechanisms of resistance for macrolides, lincosamides, streptogramins, trimethoprim, sulfonamides, aminoglycosides, and chloramphenicol are also discussed, along with the possible role that mercury resistance may play in the bacterial ecology.

In vitro susceptibility of recent gram-positive isolates to ciprofloxacin, levofloxacin, and trovafloxacin

Gram-positive isolates (n = 290) were tested for their susceptibility to three fluoroquinolone antibiotics by standard disk-diffusion technology. Overall, 59%, 72%, and 85% were susceptible and 29%, 25%, and 11% were resistant to ciprofloxacin, levofloxacin, and trovafloxacin, respectively. Of Staphylococcus aureus isolates (n = 84), 55%, 57%, and 88% were susceptible to the three antibiotics, respectively. Staphylococcus epidermidis (n = 45), too, was more susceptible to trovafloxacin, although the differences were smaller (60%, 62%, and 78%). Of 35 Enterococcus faecalis isolates, 66% and 74% were susceptible to levofloxacin and trovafloxacin, respectively, but only 9% were susceptible to ciprofloxacin.

Resistance issues and treatment implications: pneumococcus, Staphylococcus aureus, and gram-negative rods

During the last decade there has been an unexpectedly rapid evolution of antimicrobial resistance in the respiratory pathogens for community- and hospital-acquired pneumonia. In order to choose the most optimal therapy for their patients, it is essential that physicians be aware of the prevalence and mechanisms of resistance and their implications on the effectiveness of the various antimicrobials.

Successful treatment of murine listeriosis and salmonellosis with levofloxacin

Levofloxacin (L-ofloxacin) is a fluoroquinolone derivative. It is the active substance contained in ofloxacin with a broad spectrum of antibacterial activity against both Gram-negative and Gram-positive bacteria. In this work we examined the activity of levofloxacin against the facultative intracellular bacteria Listeria monocytogenes and Salmonella typhimurium in vitro, in tissue culture and in animal models of infection. The minimum inhibitory concentrations (MICs) MIC90 for Salmonella enterica and L. monocytogenes were 0.078 mg/l and 4 mg/l, respectively. Levofloxacin was bactericidal against L. monocytogenes and S. typhimurium because 8 x MIC killed 90% of the initial inoculum of L. monocytogenes EGD and S. typhimurium LT2 within 4 hours and 3 hours, respectively. Levofloxacin was more effective than ampicillin against L. monocytogenes EGD infecting tissue culture cells. Also in tissue culture cells infected with S. typhimurium LT2, levofloxacin was slightly more effective than ciprofloxacin. In animal models of infection, levofloxacin was as potent as the reference substances. In conclusion, levofloxacin is a candidate for the treatment of infections caused by facultative intracellular Gram-positive and Gram-negative bacteria.

Y-688, a new quinolone active against quinolone-resistant Staphylococcus aureus: lack of in vivo efficacy in experimental endocarditis

Y-688 is a new fluoroquinolone with increased activity against ciprofloxacin-resistant staphylococci. The MICs of Y-688 and other quinolones were determined for 58 isolates of ciprofloxacin-resistant and methicillin-resistant Staphylococcus aureus (MRSA). The MICs at which 50% and 90% of bacteria were inhibited were >/=128 and >/=128 mg/liter, respectively, for ciprofloxacin, 16 and 32 mg/liter, respectively, for sparfloxacin, and 0.25 and 1 mg/liter, respectively, for Y-688. This new quinolone was further tested in rats with experimental endocarditis due to either of two isolates of ciprofloxacin-resistant MRSA (namely, P8/128 and CR1). Infected animals were treated for 3 days with ciprofloxacin, vancomycin, or Y-688. Antibiotics were administered through a computerized pump to simulate human-like pharmacokinetics in the serum of rats. The anticipated peak and trough levels of Y-688 were 4 and 1 mg/liter at 0.5 and 12 h, respectively. Treatment with ciprofloxacin was ineffective. Vancomycin significantly decreased vegetation bacterial counts for both organisms (P less, similar 0.05). In contrast, Y-688 only marginally decreased vegetation bacterial counts (P greater, similar 0.05). Moreover, several vegetation that failed Y-688 treatment grew staphylococci for which the MICs of the test antibiotic were increased two to eight times. Y-688 also selected for resistance in vitro, and isolates for which the MICs were increased eight times emerged at a frequency of ca. 10(-8). Thus, in spite of its low MIC for ciprofloxacin-resistant MRSA, Y-688 failed in vivo and its use carried the risk of resistance selection. The fact that ciprofloxacin-resistant staphylococci became rapidly resistant to this potent new drug suggests that the treatment of ciprofloxacin-resistant MRSA with new quinolones might be more problematic than expected.

Accumulation of norfloxacin by Mycobacterium aurum and Mycobacterium smegmatis

The modified fluorescence method was used to determine the accumulation of norfloxacin by Mycobacterium aurum A+ and Mycobacterium smegmatis mc(2)155. By using an exogenous norfloxacin concentration of 10 microg/ml, a steady-state concentration (SSC) of 160 to 180 ng of norfloxacin/mg of cells was obtained for M. aurum, and an SSC of 120 to 140 ng of norfloxacin/mg of cells obtained for M. smegmatis. For both species of mycobacteria, the SSC was achieved within 5 min. The silicon oil method was investigated and gave higher SSCs than the modified fluorescence method. Further studies on the mechanism of norfloxacin accumulation by M. aurum were performed. An increase in the pH of the wash buffer from 7.0 to 9.0 did not significantly affect the final SSC obtained. Accumulation was nonsaturated over a norfloxacin concentration range of 0 to 100 microg/ml, and the proton motive force inhibitor 2,4-dinitrophenol (1 and 2 mM), whether it was added before or after norfloxacin was added, had no effect on the final SSC obtained. 2,4-Dinitrophenol also had no effect on norfloxacin accumulation by M. smegmatis. Furthermore, norfloxacin accumulation by M. aurum was unaffected by the presence of either Tween 80 or subinhibitory concentrations of ethambutol in the growth medium. Therefore, it is proposed that norfloxacin accumulation by mycobacteria occurs by simple, energy-independent diffusion.

Methyloxime-substituted aminopyrrolidine: a new surrogate for 7-basic group of quinolone

Novel fluoroquinolones containing oxime functionalized aminopyrrolidines have been synthesized. They were found to possess potent antibacterial activities against both Gram-negative and Gram-positive organisms, including methicillin resistant Staphylococcus aureus (MRSA). Among these compounds, LB20277 (compound 12) showed the most favorable in vivo efficacy and pharmacokinetic profile in animals. Based on these promising results, LB20277 was selected as a candidate for further evaluation.

In vitro extracellular and intracellular activity of two newer and two earlier fluoroquinolones against Listeria monocytogenes

Two new fluoroquinolones (trovafloxacin and sparfloxacin) with enhanced activity against gram-positive pathogens and two earlier compounds (ciprofloxacin and ofloxacin) were tested for their in vitro inhibitory and bactericidal activity against 80 strains of Listeria monocytogenes. All strains were uniformly highly susceptible to trovafloxacin, the MIC90 being 0.25 mg/l. Resistance to sparfloxacin was not detected, however the MIC90 of sparfloxacin was eight times that of trovafloxacin. A few strains were resistant to ciprofloxacin and ofloxacin (MIC90 4 mg/l for both drugs). MBCs usually exceeded MICs by 2 to 4 times. The MBC90 of trovafloxacin (1 mg/l) was lower than that of the other three drugs (8 mg/l). After checking their ability to enter and grow within human enterocyte-like Caco-2 cells, four strains were used to study the intracellular activity and eradicating power of the four quinolones. Trovafloxacin was more active than sparfloxacin and the earlier fluoroquinolones in terms of both intracellular killing and inhibition of a cytopathogenic effect. The uniform high-level activity of trovafloxacin against Listeria monocytogenes isolates in conventional in vitro assays and its extracellular and intracellular killing of invasive strains suggest that this and maybe other new fluoroquinolones should be further investigated as possible anti-listerial agents.

In vitro and in vivo antibacterial efficacies of CFC-222, a new fluoroquinolone

CFC-222 is a novel fluoroquinolone containing a C-7 bicyclic amine moiety with potent antibacterial activities against gram-positive, gram-negative, and anaerobic organisms. We compared the in vitro and in vivo activities of CFC-222 with those of ciprofloxacin, ofloxacin, and lomefloxacin. CFC-222 was more active than the other fluoroquinolones tested against gram-positive bacteria. CFC-222 was particularly active against Streptococcus pneumoniae (MIC at which 90% of isolates are inhibited [MIC90], 0.2 microg/ml), Staphylococcus aureus (MIC90, 0.2 microg/ml for ciprofloxacin-susceptible strains), and Enterococcus faecalis (MIC90, 0.39 microg/ml). Against Escherichia coli and other members of the family Enterobacteriaceae, CFC-222 was slightly less active than ciprofloxacin (MIC90s for E. coli, 0.1 and 0.025 microg/ml, respectively). The in vitro activity of CFC-222 was not influenced by inoculum size, medium composition, or the presence of horse serum. However, its activity was decreased significantly by a change in the pH of the medium from 7.0 to 6.0, as was the case for the other quinolones tested. The in vivo protective efficacy of CFC-222 by oral administration was greater than those of the other quinolones tested in a mouse model of intraperitoneally inoculated systemic infection caused by S. aureus. CFC-222 exhibited efficacy comparable to that of ciprofloxacin in the same model of infection caused by gram-negative organisms, such as E. coli and Klebsiella pneumoniae. In this infection model, CFC-222 was slightly less active than ciprofloxacin against Pseudomonas aeruginosa. These results suggest that CFC-222 may be a promising therapeutic agent in various bacterial infections.

Levofloxacin versus ciprofloxacin, flucloxacillin, or vancomycin for treatment of experimental endocarditis due to methicillin-susceptible or -resistant Staphylococcus aureus

Levofloxacin is the L isomer of ofloxacin, a racemic mixture in which the L stereochemical form carries the antimicrobial activity. Levofloxacin is more active than former quinolones against gram-positive bacteria, making it potentially useful against such pathogens. In this study, levofloxacin was compared to ciprofloxacin, flucloxacillin, and vancomycin for the treatment of experimental endocarditis due to two methicillin-susceptible Staphylococcus aureus (MSSA) and two methicillin-resistant S. aureus (MRSA) isolates. The four test organisms were susceptible to ciprofloxacin, the levofloxacin MICs for the organisms were low (0.12 to 0.25 mg/liter), and the organisms were killed in vitro by drug concentrations simulating both the peak and trough levels achieved in human serum (5 and 0.5 mg/liter, respectively) during levofloxacin therapy. Rats with aortic endocarditis were treated for 3 days. Antibiotics were injected with a programmable pump to simulate the kinetics of either levofloxacin (350 mg orally once a day), ciprofloxacin (750 mg orally twice a day), flucloxacillin (2 g intravenously four times a day), or vancomycin (1 g intravenously twice a day). Levofloxacin tended to be superior to ciprofloxacin in therapeutic experiments (P = 0.08). More importantly, levofloxacin did not select for resistance in the animals, in contrast to ciprofloxacin. The lower propensity of levofloxacin than ciprofloxacin to select for quinolone resistance was also clearly demonstrated in vitro. Finally, the effectiveness of this simulation of oral levofloxacin therapy was at least equivalent to that of standard treatment for MSSA or MRSA endocarditis with either flucloxacillin or vancomycin. This is noteworthy, because oral antibiotics are not expected to succeed in the treatment of severe staphylococcal infections. These good results obtained with animals suggest that levofloxacin might deserve consideration for further study in the treatment of infections due to ciprofloxacin-susceptible staphylococci in humans.

In vitro activity of BAY 12-8039, a novel 8-methoxyquinolone, compared to activities of six fluoroquinolones against Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis

The in vitro activity of a novel 8-methoxyquinolone, BAY 12-8039, against recent clinical isolates of Streptococcus pneumoniae (n = 404), Haemophilus influenzae (n = 330), and Moraxella catarrhalis (n = 250) was evaluated. Activity was compared to those of six other fluoroquinolones: ciprofloxacin, clinafloxacin, levofloxacin, ofloxacin, sparfloxacin and trovafloxacin. BAY 12-8039 and clinafloxacin had the highest levels of activity against S. pneumoniae, both with a MIC at which 90% of the isolates were inhibited (MIC90) of 0.06 microg/ml. Trovafloxacin and sparfloxacin were the next most active agents versus S. pneumoniae (MIC90s = 0.12 microg/ml). No differences in activity against penicillin-susceptible, -intermediate, or -resistant strains of S. pneumoniae were noted for any of the fluoroquinolones tested. MIC90s for the seven fluoroquinolones ranged from 0.008 to 0.06 microg/ml versus H. influenzae and from 0.008 to 0.12 microg/ml for M. catarrhalis. The MICs for two strains of S. pneumoniae and one strain of H. influenzae were noted to be higher than those for the general population of organisms for all of the fluoroquinolones tested. Finally, the activity of BAY 12-8039 versus S. pneumoniae was found to be diminished when MIC determinations were performed with incubation of agar dilution plates or broth microdilution trays in 5 to 7% CO2 versus ambient air.

Targeting of DNA gyrase in Streptococcus pneumoniae by sparfloxacin: selective targeting of gyrase or topoisomerase IV by quinolones

gyrA and parC mutations have been identified inn Streptococcus pneumoniae mutants stepwise selected for resistance to sparfloxacin, an antipneumococcal fluoroquinolone. GyrA mutations (at the position equivalent to resistance hot spot Ser-83 in Escherichia coli GyrA) were found in all 17 first-step mutants examined and preceded DNA topoisomerase IV parC mutations (at Ser-79 or Glu-83), which appeared only in second-step mutants. The targeting of gyrase by sparfloxacin in S. pneumoniae but of topoisomerase IV by ciprofloxacin indicates that target preference can be altered by changes in quinolone structure.

Comparative study of pharmacokinetics of two new fluoroquinolones, balofloxacin and grepafloxacin, in elderly subjects

Comparative pharmacokinetics and tolerability were studied in healthy elderly volunteers for two new fluoroquinolones, balofloxacin (Q-35) and grepafloxacin (OPC-17116), the main excretion routes being the renal and hepatic routes, respectively. Both agents were well tolerated in elderly subjects. In comparison with previously reported data from healthy younger adults, the absorption of balofloxacin was slightly delayed and urinary excretion was delayed and diminished. As a significant linear correlation was observed between renal clearance of balofloxacin and creatinine clearance, the delayed and diminished urinary recovery was attributed to the reduced renal function of the elderly subjects enrolled in the study. The absorption of grepafloxacin was also delayed, and the maximum plasma drug concentration and area under the plasma drug concentration-time curve were increased in the elderly by 31 and 48%, respectively, over those in younger adults on the basis of dose normalized to body weight. The plasma terminal elimination half-life and urinary recovery remained unchanged. Decreases in distribution volume and total body clearance in the elderly were considered to be the primary factors contributing to these differences.

Involvement of topoisomerase IV and DNA gyrase as ciprofloxacin targets in Streptococcus pneumoniae

Ciprofloxacin-resistant mutants of Streptococcus pneumoniae 7785 were generated by stepwise selection at increasing drug concentrations. Sequence analysis of PCR products from the strains was used to examine the quinolone resistance-determining regions of the GyrA and GyrB proteins of DNA gyrase and the analogous regions of the ParC and ParE subunits of DNA topoisomerase IV. First-step mutants exhibiting low-level resistance had no detectable changes in their topoisomerase quinolone resistance-determining regions, suggesting altered permeation or another novel resistance mechanism. Nine of 10 second-step mutants exhibited an alteration in ParC at Ser-79 to Tyr or Phe or at Ala-84 to Thr. Third- and fourth-step mutants displaying high-level ciprofloxacin resistance were found to have, in addition to the ParC alteration, a change in GyrA at residues equivalent to Escherichia coli GyrA resistance hot spots Ser-83 and Asp-87 or in GyrB at Asp-435 to Asn, equivalent to E. coli Asp-426, part of a highly conserved EGDSA motif in GyrB. No ParE changes were observed. Complementary analysis of two S. pneumoniae clinical isolates displaying low-level resistance to ciprofloxacin revealed a ParC change at Ser-79 to Phe or Arg-95 to Cys but no changes in GyrA, GyrB, or ParE. A highly resistant isolate, in addition to a ParC mutation, had a GyrA alteration at the residue equivalent to E. coli Asp-87. Thus, in both laboratory strains and clinical isolates, ParC mutations preceded those in GyrA, suggesting that topoisomerase IV is a primary topoisomerase target and gyrase is a secondary target for ciprofloxacin in S. pneumoniae.