In vitro and in vivo activity of LY 146032, a new cyclic lipopeptide antibiotic

The in vitro activity of LY 146032, a cyclic lipopeptide antibiotic belonging to the class of agents designated A21978C, was compared with those of vancomycin, cefpirome, cefotaxime, and clindamycin against selected gram-positive bacteria. The new drug inhibited all staphylococcal isolates, including methicillin-resistant strains, at concentrations of less than or equal to 1.0 microgram/ml. The activity of LY 146032 was comparable to that of vancomycin against most streptococci, but the latter demonstrated greater potency against Streptococcus faecium and penicillin-resistant strains of pneumococci and viridans group streptococci. LY 146032 was markedly less active than vancomycin against Listeria monocytogenes (MICs for 90% of strains tested, 16 and 1.0 microgram/ml, respectively). The activity of LY 146032 was enhanced as the concentration of calcium in the test medium was increased. MBCs were within eightfold of the MIC for each of 12 strains tested. In a rat model of enterococcal endocarditis, the administration of LY 146032 resulted in increased survival and a reduction in the bacterial titer within cardiac vegetations compared with untreated control animals.     

Antimicrobial activity and spectrum of LY146032, a lipopeptide antibiotic, including susceptibility testing recommendations.

LY146032, a new lipopeptide, was found to have a spectrum of gram-positive antimicrobial activity that includes activity against staphylococci (methicillin susceptible and resistant), beta-hemolytic Streptococcus spp., pneumococci, viridans group Streptococcus spp., anaerobic gram-positive cocci, Clostridium spp., and enterococci. The new lipopeptide was generally bactericidal and showed more rapid killing of Listeria spp. (MIC, 1 to 2 micrograms/ml) and staphylococci than either vancomycin or teicoplanin. The 30-micrograms disk was preferred to the 15-micrograms disk on the basis of the preliminary interpretive criteria for susceptibility which indicated zone diameters of greater than or equal to 16 mm for susceptible strains (MIC, less than or equal to 2.0 micrograms/ml) and greater than or equal to 12 mm for resistant strains (MIC, greater than or equal to 8.0 micrograms/ml). These criteria are valid pending the testing of additional gram-positive strains which have LY146032 MICs of greater than or equal to 8 micrograms/ml.     

In vitro activity of RP 59500, a semisynthetic injectable pristinamycin, against staphylococci, streptococci, and enterococci.

The in vitro activity of RP 59500, a semisynthetic pristinamycin, was compared with the activities of vancomycin, oxacillin, ampicillin, gentamicin, ciprofloxacin, and rifampin against five Staphylococcus species, five Streptococcus species, and four Enterococcus species. For staphylococci, MICs were 0.13 to 1 microgram/ml and the MICs for 90% of the strains tested (MIC90s) were 0.13 to 0.5 microgram/ml; there were no differences between oxacillin-susceptible and -resistant strains. For streptococci, MICs were 0.03 to 4 micrograms/ml and MIC90s were 0.25 to 2 micrograms/ml; viridans group streptococci were the least susceptible streptococci. For enterococci, MICs were 0.25 to 32 micrograms/ml and MIC90s were 2 to 4 micrograms/ml; Enterococcus faecalis was the least susceptible. Vancomycin was the only comparative drug with consistent activity against all species of gram-positive cocci. With RP 59500, raising the inoculum 100-fold, lowering the pH of cation-adjusted Mueller-Hinton broth to 5.5, or omitting cation supplementation had little effect on MICs, but 50% serum increased MICs 2 to 4 dilution steps. The differences between MBCs and MICs were greater for staphylococci and enterococci than for streptococci. Time-kill studies with 24 strains indicated that RP 59500 concentrations 2-, 4-, and 16-fold greater than the MICs usually killed bacteria of each species at similar rates; reductions in CFU per milliliter were less than those observed with oxacillin or vancomycin against staphylococci and less than those observed with ampicillin against enterococci. RP 59500 antagonized the bactericidal activities of oxacillin and gentamicin against Staphylococcus aureus ATCC 29213 and that of ampicillin against E. faecalis ATCC 29212. Against the latter, combination with gentamicin was indifferent. RP 59500 has a broad spectrum of in vitro activity against gram-positive cocci; combining it with other drugs is not advantageous.     

Comparative in-vitro activity of LY146032 a new peptolide, with vancomycin and eight other agents against gram-positive organisms

The in-vitro activity of LY146032, a new biosynthetic peptolide antibiotic, was compared with vancomycin and eight other antibiotics against 190 Gram-positive bacteria. Organisms tested included streptomycin-susceptible and resistant enterococci, nafcillin-susceptible and resistant Staphylococcus aureus, and nafcillin-susceptible and resistant Staph. epidermidis. LY146032 had excellent in-vitro inhibitory and bactericidal activity against nafcillin-susceptible and resistant staphylococci (MIC90 less than or equal to 0.5 mg/l) and against enterococci (MIC90 less than or equal to 2.0 mg/l). LY146032 was more active than vancomycin against the majority of isolated tested. With the exception of trimethoprim-sulphamethoxazole, LY146032 was the most active agent in vitro against enterococci, and was the most active against nafcillin-resistant staphylococci. LY146032 and vancomycin showed a marked increase in MIC when the inoculum was increased from 10(5) to 10(7) cfu/ml. LY146032 and vancomycin were bactericidal at concentrations within two dilutions of the MIC for staphylococci. LY146032 was bactericidal at less than or equal to 8 mg/l for all enterococcal isolates tested.     

In vitro activity of LY264826 compared to other glycopeptides and daptomycin.

LY264826 a new naturally occurring glycopeptide inhibited 90% of methicillin-susceptible and -resistant Staphylococcus aureus at 1 micrograms/ml. LY264826 had similar activity against methicillin-susceptible and -resistant coagulase-negative staphylococci. The LY264826 MIC90 for Streptococcus pyogenes was 0.25 microgram/ml, twofold more active than vancomycin and twofold less active than teicoplanin. LY264826 was eightfold more active than vancomycin and twofold more active than teicoplanin against enterococci. LY264826 inhibited Streptococcus pneumoniae at 0.25 microgram/ml and Listeria monocytogenes at 0.5 microgram/ml. Clostridium were inhibited by less than or equal to 0.25 microgram/ml of LY264826 and peptococci, peptostreptococci, and Fusobacterium were inhibited by less than 0.5 microgram/ml. Bacteroides species were LY284826 -resistant as were all Enterobacteriaceae, Flavobacterium, and Neisseria spp. Minimum bactericidal and inhibitory concentrations (MBCs and MICs) were within a dilution for S. aureus, S. pyogenes, and S. pneumoniae, but greater than or equal to 32-fold greater for enterococci.     

Antibacterial activities of cefpodoxime, cefixime, and ceftriaxone.

Cefpodoxime, cefixime, and ceftriaxone inhibited Branhamella catarrhalis at less than or equal to 1 microgram/ml, beta-hemolytic streptococci at less than or equal to 0.25 microgram/ml, Neisseria meningitidis at less than or equal to 0.06 microgram/ml, and Haemophilus influenzae (other than beta-lactamase-negative, ampicillin-resistant isolates) at less than or equal to 0.12 microgram/ml. The MICs for 50% of isolates of the family Enterobacteriaceae other than Citrobacter freundii, Enterobacter aerogenes, and Enterobacter cloacae were less than or equal to 1 microgram/ml for all three cephalosporins. The MICs of each cephalosporin for 90% of staphylococci, enterococci, and Pseudomonas aeruginosa isolates were greater than 16 micrograms/ml. Inoculum effects were noted with cefpodoxime and cefixime with beta-lactamase-positive H. influenzae.     

Activity of LY146032 compared with that of methicillin, cefazolin, cefamandole, cefuroxime, ciprofloxacin, and vancomycin against staphylococci as determined by kill-kinetic studies.

Kill-kinetic methods were used to provide data on the bactericidal activity of subinhibitory (0.5x MIC), inhibitory (1x MIC), and suprainhibitory (4x MIC) concentrations of LY146032 against methicillin-susceptible and -resistant Staphylococcus aureus and Staphylococcus epidermidis. These bactericidal activities were compared with those of methicillin, cefazolin, cefamandole, cefuroxime, ciprofloxacin, and vancomycin. LY146032 was among the most active of the antistaphylococcal agents tested, as determined by broth microdilution methods, with all strains being inhibited at concentrations of less than or equal to 1 microgram/ml. Time kill-kinetic studies demonstrated that at 4x MIC, LY146032 was rapidly bactericidal against all strains of staphylococci. Our data show that LY146032 has significant bactericidal activity against staphylococci in comparison with other antistaphylococcal agents. Further evaluation of LY146032 against serious staphylococcal infections is warranted.     

Antistaphylococcal activity of a cyclic peptide, LY146032, and vancomycin.

The inhibitory and bactericidal activities of a novel cyclic peptide antibiotic, LY146032, and vancomycin against oxacillin-susceptible and oxacillin-resistant staphylococci were compared. The MICs for 90% of strains were two- to fourfold higher for vancomycin than for LY146032. MBC/MIC ratios for all strains were less than or equal to 2. In killing rate studies with four strains of staphylococci, there was no detectable growth in the presence of 4X the MIC of either LY146032 or vancomycin after 24 h of incubation.     

In vitro activity of A-16686, a new glycopeptide

A-16686 is a novel glycopeptide antibiotic derived from Actinoplanes. A-16686 inhibited hemolytic streptococci groups A, B, C, F, and G at concentrations of less than or equal to 0.06 to 0.5 microgram/ml, with 90% inhibited by 0.5 microgram/ml, including erythromycin-resistant isolates. S. bovis, various viridans groups streptococci, S. mitis, S. mutans, and S. sanguis were inhibited by less than or equal to 1 microgram/ml, and MICs of S. faecalis and S. faecium were 0.5-2 micrograms/ml. Most staphylococci, including methicillin-resistant strains, were inhibited by 1 or 2 micrograms/ml. A-16686 was bactericidal with minimal difference between MIC and MBC for gram-positive species. A-16686 did not inhibit Enterobacteriaceae or Pseudomonas.     

In vitro antimicrobial activity of sparfloxacin (AT-4140, CI-978, PD 131501) compared with numerous other quinolone compounds

Sparfloxacin (AT-4140, CI-978, PD 131501) was tested against over 800 recent bacteremic strains and compared with ciprofloxacin and six other fluoroquinolones. The 90% minimum inhibitory concentration (MIC90) ranges for the Enterobacteriaceae species were (a) sparfloxacin, 0.03-1 microgram/ml and (b) ciprofloxacin, 0.015-0.25 microgram/ml. Moraxella catarrhalis, Haemophilus influenzae, and Neisseria gonorrhoeae were very susceptible to sparfloxacin (MIC90s, 0.004- less than or equal to 0.03 microgram/ml) and the other comparison drugs. Staphylococcus aureas and other staphylococci were generally susceptible to the tested fluoroquinolones but very susceptible to sparfloxacin and WIN 57273. All beta-hemolytic streptococci, enterococci, and pneumococci had sparfloxacin MICs of less than or equal to 1 microgram/ml. Sparfloxacin was quite active against anaerobic bacteria including Bacteroides fragilis gr. and Gram-positive strains (MIC90s, less than or equal to 2 micrograms/ml). The most resistant enteric bacilli were among Serratia marcescens and the Proteae, especially the Providencia spp. (two- to eightfold higher MICs). Pseudomonas aeruginosa strains were also susceptible to sparfloxacin (MIC90, 2 micrograms/ml). Magnesium ions, CO2 incubation, and low pH had some adverse effect on sparfloxacin MICs, and resistance development was documented among current clinical isolates of staphylococci, pseudomonas, and some enteric species.     

Comparative in vitro activity of DU-6859a, a new fluoroquinolone agent, against gram-positive cocci.

The in vitro activity of DU-6859a (DU), a new fluoroquinolone agent, was evaluated against 233 gram-positive cocci and was compared with those of ciprofloxacin, vancomycin, nafcillin, and ampicillin. The MICs of DU for 90% of the staphylococci tested were < or = 0.06 microgram/ml. All of the groups A and B and viridans group streptococci were inhibited by < or = 0.125 microgram of DU per ml, which was 32-fold more active than ciprofloxacin. On the basis of MICs for 90% of the strains tested, DU was 32- and 16-fold more active than ciprofloxacin against Enterococcus faecalis and Enterococcus faecium, respectively. The bactericidal activity of DU was demonstrated by time-kill techniques against all ciprofloxacin-susceptible enterococci. DU shows promise for the treatment of infections with gram-positive cocci and warrants further evaluation by in vitro and in vivo studies.     

The activity of metal compounds against aerobic and anaerobic bacteria.

We evaluated the antimicrobial activity of two metal compounds, JM-1397 (OsO2[xylyl]2) and JM-2469 (AuCl[S2CPEt3]). Both inhibited methicillin-susceptible and methicillin-resistant Staphylococcus aureus at concentrations of 0.5-2 micrograms/ml, with a minimum inhibitory concentration (MIC90) of 1 microgram/ml for JM-1397 and 0.5 microgram/ml for JM-2469. Similar concentrations inhibited methicillin-susceptible and -resistant coagulase-negative staphylococci (S. epidermidis, S. haemolyticus, and S. saprophyticus). JM-2469 inhibited group A, B, C, F, and G beta-hemolytic streptococci and viridans group streptococci at 1-8 micrograms/ml (MIC90 4 micrograms/ml) but Enterococcus faecalis and E. faecium had MICs of 8-16 micrograms/ml. JM-1397 had MICs for these organisms of greater than 64 micrograms/ml. Bacteroides fragilis, other Bacteroides, and Clostridium species were inhibited by less than or equal to 0.12-4 micrograms/ml (MIC90, 0.5 microgram/ml). MICs of both compounds for Enterobacteriaceae and Pseudomonas spp. were greater than 64 micrograms/ml. These studies show that osmium and gold compounds have potential as topical agents against Gram-positive and anaerobic species.     

In vitro activity of an orally administered cephalosporin, LY164846, against potentially pathogenic respiratory and dermal bacterial isolates.

The antibacterial activity of LY164846, a new orally administered semisynthetic cephalosporin, was compared with that of amoxicillin-clavulanic acid against 492 potentially pathogenic respiratory tract and dermal isolates. Against groups A, B, and G streptococci; pneumococci; staphylococci (other than methicillin resistant); Haemophilus influenzae; Branhamella catarrhalis; and meningococci, the MICs for 90% of strains tested of LY164846 and amoxicillin-clavulanic acid were less than or equal to 4 and less than or equal to 1 microgram/ml, respectively. LY164846 was equally active against beta-lactamase-positive and -negative strains of Haemophilus and Staphylococcus. MBC to MIC ratios of LY164846 versus H. influenzae were less than or equal to 2, while those with Staphylococcus aureus were more difficult to determine because of skipped tubes or paradoxic effects. There were minimal inoculum, pH, or serum effects on LY164846 activity against H. influenzae and S. aureus. In time-kill studies, LY164846 and amoxicillin-clavulanic acid at double MICs were 99.9 to 100% bactericidal to H. influenzae in 24 h; two times the MIC of LY164846 and four times the MIC of cephalexin were 99.9 to 100% bactericidal to S. aureus in 24 h. Based on error-rate-bounded analysis, the following interpretative guidelines for 30-micrograms LY164846 disk diffusion test diameters are suggested: greater than or equal to 19 mm, susceptible (MIC, less than or equal to 4 micrograms/ml); 16 to 18 mm, intermediate (MIC, greater than 4 but less than or equal to 8 micrograms/ml); less than or equal to 15 mm, resistant (MIC, greater than 8 micrograms/ml).     

In vitro activity of dirithromycin (LY 237216) compared with activities of other macrolide antibiotics.

Dirithromycin inhibited Streptococcus pyogenes, Streptococcus pneumoniae, and other hemolytic streptococci at concentrations of less than or equal to 0.03 to 0.12 micrograms/ml, with 90% inhibition at 0.12 micrograms/ml, which is comparable to results using erythromycin. Group A streptococci, listeriae, and enterococci resistant to erythromycin were resistant to dirithromycin. Erythromycin-susceptible staphylococci were inhibited by 0.5 micrograms/ml, but for erythromycin-resistant isolates MICs were greater than or equal to 8 micrograms/ml. For Haemophilus influenzae, MICs were greater than or equal to 8 micrograms/ml, two- to fourfold greater than for erythromycin. The activity of dirithromycin against staphylococci and streptococci was not decreased by the addition of human serum.     

In-vitro activity of LY 146032, a novel cyclic lipopeptide, alone and in combination with gentamicin or tobramycin against enterococci

The in-vitro activity of LY 146032, a novel cyclic lipopeptide and the effect of the combination of LY 146032 and gentamicin or tobramycin against 25 strains of enterococci isolated from blood cultures were studied. All strains of enterococci were inhibited by less than or equal to 2 mg/l LY 146032. The minimal inhibitory concentrations and minimal bactericidal concentrations were within one dilution. In the time-kill study, there was slow bactericidal activity. Complete killing of 10(7) cfu/ml of enterococci at 48 h by LY 146032 alone occurred with two strains. There was synergism between LY 146032 and gentamicin or tobramycin; complete killing at 24 h and 48 h occurred with many strains. No antagonism was demonstrated.     

Josamycin: interpretation of inhibition zones with the Bauer-Kirby agar disk diffusion test as compared with erythromycin

A total of 432 clinical isolates of Staphylococcus aureus (128), coagulase-negative staphylococci (123), group A and B beta-hemolytic streptococci (61), group D streptococci (30), Streptococcus penumoniae (29), Haemophilus influenzae (19), Haemophilus parainfluenzae (12), and Legionella pneumophila (30) were examined with the agar dilution and Bauer-Kirby agar disk diffusion tests for susceptibility to josamycin as compared with erythromycin. On a weight-for-weight basis, erythromycin was more active than josamycin against all bacterial species, including L. pneumophila. Josamycin inhibited 18 of 23 S. aureus and 11 of 16 coagulase-negative staphylococcal strains resistant to erythromycin. Utilizing minimal inhibitory concentrations (MIC) breakpoints of less than or equal to 2 micrograms/ml (sensitive), 4 microgram/ml (intermediate) and of greater than or equal to 8 micrograms/ml (resistant), and inhibition zone criteria of greater than or equal to 18 mm diameter (sensitive), 14-17 mm (intermediate), and less than or equal to 13 mm (resistant), and excluding L. pneumophila, there was good correlation between erythromycin MIC and corresponding disk diffusion data for staphylococci and streptococci, but not for Haemophilus species. In comparison, josamycin yielded a significant number of minor discrepant data for group D streptococci and Haemophilus species. It is suggested that erythromycin and josamycin should not be tested against Haemophilus species, and that josamycin should be excluded from test batteries against enterococci. Erythromycin-resistant staphylococci require separate testing with josamycin.     

In vitro activity of telavancin against gram-positive clinical isolates recently obtained in Europe

The in vitro activity of telavancin was tested against 620 gram-positive isolates. For staphylococci, MICs at which 50 and 90% of isolates were inhibited (MIC(50) and MIC(90)) were both 0.25 microg/ml, irrespective of methicillin resistance. MIC(50) and MIC(90) were 0.25 and 0.5 microg/ml for vancomycin-susceptible enterococci and 1 and 2 microg/ml for vancomycin-resistant enterococci, respectively. Streptococcus pneumoniae, group A and B beta-hemolytic streptococci, and viridans streptococci were inhibited by < or =0.12 microg/ml.     

Effect of calcium on in vitro activity of LY146032 against Clostridium difficile.

The in vitro MICs of LY146032 against 63 isolates of Clostridium difficile tested in Wilkins-Chalgren broth ranged from 0.5 to greater than 32 micrograms/ml, with MICs of 4 and 8 micrograms/ml for 50 and 90% of the isolates, respectively. However, when the test medium was supplemented with physiologic concentrations of calcium, the MIC for 90% of the isolates was reduced to less than or equal to 0.12 microgram/ml.     

An in vitro evaluation of HRE 664, a novel penem antibiotic

HRE 664 is a novel parenteral penem with a broad antimicrobial spectrum. In this study, HRE 664 inhibited 90% of Enterobacteriaceae at less than or equal to 2.0 micrograms/ml, Haemophilus influenzae and Neisseria gonorrhoeae at less than or equal to 0.5 microgram/ml, oxacillin-susceptible staphylococci at less than or equal to 0.13 microgram/ml, oxacillin-resistant staphylococci at less than or equal to 8.0 micrograms/ml, enterococci at less than or equal to 8.0 micrograms/ml, and streptococci at less than or equal to 0.13 microgram/ml. All strains of Pseudomonas aeruginosa were resistant (MICs were greater than 32 micrograms/ml). HRE 664 exhibited a minimal inoculum effect and good bactericidal activity with all organisms tested except an oxacillin-resistant Staphylococcus aureus. With the latter, there was a marked inoculum effect and no on-scale bactericidal endpoints. No measurable hydrolysis of HRE 664 occurred with any of the five Gram-negative bacterial beta-lactamases tested. When stored at -20 degrees C, HRE 664 showed no significant loss of activity for up to 6 wk, but detectable deterioration occurred thereafter. At -60 degrees C, no loss in HRE 664 potency was observed for up to 12 wk. Proposed HRE 664 MIC quality control parameters are: 0.03-0.13 microgram/ml for S. aureus ATCC 29213, 0.25-1.0 micrograms/ml for Escherichia coli 25922, and 2.0-8.0 micrograms/ml for Enterococcus faecalis ATCC 29212.     

Semisynthetic glycopeptide antibiotics derived from LY264826 active against vancomycin-resistant enterococci.

Certain derivatives of the glycopeptide antibiotic LY264826 with N-alkyl-linked substitutions on the epivancosamine sugar are active against glycopeptide-resistant enterococci. Six compounds representing our most active series were evaluated for activity against antibiotic-resistant, gram-positive pathogens. For Enterococcus faecium and E. faecalis resistant to both vancomycin and teicoplanin, the MICs of the six semisynthetic compounds for 90% of the strains tested were 1 to 4 micrograms/ml, compared with 2,048 micrograms/ml for vancomycin and 256 micrograms/ml for LY264826. For E. faecium and E. faecalis resistant to vancomycin but not teicoplanin, the MICs were 0.016 to 1 micrograms/ml, compared with 64 to 1,024 micrograms/ml for vancomycin. The compounds were highly active against vancomycin-susceptible enterococci and against E. gallinarum and E. casseliflavus and showed some activity against isolates of highly vancomycin-resistant leuconostocs and pediococci. The MICs for 90% of the strains of methicillin-resistant Staphylococcus aureus tested were typically 0.25 to 1 micrograms/ml, compared with 1 microgram/ml for vancomycin. Against methicillin-resistant S. epidermidis MICs ranged from 0.25 to 2 micrograms/ml, compared with 1 to 4 micrograms/ml for vancomycin and 4 to 16 micrograms/ml for teicoplanin. The spectrum of these new compounds included activity against teicoplanin-resistant, coagulase-negative staphylococci. The compounds exhibited exceptional potency against pathogenic streptococci, with MICs of < or = 0.008 microgram/ml against Streptococcus pneumoniae, including penicillin-resistant isolates. In in vivo studies with a mouse infection model, the median effective doses against a challenge by S. aureus, S. pneumoniae, or S. pyogenes were typically 4 to 20 times lower than those of vancomycin. Overall, these new glycopeptides, such as LY307599 and LY333328, show promise for use as agents against resistant enterococci, methicillin-resistant S. aureus, and penicillin-resistant pneumococci.