E Huczko

In Vitro and In Vivo Activities of a Novel Cephalosporin, BMS-247243, against Methicillin-Resistant and -Susceptible Staphylococci

ABSTRACT The recent emergence of methicillin-resistant Staphylococcus aureus (MRSA) with decreased susceptibility to vancomycin has intensified the search for alternative therapies for the treatment of infections caused by this organism. One approach has been to identify a β-lactam with improved affinity for PBP 2a, the target enzyme responsible for methicillin resistance in staphylococci. BMS-247243 is such a candidate, with MICs that inhibit 90% of isolates tested (MIC90s) of 4, 2, and 8 μg/ml for methicillin-resistant strains of S. aureus, S. epidermidis, and S. haemolyticus, respectively, as determined on plates with Mueller-Hinton agar and 2% NaCl. The BMS-247243 MICs for MRSA were minimally affected by the susceptibility testing conditions (inoculum size, prolonged incubation, addition of salt to the test medium) or by staphylococcal β-lactamases. BMS-247243 MIC90s for methicillin-susceptible staphylococcal species ranged from ≤0.25 to 1 μg/ml. The BMS-247243 MIC90 for β-lactamase-producing S. aureus strains was fourfold higher than that for β-lactamase-nonproducing strains. BMS-247243 is hydrolyzed by staphylococccal β-lactamases at 4.5 to 26.2% of the rates measured for cephaloridine. The affinity of BMS-247243 for PBP 2a was >100-fold better than that of methicillin or cefotaxime. BMS-247243 is bactericidal for MRSA, killing the bacteria twice as fast as vancomycin. These in vitro activities of BMS-247243 correlated with its in vivo efficacy against infections in animals, including the neutropenic murine thigh and rabbit endocarditis models involving MRSA strains. In conclusion, BMS-247243 has in vitro and in vivo activities against methicillin-resistant staphylococci and thus may prove to be useful in the treatment of infections caused by these multidrug-resistant organisms.

In vitro antifungal and fungicidal spectra of a new pradimicin derivative, BMS-181184.

A new pradimicin derivative, BMS-181184, was compared with amphotericin B and fluconazole against 249 strains from 35 fungal species to determine its antifungal spectrum. Antifungal testing was performed by the broth macrodilution reference method recommended by the National Committee for Clinical Laboratory Standards (document M27-P, 1992). BMS-181184 MICs for 97% of the 167 strains of Candida spp., Cryptococcus neoformans, Torulopsis glabrata, and Rhodotorula spp. tested were < or = 8 micrograms/ml, with a majority of MICs being 2 to 8 micrograms/ml. Similarly, for Aspergillus fumigatus and 89% of the 26 dermatophytes tested BMS-181184 MICs were < or = 8 micrograms/ml. BMS-181184 was fungicidal for the yeasts, dermatophytes, and most strains of A. fumigatus, although the reduction in cell counts was less for A. fumigatus than for the yeasts. BMS-181184 was active against Sporothrix schenckii, dematiaceous fungi, and some members of the non-Aspergillus hyaline hyphomycetes. BMS-181184, however, was not fungicidal against members of the family Dematiaceae. BMS-181184 lacked activity or had poorer activity (MICs, > or = 16 micrograms/ml) against Aspergillus niger, Aspergillus flavus, Malassezia furfur, Fusarium spp., Pseudallescheria boydii, Alternaria spp., Curvularia spp., Exserohilum mcginnisii, and the zygomycetes than against yeasts. The activity of BMS-181184 was minimally (twofold or less) affected by changes in testing conditions (pH, inoculum size, temperature, the presence of serum), testing methods (agar versus broth macrodilution), or test media (RPMI 1640, yeast morphology agar, high resolution test medium). Overall, our results indicate that BMS-181184 has a broad antifungal spectrum and that it is fungicidal to yeasts and, to a lesser extent, to filamentous fungi.

Antibacterial activities of cefprozil compared with those of 13 oral cephems and 3 macrolides.

Thirteen oral cephems (cefprozil, loracarbef, cefaclor, cefuroxime axetil, cefpodoxime proxetil, cefetamet pivoxil, cefixime, cefdinir, cefadroxil, cephradine, cephalexin, cefatrizine, and cefroxadine), the cephalosporin class representative cephalothin, cefazolin, and the macrolides erythromycin, clarithromycin, and azithromycin were compared for their antibacterial activities against 790 recent clinical isolates. These oral agents differed in their spectra and antibacterial potencies against community-acquired pathogens.

Frequency of in vitro resistance of Pseudomonas aeruginosa to cefepime, ceftazidime, and cefotaxime.

The selection frequencies of cefepime (BMY 28142), ceftazidime, and cefotaxime resistance among Pseudomonas aeruginosa strains were determined. Cefepime-resistant mutants were not selected by cefepime (frequency, less than 10(-11)). Ceftazidime- and cefotaxime-resistant mutants were isolated at frequencies of 10(-5) to 10(-10) and were often cross-resistant. However, cefepime resistance among ceftazidime- and cefotaxime-resistant mutants was rare. Selected mutants resistant to cefepime constitutively produced 40- to 450-fold more beta-lactamase than did the parent strain.

Susceptibility of bacterial isolates to gatifloxacin and ciprofloxacin from clinical trials 1997–1998

MICs of gatifloxacin and ciprofloxacin against 3482 pre-treatment, clinical trial isolates collected during 1997-1998 are reported. These data suggested that gatifloxacin was four- to eight-fold more active than ciprofloxacin against Gram-positive bacteria, with gatifloxacin MIC(90)s < or = 0.33 mg/l against Staphylococcus aureus and Streptococcus pneumoniae, and < or = 1.0 mg/l versus viridans streptococci and Enterococcus faecalis. Both quinolones had similar MIC(90)s versus Enterobacteriaceae (generally < or = 0.38 mg/l, except 0. 7-0.8 mg/l for Citrobacter freundii) and Pseudomonas aeruginosa ( approximately 8 mg/l). A total of 78% P. aeruginosa had gatifloxacin MICs < or = 2 mg/l. Gatifloxacin was more active than ciprofloxacin against Acinetobacter species and non-P. aeruginosa pseudomonads. Both had exceptional activity versus Haemophilus spp, Moraxella catarrhalis and Neisseria gonorrhoeae. In summary, compared to ciprofloxacin, gatifloxacin had improved activity against Gram-positive bacteria and comparable activity against Gram-negative bacteria.

Activity of gatifloxacin against strains resistant to ofloxacin and ciprofloxacin and its ability to select for less susceptible bacterial variants

Gatifloxacin is an 8-methoxy fluoroquinolone. On quinolones, this side chain imparts increased activity against Gram-positive bacteria and enhanced killing. Gatifloxacin was tested against ofloxacin non-susceptible (ofloxacin MIC>2 mg/l) strains of Streptococcus pneumoniae (gatifloxacin MIC(90), 1 mg/l) and methicillin-resistant Staphylococcus aureus (MRSA, gatifloxacin MIC(90), 4 mg/l), and to ciprofloxacin non-susceptible (ciprofloxacin MIC>1 mg/l) strains of Escherichia coli (gatifloxacin MIC(90),>16 mg/l) and ciprofloxacin non-susceptible (ciprofloxacin MIC>0.06 mg/l) Neisseria gonorrhoeae (gatifloxacin MIC(50), 0.12 mg/l and MIC(90), 0.5 mg/l). Though gatifloxacin showed some reduced susceptibility to these populations, the MIC(50) and MIC(90) values suggest that gatifloxacin may be useful against pneumococci and some gonococcal strains not susceptible to other fluoroquinolones. Gatifloxacin did not select for less susceptible variants of MRSA and pneumococci, in contrast to the 10- to 100-fold higher selection frequencies with ciprofloxacin and ofloxacin. The single-step E. coli mutants selected by gatifloxacin and the comparator quinolones had quinolone MICs within the susceptible range. These data suggest that gatifloxacin use may hinder the development of quinolone-resistance, particularly in Gram-positive bacteria.

Structure-activity relationships of carbapenems that determine their dependence on porin protein D2 for activity against Pseudomonas aeruginosa.

A number of carbapenem derivatives were examined to determine the structure-activity relationships required for dependence on porin protein D2 for activity against Pseudomonas aeruginosa. As suggested by J. Trias and H. Nikaido (Antimicrob. Agents Chemother. 34:52-57, 1990), carbapenem derivatives, such as imipenem and meropenem, containing a sole basic group at position 2 of the molecule utilize the D2 channel for permeation through the outer membrane of pseudomonads; they are more active against D2-sufficient strains of P. aeruginosa. Our results indicated that carbapenems with a basic group at position 1 or 6 of the molecule did not depend on the D2 channel for activity; i.e. they were equally active against D2-sufficient and D2-deficient pseudomonal strains. However, addition of a basic group at position 1 or 6 of a carbapenem derivative already containing a basic group at position 2 resulted in its lack of dependency on the D2 pathway. Comparison between meropenem and its 1-guanidinoethyl derivative, BMY 45047, indicated that they differed in their dependence on D2; while meropenem required the D2 channel for uptake, BMY 45047 activity was independent of D2. Meropenem and BMY 45047 had similar affinities for the penicillin-binding proteins of P. aeruginosa. However, BMY 45047 and meropenem differed in the morphological changes that they induced in pseudomonal cells. While meropenem induced filamentation, BMY 45047 induced filaments only in BMS-181139-resistant mutants and not in imipenem-resistant mutants or in carbapenem-susceptible P. aeruginosa strains. These results suggested that in Mueller-Hinton medium the uptake of BMY 45047 through the non-D2 pathway is more rapid than that of meropenem through the D2 porin. In summary, the presence of a basic group at position 2 of a carbapenem is important for its preferential uptake by the D2 channel. However the addition of a basic group at position 1 or 6 of a carbapenem already containing a basic group at position 2 dissociates its necessity for porin protein D2 for activity.

In vitro activities of cefepime alone and with amikacin against aminoglycoside-resistant gram-negative bacteria.

The in vitro activity of cefepime was compared with those of ceftazidime, cefotaxime, and cefpirome against aminoglycoside-resistant gram-negative bacteria. Cefepime was the most active cephalosporin, with a MIC for 90% of strains tested for all non-Pseudomonas aeruginosa species of less than or equal to 4 micrograms/ml. No cefepime resistance was encountered among members of the family Enterobacteriaceae. Of the 40 aminoglycoside-resistant P. aeruginosa isolates, 15% were resistant to cefepime, compared with 18% for ceftazidime, 30% for cefpirome, and 35% for cefotaxime. Synergism between cefepime and amikacin was observed and occurred most frequently in P. aeruginosa strains resistant to cefepime but susceptible to amikacin. In no case did cefepime and amikacin exhibit antagonism against P. aeruginosa.

Synergistic activity of the novel des-fluoro(6) quinolone, garenoxacin (BMS-284756), in combination with other antimicrobial agents against Pseudomonas aeruginosa and related species

Non-fermentative Gram-negative bacteria (Pseudomonas aeruginosa, Burkholderia cepacia, Stenotrophomonas maltophilia and Acinetobacter spp.) are intrinsically less susceptible to many antimicrobial agents. Two-drug combinations have been used to treat infections caused by less susceptible pathogens. In this study, the antibacterial activity of garenoxacin (GARX) with non-quinolones was examined. The non-quinolones evaluated were cefepime (CEPI), imipenem (IMIP), aztreonam (AZTR), piperacillin-tazobactam (PIPC/TZ), amikacin (AMK), ceftazidime (CTAZ), trimethoprim-sulphamethoxazole (TMP/SMX) and ticarcillin-clavulanate (TICC/CA). Synergism was determined by time-kill analysis using GARX (at 2 x its MIC, not to exceed 4 mg/l) and the second drug (at 1 x MIC, not to exceed its susceptible MIC breakpoint), and is defined as > or = 2 log(10) enhanced killing at 24 h with the combination. Partial synergy is defined as > or = 1.5 log(10) but < 2 log(10) enhanced killing with the drug combination. Synergy/partial synergy was observed most often with GARX plus: CEPI, AZTR, PIPC/TZ, IMIP (five strains each) or AMK (four strains) vs. eight P. aeruginosa; CTAZ, AZTR (five strains each) vs. six B. cepacia; TICC/CA (six strains), CEPI, CTAZ or AMK (five strains each) vs. eight S. maltophilia; and CEPI, AMK (three strains each) or CTAZ, TICC/CA (two strains each) vs. four Acinetobacter spp. In conclusion, synergistic killing was observed frequently with GARX plus a non-quinolone bactericidal agents against non-fermentative Gram-negative bacteria, including strains intermediately susceptible/resistant to one or both agents.

In vitro activity of BMS-181139, a new carbapenem with potent antipseudomonal activity.

The in vitro activities of the carbapenem BMS-181139 were determined in comparison with those of imipenem, meropenem, ciprofloxacin, ceftriaxone, and vancomycin. BMS-181139 was the most active against species of Pseudomonas and related genera Alteromonas and Burkholderia, with MICs for 147 of 149 isolates of < 4 micrograms/ml. Of 22 imipenem-resistant (MIC > 8 micrograms/ml) P. aeruginosa strains, only 1 required an MIC of BMS-181139 of > 4 micrograms/ml, compared with 14 requiring the same meropenem MIC. BMS-181139 was the most active carbapenem against the majority of other gram-negative species except members of the tribe Proteeae, against which meropenem was more active. Although imipenem was more active against gram-positive species, BMS-18139 MICs at which 90% of strain tested were inhibited were < 1 microgram/ml for these species. BMS-181139 was generally active against isolates resistant to ciprofloxacin or broad-spectrum cephalosporins, including those containing plasmid-encoded beta-lactamases or high levels of chromosome-encoded beta-lactamases, as well as anaerobes except Clostridium difficile. Inoculum effects were noted for all three carbapenems against Klebsiella pneumoniae, Enterobacter cloacae, and Serratia marcescens but not Escherichia coli, Pseudomonas aeruginosa, or Staphylococcus aureus. BMS-181139s inoculum effect tended to be more marked. BMS-181139 exhibited bactericidal activity at the MIC for some strains and up to four to eight times the MIC for others. The postantibiotic effect of BMS-181139 was equal to or less than that of imipenem and, like meropenem, exhibited intraspecies variability. BMS-181139 was 30-fold more stable than imipenem and 7-fold more stable than meropenem to hydrolysis by hog kidney dehydropeptidase.