130 research outputs found

    In-vitro activity of RP 59500, a semisynthetic streptogramin, against staphylococci and streptococci

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    The in-vitro activity of RP 59500, an injectable streptogramin derived from pristinamycin, was determined by agar dilution and compared with that of pristinamycin. Two hundred and sixty-one recent clinical isolates of Gram-positive cocci were tested against both antibiotics. The two compounds displayed similar activities. The MIC90S of RP 59500 ranged from 0·5 to 2 mg/L in 114 strains of Staphylococcus aureus showing various phenotypes of antibiotic resistance (penicillin-susceptible; penicillin-resistant and methicillin-susceptible; methicillin-resistant; erythromycin-resistant, either inducible or constitutive; quinolone-resistant). Similar results were obtained with coagulase-negative staphylococci. RP 59500 was consistently active against streptococci, with MIC90s of 0·25, 0·25 and 0·50 mg/L for Streptococcus pyogenes (n = 20), Streptococcus agalactiae (n = 20) and Streptococcus pneumoniae (n = 20), respectively. Enterococcus faecalis (n = 20) appeared to be notably less susceptible (MIC90, 8 mg/L). In view of this consistent activity against all staphylococci and streptococci tested, including multiply resistant isolates, RP 59500 merits further investigatio

    Bacteriological activity of trovafloxacin, a new quinolone, against respiratory tract pathogens

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    The use of established fluoroquinolones, such as ciprofloxacin and ofloxacin, as empirical therapy for the treatment of moderate-to-severe respiratory tract infections is limited by their poor activity against gram-positive and atypical pathogens. Data from in vitro susceptibility studies and in vivo animal protection models suggest that the new fluoroquinolone, trovafloxacin, compared with ciprofloxacin and ofloxacin offers equivalent activity against gram-negative pathogens and improved activity against gram-positive pathogens. In particular, susceptibility data indicate that trovafloxacin is at least 16-fold more potent than either ciprofloxacin or ofloxacin against penicillin-susceptible and penicillin-resistant strains ofStreptococcus pneumoniae. Other susceptible pathogens includeStreptococcus pyogenes, vancomycin-susceptibleEnterococcus faecalis and the atypical respiratory pathogensLegionella pneumophila, Mycoplasma pneumoniae andChlamydia pneumoniae. In vivo studies involving models of protection against acute systemic infection and pneumococcal pneumonia in mice, and Legionnaires' disease in guinea pigs, indicate that the antibacterial spectrum observed for trovafloxacin in vitro extends to the in vivo setting. Together, these findings suggest that trovafloxacin may offer clinical efficacy against respiratory pathogens superior to that of ciprofloxacin and of ofloxacin, and may find a useful role as empiric therapy in both the community and hospital settin

    In-vitro activity of roxithromycin against respiratory and skin pathogens

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    The activity of roxithromycin was determined by a microdilution method, in comparison with erythromycin, spiramycin and josamycin. Roxithromycin and erythromycin showed very similar MICs against staphylococci, Streptococcus pneumoniae, Str. pyogenes and Haemophilia influenzae. In most cases, spiramycin and josamycin appeared similarly or more active. The activity of roxithromycin against Mycoplasma pneumoniae, Legionella spp., Chlamydia psittaci and, to some extent, against Pasteurella spp. was also assessed, by suitable in-vitro methods. Roxithromycin has a promising potential for treating selected skin and respiratory infection

    How predictable is development of resistance after β-lactam therapy in Enterobacter cloacae infection?

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    Certain non-fastidious Gram-negative bacilli, notably Enterobacter cloacae, although classified as susceptible by usual in-vitro susceptibility testing, often become resistant in patients treated with newer β-lactam antibiotics. Here various in-vitro tests were carried out together with an animal model allowing the quantification of resistance that emerges after short term therapy. Mice were challenged (102 cfu plus talcum) intraperitoneally with one each of four strains of Ent. cloacae. Two hours later, a single β-lactam dose was administered subcutaneously. The following day, the peritoneal bacterial population was analysed by using antibiotic-containing gradient plates. Development of resistance after therapy varied according to the compound considered. Imipenem (50 mg/kg) produced no resistance, and piperacillin (200 mg/kg) only a few, while resistance occurred frequently after therapy with aztreonam (50 mg/kg), ceftazidime (50 mg/kg), cefotaxime (50 mg/kg) and cefpirome (50 mg/kg). MICs increased by at least 16-fold when resistance developed. No simple correlations were found between these in-vivo results and initial MICs, killing kinetics, frequency of resistant variants within the bacterial populations before therapy, initial MIC of these variants or antibiotic concentrations assayed in peritoneal fluid 60 min after dosing. The most reliable predictive in-vitro test appeared to be the determination of resistance emerging in broth containing at least 16 times the MIC of the antibiotic tested. Such a test is unlikely to be used on a routine basis. When a β-lactam compound seems appropriate for treating an Enterobacter infection, it may be advisable to avoid drugs that are prone prone to produce resistance in experimental or clinical infections, whatever the results of conventional in-vitro susceptibility test

    Usual and unusual antibacterial effects of quinolones

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    Recently documented antibacterial effects of quinolones are reviewed. DNA gyrase is most likely to be the primary target site for these agents. Quinolones rapidly kill susceptible bacteria; the mechanisms of the bactericidal activity, still poorly understood, probably involve new protein synthesis. Quinolones alter membrane integrity before cell death, leading to leakage of cytoplasmic constituents. In Gram-negative bacteria, quinolones act as chelating agents for outer membrane divalent cations, disorganizing the bacterial lipopolysaccharide layer and facilitating the further entry of quinolone molecules in a ‘self-promoted' pathway. Quinolones inhibit plasmid replication and reduce the efficacy of plasmid conjugation. Subinhibitory concentrations of quinolones can interfere with bacterial virulence factors, such as bacterial adherence to the host cell, phagocytosis and production of enzymes implicated in virulence. Recent studies also indicate synergism of quinolones with oxacillin against methicillin-resistant staphylococci and describe improved activity of newer compounds against Gram-positive pathogen

    Laboratory assessment of antibacterial activity of zwitterionic 7-methoxyimino cephalosporins

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    Zwitterionic 7-methoxyimino cephalosporins (cefpirome, cefepime, cefclidin, DQ2556, FKO37 and SCE2787) possess a variable substitution at C3 which contains a quarernary nitrogen. These cephalosporins display low affinities for Class I /7-lactamase and rapid penetration through the outer membrane of Gram-negative bacilli, so that an increased number of periplasmic β-lactam molecules interact with PBP's per unit of time. As a consequence, the new zitterionic compounds remain active against some, but not all, ceftazidime-resistant Enterobacteriaceae producing high levels of Class Iβlactamase or Bush type 2bβlactamases. Antipseudomonas activities are generally similar to that of ceftazidime except that cefclidin is more active. The new zwitterionic compounds, especially cefpirome and FK037, express greater antistaphylococcal potency than does ceftazidime. A variety of animal models including meningitis and endocarditis have confirmed the potential of these compounds in-vivo. On the basis of structural and antibacterial characteristics, the expression ‘forth generation' is acceptable to describe the zwitterionic 7-methoxyimino cephalosporin

    In-vitro activity of newer quinolones against aerobic bacteria

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    Nalidixic and five newer 4-quinolones, ciprofloxacin, enoxacin, norfloxacin, ofloxacin and pefloxacin were tested against 576 recent clinical aerobic bacterial isolates. The 4-quinolones were regularly active (MIC90 < 4 mg/1) against the following bacteria: Staphylococcus aureus, S. epidermidis, S. saprophyticus, different Enterobacteriaceae, Haemophilus influenzae, Campylobacter jejuni, Pseudomonas aeruginosa, Agrobacter spp., Aeromonas spp., Plesiomonas spp., Neisseria meningitidis. Other bacteria were usually intermediately susceptible or resistant: different streptococci, Listeria monocytogenes, Nocardia asteroides, P. maltophilia, Achromobacter xylosoxydans and Alcaligenes denitrificans. Ciprofloxacin was the most potent compound, followed by ofloxacin and pefloxacin, norfloxacin and enoxacin being less active. All the 4-quinolones were much more active than nalidixic acid. The MBC/MIC ratios of the 4-quinolones were between 1 and 2 with a majority of strains, and between 2 and 3 with Streptococcus agalactiae, Str. faecalis and L. monocytogenes. A two- to eight-fold increase of MIC was observed by increasing the inoculum 10,000-fold with most of the strains tested. Susceptible bacterial population of Klebsiella pneumoniae, Enterobacter cloacae, Serratia marcescens and P. aeruginosa contained more clones resistant to nalidixic acid (104 to 108 at four times the MIC) than to 4-quinolones (105 to 109 at four times the MIC). Supplementing the media with MgSO4 produced smaller inhibition zone diameters with a disc diffusion method than those obtained with non-supplemented agar, with all quinolone or strains. Less regular effect, or no effect was obtained after supplementation with ZnSO4 or Ca(NO3)
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