In-vitro and in-vivo antibacterial activity of quinupristin/dalfopristin.

Quinupristin/dalfopristin is a new water-soluble streptogramin antimicrobial agent comprising quinupristin and dalfopristin in a ratio of 30:70. The in-vitro spectrum of activity includes most multi-resistant Gram-positive aerobes, important Gram-negative aerobes, Gram-positive anaerobes and intracellular bacteria that are causal agents of respiratory, blood and cutaneous infections. Of particular note, quinupristin/dalfopristin is active against multidrug-resistant isolates of Staphylococcus aureus, Staphylococcus epidermidis and Enterococcus faecium, and against penicillin-resistant and/or erythromycin-resistant Streptococcus pneumoniae. The combination is also active against staphylococci showing both constitutive and inducible erythromycin resistance. Bactericidal activity and a prolonged post-antibiotic effect have also been noted for quinupristin/dalfopristin against Gram-positive cocci. Gram-negative bacteria susceptible to quinupristin/dalfopristin include Moraxella catarrhalis, Legionella spp. and Mycoplasma spp. Overall, the spectrum of antibacterial activity indicates a potential role for this combination in the treatment of difficult-to-treat Gram-positive infections, including those caused by multidrug-resistant organisms. Since this activity extends to Gram-negative respiratory bacteria, quinupristin/dalfopristin may also find a role in the treatment of atypical, as well as typical, pneumonia.

A review of the in-vitro activity of quinupristin/dalfopristin against intracellular pathogens and mycoplasmas.

Quinupristin/dalfopristin displays in-vitro bacteriostatic activity against all Legionella spp. (MICs = 0.06-2 mg/L), with Legionella pneumophila usually being at least two-fold more sensitive to quinupristin/dalfopristin than Legionella bozemanii, Legionella dumoffii, Legionella gormanii and Legionella micdadei (MIC = 0.06-2 vs 1-2 mg/L, respectively). Against Legionella spp., quinupristin/dalfopristin was at least as active as erythromycin. Quinupristin/dalfopristin was active in vitro against all Mycoplasma spp. tested (MIC = 0.05-2 mg/L), with Mycoplasma hominis being less susceptible than other species. Quinupristin/dalfopristin was active against erythromycin-resistant strains of Mycoplasma fermentans and M. hominis (MIC90 = 0.5 and 2 mg/L, respectively), and doxycycline-resistant strains of Ureaplasma urealyticum (MIC90 = 1 mg/L). The in-vitro bacteriostatic activity against Mycoplasma pneumoniae and Mycoplasma genitalium (MIC90 = 0.1 and 0.05 mg/L, respectively) was similar to that of erythromycin and doxycycline. Quinupristin/dalfopristin was actively taken up by murine macrophages, and incubation of the drug (2.5 mg/L) with macrophages containing ingested Staphylococcus aureus resulted in the death of 70% of intracellular bacteria within 120 min. Intracellular concentrations of quinupristin/dalfopristin reached 50 and 30 times the extracellular concentration, respectively, showing that these compounds readily penetrate into cells. The intracellular activity of quinupristin/dalfopristin may make it suitable for use in some, presently difficult-to-treat, infections caused by intracellular organisms.

Antimicrobial activity against Staphylococcus aureus of semisynthetic injectable streptogramins: RP 59500 and related compounds.

Pristinamycin displays unique antibacterial properties due to the synergy between its two components, pristinamycin I and pristinamycin II. Because this antibiotic is not water-soluble, its administration is restricted to the oral route, and its therapeutic potential is thereby limited. Novel water-soluble derivatives of the naturally-occurring antibiotic pristinamycin were obtained by modifications of its two major components. The modifications included regioselective and stereoselective substitution alpha to the carbonyl group in the 4-oxo-pipecolic acid residue of pristinamycin IA (PIA) and stereoselective conjugate addition to the double bond of the dehydroproline ring in pristinamycin IIA (PIIA). We report here the in-vitro and in-vivo activities of some representative water-soluble derivatives of pristinamycin IA and pristinamycin IIA against Staphylococcus aureus reference strains, sensitive or resistant to methicillin and/or macrolides.

Post-antibiotic effects of RP 59500 with Staphylococcus aureus.

The post-antibiotic effect (PAE) of the semisynthetic streptogramin RP 59500 was evaluated with four clinical isolates of Staphylococcus aureus (two strains susceptible to methicillin and to the macrolide-lincosamide-streptogramin B (MLSB) group and two strains resistant to these drugs). The PAE was defined as the time required for either the viable counts to increase by one log10 or for bacteria to regain their maximal rate of growth. Similar results were obtained regardless of which definition was used. For each experiment, the time of exposure of the bacteria to the drug ranged from 15-80 min. At a concentration of 0.5 x MIC and an exposure time of 80 min, RP 59500 produced a PAE in three of the four strains examined. At higher concentrations (1, 2 and 4 x MIC), a PAE was observed with all four strains. When considered as the time required for bacterial growth to return to its maximal rate, the PAE lasted for at least 7 h with the two methicillin-susceptible strains when they were exposed for 80 min to RP 59500 at 4 x MIC, compared with 5 h for the two methicillin-resistant strains and the same exposure conditions. The concentration of antibiotic was found to be a more important parameter in determining the PAE than the time of exposure.

In-vitro and in-vivo synergic activity and fractional inhibitory concentration (FIC) of the components of a semisynthetic streptogramin, RP 59500.

RP 59500 is a new semisynthetic injectable streptogramin antibiotic composed of two compounds which interact synergically, RP 57669 and RP 54476, derived from pristinamycin IA and pristinamycin IIB, respectively. The bacteristatic and bactericidal activities of RP 57669 and RP 54476 alone or combined in various proportions were tested by the chequerboard dilution technique. The fractional inhibitory concentration (FIC) index was determined for 14 Staphylococcus aureus isolates (including methicillin- and macrolide-resistant strains) and one culture collection strain. The FIC index was found to be much lower than 0.5, indicating the presence of synergy for all strains tested, whatever their resistance pattern. The ED50 of RP 57669 and RP 54476 in various combinations were also determined in three experimental murine models of septicaemia, caused by either S. aureus or Streptococcus pneumoniae, and a thigh abscess model caused by S. aureus. The combinations which performed best in the model of septicaemia were those in which the RP 57669: RP 54476 ratio ranged from 16:84 to 92:8, while those active against the thigh abscess model had ratios ranging from 8:92 to 84:16. That the drugs were active over a wide range of ratios suggests that synergy will be maintained even if one drug is cleared more rapidly than the other. The combination of 30:70, referred to as RP 59500, was selected for further studies, both in vitro and in various experimental models of infections.

[Relationship between virulence and resistance to antibiotics in pneumococci. Contribution of experimental data obtained in an animal model]. / Relation entre virulence et résistance aux antibiotiques des pneumocoques. Apport des donnée expérimentales sur un modèle animal.

Epidemiologic data show that the organ affinity of Streptococcus pneumoniae varies across serotypes. As a result of this heterogeneous distribution, exposure to antimicrobials is greater for serotypes 6, 14, 19 and 23. Most strains with resistance to antimicrobials are found among these four serotypes. Virulence of the various serotypes of pneumococci varies with adhesion, enzyme secretion, and resistance to phagocytosis. In a mouse model of experimental septicemia, neither the origin of strains nor the acquisition of a resistant phenotype modified virulence, which appeared as an intrinsic feature specific to each phenotype. Strains belonging to serotypes 6, 14, 19 and 23 with or without resistance to antimicrobials were only very rarely virulent in the experimental model used. As an indirect result, resistance to antimicrobials and virulence were inversely related among the strains of S. pneumoniae tested.

[In vitro comparative bactericidal effect of cefotaxime and cefixime in a kinetic model]. / Activité bactéricide comparée du céfotaxime et du céfixime dans un modèle cinétique in vitro.

The bactericidal activity of cefotaxime against Escherichia coli, Klebsiella pneumoniae and Serratia marcescens, was compared with that of cefixime in an in vitro model simulating the human pharmacokinetics of these antibiotics. Kinetic parameters in this model were T1/2 = 1.3 h and Cmax = 45 mg/l for cefotaxime; T1/2 = 3.5 h and Cmax = 5 or 3.5 mg/l for cefixime. These parameters mimicked those obtained after a 1 g intravenous infusion of cefotaxime and an oral uptake of 0.4 or 0.2 g of cefixime, respectively. Both antibiotics demonstrated a strong bactericidal activity. Against Escherichia coli, the bactericidal effect of cefotaxime was slightly more rapid and more prolonged than that of cefixime: -5 log10 CFU/ml over 4 h vs -3 log10 CFU/ml over 8 h respectively. Against Klebsiella pneumoniae and Serratia marcescens, both drugs exhibited similar bactericidal activity despite different dosages and routes of administration: -2 to -3 log10 CFU/ml over 4 h.

[Comparison of the in vitro post-antibiotic effect of C14 macrolides (erythromycin and roxithromycin) and C16 macrolides (josamycin and spiramycin) against Staphylococcus aureus]. / Comparaison de l'effet post-antibiotique in vitro de macrolides en C14 (érythromycine et roxithromycine) et en C16 (josamycine et spiramycine) vis-a-vis de Staphylococcus aureus.

In vitro post-antibiotic effect (PAE) induced by erythromycin, roxithromycin, josamycin and spiramycin has been compared on Staphylococcus aureus. Three MLSB sensitive and three MLSB inducible resistant S. aureus strains have been used. delta t was the time required for culture to increase by 1 log10 after drug removal in comparison with controls. For erythromycin and roxithromycin delta t ranged from 6 minutes at 1 x MIC to 48 minutes at 4 x MIC (average of the six strains at 4 x MIC: 33 minutes). For josamycin and spiramycin, delta t ranged from 36 at 1/2 x MIC to 138 minutes at 4 x MIC (average at 4 x MIC: 101 minutes). No difference was observed between MLSB sensitive and MLSB inducible resistant S. aureus strains. In our experimental conditions, PAEs observed with josamycin and spiramycin (16-membered-ring macrolides) were 2.5 to 3 times longer than those observed with erythromycin and roxithromycin (14-membered-ring macrolides). These results added to biological differences previously observed between 14-membered-ring and 16-membered-ring macrolides.

[Antipneumococcal activity of erythromycin and spiramycin in 2 experimental models in mice]. / Activité antipneumococcique de l'érythromycine et de la spiramycine dans deux modèles expérimentaux chez la souris.

Macrolides often remain the first intention treatment in many chest infections caused by S. pneumoniae. Antipneumococcal activities of spiramycin and erythromycin have then been tested in a septicaemia model and in a pulmonary infection model in mice. In the septicaemia model, spiramycin has been found 5 to 15 times more active than erythromycin by subcutaneous route and 1.5 to 6 times by oral route. In the pneumonia model, spiramycin has been found as active (one strain) to 5 times more active than erythromycin (three strains) by both subcutaneous and oral route. These data might indicate that better tissular penetration of spiramycin is responsible for better in vivo activity. These facts also support the statement that MIC should not be the only choice standard of infectious chemotherapy.

[Curative activity of spiramycin adipate by parenteral route in experimental septicemia in mice. Comparison with orally administered basic spiramycin]. / Activité curative de l'adipate de spiramycine utilisé par voie parentérale dans la septicémie expérimentale de la souris. Comparaison avec la spiramycine base administrée par voie orale.

Experimental septicemia was induced in mice by intraperitoneal injection of 10 to 100 lethal doses of Staphylococcus aureus and Streptococcus pneumoniae. Animals were treated by a mixture of adipic acid and spiramycin (subcutaneous route) or by spiramycin base (oral route), 1 and 6 hours after infection. To determine the effective dose 50% that achieves survival of half the mice after 7 days, each drug was used in 6 dosages (mg/kg) and each dosage was given to 12 mice. In 21 independent experiments, ED50S of spiramycin adipate by the subcutaneous route were found to be 5 to 50 times lower than those of spiramycin base per os. These results are consistent with the high serum peak concentrations of spiramycin adipate observed following subcutaneous administration.

Comparative efficacy of pefloxacin and six other antimicrobial agents on Staphylococcus aureus experimental abscesses.

Pefloxacin (Pef) is a new quinolone which has been shown to have good in-vitro activity against Staphylococcus aureus, and to reach high tissue concentrations. Its efficacy was compared to that of 2 quinolone derivatives, norfloxacin (Nor) and ciprofloxacin (Cip) and to that of methicillin (Meth), cephalothin (Cep), pristinamycin (Pri) and vancomycin (Van), in an experimental model of S. aureus abscesses. Mice challenged with an intramuscular thigh injection of a calibrated inoculum developed local abscesses. Three S. aureus strains (with different antibiotic resistance profiles (Pase-, Pase+, MethR)) were used. In this model, the antibiotics showing the best ED50 following oral administration, against all three strains were Pef greater than Cip greater than Pri greater than Nor, by subcutaneous administration for the Pase- strain Pef = Cip greater than Cep greater than Van; for the Pase+ strain Pef = Cip greater than Van greater than Meth and for the Pase+ MethR strain: Pef = Cip greater than Van greater than Cep. These data indicate that pefloxacin and ciprofloxacin are highly active in vivo against various strains of S. aureus, and appear to be more potent than norfloxacin, vancomycin, cephalothin and methicillin.

[A simple in vitro system for comparing the bactericidal activity of antibiotics at variable concentrations]. / Mise au point d'un système simple, in vitro, permettant de comparer l'activité bactéricide d'antibiotiques à concentrations variables.

An in vitro device is described that allows the study of bactericidal activity of decreasing antibiotic concentrations. This simple and easily set up device was found to be accurate and reliable. The bactericidal kinetics of three antibacterial compounds (cephalothin, norfloxacin and pristinamycin) on Staphylococcus aureus were compared in a system simulating serum concentration and half-life of each antibacterial compound. The results show the importance of pharmacokinetic parameters on antibacterial activity and their usefulness in new antibiotics evaluation.

Protective activity of habekacin and four other aminoglycosides in mouse septicaemia caused by Enterobacteriaceae.

The in vivo efficacy of habekacin, an aminoglycoside antibiotic obtained by chemical derivation from dibekacin, was compared to that of gentamicin (GEN), tobramycin (TOB), kanamycin (KAN) and amikacin (AMI) in a protection test in mice. The 50% effective dose (ED50) was determined in groups of animals challenged with bacterial suspensions injected intraperitoneally together with mucin, and treated subcutaneously 1 h and 6 h later. The bacterial strains used were: Escherichia coli (three GEN sensitive strains and one GEN-KAN-TOB resistant strain), Enterobacter cloacae (one GEN-KAN resistant strain), Serratia marcescens and Klebsiella pneumoniae (one GEN sensitive strain and one GEN resistant strain). In this model, habekacin was found to be as active as GEN against GEN sensitive strains and more active than AMI on GEN, GEN-KAN and GEN-KAN-TOB resistant strains.

[Structure-activity relationship of semi-synthetic derivatives of the PIA component of pristinamycin]. / Relations structure-activité de dérivés semi-synthétiques du constituant PIA de la pristinamycine.

Pristinamycin is a naturally occurring streptogramin made up of 2 groups of synergistic components (PI and PII). Because these components are not water soluble, use of pristinamycin has up till now been confined to the oral route. Water soluble semisynthetic derivatives of the PIA component, appropriate for parenteral use, have lately been developed. PIA is a peptidic macrolactone. As opening of the lactone results in total loss of biologic activity, semisynthesis must spare this function and preserve the macrocycle. Reactions at 5 gamma and 5 delta yielded 4 families of derivatives. Antimicrobial activity has been studied for more than 80 compounds. Several derivatives are promising as they are water soluble and have in vitro and in vivo (mice) activities similar to those of the original PIA component.

[Comparative effects of 4 cephalosporins on the incorporation of tritiated diaminopimelic acid during bacterial growth]. / Effects comparés de quatre céphalosporines sur l'incorporation d'acide diaminopimélique tritié au cours de la croissance bactérienne.

When comparing antibiotic activities, it might be of interest to study parameters other than minimal inhibitory concentrations (MIC's). Specific activity of beta-lactams on bacterial cell wall makes it possible to determine radiolabelled diaminopimelic acid (DAP) incorporation in growing cultures. We have studied the effects of various concentrations of cefalotin , cefotaxime, latamoxef (moxalactam) and ceftiolene (42 980 RP) on DAP incorporation in 6 strains of E. coli, E. cloacae and S. aureus. Drug concentration which inhibits 90 % of radioactivity incorporation (CII 90) was found to vary from 0.1 X MIC to 3 X MIC. This fact suggests that beta-lactam action on cell wall synthesis and/or structure and MIC's are not always strictly correlated.

Recovery period and the exposure of bacteria to subminimal inhibitory concentrations of antibiotics.

The minimal antbiotic concentration (MAC) refers to the lowest concentration of drug that results in a detectable effect on bacteria (e.g., inhibition of growth, change in morphology, and delay in recovery to normal growth in drug-free medium). Strains of Escherichia coli and Staphylococcus aureus were subjected to a range of subminimal inhibitory concentrations of four drugs-ampicillin, gentamicin, rosaramicin, and tetracycline. Inhibition curves (percentage of normal growth vs. concentration of drug) were related to the period of recovery before resumption of normal growth, which was chosen to express MAC value. In both E. coli and S. aureus, the longest delay in recovery of normal growth was observed with rosaramicin. Ampicillin resulted in a delay in recovery only with S. aureus.

Molecular studies and possible relatedness between R plasmids from groups B and D streptococci.

Resistance plasmids isolated from Streptococcus agalactiae (group B) and S. faecalis (group D) have been compared in regard to resistance markers, molecular weight, and DNA-DNA homology. Three of them (pIP501, pIP612, and pIP613) have been found to confer identical (or very similar) resistance patterns (erythromycin, lincomycin, and streptogramin B, respectively) and to have similar molecular weights (19.8 x 10(6), 22.7 x 10(6), and 17.6 x 10(6), respectively) and a high level of DNA-DNA homology in hybridization experiments (90 to 100%). These results are compatible with the view that these plasmids may derive from one common ancestor, and/or that they can be transferred between unrelated Streptococcus strains belonging to the same or different groups.