In vitro development of resistance of Streptococcus pneumoniae to beta-lactam antibiotics.

In recent years, increasing numbers of Streptococcus pneumoniae strains displaying relative resistance to penicillin have been reported. Epidemiological studies have shown a correlation between aminopenicillin administration and resistance. We investigated the development of resistance in six strains (four sensitive and two intermediate-resistant to penicillin) by serial daily passages in subinhibitory concentrations of amoxicillin (AMX), amoxicillin + clavulanic acid (AMC), imipenem (IMP), cefixime (CFM), cefatrizine (CTZ), cefadroxil (CDX), and cefuroxime (CXM). MICs were determined by the macrodilution method in brain-heart broth for each daily passage. The number of daily passages needed to increase the MIC by a factor of 8 was achieved with AMX, AMC, and CFM for most of the strains after a mean of 24, 20, and 11 passages, respectively, and for one-third of the strains, with CDX, IMP, and CTZ after 11, 11, and 21 passages, respectively. Decreased susceptibility to breakpoints for intermediate-resistant S. pneumoniae populations was noted for all strains with CFM, AMX, and AMC after a mean of 10, 18, and 21 serial passages, respectively, and for four of five strains with IMP and CTZ after 12 and 13 passages. CTZ-, CDX-, and CXM-passaged variants had increased MIC values only for cephalosporins, while AMX-, AMC-, IMP-, and CFM-passaged variants exhibited increased MICs to all antibiotics tested. These in vitro data appear to be in agreement with epidemiological studies and warrant further exploration with respect to possible clinical implications.

Effect of beta-lactam antibiotics on the in vitro development of resistance in Pseudomonas aeruginosa.

OBJECTIVE: To investigate whether stepwise selection of resistance mutations may mirror the continued bacterial exposure to antibiotics that occurs in the clinical setting. METHODS: We examined the in vitro development of resistance to a number of commonly used antibiotics (cefepime, cefpirome, ceftazidime, cefotaxime, piperacillin and imipenem) in Pseudomonas aeruginosa, a significant nosocomial pathogen. Stepwise resistance was assessed by serial passage of colonies located nearest to the inhibition zone on antibiotic-containing gradient plates. RESULTS: The lowest frequencies of spontaneous resistance mutations were found with cefepime and imipenem; these drugs also resulted in the slowest appearance of resistance of spontaneous resistance mutations. In five wild-type P. aeruginosa strains, cefepime-selected isolates required a mean of 30 passages to reach resistance; resistance occurred more rapidly in strains selected with other cephalosporins. P. aeruginosa strains that produced beta-lactamase or non-enzymatic resistance generally developed resistance more rapidly than wild-type strains. For most strains, resistance to all antibiotics except imipenem correlated with increased levels of beta-lactamase activity. Cross-resistance of cephalosporin-selected resistant mutants to other cephalosporins was common. Cephalosporin-resistant strains retained susceptibility to imipenem and ciprofloxacin. CONCLUSIONS: From our in vitro study, we can conclude that the rate of development of resistance of P. aeruginosa is lower with cefepime compared with other cephalosporines.

Efficacy of subinhibitory concentration of pefloxacin in preventing experimental Staphylococcus aureus foreign body infection in mice.

Adhesion is the first step leading to colonization and infection of a foreign body (FBI). To assess the ability of a subinhibitory concentration (subMIC) of pefloxacin (P) to prevent such infection, an experimental model was developed in Swiss albino mice. Subcuts of polyurethane catheters (Vygon) were placed in the peritoneal cavity of animals and 24 hours later, different inocula of an adherent strain of Staphylococcus aureus (SA) (MIC of P:0.8 mg/l) were injected i.p. Unexposed SA served as controls. Two days later the removed catheters, blood and spleen specimens were quantitatively cultured for bacterial content and identity. Infection was defined as more than 10 CFU/ml of SA recovered. Significant protection of mice, with lower dissemination, was found with inoculum sizes of 10(5) and 10(6). These results suggest that subMICs of P may confer protection against foreign body infection.

Steady-state serum pharmacokinetics and bioequivalence of 500 mg oral versus 200 mg intravenous ciprofloxacin.

The pharmacokinetics of ciprofloxacin were examined after five days of treatment with 500 mg orally and 200 mg intravenously twice a day, in six healthy volunteers in an open, randomized crossover study. The ciprofloxacin concentrations were determined in serum by high performance liquid chromatography. The mean serum peak concentrations were obtained in 1 to 1.5 h by the oral route and the values reached were similar after the oral and intravenous dose (2.56 +/- 0.62 micrograms/ml and 2.6 +/- 0.67 micrograms/ml respectively). The terminal elimination half-life was about 4.5 h for oral form and 5 h for intravenous form. The absolute bioavailability of the oral ciprofloxacin was about 83%.

A new approach to optimal antibiotic dosage regimen by coupling pharmacokinetics and killing curve parameters.

Antibiotic therapy is directed against bacteria responsible for infectious pathology which are able to resist treatment mainly when the dosage is misadapted. The choice of the initial dosage regimen actually takes into account toxicological, bacteriological and pharmacokinetic parameters. The determination of the classical bacteriological data is performed in vitro using fixed drug concentrations that are far from human therapy conditions, and moreover the efficiency is not well defined. The estimation of the pharmacokinetic parameters is realized in animals, healthy subjects or ill patients but takes into account only the drug disposition without correspondence with the kinetics of the antibiotic effect on the bacteria. Thus, each type of evaluation is made independently from the others without any correlation between the observed phenomena. It appears, therefore, interesting to propose a new approach including pharmacokinetic and bacteriological data to enable approximation of drug efficacy. The coupled evaluation of individual pharmacokinetic estimation and the killing curve determinations of an antibiotic will allow this type of development. On the basis of these data, a preliminary profile of the optimal dosage would be possible. This methodology has been applied to three antibiotics: teicoplanin, amikacin and ofloxacin and demonstrates a time- or dose-dependent activity, with interesting possibilities for optimization of dosage.

Pharmacokinetic parameters and killing rates in serum of volunteers receiving amoxicillin, cefadroxil or cefixime alone or associated with niflumic acid or paracetamol.

Pharmacokinetic parameters and killing rates in serum of volunteers receiving amoxicillin, cefadroxil or cefixime alone or associated with niflumic acid or paracetamol were studied. Niflumic acid (250 mg) or analgesic and antipyretic drugs such as paracetamol (500 mg) are often combined with antibiotics to avoid inflammation and pain in acute ear, nose and throat diseases. Pharmacokinetic interactions between these two classes of drugs have been described in experimental models, and exceptionally in humans. The aim of the present investigation was to study the interactions of these two drugs with three antibiotics (amoxicillin 500 mg x 2, cefadroxil 500 mg x 2, cefixime 200 mg and one placebo capsule) on pharmacodynamic parameters and on rate of killing in the serum of six healthy volunteers receiving the antibiotic associated or not with the product in a randomized cross-over double-blind trial. The bacteria most often involved in sinusitis, bronchitis and otitis media (Haemophilus influenzae, Streptococcus pneumoniae, Staphylococcus aureus) three target diseases for oral cephalosporins and amoxicillin, were chosen for bacteriological study. Blood samples were obtained at 0.25, 0.50, 1, 1.5, 2, 4, 6 and 12 h after oral administration of antibiotics alone or associated with the drugs. There was a wash-out period of at least 1 week between the eleven sequences. Antibiotics were measured by two methods: bioassay and high performance liquid chromatography (HPLC). All serum samples obtained at peak level, 4 and 6 h were tested for killing rate. Area under the time kill curve was calculated by the trapezoidal rule method and relative bioactivity in percent was defined as follows: (AUC control - AUC test)/AUC control x 100. No pharmacokinetic interaction was found in the AUC and T1/2 of the plasma concentrations of the antibiotics or associated with the drugs, regardless of dose, as determined by HPLC or microbiological assay. For these beta-lactam antibiotics killing rate was found to be time-dependent. Bactericidal activity was improved on H. influenzae when cefixime was associated with niflumic acid and became concentration-dependent. A significant concentration relation was also found with niflumic acid or paracetamol associated with cefixime on Strep. pneumoniae.

[Infection prophylaxis in open leg fractures. Comparison of a dose of pefloxacin and 5 days of cefazolin-oxacillin. A randomized study of 616 cases]. / Prophylaxie des infections dans les fractures ouvertes de jambe. Comparaison entre une dose de péfloxacine et 5 jours cefazoline-oxacilline. Etude randomisée sur 616 cas.

THE PURPOSE OF THE STUDY: Was to compare the efficacy of a single 800 mg injection of Pefloxacin (PF) versus 2 days of cefazolin (1 gr.Q.6 H) followed by 3 days of oxacillin (1 gr.Q.8 H) in patients with an open tibial fracture and to examine the predictive factors for infection. A double-blind double dummy, multicentric, randomized trial was performed. 616 adults with an open tibial fracture requiring single-stage bone coverage were included. The end point was wound infection within 3 months. RESULTS: Within 3 months, 21/316 patients were infected in the PF group (6.6 p. 100) versus 24/300 in the CZ-OX group (8 p. 100), the difference was not significant (95 p. 100 Cl for difference: -4.8 p. 100 to 2.1 p. 100). Twenty one strains were isolated in 18 infected patients in the PF group, and 27 in 20 patients in the CZ-OX group. Negative gram bacteria were less frequent in the PF group (10 p. 100) than in the CZ-OX group (48 p. 100), and positive gram bacteria were more frequent in the PF group (90 p. 100) than in the CZ-OX group (52 p. 100). Independent risk factors for infection were severe contamination, widespread contusion, unstable fracture, positive sample in the emergency room and at the end of surgery. Resistant infecting bacteria rate was 24 p. 100 in infected cases. CONCLUSION: There was no difference in infection rates after surgery for open tibial fractures between a 800 mg injection of Pefloxacin and 2 days of pephazolin followed by 3 days of oxacillin. Infecting bacteria were mainly nosocomially acquired.

Effect of beta-lactam antibiotics on the in vitro development of resistance in Pseudomonas aeruginosa.

OBJECTIVE: To investigate whether stepwise selection of resistance mutations maz mirror the continued bacterial exposure to antibiotics that occurs in the clinical setting. METHODS: We examined the in vitro development of resistance to a number of commonly used antibiotics (cefepime, cefpirome, ceftazidime, cefataxime, piperacillin and imipenem) in Pseudomonas aeruginosa, a significant nosocomial pathogen. Stepwise resistance was assessed by serial passage of colonies located nearest to the inhibition zone on antibiotic-containing gradient plates. RESULTS: The lowest frequencies of spontaneous resistance mutations were found with cefepime and imipenem; these drugs also resulted in the slowest appearance of resistance of spontaneous resistance mutations. In five wild-type P. aeruginosa strains, cefepime-selected isolates required a mean of 30 passages to reach resistance; resistance occurred more rapidly in strains selected with other cephalosporins. P. aeruginosa strains that produced beta-lactamase or non-enzymatic resistance generally developed resistance more rapidly than wild-type strains. For most strains, resistance to all antibiotics except imipenem correlated with increased levels of beta-lactamase activity. Cross-resistance of cephalosporin-selected resistant mutants to other cephalosporins was common,. Cephalosporin-resistant retained susceptibility to imipenem and ciprofloxacin. CONCLUSIONS: From our in vitro study, we can conclude that the rate of development of resistance of P. aeruginosa is lower with cefepime compared with other cephalosporines.

The diffusion of pefloxacin into bone and the treatment of osteomyelitis.

Pefloxacin was evaluated in the treatment of bone infections. A clinical trial was performed in 15 patients with chronic osteitis (5 Staphylococcus aureus, 5 Pseudomonas aeruginosa, 3 Serratia sp., 1 Proteus mirabilis, and a mixed infection with a Streptococcus faecalis and Escherichia coli). Patients were given pefloxacin 400 mg 12-hourly iv for 48 h followed by oral treatment. Bone biopsies from the iliac crest were carried out after at least seven days treatment, 2 h after the last dose. Serum levels were estimated at the same time. In 13 patients the pefloxacin levels were between 2 and 10 mg per g of bone and always greater than, or equal to, the MIC for the infecting organism. In 11 patients treated for six months and followed up for up to 14 months after the completion of treatment, the therapy was successful. In another two patients, the results were excellent with closure of fistulae, but there was only limited follow-up. There were two failures: in one (post-radiation osteitis) the infection persisted and in the other there was intolerance of the antimicrobial. In both cases there was no increase in the MIC of pefloxacin against the organisms. Three patients underwent operations for orthopaedic indications, after at least two months of treatment. Bone cultures from the initial focus remained sterile. Side-effects were mild.

[Selection of mutant rifampin-resistant Staphylococcus aureus during the therapeutic use of this antibiotic in combinations. 3 cases]. / Sélection de Staphylococcus aureus mutants résistants à la rifampicine lors de l'utilisation de cet antibiotique en association. Trois observations.

Selection of rifampicin-resistant Staphylococcus aureus has been described in vitro and in vivo when this compound is given as monotherapy or orally. That this occurrence may be prevented by combination-antibiotic therapy is generally accepted. We report three cases of serious staphylococcal infection treated by a synergic association of rifampicin with either an aminoglycoside or vancomycin. Therapy failed as a result of selection of the same rifampicin-resistant Staphylococcus aureus (serotype and lysotype). These observations may be explained by insufficient diffusion or inactivation of the other antibiotic in the infection site.

Evaluation of pefloxacin, ofloxacin and ciprofloxacin in the treatment of thirty-nine cases of chronic osteomyelitis.

From October 1983 to October 1986, 39 patients with chronic osteomyelitis (of at least two month's duration) were treated with either pefloxacin (n = 15), ofloxacin (n = 17), or ciprofloxacin (n = 7). The length of treatment ranged from 3 to 6 months; follow-up examinations were performed up until July 1988. The infecting bacterial strains (19 Staphylococcus aureus, 2 Staphylococcus epidermidis, 10 Escherichia coli, 8 Pseudomonas aeruginosa) were all sensitive to the quinolone prescribed. Twenty-nine of the 38 evaluable patients had a satisfactory outcome at follow-up examinations 14 to 48 months after the end of treatment. Fourteen of the 21 patients with gram-positive bacterial infections responded satisfactorily, as did 15 of the 17 patients infected by gram-negative bacteria. Nine cases of failure were observed (2 for pefloxacin, 4 for ofloxacin, 3 for ciprofloxacin). The infecting bacteria were Staphylococcus aureus in six cases (3 on ofloxacin, 3 on ciprofloxacin). The infecting bacteria were Staphylococcus aureus in six cases (3 on ofloxacin, 3 on ciprofloxacin), and Staphylococcus epidermidis (ofloxacin), Escherichia coli (pefloxacin), and Pseudomonas aeruginosa (pefloxacin) in one case each. In all these cases, local conditions (presence of a foreign body in 5 cases, sequestra in 3, and post-radiotherapy necrosis in 1) could have been responsible for treatment failure. Tolerance was good; adverse effects observed in the pefloxacin and ofloxacin groups disappeared after treatment was ended. Bone levels varied but were always superior to the MIC for the pathogen. In view of the satisfactory results, the possibility of oral administration, and the good tolerance, these quinolones should be considered as alternative agents for the treatment of chronic osteomyelitis.

[Bone infections: treatment by ofloxacin. Apropos of 10 cases]. / Infections osseuses: traitement par l'ofloxacine. A propos de dix cas.

Because of its pharmacokinetic, broad spectrum and oral administration, ofloxacin can be used in the treatment of chronic bone infections. A clinical trial was performed in 10 patients with subacute or chronic osteitis (5 Staphylococcus aureus, 1 Staphylococcus epidermidis, 1 Klebsiella oxytoca, 1 Escherichia coli, 1 Serratia marcescens, 1 Pseudomonas aeruginosa). Patients were given orally 200 mg 12 hourly. Treatment duration went on from 2 to 6 months. In this trial, the evaluation was successful in the 10 cases with a delay of 2 to 13 months (m 8,9) after the end of the treatment. Prosthetic material has been taken off in 1 case out of 4 patients (prosthetic hip) because of persistaet free bacteria outflow. For one patient, a superinfection with a Pseudomonas aeruginosa resistant to ofloxacin was noticed at the second month. Bone levels (microbiological method) were between 1,3 and 9,7 mg/l and always higher to the MIC of the bacteria. Biological tolerance was satisfactory in spite of a rise of transaminase level, a transient renal disfunction whom relationship to the treatment was difficult. 3 transient photosensitivities were also noticed.

[Evaluation of the use of rifampin combinations in severe staphylococcal infections. Apropos of the selection of 7 resistant mutants]. / Evaluation de l'utilisation de la rifampicine en association dans les staphylococcies graves. A propos de la sélection de sept mutants résistants.

Selection of rifampicin-resistant Staphylococcus aureus has been described in vitro and in vivo when this compound is given as monotherapy or orally. That this occurrence may be prevented by combination antibiotic therapy is generally accepted. We report 25 cases of severe staphylococcal infection treated by a synergistic association of rifampicin with an aminoglycoside, vancomycin, or a macrolide. Therapy failed as a result of selection of the same rifampicin-resistant Staphylococcus aureus (serotype and lysotype) in seven cases. This finding may be explained by insufficient diffusion or inactivation of the other antibiotic in the infection site.

[Bone levels of dibekacin]. / Concentration osseuse de la dibékacine.

Levels of an aminoglycoside, dibekacin, are studied in bone. Fifteen specimens were obtained by Tanzer trocar biopsy three hours after the ninth injection of dibekacin (1 mg/kg). Separation of cortical and spongy bone was not feasible owing to the small weight of specimens. Dibekacin concentrations were determined by microbiological assay. These concentrations were evaluated using a reference range in bone tissue determined with the same method and must be corrected according to blood levels. Dibekacin levels were 0.22 +/- 0.10 mg/l in healthy, non- contaminated specimens, and 1.70 and 1.80 mg/l in infected bone tissue.

Pneumococcal resistance patterns in Europe.

The emergence of Streptococcus pneumoniae strains with decreased susceptibility to penicillin has been reported worldwide over the past 20 years. However, there are striking discrepancies in penicillin susceptibility among various European countries, suggesting that local conditions may affect clonal propagation or de novo selection of resistant strains. In the present study, data on penicillin resistance patterns, antibiotic use and mode of administration, and treatment compliance in five European countries (France, Spain, Germany, Italy, and the UK) were compared. High prevalence rates of penicillin-resistant pneumococci have been reported in Spain and France, where antibiotics are widely prescribed, and overall in Europe, patient compliance with more than 50% of oral antimicrobial prescriptions is inadequate. The low prevalence of penicillin resistance in Germany and the UK coincides with lower antibiotic consumption and better treatment compliance in these countries. Recent attempts to raise public awareness and to restrict and improve indications for antimicrobial agents have resulted in decreased pneumococcal resistance in Hungary and Iceland, suggesting that pneumococcal resistance can be reversed.

[Pulmonary mycobacteriosis due to Mycobacterium chelonei: a report on a new case (authors' transl)]. / Mycobactériose pulmonaire à Mycobactérium chelonei. Une nouvelle observation.

Mycobacterium chelonei is a saprophytic germ usually devoid of pathogenic activity. Over a period of about the last ten years, however, several cases have been reported, including twelve cases of bronchopulmonary affections, in which it has been the infecting organism. The radiographic appearance is in every respect similar to that observed in pulmonary tuberculosis. A positive diagnosis of infection due to this germ can be made by the absence of Kuch's bacillus the lack of therapeutic effect of antituberculous medication, a positive skin reaction to specific antigens, and positive Mycobacterium Chelonei cultures from biopsy specimens. A new case of this infection is reported.

Effect of subinhibitory concentrations of cefamandole and cefuroxime on adherence of Staphylococcus aureus and Staphylococcus epidermidis to polystyrene culture plates.

The ability of cefamandole and cefuroxime to inhibit adherence of staphylococci to polystyrene culture plates was tested in an in vitro assay using eight strains each of Staphylococcus aureus and Staphylococcus epidermidis. The results indicated that subinhibitory concentrations of cefamandole and cefuroxime altered the adherence ability of both staphylococcal species, inhibition of adherence being more marked in the presence of cefamandole. It may be important to consider antiadherence properties in association with bactericidal activity when selecting agents for antibiotic prophylaxis.