In vitro activity of gemifloxacin and contemporary oral antimicrobial agents against 27247 Gram-positive and Gram-negative aerobic isolates: a global surveillance study.

This study was a multi-centre, multi-country surveillance of 27247 Gram-positive and Gram-negative isolates collected from 131 study centres in 44 countries from 1997 to 2000. MICs of gemifloxacin were compared with penicillin, amoxicillin-clavulanic acid, cefuroxime, azithromycin, clarithromycin, trimethoprim-sulphamethoxazole, ciprofloxacin, grepafloxacin and levofloxacin by broth microdilution. Penicillin resistance in Streptococcus pneumoniae was extremely high in the Middle East (65.6%), Africa (64.0%) and Asia (60.4%) and lower in North America (40.3%), Europe (36.9%) and the South Pacific (31.8%). Macrolide resistance in S. pneumoniae was highest in Asia (51.7%) but varied widely between laboratories in Europe (26.0%), North America (21.6%), the Middle East (13.7%), the South Pacific (10.6%) and Africa (10.0%). All the study quinolones were highly active against penicillin-resistant and macrolide-resistant S. pneumoniae. Overall, gemifloxacin had the lowest MIC(90) at 0.06 mg/l with MICs 4-64-fold lower than ciprofloxacin, levofloxacin and grepafloxacin against S. pneumoniae. Gemifloxacin MICs were more potent than grepafloxacin > levoflaxacin > ciproflaxin against the Gram-positive aerobes and shared comparable Gram-negative activity with ciprofloxacin and levofloxacin.

Comparative in vitro potency of amoxycillin-clavulanic acid and four oral agents against recent North American clinical isolates from a global surveillance study.

The in vitro activity of amoxycillin-clavulanic acid was compared with four comparator oral antimicrobial agents; ampicillin, azithromycin, cefuroxime and trimethoprim-sulphamethoxazole against 4536 recent clinical isolates covering 29 species isolated in the US and Canada between 1997 and 1999. Based upon Minimum inhibitory concentrations (MICs), amoxycillin-clavulanic acid was the most active agent against many Gram-positive species and phenotypes including methicillin susceptible Staphylococcus aureus (MSSA) Staphylococcus epidermidis, Enterococcus faecalis, Streptococcus pyogenes, Streptococcus pneumoniae including penicillin intermediate and macrolide resistant strains and was as active as ampicillin against Streptococcus agalactiae, penicillin resistant S. pneumoniae and viridans streptococci. Against Enterobacteriaceae amoxycillin-clavulanic acid in general, displayed weak activity with only Proteus mirabilis and Proteus vulgaris displaying levels of susceptibility above the 90th percentile. Amoxycillin-clavulanic acid had significant activity against many species of Gram-negative non-Enterobacteriaceae including Haemophilus influenzae, Haemophilus parainfluenzae and Moraxella catarrhalis but negligible activity against Burkholderia cepacia, Pseudomonas aeruginosa and Stenotrophomonas maltophilia. Amoxycillin-clavulanic acid continues to retain excellent activity against the majority of targeted pathogens despite 20 years of clinical use.

Comparative in vitro surveillance of amoxicillin-clavulanic acid and four oral comparators against 21232 clinical isolates from europe.

The present study was conducted to determine the in vitro activity of amoxicillin-clavulanic acid compared to that of four newer antimicrobial agents (ampicillin, azithromycin, cefuroxime and trimethoprim-sulfamethoxazole). All of the agents were tested against 21232 recent clinical isolates encompassing 37 species submitted from 16 European countries between 1997 and 1999. After 20 years of clinical use, amoxicillin-clavulanic acid continues to retain much of its initial activity against targeted gram-positive organisms, selected gram-negative organisms and major respiratory pathogens.

The growth and survivability of Streptococcus pneumoniae clinical isolates subjected to various environmental conditions.

Historically, it has been hypothesized that environmental stress would favor the survival of antibiotic susceptible bacteria over resistant ones; however, there is little direct evidence to support this theory. Clinical isolates of S. pneumoniae were chosen and categorized as: penicillin susceptible, quinolone susceptible (PSQS, n = 3); penicillin resistant, quinolone susceptible (PRQS, n = 3); and penicillin resistant, quinolone resistant (PRQR, n = 5). Baseline growth of each isolate was measured by optical density for 24 h. The resulting optical density curves were compared to those obtained for the same isolates subjected to changes in environmental conditions, such as various temperature, pH, and diluted media. In addition, each isolate was inoculated onto cotton fiber disks, held at room temperature, and the recoverable CFU measured over 144 h. In comparison to controls grown under ideal conditions, the density of PSQS isolates was significantly lower than PRQR isolates after 24 h for the following conditions (p < 0.01): incubation at 40 degrees C (1.3 log10 lower); at pH 6.5 (1.6 log10 lower); and in limited nutrient conditions (1.36 log10 lower). When inoculated onto cotton fiber disks, the PRQR isolates decreased an average of 5.0 log10 after 72 h as compared to controls. In contrast, PSQS isolates decreased an average of 8.1 log10 (p < 0.01). Results of this study support the concept that antibiotic resistant isolates may not be at a competitive disadvantage in comparison to susceptible isolates when subjected to some adverse environmental conditions.

Comparative in vitro activity of gemifloxacin, ciprofloxacin, levofloxacin and ofloxacin in a North American surveillance study.

The in vitro activity of gemifloxacin, a new fluoroquinolone, was compared to three marketed fluoroquinolones; ciprofloxacin, levofloxacin and ofloxacin against over 4,000 recent clinical isolates covering 29 species isolated in the United States and Canada between 1997-1999. Based on MIC(90)s, gemifloxacin was the most potent fluoroquinolone tested against a majority of Gram-positive isolates: Streptococcus pneumoniae, penicillin resistant S. pneumoniae, macrolide resistant S. pneumoniae, ciprofloxacin non-susceptible (MIC > or = 4 microg/mL) S. pneumoniae, S. pyogenes, S. agalactiae, viridans streptococci, Enterococcus faecalis, methicillin susceptible Staphylococcus aureus, methicillin resistant S. aureus, S. epidermidis, S. hemolyticus, and S. saprophyticus. Against Enterobacteriaceae and aerobic non-Enterobacteriaceae Gram-negatives, gemifloxacin was usually comparable to ciprofloxacin and levofloxacin and more potent than ofloxacin for the following species: Citrobacter freundii, Enterobacter aerogenes, E. cloacae, Escherichia coli, Klebsiella oxytoca, Klebsiella pneumoniae, Morganella morganii, Proteus mirabilis, P. vulgaris, Providencia stuartii, Serratia marcescens, Acinetobacter lwoffii, A. baumannii, Burkholderia cepacia, Haemophilus influenzae, H. parainfluenzae, Moraxella catarrhalis, Pseudomonas aeruginosa, and Stenotrophomonas maltophilia. Gemifloxacin was generally 16-64 fold more potent than the other fluoroquinolones tested against Gram-positive organisms and retains excellent activity comparable with ciprofloxacin and levofloxacin against a majority of Gram-negative pathogens.

Comparative in vitro potency of gemifloxacin and fluoroquinolones against recent European clinical isolates from a global surveillance study.

Gemifloxacin, a new fluoroquinolone with enhanced activity against gram-positive aerobes, was compared to ciprofloxacin, levofloxacin and ofloxacin against 21,464 recent isolates from 16 European countries. Gemifloxacin was the most potent fluoroquinolone against streptococci including penicillin-, macrolide- and ciprofloxacin-resistant Streptococcus pneumoniae, Staphylococcus aureus, coagulase-negative staphylococci, Acinetobacter spp., Haemophilus spp. and Moraxella catarrhalis. This drug was more potent than or comparable to ciprofloxacin against members of the family Enterobacteriaceae, Burkholderia cepacia, Pseudomonas aeruginosa and Stenotrophomonas maltophilia. Gemifloxacin is a promising fluoroquinolone with potent in vitro activity.

A comparative In vitro surveillance study of gemifloxacin activities against 2,632 recent Streptococcus pneumoniae isolates from across Europe, North America, and South America. The Gemifloxacin Surveillance Study Research Group.

From 1997 to 1999, 94 study centers in 15 European, 3 North American, and 2 South American countries contributed 2,632 isolates of Streptococcus pneumoniae to an international antimicrobial susceptibility testing study. Only 62.0% of isolates were susceptible to penicillin, while 22.3% were penicillin intermediate and 15.6% were penicillin resistant. Resistance to trimethoprim-sulfamethoxazole (24.4%), azithromycin (26.0%), and clarithromycin (27.1%) was also highly prevalent. For the penicillin-resistant isolates (n = 411), the MICs at which 90% of isolates are inhibited (MIC(90)s) for gemifloxacin, levofloxacin, ofloxacin, clarithromycin, and azithromycin were 0.03, 1, 2, >16, and >64 microgram/ml, respectively. Similarly, for isolates resistant to both azithromycin and clarithromycin (n = 649), gemifloxacin, levofloxacin, ofloxacin, and penicillin MIC(90)s were 0.03, 1, 2, and 4 microgram/ml, respectively. Overall rates of resistance to trovafloxacin (0.3%), levofloxacin (0.3%), grepafloxacin (0.6%), and ofloxacin (0.7%) were low. For ofloxacin-intermediate and -resistant isolates (n = 142), gemifloxacin had the lowest MIC(90) (0.12 microgram/ml) compared to the MIC(90)s of trovafloxacin (0.5 microgram/ml), grepafloxacin (1 microgram/ml), and levofloxacin (2 microgram/ml). For all S. pneumoniae isolates tested, gemifloxacin MICs were

Comparison of cation-adjusted Mueller-Hinton broth with Iso-Sensitest broth for the NCCLS broth microdilution method.

Comparison of MIC results obtained in different parts of the world is currently difficult because of variations in methods. In this study, cation-adjusted Mueller-Hinton broth, the NCCLS-recommended medium, was compared with Iso-Sensitest broth, which is widely used in Europe. Microbroth dilution testing, using the NCCLS procedure, was performed on 124 Gram-positive (staphylococci and enterococci) and Gram-negative (Enterobacteriaceae and Pseudomonas aeruginosa) isolates from the CDC reference set, with the only variable being the medium used. Twelve antimicrobial agents were tested: amoxycillin-clavulanic acid, ampicillin, ciprofloxacin, erythromycin, gentamicin, imipenem, levofloxacin, oxacillin, gemifloxacin, trimethoprim- sulphamethoxazole, tetracycline and vancomycin. Vancomycin, erythromycin and oxacillin were only evaluated for the Gram-positive organisms. Trimethoprim-sulphamethoxazole was only evaluated for a subset of Gram-negative organisms because of off-scale results. The 124 isolates were tested in one American and one UK laboratory with two batches of cation-adjusted Mueller-Hinton broth and two of Iso-Sensitest broth. A statistical evaluation of the data used a 24 fully specified factorial analysis to determine if there were significant differences in results owing to Gram reaction, site of testing and type and/or batch of broth. In addition, the cumulative results for each antimicrobial agent in each broth were plotted against the range of MIC dilutions tested. MICs of ciprofloxacin, levofloxacin, gemifloxacin, gentamicin and tetracycline were slightly higher (half a doubling dilution) with Iso-Sensitest broth than with Mueller-Hinton broth. MIC results for the other antimicrobial agents were equivalent. Essential and category agreement rates were comparable for all agents (88.4-100% and 88.2-99.0%, respectively).

Differences between the activity of penicillin, amoxycillin, and co-amoxyclav against 5,252 Streptococcus pneumoniae isolates tested in the Alexander Project 1992-1996.

A number of published studies have shown that the MICs of amoxycillin and/or co-amoxyclav are lower than those of ampicillin and/or penicillin for Streptococcus pneumoniae. Other published studies have concluded that the activities of amoxycillin and co-amoxyclav are comparable with that of penicillin for S. pneumoniae. A collection of 5252 S. pneumoniae isolates obtained during a 5 year period (1992-1996) was analysed to determine differences between the MICs of penicillin, amoxycillin and co-amoxyclav. Among the isolates analysed, 3788 (72%) were penicillin-susceptible, 615 (12%) were penicillin-intermediate and 849 (16%) were penicillin-resistant. Differences between the agents were assessed by examination of MIC distribution functions and simultaneous 95% CIs. In addition, penicillin-intermediate and -resistant isolates were analysed to determine the number and percentage of isolates which had an amoxycillin and co-amoxyclav MIC less than, equal to, or greater than the penicillin MIC. Results showed that the amoxycillin and co-amoxyclav MIC90s were one two-fold dilution lower than those of penicillin for all isolates collected between 1992-1993 and 1994-1996. Simultaneous 95% CIs showed that the mean differences between MICs of amoxycillin and penicillin, and between MICs of co-amoxyclav and penicillin, were less than zero. The majority of the penicillin-intermediate and penicillin-resistant isolates had an amoxycillin and co-amoxyclav MIC less than the penicillin MIC. In conclusion, amoxycillin and co-amoxyclav MICs were shown to be lower than the penicillin MICs for the S. pneumoniae isolates analysed in this study.

Escherichia coli ATCC 35218 as a quality control isolate for susceptibility testing of Haemophilus influenzae with haemophilus test medium.

Current National Committee for Clinical Laboratory Standards (NCCLS) susceptibility guidelines for quality control testing with Haemophilus influenzae do not include a beta-lactamase-producing strain that could detect the deterioration of the beta-lactamase inhibitor components of amoxicillin-clavulanic acid, ampicillin-sulbactam, and piperacillin-tazobactam. The objective of the study was to determine if comparable quality control results for Escherichia coli ATCC 35218, a beta-lactamase-producing strain, would be produced for the three beta-lactam-beta-lactamase inhibitor agents with Haemophilus test medium and Mueller-Hinton medium. The criteria used in this study to determine if Haemophilus test medium was acceptable for quality control testing of E. coli ATCC 35218 was that 100% of the results obtained with an antimicrobial agent-methodology combination needed to be within the acceptable NCCLS ranges established with Mueller-Hinton medium. The MIC testing results obtained by the broth microdilution and E-test methods with amoxicillin-clavulanic acid and piperacillin-tazobactam were all within the NCCLS ranges; however, the results obtained with ampicillin-sulbactam by both methods were not within the NCCLS ranges. Acceptable results were obtained by the disk diffusion methodology with ampicillin-sulbactam and piperacillin-tazobactam but not with amoxicillin-clavulanic acid. When performing susceptibility testing with H. influenzae with the beta-lactam-beta-lactamase inhibitors, in addition to quality control testing with H. influenzae ATCC 49247, testing of E. coli ATCC 35218 on Haemophilus test medium is an effective way to monitor the beta-lactamase inhibitors in some antimicrobial agent-methodology combinations.

A 5-year surveillance study of 44,691 isolates of Haemophilus influenzae project Beta-Alert 1993-1997.

Beta-Alert is a surveillance program developed in 1993 to monitor the percentage of beta-lactamase-producing Haemophilus influenzae isolates obtained from specimens submitted to regional commercial laboratories. The results of this study demonstrate that levels of beta-lactamase producers have remained between 31 and 38% in the United States over the past 5 years.

Interpretive criteria for testing susceptibility of staphylococci to mupirocin.

To determine appropriate mupirocin susceptibility testing interpretive criteria, 177 staphylococci were tested by agar dilution, disk diffusion, and E test. E test was found to be a reliable method for determining susceptibility of staphylococci to mupirocin. The agar dilution and disk diffusion results were plotted on a scattergram, and error rates were calculated. No errors were found with susceptibility breakpoints of > or = 4 microg/ml (MIC) and > or = 14 mm (zone diameter).

Evaluation of 500 gram negative isolates to determine the number of major susceptibility interpretation discrepancies between the Vitek and MicroScan Walkaway for 9 antimicrobial agents.

Although the Vitek and MicroScan Walkaway are two of the most commonly used automated antimicrobial susceptibility test systems, few studies have been performed comparing discrepancies between these systems. In this study, 500 Gram negative clinical isolates were tested against ampicillin, ampicillin/sulbactam, ticarcillin, ticarcillin/clavulanate, imipenem, ciprofloxacin, norfloxacin, mezlocillin, and piperacillin to determine the number of major interpretation discrepancies between the two systems. The 500 isolates consisted of 100 isolates each of Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Proteus mirabilis and Enterobacter species. Each isolate was tested simultaneously in both systems using the same standardized inoculum. Eighty-four major discrepancies occurred, of which 48 were reproducible. The reproducible discrepancy rate, for the 4,500 isolate/antimicrobic combinations tested, was 48 of 4500 (1.06%). The rate for individual antimicrobics varied from 17 of 500 (3.4%) for ampicillin to no discrepancies for ticarcillin or ciprofloxacin. Of the 48 reproducible discrepancies, 44 (92%) were Vitek resistant, MicroScan susceptible. Fifteen (31%) of the Vitek and 21 (44%) of the MicroScan results were confirmed by broth microdilution. Disk diffusion results were in agreement with 15 (31%) of the Vitek and 21 (44%) of the MicroScan results. Twelve (25%) of the broth microdilution and 12 (25%) of the disk diffusion results were intermediate. The broth microdilution and disk diffusion results for the 48 isolates with reproducible discrepancies were in agreement more often with MicroScan. However, there was less very major error comparing the Vitek results for these isolates to the broth microdilution and disk diffusion. Overall, the result of this evaluation indicate that the number of major interpretation discrepancies between the two systems is minimal for the isolate/antimicrobic combinations tested.

Stability of amoxicillin-clavulanate in BACTEC medium determined by high-performance liquid chromatography and bioassay.

The stabilities of amoxicillin (16 micrograms/ml) and clavulanate (8 micrograms/ml), alone and in combination in BACTEC medium (Middlebrook 7H12B medium), were determined by high-performance liquid chromatography (HPLC) and bioassay. By HPLC, the half-life of amoxicillin (trihydrate and sodium) in combination with clavulanate in nonradiolabelled 7H12B medium was 6.7 days, whereas the half-life of clavulanate in combination with amoxicillin was 2.0 days. By bioassay, the half-lives of amoxicillin trihydrate and clavulanate in radiolabelled 7H12B medium were comparable (7 and 2 days, respectively) to those determined by HPLC. When clavulanate was tested alone, the half-life was determined to be 1.88 days by HPLC and 1.87 days by bioassay. The relatively short half-life of clavulanate can be adjusted by a procedure of "topping up," or adding one-half the concentration of clavulanate every second day, in order to allow accurate amoxicillin-clavulanate MIC testing with the BACTEC mycobacterial susceptibility system.

Update on mupirocin resistance.

Mupirocin inhibits the activity of bacterial isoleucyl-tRNA synthetase resulting in a decrease or cessation of protein synthesis. Expression of resistance in staphylococci has been divided arbitrarily into two groups, low level (minimum inhibitory concentrations [MIC] of between 8 and 256 mg/L) and high level (MICs of > or = 512 mg/L). Low level resistance is associated with spontaneous mutational events, while high level resistance is mediated by a large transferable plasmid. The introduction of a nasal formulation of mupirocin raises many issues concerning staphylococcal breakpoints, since 20,000 mg/L is applied to the mucosal surface to eradicate nasal colonisation with staphylococci, as opposed to eliminating infection. For several years after its introduction reports of resistance in staphylococci were rare. However, the contemporary literature indicates reports of resistance in select populations, particularly associated with dermatology patients. The overall rate of resistance for organisms isolated from the nares is currently unknown. The recent introduction of the E test combined with the 5 microgram screening disk may assist in determining resistance rates in large populations.

Susceptibilities of nontuberculosis mycobacterial species to amoxicillin-clavulanic acid alone and in combination with antimycobacterial agents.

Neither amoxicillin nor clavulanic acid used alone was active at the highest level tested, i.e., 256.0 micrograms/ml, in vitro against 24 isolates of Mycobacterium fortuitum, Mycobacterium kansasii, and Mycobacterium marinum. However, the MIC of an amoxicillin-clavulanic acid combination of 2:1 was < or = 8.0/4.0 micrograms/ml for 50 percent of the isolates tested, with all isolates being inhibited in the range of 4.0/2.0 to 32.0/16.0 micrograms/ml, respectively. Titration of amoxicillin-clavulanic acid with a fixed 2-micrograms/ml concentration of ethambutol resulted in synergistic activity against 3 of 9 isolates of M. fortuitum, 10 of 10 isolates of M. kansasii, and 5 of 5 isolates of M. marinum. This observation was confirmed in a checkerboard analysis in which fractional inhibitory concentrations were < or = 0.5 for 20 of the 24 isolates. Synergistic activity was observed against the other four isolates in one of two trials. On the other hand, titration of amoxicillin-clavulanic acid in the presence of either one or two fixed concentrations of isoniazid, rifampin, cycloserine, tetracycline, or amikacin failed to result in synergism.

A survey of beta-lactamase-producing Haemophilus influenzae. An evaluation of 5750 isolates.

Previous studies have reported that 15%-34% of Haemophilus influenzae produce beta-lactamase. A surveillance program was developed by SmithKline Beecham Clinical Laboratories to determine the current percentage of beta-lactamase-producing H. influenzae from five selected geographic locations in the United States. In 1993, results of 5750 isolates from specimens submitted to five reference clinical laboratories were evaluated. Data were collected from 29 states and the District of Columbia. The percentages of beta-lactamase-producing H. influenzae was 33% and ranged from 22%-40% for the individual states.

Comparison of mupirocin susceptibility of nasal and nonnasal Staphylococcus aureus isolates.

Susceptibilities of 414 nasal and 586 nonnasal Staphylococcus aureus isolates, both methicillin resistant and methicillin susceptible, to the topical antimicrobial agent mupirocin were compared. A susceptibility of 99.1% was observed for the 1000 isolates. Nasal and nonnasal isolates showed a similar 90% minimum inhibitory concentration (MIC90) and statistically equivalent percent susceptibilities.

Comparison of three methods for determination of a single MIC of an antimicrobial agent.

Determining a single MIC of an antimicrobial agent that is not included on a routine susceptibility panel can be significantly time-consuming and costly. The UniScept MICRO-MIC, the JustOne, and the E test are single-MIC systems. These systems as well as disk diffusion were compared on the bases of time, cost, and ease of use.