a Department of Paediatrics, Division of Infectious Diseases and Geographic Medicine, b Clinical Microbiology Laboratory, Primary Children's Medical Center and c Department of Pathology, University of Utah School of Medicine, Salt Lake City, UT, USA
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Abstract |
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Introduction |
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Materials and methods |
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Susceptibility testing was performed using the disc diffusion method as described by the NCCLS.8 Briefly, all inocula were prepared from a pure agar plate culture, with isolates that were 1824 h old. Organisms were prepared in 0.85% saline and adjusted to match a 0.5 McFarland standard with a photometer. All organisms were tested on MuellerHinton agar (Becton Dickinson, Cockeysville, MD, USA). Discs containing 10 µg of imipenem or meropenem, or 30 µg of ceftazidime or cefepime were obtained from Becton Dickinson. Zone diameters were measured after incubation of plates in ambient air at 35°C for 1618 h. Interpretation of zone diameters for cefepime, ceftazidime and imipenem as susceptible, intermediate or resistant was based upon NCCLS guidelines.9 Interpretation of zone diameters for meropenem was based upon the manufacturer's guidelines.10 Escherichia coli ATCC 25922 and P. aeruginosa ATCC 27853 were included as quality control strains following the protocol described above.
The activity of other antimicrobial agents commonly used to treat pulmonary infections in CF patients was tested using the technique described above. NCCLS guidelines were used to interpret the results.9
The majority of CF patients in our institution receive antimicrobial therapy consisting of combinations of ticarcillinclavulanic acid and tobramycin or ceftazidime and tobramycin. Nebulized colistin and tobramycin are also commonly used. Specific details of antimicrobial therapy for each patient submitting sputum specimens for culture were not collected.
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Results |
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Data on the in vitro susceptibility of P. aeruginosa isolates to other antimicrobial agents was available for 55 of the isolates. These data are presented in Table II. Many of our isolates were resistant to trimethoprim sulphamethoxazole, amikacin and tobramycin. The majority (
80%) of isolates tested were susceptible to the ß-lactam antibiotics tested. Forty-two per cent of the P. aeruginosa isolates were mucoid in phenotype. No difference in susceptibility was observed between mucoid and non-mucoid isolates.
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Discussion |
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More discrepancies were seen when comparing cefepime with ceftazidime. Four (6.0%) of the 67 isolates were more susceptible to cefepime than to ceftazidime, but eight (11.9%) showed the reverse pattern.
Based on our data, meropenem and cefepime may be of value for the treatment of pulmonary exacerbations in patients with CF, especially in those patients infected with multiple organisms such as Staphylococcus aureus and P. aeruginosa.
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Acknowledgments |
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Notes |
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References |
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2 . Webb, A. K. (1995). The treatment of pulmonary infection in cystic fibrosis. Scandinavian Journal of Infectious Diseases 96, Suppl., 247.
3 . Arrieta, A. (1997). Use of meropenem in the treatment of serious infections in children: review of the current literature. Clinical Infectious Diseases 24, Suppl. 2, S20712.[ISI][Medline]
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5 . Byrne, S., Maddison, J., Connor, P., Doughty, I., Dodd, M., Jenney, M. et al. (1995). Clinical evaluation of meropenem versus ceftazidime for the treatment of Pseudomonas spp. infections in cystic fibrosis patients. Journal of Antimicrobial Chemotherapy 36, Suppl. A, 13543.[ISI][Medline]
6 . Huls, C. E., Prince, R. A., Seilheimer, D. K. & Bosso, J. A. (1993). Pharmokinetics of cefepime in cystic fibrosis patients. Antimicrobial Agents and Chemotherapy 37, 14146.[Abstract]
7 . Barradell, L. B. & Bryson, H. M. (1994). Cefepime: a review of its antibacterial activity, pharmacokinetic properties and therapeutic use. Drugs 47, 471505.[ISI][Medline]
8 . National Committee for Clinical Laboratory Standards. (1997). Performance Standards for Antimicrobial Disk Susceptibility TestsSixth Edition: Approved Standard M2-A6. NCCLS, Villanova, PA.
9 . National Committee for Clinical Laboratory Standards. (1997). Performance Standards for Antimicrobial Susceptibility Tests: Approved Standard M100-S7. NCCLS, Villanova, PA.
10 . Zeneca Pharmaceuticals. (1996). Susceptibility Test Criteria. Zeneca Pharmaceuticals. Wilmington, DE.
11 . Bauernfeind, A., Jungwirth, R. & Schweighart, S. (1989). In-vitro activity of meropenem, imipenem, the penem HRE 664 and ceftazidime against clinical isolates from West Germany. Journal of Antimicrobial Chemotherapy 24, Suppl. A, 7384.
12 . Ballestero, S., Fernandez-Rodriguez, A., Villaverde, R., Escobar, H., Perez-Diaz, J. C. & Baquero, F. (1996). Carbapenem resistance in Pseudomonas aeruginosa from cystic fibrosis patients. Journal of Antimicrobial Chemotherapy 38, 3945.[Abstract]
Received 9 July 1999; returned 11 November 1999; revised 22 December 1999; accepted 17 January 2000