a Departments of Clinical Microbiology, St Paul's Hospital (Grey Nuns') and Saskatoon and District Health b Department of Pathology, Royal University Hospital c the Department of Microbiology, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
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Abstract |
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Introduction |
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Non-fermentative Gram-negative bacilli are primarily nosocomial pathogens, are associated with infection at any anatomical location and are frequently classified as `opportunistic organisms'. Nosocomial Pseudomonas aeruginosa infections are associated with significant morbidity and mortality.2 Coincidentally, these organisms are often multi-resistant to a broad range of antimicrobial agents,2 and/or have the ability to develop resistance during therapy when a single antibiotic is used.
Cefepime is a broad-spectrum, fourth-generation cephalosporin with significant in-vitro antimicrobial advantages over other ß-lactam antimicrobial agents.3,4 Cefepime is active in vitroagainst the majority of bacterial pathogens that cause infections of the lower respiratory tract, urinary tract, skin and soft tissue and bacteraemia, including non-fermentative Gram-negative bacilli.
To date, there are limited Canadian studies testing large numbers of these organisms against a wide variety of antimicrobial agents. In this study we collected and tested 1466 isolates of P. aeruginosa, 21 isolates of Acinetobacter spp. and 31 isolates of Stenotrophomonas maltophilia against cefepime and seven other antimicrobial agents.
These data will contribute to currently available published literature, and collectively serve to establish baseline information on non-fermentative Gram-negative bacilli and their in-vitro susceptibility to antimicrobial agents from Canadian health care facilities.
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Materials and methods |
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All isolates were tested centrally at the Royal University Hospital in Saskatoon, Saskatchewan, Canada. MICs were determined using the broth microdilution method as recommended by the National Committee for Clinical Laboratory Standards (NCCLS).5 The MIC was defined as the lowest concentration of antimicrobial to allow no growth. The following American type culture collection (ATCC) microorganisms were tested each time susceptibility testing was performed: Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 25923 and P. aeruginosa ATCC 27853.
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Results |
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Discussion |
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While susceptibility data for these organisms have been published for the majority of antimicrobial agents tested in this study, only limited Canadian data exists for cefepime. Scriver et al.11 collected and tested 228 nosocomial P. aeruginosa isolates from 10 Canadian medical centres. The following resistance rates were determined: ceftazidime, 11.7%; cefepime, 28.6%; piperacillin/trazobactam, 10.9%; imipenem, 23.3%; gentamicin, 15.1%; tobramycin, 2.7% and ciprofloxacin, 4.8%. The susceptibility results recorded in this study are similar (within 2.52.6%) to those reported by Scriver et al.11 for ceftazidime, piperacillin/tazobactam and tobramycin, but not for the remaining agents. With the exception of ciprofloxacin, all other agents had higher resistance rates to comparable agents in the study of Scriver et al. versus this current investigation. The most dramatic differences seen between these studies were for cefepime (28.6% resistant versus 6.4% in our study) and imipenem (23.3% versus 5.2%). This difference may relate simply to the observation that our study involved collection of isolates from both in-patients and out-patients while the work of Scriver et al. was based on nosocomial isolates only. Also, the difference in the number of isolates tested, 1466 versus 228, may also account for some of the differences in resistance.
This current study is important because a large number of isolates have been tested against a wide variety of antimicrobial agents likely to be suitable for treatment of patients infected with non-fermentative Gram-negative bacilliespecially P. aeruginosa. To our knowledge, this is the largest Canadian study to date that has examined the in-vitro susceptibility of cefepime against non-fermentative Gram-negative bacilli. Our data suggest that cefepime is a useful agent for treating patients infected with P. aeruginosa and Acinetobacter spp.; however, its use, where infection by S. maltophiliaoccurs, is unlikely.
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Notes |
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References |
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2 . Pollack, M. (1990). Pseudomonas aeruginosa. In Principles and Practices of Infectious Diseases, 3rd edn (Mandell, G. L., Douglas, R. G. & Bennett, J. E., Eds), pp. 167391. Churchill Livingston, New York, NY.
3 . Clarke, A. M., Zemcov, S. J. & Wright, J. M. (1985). HR 810 and BMY-28142, two new cephalosporins with broad-spectrum activity: an in-vitro comparison with other ß-lactam antibiotics. Journal of Antimicrobial Chemotherapy 15, 30510.[Abstract]
4 . Tsuji, A., Maniatis, A., Bertram, M. A. & Young, L. S. (1985). In-vitro activity of BMY-28142 in comparison with those of other ß-lactam antimicrobial agents. Antimicrobial Agents and Chemotherapy 27, 5159.[ISI][Medline]
5 . National Committee for Clinical Laboratory Standards. (1997). Methods for Dilution Antimicrobial Susceptibility Tests for Bacteria that Grow AerobicallyFourth Edition: Approved Standard M7-A4. NCCLS, Wayne, PA.
6 . Chamberland, S., L'Ecuyer, J., Lessard, C., Bernier, M., Provencher, P., Bergeron, M. G. et al. (1992). Antibiotic susceptibility profiles of 941 Gram-negative bacteria isolated from septicemic patients throughout Canada. The Canadian Study Group. Clinical Infectious Diseases 15, 61528.[ISI][Medline]
7 . Hoban, D. J. & Jones, R. N. (1995). Canadian ofloxacin susceptibility study: a comparative study from 18 medical centers. Canadian Ofloxacin Study Group. Chemotherapy 41, 348.[ISI][Medline]
8 . Hoban, D. J. & Jones, R. N. (1993). The North American component (USA, Canada) of an international comparative MIC trial monitoring ofloxacin resistance. Drugs 45, Suppl. 3, 1679.
9 . Blondeau, J. M., Yaschuk, Y., Smith, J. A., Noble, M. A., Kibsey, P., Horsman, G. B. et al. (1996). Canadian ciprofloxacin susceptibility study: comparative study from 15 medical centers. Antimicrobial Agents and Chemotherapy 40, 172932.[Abstract]
10 . Forward, K. R., Low, D. E., Laverdiere, M., Rennie, R., Simor, A. E. & Franks, P. A. (1997). Study of the comparative activity of piperacillin/tazobactam with currently available antibiotics against 8206 aerobic isolates. Canadian Journal of Infectious Diseases 8, 14753.
11 . Scriver, S. R. & Low, D. E. (1995). Comparative activity of several antimicrobial agents against nosocomial Gram-negative rods isolated across Canada. Canadian Journal of Infectious Diseases 6, 7682.
Received 4 November 1998; returned 29 March 1999; revised 19 May 1999; accepted 1 June 1999