Contemporary in vitro spectrum of activity summary for antimicrobial agents tested against 18 569 strains non-fermentative Gram-negative bacilli isolated in the SENTRY Antimicrobial Surveillance Program (1997–2001)

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Abstract

The frequency of occurrence and antimicrobial susceptibility patterns of 18 569 non-fermentative Gram-negative bacilli consecutively collected as part of the SENTRY Antimicrobial Surveillance Program were summarized. The isolates were tested by the broth microdilution method in three coordinator laboratories using common reagents and reference methodologies. The most frequently isolated pathogen was Pseudomonas aeruginosa (11 968 isolates; 64.5%) followed by Acinetobacter spp. (3468 isolates; 18.7%) and Stenotrophomonas maltophilia (1488 isolates; 8.0%). The lowest resistance rates for P. aeruginosa documented were for amikacin (8%), meropenem (10%) and cefepime (10%), and all fluoroquinolones tested showed similar resistance rates (22–24%). The most active compounds against Acinetobacter spp. were the carbapenems, imipenem (11% resistance) and meropenem (12% resistance) followed by cefepime (31% resistance) and gatifloxacin (32% resistance). Very few compounds showed reasonable in vitro activity against S. maltophilia, with the most active antimicrobial agents being trimethoprim/sulphamethoxazole, gatifloxacin and levofloxacin (5–6% resistance). Resistance surveillance among these organisms remains necessary to guide empirical antimicrobial therapy, especially for these less frequently isolated and difficult to test pathogens.

Introduction

Non-fermentative Gram-negative bacilli (NFB) are primarily opportunists, mainly causing infections in seriously ill, hospitalised patients, immunocompromised hosts, and patients with cystic fibrosis. NFBs can be isolated from the environment, are intrinsically resistant to many commonly used antimicrobial agents and can cause indwelling device-related infections. Most of these organisms have the potential to spread horizontally on fomites or on the hands of medical personnel, and recent exposure to broad spectrum antimicrobial agents represents an important risk factor for acquisition of these organisms [1], [2], [3], [4].

Pseudomonas aeruginosa is a leading cause of nosocomial infection, especially among patient hospitalised in intensive care units [5], [6], [7]. This organism is the second most common cause of nosocomial pneumonia and the third most common cause of urinary tract infections in United States hospitals [8]. Acinetobacter spp. have also become an important cause of nosocomial infection, especially pneumonia, in the last years and the prevalence of Acinetobacter spp. infections shows intriguing regional and seasonal variations [1], [9], [10]. All other NFB are less frequently isolated, but the prevalence of infections caused by these pathogens has been constantly increasing [2], [3], [4]. In addition, susceptibility testing methodologies are not completely standardized for most of these organisms, especially routine tests used in clinical microbiology laboratories. Thus, the knowledge of their epidemiology and antimicrobial susceptibility patterns are necessary in order to allow the development of therapeutic strategies [11].

The objective of the present report was to establish the frequency of occurrence and the antimicrobial susceptibility of contemporary NFB species collected during the first 5 years (1997–2001) of the SENTRY Antimicrobial Surveillance Program worldwide.

Section snippets

Material and methods

The SENTRY Program monitored the predominant pathogens and antimicrobial resistance patterns of nosocomial and community-acquired infections via a broad network of sentinel hospitals in four major world regions: Asia-Pacific, Europe, Latin America, and the United States/Canada. The program was started in January 1997 and the primary monitored infections have been blood stream infections, outpatient respiratory tract infections due to specific fastidious organisms, pneumonia in hospitalised

Results

Table 1 shows the frequency of occurrence of various genus and species groups among the NFB. P. aeruginosa was the most frequently isolated pathogen (11 968 isolates; 64.5%), followed by Acinetobacter spp. (3468 isolates; 18.7%) and S. maltophilia (1488 isolates; 8.0%). These three pathogens accounted for more than 90% of the isolates processed. Any other pathogen accounted for ≤3% of the collection. The antimicrobial susceptibility patterns of P. aeruginosa, Acinetobacter spp. and S.

Discussion

Systemic infections due to NFB are usually difficult to treat because of relatively limited choice of effective antimicrobial agents. In addition, these pathogens frequently cause disease in severely debilitated or immunocompromised patients. Thus, mortality rates of NFB infections are generally high and the rapid introduction of appropriate empirical antimicrobial therapy is crucial to improve clinical outcome [1], [2], [3], [4], [11], [15].

P. aeruginosa is an important cause of a wide variety

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