Review
Antimicrobial susceptibility of uncommonly isolated non-enteric Gram-negative bacilli

https://doi.org/10.1016/j.ijantimicag.2004.10.002Get rights and content

Abstract

The frequency of occurrence and antimicrobial susceptibility patterns of 3059 non-enteric Gram-negative bacilli (NGB), other than Pseudomonas aeruginosa and Acinetobacter spp., consecutively collected as part of the SENTRY Antimicrobial Surveillance Program (1997–2003) were reviewed. During this period, a total of 221,084 bacterial isolates were collected from several clinical specimens worldwide, including 25,305 (11.5%) NGB. Acinetobacter spp. and P. aeruginosa accounted for 82.7% of the NGB isolates and have been excluded from this analysis. The antimicrobial susceptibility results of 3509 strains from 13 species/genera have been analysed in this review. The isolates were tested by reference broth microdilution methods in three central laboratories using common reagents and procedures. More than 30 antimicrobial agents were tested and the results for the 18 most active compounds are reported here. Stenotrophomonas maltophilia (2076 strains; 59.2%) was the most frequently isolated pathogen in this group, followed by Aeromonas spp. (385 strain; 11.0%), Burkholderia cepacia (269 strains; 7.7%), Pseudomonas fluorescens/putida (253 strains; 7.2%) and Alcaligenes spp. (236 strains; 6.7%). All other species/genera accounted for less than 3% of the isolates analysed. The antimicrobial agents with the most consistent activity against the NGB evaluated in the present study were the newer fluoroquinolones gatifloxacin and levofloxacin with 84.1 and 84.9% susceptibility overall. Trimethoprim/sulphamethoxazole was active against 85.3% of the isolates tested, but showed reduced activity against P. fluorescens/putida (22.1% susceptibility). Antimicrobial susceptibility varied significantly between species/genera and the geographical regions evaluated. Thus, proper identification and quantitative susceptibility testing will be required for the treatment of NGB infections. Extensive worldwide surveillance programmes remain extremely important to guide empirical antimicrobial therapy for rarely isolated pathogens and also for pathogens that are not routinely tested due to the lack of standardised susceptibility testing methods.

Introduction

Non-enteric Gram-negative bacilli (NGB) are primarily opportunists, causing infections in immunocompromised hosts and seriously ill hospitalised patients. NGBs can be isolated from the environment and are often intrinsically resistant to commonly used antimicrobial agents. Most of these organisms have the potential to contaminate the hospital environment and to spread horizontally on fomites or the hands of healthcare workers, and are frequently linked to hospital outbreaks. Recent exposure to broad-spectrum antimicrobial agents, central venous catheters or invasive diagnostic procedures represent important risk factors for acquisition of these pathogens [1], [2], [3], [4], [5].

Pseudomonas aeruginosa and Acinetobacter spp. are responsible for more than 80% of the NGB infections. P. aeruginosa is a leading cause of nosocomial infection, especially among patients hospitalised in intensive care units [6], [7]. This organism is the second most common cause of nosocomial pneumonia and third in occurrence as a cause of urinary tract infections in United States hospitals [8]. Acinetobacter spp. have also become an important cause of nosocomial infection, especially pneumonia [9]. All other NGBs are less frequently encountered, but the prevalence of infections caused by these pathogens in general has been constantly increasing [1], [2], [3], [4], [5]. In addition, susceptibility testing methodologies are not standardised for most of these organisms, especially routine or automated commercial tests used in clinical microbiology laboratories, although some standard-defining organisations are actively seeking validated standardised methods [NCCLS, 2005]. Thus, the knowledge of their epidemiology and antimicrobial susceptibility patterns is necessary to allow the development of empirical therapeutic strategies [10].

The objective of this report was to review the antimicrobial susceptibility of contemporary less frequently isolated NGB species from resources using reference MIC methods.

Section snippets

Form of study

The SENTRY Antimicrobial Surveillance Program monitors the predominant pathogens and antimicrobial resistance patterns of nosocomial and community-acquired infections via a broad network of sentinel hospitals in four major geographical regions: Asia-Pacific (also South Africa), Europe, Latin America, and the United States/Canada. The programme was initiated in early 1997 and the primary monitored infections have uniformly been bloodstream infections, outpatient respiratory tract infections

Frequency of occurrence

A total of 221,084 bacterial isolates were collected by the SENTRY Program between January 1997 and December 2003. Among those, 25,305 isolates (11.5%) were NGB. P. aeruginosa (16,247 strains) and Acinetobacter spp. (4677 strains) represented 82.7% of NGB and these species were excluded from further analysis. The 3509 isolates analysed here represented 13.9% of the NGB or 1.6% of the total number of isolates collected by the SENTRY Program during this 7-year period.

Table 1 lists the frequency

Aeromonas spp.

Aeromonas is the only genus within the family Aeromonadaceae that is pathogenic for humans [13], [14]. Aeromonads are inhabitants of aquatic ecosystems worldwide, including groundwater and drinking water at treatment plants and in distributions systems or reservoirs as well as clean or polluted lakes and rivers [15], [16]. Most Aeromonas species, particularly those associated with human infections, are found on a wide variety of fresh produce, meat (beef, poultry, pork) and dairy products (raw

Potency and spectrum of the most active antimicrobials

Table 3 shows the in vitro activity of key antimicrobial agents in each class. The percentages of susceptibilities were calculated based on the breakpoints established by the NCCLS for non-enteric bacilli [12], [27]. The activity of the two cephalosporins mostly used to treat infections caused by non-enteric bacilli (ceftazidime and cefepime) varied significantly among the pathogens evaluated. Ceftazidime showed higher activity than cefepime against Alcaligenes spp., B. cepacia, Comamonas spp.,

Discussion

Systemic infections due to NGB have become increasingly more frequent in recent years [3], [4], [5]. During the 1997–2003 period, the SENTRY Program collected 109,225 bacterial isolates from bloodstream infections worldwide and 10,120 (9.3%) were represented by NGB. P. aeruginosa and Acinetobacter spp. were by far the most frequent pathogens, representing 7.5% of all bacterial pathogens and more than 80% of NGB isolated from bloodstream infections. Systemic infections due to NGB are usually

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