Resistance of gram-negative non-fermentative bacilli causing bloodstream infection, Vienna, 1996-2003

High resistance of Pseudomonas aeruginosa to paromomycin, an agent used for selective bowel decontamination (SBD)

BACKGROUND

Paromomycin is used for selective bowel decontamination (SBD) in patients undergoing bone marrow transplantation in many hospitals, but there are no published resistance data for this compound in the recent medical literature. The aim of this study was to investigate the in vitro activity of paromomycin against the common intestinal bacteria E. coli and P. aeruginosa.

METHODS

94 E. coli isolates and 77 P. aeruginosa isolates derived from clinical specimens were tested by broth microdilution against paromomycin and amikacin, respectively, following the CLSI recommendations for testing amikacin.

RESULTS

86 of 94 E. coli isolates (91%) and 71 of 77 P. aeruginosa isolates (92%) showed in vitro susceptibility to amikacin (MIC90 for both compounds: 16 µg/ml, range: 1-32 µg/ml for E. coli and 1->128 µg/ml for P. aeruginosa). Paromomycin was active against 83/94 E. coli isolates (88%; MIC90: 32 µg/ml, range: 2->128 µg/ml), but showed poor in vitro activity against P. aeruginosa (3/77 isolates susceptible [4%]; MIC90: >128 µg/ml, range: 2->128 µg/ml).

CONCLUSION

If SBD with inclusion of an aminoglycoside antibiotic is applied, paromomycin should not be used unless local resistance data provide evidence of a sufficient in vitro activity of this compound against P. aeruginosa.

Epidemiology of bacteremia caused by uncommon non-fermentative gram-negative bacteria

Background

Prevalence of bacteremia caused by non-fermentative gram-negative bacteria (NFGNB) has been increasing over the past decade. Although many studies have already investigated epidemiology of NFGNB bacteremia, most focused only on common NFGNB including Pseudomonas aeruginosa (PA) and Acinetobacter baumannii (AB). Knowledge of uncommon NFGNB bacteremia is very limited. Our study aimed to investigate epidemiology and identify factors associated with uncommon NFGNB bacteremia.

Methods

This observational study was conducted at a university hospital in Thailand during July 1, 2007-Dec 31, 2008. All patients who had at least one blood culture positive for NFGNB and met the criteria for systemic inflammatory response syndrome within 24 hours before/after obtaining the blood culture were enrolled. The NFGNB isolates that could not be satisfactorily identified by the standard biochemical assays were further characterized by molecular sequencing methods. To identify factors associated with uncommon NFGNB bacteremia, characteristics of patients in the uncommon NFGNB group were subsequently compared to patients in the common NFGNB group (AB and PA bacteremia).

Results

Our study detected 223 clinical isolates of NFGNB in 221 unique patients. The major causative pathogens were AB (32.7%), followed by PA (27.8%), Stenotrophomonas maltophilia (5.4%), Acinetobacter lwoffii (4.9%) and Burkholderia pseudomallei (2.7%). Infection-related mortality was 63.0% in the AB group, 40.3% in the PA group and 17.4% in the uncommon NFGNB group. Factors associated with uncommon NFGNB bacteremia (OR [95% CI]; p-value) were male sex (0.28 [0.14-0.53]; p < 0.001), hospital-acquired infection (0.23 [0.11-0.51]; p < 0.001), recent aminoglycosides exposure 0.23 [0.06-0.8]; p = 0.01), primary bacteremia (6.43 [2.89-14.2]; p < 0.001]), catheter related infection (4.48 [1.54-13.06]; p < 0.001) and recent vancomycin exposure (3.88 [1.35-11.1]; p = 0.02).

Conclusions

Our distribution of causative pathogens was slightly different from other studies. The common NFGNB group had a remarkably higher ID-mortality than the uncommon NFGNB group. Knowledge of factors associated with uncommon NFGNB bacteremia would help physicians to distinguish between low vs. high risk patients.

The comparison of susceptibility patterns of Gram-negative invasive and non-invasive pathogens in Estonian hospitals

A total of 560 invasive and 1062 non-invasive isolates were collected. The antimicrobial susceptibility of invasive versus non-invasive Pseudomonas aeruginosa, Acinetobacter baumannii, and Klebsiella pneumoniae isolates were evaluated using the E-tests. The equal domination of Gram-negative among both invasive and non-invasive pathogens was estimated in our study if contaminants were excluded. The emergence trend of Gram-positive microbes especially of coagulase negative staphylococci may be proved only after application of exclusive algorithms. Due to similar susceptibility, the data of non-invasive Gram-negative pathogens can be useful to predict resistance of invasive ones. Also, the surveillance of invasive pathogens provides useful information about the general susceptibility of pathogens.

Acinetobacter baumannii: emergence and spread in Israeli hospitals 1997-2002

The incidence of multi-drug-resistant Acinetobacter baumannii bloodstream infections (BSIs) increased two- to four-fold in three Israeli hospitals between 1997 and 2002, accounting for 3.5-18% of all hospital-acquired BSIs. This was associated with increasing carbapenem resistance reaching 35-54%, and by a dramatic increase in carbapenem consumption. In-hospital fatality rates ranged between 47% and 58% and were significantly higher than those seen with other nosocomial Gram-negative pathogens. A. baumannii was not restricted to intensive care units, but had spread to all hospital wards. Multi-drug-resistant A. baumannii has the potential to reach endemicity in hospitals and warrants more vigorous and innovative efforts to limit its spread.

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

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.