Evaluation of an accelerated protocol for detection of extended-spectrum beta-lactamase-producing gram-negative bacilli from positive blood cultures

Multiresistant Enterobacteriaceae: new threat of an old problem

The Enterobacteriaceae are among the most important causes of serious nosocomial and community-onset bacterial infections in humans, and resistance to antimicrobial agents in these species has become an increasingly relevant problem for healthcare providers. beta-lactam and fluoroquinolone antibiotics are important drug classes used to treat infections caused by Enterobacteriaceae. Emerging resistance mechanisms against these agents have recently been described in Enterobacteriaceae and include the production of newer beta-lactamases and plasmid-mediated quinolone resistance. The newer beta-lactamases consist of the following: plasmid-mediated AmpC beta-lactamases (e.g., ephamycin [CMY], CMY types), extended-spectrum beta-lactamases (e.g., cefotaxime [CTX], CTX-M first isolated at Munich) and carbapenem-hydrolyzing enzymes (e.g., Klebsiella pneumoniae carbapenemase [KPC], KPC types and the metallo-beta-lactamases). Recent developments in the epidemiology, clinical relevance and laboratory detection of infections caused by multiresistant Enterobacteriaceae with these new types of resistance mechanisms will be addressed in this review.

Predictors of mortality in patients with bloodstream infection due to ceftazidime-resistant Klebsiella pneumoniae

Bloodstream infection (BSI) due to multidrug-resistant Klebsiella is associated with high rates of morbidity and mortality. The aim of this study was to identify predictors of in-hospital mortality among patients with BSI due to ceftazidime-resistant (CAZ-R) Klebsiella pneumoniae at a tertiary care medical center. Patients with CAZ-R K. pneumoniae BSI were identified by our microbiology laboratory between January 1995 and June 2003. Clinical data were collected retrospectively. Logistic regression was used to identify independent predictors of all causes of in-hospital mortality. Of 779 patients with K. pneumoniae BSI, 60 (7.7%) had BSI due to CAZ-R K. pneumoniae; 43 (72%) of these were nosocomial infections. Pulsed-field gel electrophoresis identified a single predominant strain in 17 (28%) patients. The in-hospital mortality rate was 43% (n = 26). Among patients with CAZ-R K. pneumoniae BSI, those who died were similar to survivors with respect to demographic, clinical, and antimicrobial susceptibility characteristics. Only 43 (72%) patients received effective therapy within 5 days of BSI. In bivariable analysis, delay in initiation of effective therapy for >72 h after diagnosis of BSI was associated with death (P = 0.03). Strain genotype was not predictive of outcome. In multivariable analysis, delay in initiation of effective therapy for >72 h after diagnosis of BSI was an independent predictor of death (odds ratio, 3.32; 95% confidence interval, 1.07 to 10.3). Thus, among patients with BSI due to CAZ-R K. pneumoniae, a delay in the initiation of effective therapy of greater than 72 h after BSI was associated with a >3-fold increase in mortality risk.

Influx of extended-spectrum beta-lactamase-producing enterobacteriaceae into the hospital

BACKGROUND

The prevalence of infections caused by extended-spectrum beta -lactamase (ESBL)-producing Enterobacteriaceae is increasing worldwide. The influx of these bacteria into hospitals has major implications for infection-control and empirical treatment strategies.

METHODS

Isolates from 2 patient cohorts--patients with gram-negative bacteremia within 2 days after admission and patients screened for fecal colonization at admission--were assessed for ESBL production. ESBL phenotype was confirmed according to Clinical and Laboratory Standards Institute guidelines. Predictors of ESBL phenotype were examined by univariate and multivariate analyses.

RESULTS

Of 80 Enterobacteriaceae isolates from blood samples obtained at admission to the hospital, 13.7% produced ESBL. Thirty-eight patients with ESBL-positive isolates and 72 with ESBL-negative isolates were included in a case-control study. Predictors of ESBL production were male sex and nursing home residence (area under receiver operator characteristic curve, 0.7). Of 241 persons screened at admission, 26 (10.8%) had fecal carriage of ESBL-producing Enterobacteriaceae. Predictors of fecal carriage were poor functional status, antibiotic use, chronic renal insufficiency, liver disease, and use of histamine2 blockers (area under receiver operator characteristic curve, 0.8). Four (15.4%) of the 26 individuals with fecal carriage had subsequent bacteremia with ceftazidime-resistant Enterobacteriaceae, compared with 1 (0.5%) noncarrier (odds ratio, 38.9; P<.001). Of 80 ESBL-producing Enterobacteriaceae isolates obtained at admission, 65 were health care associated, and 15 were community acquired. The 15 community-acquired ESBL-producing Enterobacteriaceae belonged to diverse clones. The most prevalent ESBL gene among these isolates was CTX-M-2 (found in 53.3% of the isolates).

CONCLUSIONS

We report high rates of bacteremia and colonization with ESBL-producing Enterobacteriaceae at admission to our institution, which may undermine infection-control measures and complicate the selection of empirical treatment.