Changes in susceptibility profile of Gram-negative organisms from bloodstream infection during 2005 to 2009 in a tertiary care hospital

Background:

Increasing resistance to broad-spectrum cephalosporins and carbapenens among Gram-negative isolates causing infections is a major challenge to medical practitioners and institutions. Variability between institutes is substantial, and requires timely microbiological surveillance and assessment of antimicrobial resistance of local trends since local epidemiology is essential for a correct empiric treatment and successful outcome.

Objective:

This retrospective review was conducted to evaluate the microbiological spectrum and susceptibility pattern of Gram-negative bacteria isolated from bloodstream infection (BSI).

Methods: Clinical species isolated from bloodstream infections in Hospital Heliópolis, a teaching tertiary hospital located in the city of São Paulo, Brazil were analysed. Data was grouped in two periods: from August 2005 to  July 2007 (period 1) and from to August 2007 to July 2009 (period 2). Identification and antimicrobial susceptibility testing were performed with the automated MicroScan system and later confirmed for the ESBL and carbapenemase-producing phenotypes by the standard doubledisc synergy test, Etest and a modified Hodge test. Nominal parameters were compared using the χ2 test, p-values ≤0.05 were considered to be statistically significant. The statistical software package SPSS v13.0 (SPSS, Inc., Chicago, IL, USA) was used for all of the data analyses.

Results:

 Gram-negative accounted for 351 episodes of bacteremia , mainly Acinetobacter baumannii, Klebsiella pneumoniae, Escherichia coli and Pseudomonas aeruginosa. Carbapenem-resistant (CR) A. baumanni accounted for 60% and 55% for the isolates in period 1 and 2 respectively (p=0.5), CR P. aeruginosa accounted for  50% and 39% (p=0.3) isolates  between the periods. There was a significant increase in the incidence of ESBL-producing K. pneumoniae, 52% in the first period and 78% in the second period (p=0.02). Fluoroquinolones susceptibility rates for K. pneumoniae were significaltly lower in the second period (56% to 29%, p=0.03). During the second period 11% of K. pneumoniae isolates were carbapenem-producing K. pneumoniae (p=0.06). Resistance profile of other Enterobacteriaceae  to cephalosporins and carbapenens did not differ from the first to the second period.

Conclusions:

In an era of pan-resistant bacteria when few antibiotic options are available, local susceptibility data is essential for empirical therapy. The results of this study showed high rates of resistance to carbapenens among three of the four most important bacteria responsible for BSI in our institution.