Genodiversity of resistant P. aeruginosa in ICUs varies in relation to antimicrobial usage and resistance rates

Abstract number: p1364

Jonas  D., Meyer  E., Schwab  F., Spitzmüller  B., Daschner  F., Grundmann  H.


The prevalence of resistant strains in health care institutions depends on the selection of imported resistance traits and the rate of spontaneously arising mutants, but can also be due to expansion by cross-transmission of resistant strains. To improve our understanding of the underlying dynamics, the frequency of different genotypes was determined in P. aeruginosa isolates from ICUs and correlated with antimicrobial usage densities (AD) and resistance rates (RR). The numbers of indistinguishable genotypes found were considered as an indirect measure of cross- transmission events.


From the German SARI surveillance project, 273 ciprofloxacin- and 317 imipenem-resistant isolates of P. aeruginosa were obtained from 29 ICUs, together with unit - based antimicrobial consumption data (AD) and resistance rates (RR). Additionally, for one month in spring 2003, the participants collected a cross sectional sample of 146 clinical P. aeruginosa isolates irrespective of the antimicrobial susceptibility. ICUs were grouped according to their relative positions above or below the median RR and AD of all ICUs. All strains were assigned ICU-based to genotypes by use of AFLP. ICU-specific diversity (Div) was expressed as the numbers of different genotypes per numbers of typed strains per ICU.


In ICUs with high RR and low AD, the genodiversity of resistant P. aeruginosa - isolates was significantly lower (Fisher P < 0.05) than in those ICUs that featured low RR in the presence of high AD. No such differences could be shown in the cross sectional sample of P. aeruginosa isolates irrespective of their antimicrobial susceptibility. RR correlated with AD. However, in ICUs with a low diversity of resistant P. aeruginosa - isolates there was a stronger rise of RR with increasing AD than in those ICUs with a high diversity.


This study on resistant P. aeruginosa supports the assumption that a high RR in the presence of low AD results from more frequent cross-transmission events. A stronger rise of RR in ICUs with a low genodiversity indicates that RR in ICUs might be markedly determined by cross-transmission events beside AD.

Session Details

Date: 01/08/2007
Time: 00:00-00:00
Session name: XXIst ISTH Congress
Location: Oxford, UK
Presentation type:
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