This study investigated the extent to which multidrug resistance (MDR) among Enterobacteriaceae is related to DNA elements called "integrons," whether the relationship is species dependent or origin dependent, and which resistance patterns are associated with integrons. Analysis of 867 nonrepeat isolates comprising 8 species and originating from the community and 23 European hospitals showed a significant relation between MDR and integrons, independent of species or origin. Although resistance to each tested antimicrobial agent was significantly associated with integrons, only resistance to sulfamethoxazole, cotrimoxazole, gentamicin, tobramycin, ampicillin, piperacillin, and cefuroxime predicted the presence of integrons. Combined resistance to both ampicillin and sulfamethoxazole-trimethoprim was the starting point for the development of resistance to additional beta-lactams, aminoglycosides, cephalosporins, and ciprofloxacin, a development paralleled by an increasing prevalence of integrons. The acquisition of resistance genes is not random, and the transfer of integron-carrying elements plays a dominant role in the development of MDR by Enterobacteriaceae.

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SOD and SDD have marked effects on the bacterial ecology in an ICU, with rising ceftazidime resistance prevalence rates in the respiratory tract during intervention and a considerable rebound effect of ceftazidime resistance in the intestinal tract after discontinuation of SDD.

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Multidrug resistance in gram-negative bacteria appears to be primarily the result of the acquisition of resistance genes by horizontal transfer. To what extent horizontal transfer may be responsible for the emergence of multidrug resistance in a clinical setting, however, has rarely been investigated. Therefore, the integron contents of isolates collected during a nosocomial outbreak of genotypically unrelated multidrug-resistant Enterobacteriaceae were characterized. The integron was chosen as a marker of transfer because of its association with multiresistance. Some genotypically identical isolates harbored different integrons. Grouping patients carrying the same integron yielded 6 epidemiologically linked clusters, with each cluster representing a different integron. Several patients carried multiple species harboring the same integron. Conjugation experiments with these strains resulted in the transfer of complete resistance patterns at high frequencies (10(-2) to 10(-4)). These findings provide strong evidence that the horizontal transfer of resistance genes contributed largely to the emergence of multidrug-resistant Enterobacteriaceae in this clinical setting.

The proportion of enterococcal infections caused by ampicillin-resistant Enterococcus faecium (AREfm) in a European hospital increased from 2% in 1994 to 32% in 2005, with prevalence rates of AREfm endemicity of up to 35% in at least six hospital wards. Diabetes mellitus, three or more admissions in the preceding year, and use of beta-lactams and fluoroquinolones, were all associated with AREfm colonisation. Of 217 AREfm isolates that were genotyped, 97% belonged to clonal complex 17 (CC17). This ecological change mimics events preceding the emergence of vancomycin-resistant E. faecium (VREF) in the USA and may presage the emergence of CC17 VREF in European hospitals.

Integrons are strongly associated with the multidrug resistance seen in gram-negative bacilli in the hospital environment. No data, however, are available on their prevalence in the community. This study is the first to show that integrons are widespread in Enterobacteriaceae in the community and that integron-associated resistance genes in the community constitute a substantial reservoir for multidrug resistance in the hospital.Multidrug resistance among Enterobacteriaceae in the hospital setting is an increasing problem. The development of control strategies, therefore, is of major importance. The acquisition of an array of resistance genes by horizontal transfer, mediated by plasmids and transposons, is currently thought to play an increasing role in the development of this multiresistance. A substantial portion of the resistance genes present on plasmids and transposons is integrated into DNA elements called class 1 integrons (4, 9). These genetic elements comprise a site-specific recombination system capable of integrating and expressing those genes contained in cassette-like structures.

Postexposure screening of HCWs allowed early detection of MRSA carriage and prevention of subsequent transmission to patients. Where the MRSA prevalence is higher, the role of HCWs may be greater. In such settings, an adapted version of our program could help prevent dissemination.