In summary, our results denote the importance of the intestinal tract as a reservoir for ESBL-producers both in the community and in the hospital settings. Besides being able to serve as outbreak sources directly, they may also act as resistance gene reservoirs. The study draws attention to the different epidemiology of colonization with ESBL-producers in both hospital and community. Sources of colonization in the employment screening group in 2009-10, outpatients, screened medical students and pediatric patients in 2010-13, seem to involve environment-based besides nosocomial sources. In contrast, it was shown that colonization precedes infection in case of adults and they are more likely to acquire colonizer strains in the hospital. Intestinal colonization by these organisms among pediatric patients, can be a source for influx of ESBL determinants into the hospital settings and can represent a risk factor for colonization as well as infection of other hospitalized patients and health workers. We found a marked decrease of diversity in ESBL genes among the employment screening group in 2013-14. This suggests that ESBL-producers originating from different sources in 2009-10, have been replaced by highly successful blaCTX-M-15 producing E. coli. This was in line with our observation of the increase in the importance of blaCTX-M-15 gene in both E. coli and K. pneumoniae in 2010-13. The reason might be related to the exportation of blaCTX-M-15 producing E. coli, with majority belonged to phylogroup B2, from hospital to the community, and consequently further spread within the community.