Prevalence and genetic diversity of extended-spectrum β-lactamase (ESBL)-producing Escherichia coli in nursing homes in Bavaria, Germany

Main goal of this study was to determine the prevalence and molecular epidemiology of extended-spectrum β-lactamase (ESBL)-producing Enterobacteriaceae among 156 nursing home residents in Bavaria and to compare the results with healthy individuals from the Bavarian community. Intestinal colonisation by ESBL-producing Escherichia coli was detected in 23 nursing home residents (14.7%) using MacConkey agar supplemented with cefotaxime (1 mg/L) for screening and the combined disc method for ESBL confirmation. Antimicrobial susceptibility testing revealed co-resistance to ciprofloxacin in 86.9% of the ESBL-producers. All isolates harboured CTX-M-ESBL with CTX-M-15 (65.2%) and CTX-M-27 (21.7%) as the most common types. Moreover, 16 isolates (69.6%) could be assigned by PCR-typing to the epidemic clonal lineage E. coli O25b-ST131. Further typing by rep-PCR and XbaI-macrorestriction with subsequent pulsed-field gel electrophoresis, respectively, revealed that two or more residents shared the same ESBL-producing E. coli clone in four nursing homes. In conclusion, we could show a high prevalence of ESBL-producing E. coli in Bavarian nursing homes (14.7%) compared to the healthy population (6.3%). Although the prevalence of ESBL-type CTX-M-15 in E. coli was similar in nursing home residents (65.2%) and healthy individuals (46%) the presence of E. coli O25b-ST131 clones differed substantially (69.6% and 14.2%, respectively). Furthermore, this study demonstrates that a person-to-person transmission or a common source of infection for ESBL-producing microorganisms may occur in these facilities. Therefore, basic hygiene measures should be assiduously implemented to prevent the further spread of these multidrug-resistant bacteria.