Epidemiology of ESBL-producing E. coli with special reference to outbreak detection

Abstract: Multidrug resistant bacteria, particularly extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae (EPE), are becoming a major health concern. ESBL-producing Escherichia coli (ESBL-E. coli) is the most prevalent type. ESBL-genes are carried on plasmids, often by bacteria belonging to clones with properties that facilitate transmission. An example is E. coli of sequence type (ST) 131, and its sublineage ST131-O25b. The most prevalent ESBLs world-wide are the CTX-M enzymes, most often belonging to the CTX-M-1 group. In Paper I the epidemiology of ESBL-E. coli causing urinary tract infection was studied from the first detected cases until these bacteria were established in the greater Gothenburg area. The first cases where seen in women from the community setting in 2003-2005. In 2008-2009, the elderly and men were also affected. The ST131-O25b sublineage became established during the study period, but otherwise the emergence of ESBL-E. coli was polyclonal. There was a shift in ESBL types in favor of the CTX-M-1 group enzymes. In Papers II and III PFGE, standard method for epidemiological typing at the time, was compared to other methods. For investigation of a polyclonal ESBL-E. coli outbreak, MLVA was found comparable to PFGE, whereas MLST-analysis was not useful. For continuous epidemiological surveillance of ESBL-E. coli, both MLVA and MLST were inferior to PFGE, especially for typing the ST131-O25b sublineage. This thesis demonstrates how the epidemiology of ESBL-E. coli might change over time, emphasising the need of continuous surveillance using optimal typing methods to detect outbreaks at the local level. We propose that an abbreviated MLVA might be useful to preselect isolates for more discriminating typing methods.