Transmission of bacterial strains between patients is a serious problem in hospitals and with the increasing rate of antibiotic resistance the problem has farther escalated. Enterobacteriaceae produced extended-spectrum beta-lactamses (ESBLs), especially Escherichia coli (E-coli), are increasingly important nosocomial pathogens (7, 8). These bacteria are often multiple resistant and are responsible for many intestinal infections and urinary tract infections (2, 5). With the more frequent use of invasive devices in hospital care, these types of nosocomial infections have increased, particularly in seriously ill patients.

In order to diminish transmission of bacterial strains between patients and to study the epidemiology of these bacteria, it is of great importance to develop rapid and specific methods to be able to subtype on strain-level, i.e. to create a fingerprint of the isolates. The method may be based on phenotypic or genotypic characteristics of the microorganism. Any typing method must have high reproducibility and discrimination power to differentiate unrelated strains and also to demonstrate relationship of organisms deriving from the same source. In the present project, a Pulsed-Field Gel Electrophoresis (PFGE) assay for genotyping clinical E. coli isolates was used. PFGE can be used as a genotyping tool and is widely used to type bacteria and trace nosocomial infection. However, the method is time-consuming and relatively expensive in compare with other methods like PCR. In this study, a total of 93 strains were collected. The study was aimed to investigate the genotypes of the collected isolates and to identify and potential the outbreak strains.

The isolates investigated were genotypically diverse shown by a variety of PFGE banding patterns. However, clusters of closely related isolates involved in outbreaks were also identified.

In conclusion, when analyzing a large number of strains, a combination of a rapid phenotyping or genotyping method and a powerful genotyping method like PFGE would be an appropriate strategy for studying clonal relationship among isolates e.g. for detecting cross-transmission of nosocomial pathogens.