Comparison of pulsed-field gel electrophoresis & repetitive sequence-based PCR methods for molecular epidemiological studies of Escherichia coli clinical isolates.

BACKGROUND & OBJECTIVES: PFGE, rep-PCR, and MLST are widely used to identify related bacterial isolates and determine epidemiologic associations during outbreaks. This study was performed to compare the ability of repetitive sequence-based PCR (rep-PCR) and pulsed-field gel electrophoresis (PFGE) to determine the genetic relationships among Escherichia coli isolates assigned to various sequence types (STs) by two multilocus sequence typing (MLST) schemes. METHODS: A total of 41 extended-spectrum ß-lactamase- (ESBL-) and/or AmpC ß-lactamase-producing E. coli clinical isolates were included in this study. MLST experiments were performed following the Achtman's MLST scheme and the Whittam's MLST scheme, respectively. Rep-PCR experiments were performed using the DiversiLab system. PFGE experiments were also performed. RESULTS: A comparison of the two MLST methods demonstrated that these two schemes yielded compatible results. PFGE correctly segregated E. coli isolates belonging to different STs as different types, but did not group E. coli isolates belonging to the same ST in the same group. Rep-PCR accurately grouped E. coli isolates belonging to the same ST together, but this method demonstrated limited ability to discriminate between E. coli isolates belonging to different STs. INTERPRETATION & CONCLUSIONS: These results suggest that PFGE would be more effective when investigating outbreaks in a limited space, such as a specialty hospital or an intensive care unit, whereas rep-PCR should be used for nationwide or worldwide epidemiology studies.

Application of BRAF, NRAS, KRAS mutations as markers for the detection of papillary thyroid cancer from FNAB specimens by pyrosequencing analysis.

BACKGROUND: BRAFV600E, the most common BRAF gene mutation, is detected in approximately 50% of sporadic papillary thyroid carcinoma (PTC) and may be associated with triggering tumorigenesis of PTC. The aim of our study was to discover additional mutations to increase the diagnostic performance of molecular tests in screening for thyroid cancer from fine needle aspiration biopsy (FNAB) specimens. METHODS: DNA was extracted from 120 freshly obtained FNAB specimens selected according to cytopathology grades of the Bethesda system. A conventional BRAF V600E test was carried out with real-time PCR, and further mutation screening for BRAF mutations in codons 464, 466, 469, NRAS and KRAS codons 12/13 and 61 was done by pyrosequencing. Histopathology reports were reviewed for those who underwent thyroidectomy (n=83). RESULTS: The real-time PCR method detected 45 BRAF V600E- positive cases whereas pyrosequencing detected 30 cases. Additional BRAF (n=4), NRAS (n=11) and KRAS (n=3) mutations were detected in 17 cases (one overlapping BRAF and NRAS mutation). Among 11 NRAS-mutated cases, eight were confirmed as PTC and one as FVPTC on histopathology reports. Five PTC-confirmed cases with BRAF V600E mutation showed additional mutations, all of which were NRAS mutations. DISCUSSION: Despite the higher sensitivity of real-time PCR for detecting BRAFV600E mutations, pyrosequencing easily detected additional point mutations. NRAS mutations were the most prevalently identified additional mutations and were highly associated with malignancy. In conclusion, our findings demonstrate that additional mutations identified by pyrosequencing may help in the pre-operative process in determining the possibility of malignancy and further studies on the occurrence of simultaneous mutations of BRAF, KRAS and NRAS may be warranted.