ABSTRACTDespite the emergence of non-O157 Shiga toxin-producingEscherichia coli(STEC) infections,E. coliserotype O157 is still the most commonly identified STEC in the world. It causes high morbidity and mortality and has been responsible for a number of outbreaks in many parts of the world. Various methods have been developed to detect this particular serotype, but standard bacteriological methods remain the gold standard. Here, we propose a new peptide nucleic acid fluorescencein situhybridization (PNA-FISH) method for the rapid detection ofE. coliO157. Testing on 54 representative strains showed that the PNA probe is highly sensitive and specific toE. coliO157. The method then was optimized for detection in food samples. Ground beef and unpasteurized milk samples were artificially contaminated withE. coliO157 concentrations ranging from 1 × 10−2to 1 × 102CFU per 25 g or ml of food. Samples were then preenriched and analyzed by both the traditional bacteriological method (ISO 16654:2001) and PNA-FISH. The PNA-FISH method performed well in both types of food matrices with a detection limit of 1 CFU/25 g or ml of food samples. Tests on 60 food samples have shown a specificity value of 100% (95% confidence interval [CI], 82.83 to 100), a sensitivity of 97.22% (95% CI, 83.79 to 99.85%), and an accuracy of 98.33% (CI 95%, 83.41 to 99.91%). Results indicate that PNA-FISH performed as well as the traditional culture methods and can reduce the diagnosis time to 1 day.
Inhibiting Gene Expression with Peptide Nucleic Acid (PNA)−Peptide Conjugates That Target Chromosomal DNA†