**4.3 Nucleic acid hybridization technologies in pathogen detection**

A general method of fluorescence in situ hybridization (FISH) using oligonucleotide probes of rRNA for nonmolecular technology. Probe lengths of 15 to 25 nucleotides labeled at the 5′ end were used for FISH. The specifically labeled cells were detected by an apparent fluorescence microscope. Rapid culture and independent detection of *Salmonella* were successfully performed using FISH combined with flow cytometry [48–50].

Line probe analysis (LIPA) is composed of oligonucleotide probes with specific oligonucleotides and nitrocellulose bands, which are connected by parallel lines along with the bands and discrete lines. The color change of hybridization results can be detected by vision. Innogenetics has produced several line probes for bacterial detection, such as *Escherichia coil*. The test results are consistent with those of antibiotics. Recently, 599 strains of *Escherichia coil* were improved and evaluated, and the sensitivity and specificity of the method were proved [51, 52].

Nielson et al. found a DNA analog called peptide nucleic acid (PNA) for detecting foodborne pathogens. This probe is more stable because PNA is not charged. In addition, PNA has a greater advantage in that it is relatively hydrophobic and easier to enter nonbacterial cells. PNA has higher specificity than DNA oligomer because the TM of the PNA probe is higher than that of its DNA probe. Theoretically, in addition to PNA and FISH, PNA can also replace DNA oligonucleotides to improve analytical performance [53, 54].
