Peptide nucleic acid (PNA)-deoxyribonucleic acid (DNA) oligomers and methods of using the PNA-DNA oligomers to detect and/or amplify a target nucleic acid in a sample are provided. The PNA-DNA oligomers of the invention are relatively insensitive to ionic concentration and many inhibitory proteins and, consequently, are particularly advantageous for direct use in environmental or challenging samples to detect nucleic acid, especially that of microorganisms, including food and water pathogens and/or bioterrorism agents. Methods are also provided for use of the PNA-DNA oligomers in applications including polymerase chain reaction, nucleic acid sequencing, mutation detection and as nucleic acid probes.