We describe rapid PCR-biprobe identification of Campylobacter spp.. This is based on real-time PCR with product analysis in the same system. The assay identifies enteropathogenic campylobacters to the species level on the basis of their degree of hybridization to three 16S ribosomal DNA (rDNA) biprobes. First-round symmetric PCR is performed with genus-specific primers which selectively target and amplify a portion of the 16S rRNA gene common to all Campylobacter species. Second-round asymmetric PCR is performed in a LightCycler in the presence of one of three biprobes; the identity of an amplified DNA-biprobe duplex is established after determination of the species-specific melting peak temperature. The biprobe specificities were determined by testing 37 reference strains of Campylobacter, Helicobacter, and Arcobacter spp. and 59 Penner serotype reference strains of Campylobacter jejuni and C. coli. From the combination of melting peak profiles for each probe, an identification scheme was devised which accurately detected the five taxa pathogenic for humans (C. jejuni/C. coli, C. lari, C. upsaliensis, C. hyointestinalis, and C. fetus), as well as C. helveticus and C. lanienae. The assay was evaluated with 110 blind-tested field isolates; when the code was broken their previous phenotypic species identification was confirmed in every case. The PCR-biprobe assay also identified campylobacters directly from fecal DNA. PCR-biprobe testing of stools from 38 diarrheic subjects was 100% concordant with PCR-enzyme-linked immunosorbent assay identification (13, 20) and thus more sensitive than phenotypic identification following microaerobic culture.

Biprobe identification assays based on real-time PCR were designed for 15 species of coagulase-negative staphylococci (CNS). Three sets of primers and four biprobes were designed from two variable regions of the 16S rRNA gene. An identification scheme was developed based on the pattern of melting peaks observed with the four biprobes that had been tested on 24 type strains. This scheme was then tested on 100 previously identified clinical isolates and 42 blindly tested isolates. For 125 of the 142 clinical isolates there was a perfect correlation between the biprobe identification and the result of the ID 32 Staph phenotypic tests and PCR. For 12 of the other isolates a 300-bp portion of the 16S rRNA gene was sequenced to determine identity. The remaining five isolates could not be fully identified. LightCycler real-time PCR allowed rapid and accurate identification of the important CNS implicated in infection.

A biprobe assay utilizing LightCycler technology was developed to detect rifampin resistance-associated gene mutations in the Mycobacterium tuberculosis rpoB gene. Three biprobes detected all mutations present in the 46 rifampin-resistant isolates. Wild-type sequences were correctly identified in each case. The method was reproducible, accurate, and easy to use.

The potential of incorporating a real-time PCR for amplification and detection of 16S rRNA gene signatures directly from clinical samples was assessed as a tool for diagnostics. Universal PCR primers spanning short variable regions (~500 bp) were optimized for real-time PCR and tested in comparison with a longer fragment (~1400 bp) generated from block-based amplification. Real-time PCR had improved sensitivity of detection (8 % increase), decreased amplification time and simplified downstream processing. The real-time PCR primers also offered an improvement in detection of bacteria from samples that demonstrated inhibition with the block-based primers and in the resolution of mixed-sequence traces. In addition to testing primer sensitivity, the effect of amplifying and sequencing two different variable regions of the 16S rRNA gene on organism identification was compared. By amplifying and sequencing a shorter variable region, the number of species that were identified to the species level was reduced by 18 %.

The acetan biosynthetic pathway in Acetobacter xylinum is an ideal model system for engineering novel bacterial polysaccharides. To genetically manipulate this pathway, an Acetobacter strain (CKES), more susceptible to gene-transfer methodologies, was developed. A new gene, aceP, involved in acetan biosynthesis was identified, sequenced and shown to have homology at the amino acid level with /?-D-glucosyl transferases from a number of different organisms. Disruption of aceP in strain CKE5 confirmed the function assigned above and was used to engineer a novel polysaccharide with a pentasaccharide repeat unit.