A complex of species has been associated with dental caries under the ecological hypothesis. This study aimed to develop a rapid, sensitive PCR-dipstick DNA chromatography assay that could be read by eye for multiplex and semiquantitative analysis of plaque bacteria. Parallel oligonucleotides were immobilized on a dipstick strip for multiplex analysis of target DNA sequences of the caries-associated bacteria,Streptococcus mutans,Streptococcus sobrinus,Scardovia wiggsiae,Actinomycesspecies, andVeillonella parvula. Streptavidin-coated blue-colored latex microspheres were to generate signal. Target DNA amplicons with an oligonucleotide-tagged terminus and a biotinylated terminus were coupled with latex beads through a streptavidin-biotin interaction and then hybridized with complementary oligonucleotides on the strip. The accumulation of captured latex beads on the test and control lines produced blue bands, enabling visual detection with the naked eye. The PCR-dipstick DNA chromatography detected quantities as low as 100 pg of DNA amplicons and demonstrated 10- to 1000-fold higher sensitivity than PCR-agarose gel electrophoresis, depending on the target bacterial species. Semiquantification of bacteria was performed by obtaining a series of chromatograms using serial 10-fold dilution of PCR-amplified DNA extracted from dental plaque samples. The assay time was less than 3 h. The semiquantification procedure revealed the relative amounts of each test species in dental plaque samples, indicating that this disposable device has great potential in analysis of microbial composition in the oral cavity and intestinal tract, as well as in point-of-care diagnosis of microbiota-associated diseases.

Postoperative pneumonia may occur when upper respiratory tract protective reflexes such as cough and/or swallowing reflexes are impaired; thus, silent aspiration of oral bacteria may be a causative factor in postoperative pneumonia. This study aimed to quantify and identify bacteria in intraoperative bronchial fluids and to evaluate the relationship between impairment of cough/swallowing reflexes and silent aspiration of oral bacteria in elderly patients. After obtaining informed consent, cough and swallowing reflexes were assessed using an ultrasonic nebulizer and a nasal catheter, respectively. Using a micro‐sampling probe, intraoperative bronchial fluids were collected from nine subjects with pulmonary carcinoma and cultured anaerobically on blood agar plates. After 7 days, CFUs were counted and isolated bacteria were identified by 16S rRNA gene sequencing. Four subjects (aged 71.0 ± 8.4 years) had impaired swallowing reflexes with normal cough reflexes, whereas five subjects (73.6 ± 6.5 years) had normal cough and swallowing reflexes. The bacterial counts (mean CFU ± SD) tended to be higher in intraoperative bronchial fluids of subjects with impaired swallowing reflexes ([5.1 ± 7.7] × 10⁵) than in those of subjects with normal reflexes ([1.2 ± 1.9] × 10⁵); however, this difference was not statistically significant. Predominant isolates from intraoperative bronchial fluids were Streptococcus (41.8%), Veillonella (11.4%), Gemella (8.9%), Porphyromonas (7.6%), Olsenella (6.3%) and Eikenella (6.3%). These findings indicate that intraoperative bronchial fluids contain bacteria, probably derived from the oral microbiota, and suggest that silent aspiration of oral bacteria occurs in elderly patients irrespective of impairment of swallowing reflex.