It has been hypothesized that when individuals drink tea directly from plastic bottles, oral microorganisms may be transferred to the bottle surface and subsequently proliferate in the leftover tea. This study investigated the transfer of oral bacteria to the bottle mouth and their persistence in residual tea immediately after consumption and following 24 hours of incubation at 37 °C. Twelve healthy participants aged 19–23 years each consumed approximately 50 mL of unsweetened tea directly from a plastic bottle. Sterile cotton swabs were used to collect samples from the bottle mouths, while the remaining tea was analyzed using anaerobic culture and 16S rRNA gene sequencing, including metagenomic profiling. The mean bacterial counts at the bottle mouth were (1.8 ± 1.7) × 10⁴ CFU/mL immediately after drinking and (1.4 ± 1.5) × 10⁴ CFU/mL after 24 hours. In the residual tea, bacterial levels were (0.8 ± 1.6) × 10⁴ CFU/mL right after drinking and increased markedly to (2.5 ± 2.6) × 10⁶ CFU/mL after 24 hours. Streptococcus (59.9%) was the dominant genus detected at the bottle mouth immediately after consumption, with smaller proportions of Schaalia (5.5 percent), Gemella (5.5 percent), Actinomyces (4.9 percent), Cutibacterium (4.9 percent), and Veillonella (3.6 percent). Culture and metagenomic analyses revealed comparable bacterial profiles, highlighting Streptococcus (59.9 percent and 10.711 percent), Neisseria (1.6 percent and 24.245 percent), Haemophilus (0.6 percent and 15.658 percent), Gemella (5.5 percent and 0.381 percent), Cutibacterium (4.9 percent and 0.041 percent), Rothia (2.6 percent and 4.170 percent), Veillonella (3.6 percent and 1.130 percent), Actinomyces (4.9 percent and 0.406 percent), Prevotella (1.6 percent and 0.442 percent), Fusobacterium (1.0 percent and 0.461 percent), Capnocytophaga (0.3 percent and 0.028 percent), and Porphyromonas (1.0 percent and 0.060 percent), respectively. Streptococcus remained the predominant bacterial genus even after 24 hours of storage. Overall, the findings confirmed that oral bacteria were transferred to both the bottle mouth and the residual tea following direct consumption.
