Salivary bacterial fingerprints in healthy adult individuals: A proof-of-concept study based on heat, dehydration, and antibiotic resistance

The human oral cavity harbors a diverse microbial ecosystem that plays a vital role in health. Although microbial fingerprints have been proposed for personal identification, limited attention has been given to the stability of salivary bacteria exhibiting resistance to heat, dehydration, and antibiotics. This study aimed to assess whether the salivary microbiota of healthy adults could serve as a reliable microbial fingerprint by focusing on the abundance and stress-resistance traits of bacterial isolates. In a cross-sectional, proof-of-concept study, saliva samples were collected from 28 healthy volunteers. Culturable bacteria were collected using standard techniques, focusing on strains that can survive heat and drying, and colony-forming units per milliliter (CFU/mL) were quantified. The identification and susceptibility testing were done using VITEK® MS and VITEK® 2 Compact. Six samples yielded no cultivable bacteria. The identified bacterial isolates (N=1452) belonged to the genera
Staphylococcus
and
Streptococcus
. These bacterial strains showed significant inter-individual variation based on microbial abundance and their resistance to heat, dehydration, and antibiotics. The results indicated that approximately 29.7% of the bacterial isolates were resistant to benzylpenicillin, 12% to vancomycin, and smaller percentages to other clinically relevant antibiotics (e.g., tetracycline, fluoroquinolones). In this work, no tigecycline- and linezolid-resistant bacteria strains were isolated. In this study, all dehydration-resistant
S. epidermidis
strains were found to be sensitive to vancomycin, while the heat-tolerant strains showed resistance. No resistance to any of the study’s antibiotics was observed in either dehydration-tolerant or dehydration-intolerant
S. oralis
strains. In contrast, some thermotolerant
S. salivarius
strains showed resistance to tetracycline and benzylpenicillin. Unlike previous fingerprinting studies that focused primarily on taxonomic profiles, the present study highlights the novelty of incorporating salivary microbial resistance traits, specifically tolerance to heat, dehydration, and antibiotics, as reliable identifiers of healthy individuals. Our findings indicate that specific bacterial strains, particularly those resistant to heat and dehydration stress, persist across individuals, differing in abundance and antibiotic response patterns. These collective features can distinguish individuals via salivary microbial profiling. Furthermore, identifying opportunistic bacterial pathogens with recorded resistance profiles suggests potential for early risk assessment and personalized antibiotic guidance. In conclusion, this study provides initial evidence that salivary bacterial fingerprints, defined by abundance and resistance, can differentiate healthy individuals. The employed methodology is simple, cost-effective, and scalable, laying the foundation for applications in forensic microbiology and personalized medicine. Larger, more diverse population studies are recommended for validation.