Bacteria Abundance Positively Correlates with Hand Dominance Independent of Time and Dependent on Physical Activity

Abstract

Human hands serve as vectors for the transmission of infectious diseases due to their continuous exposure to diverse biomes and their capacity to adapt by selection of spontaneous mutants. Hand hygiene, particularly routine washing, reduces transient microbial flora on both dominant and nondominant hands, limiting the spread of gram-positive and gram-negative pathogens. This study investigated bacterial distribution across dominant and nondominant hands concerning activity level and time of day. Samples were collected from 30 subjects at three intervals—morning, noon, and evening—and processed using a standardized six-step methodology: 1) nutrient agar preparation, 2) petri dish segmentation for bacterial isolation, 3) swab sampling from both hands, 4) 72-hour incubation at 25 °C, 5) colony quantification via ImageJ analysis, and 6) sterilization and Gram staining. Results indicated significantly higher bacterial counts on the dominant hand, with approximately 50% more colonies than the nondominant hand, independent of time of day. However, bacterial distribution across individual fingers was relatively uniform. Growth rate correlated strongly with subject activity rather than circadian variation. Additionally, dormant periods yielded reduced bacterial counts, reflecting the stable presence of resident skin flora. Most isolated bacterial colonies were gram-positive, attributed to limited exposure to enteric or contaminated environments necessary for gram-negative proliferation. These findings highlight the role of dominant-hand activity in microbial transmission and emphasize the necessity of rigorous hand hygiene practices. The implications of this study extend to clinical and food-handling settings, where preventing disease transmission to immune-compromised individuals and ensuring sanitization in food preparation are critical.