In vitro Study on the Antimicrobial Activity of Human Tears with Respect to Age

Lysozyme is present in tears and has the ability to inhibit bacterial growth. In addition, it acts as a physiological scavenger for harmful substances. In the present study, sixteen tear samples from people of different ages were evaluated for their antibacterial spectrum against selected bacterial strains (Escherichia coli, Shigella sonnei, Staphylococcus aureus, Salmonella enterica Typhi). A radial diffusion assay was used to evaluate the antibacterial potential of tear samples. To correlate the antibacterial activities of these tear samples, the concentration of lysozyme in the tear samples was also determined. Ampicillin was used as a standard drug. The zone of inhibition (mm) was used to measure the antibacterial property of the tears. All samples showed good antibacterial activities. The tear samples of children showed antibacterial activities in the range of 4.40~5.00 mm inhibition zones against the selected bacterial strains. The tear samples from the young and adults showed good antibacterial potential with a zone of inhibition in the range of 3.20~4.00 and 4.00~5.50 mm, respectively. The tear samples from the old age group showed inhibition zones from 1.50~5 mm. The adult tear samples showed the maximum inhibition against the selected bacterial strains among all groups. The lysozyme concentration was 1.7 mg/mL, 1.95 mg/mL, 2.13 mg/mL, and 1.76 mg/mL for children, young, adults, and elderly, respectively. In conclusion, the tears from adults have the high inhibition potential. In addition, this data also showed that the lysozyme contents in the tear sample increased with age until 40~42 years.