How Can We Preserve The Antimicrobial Activity of Nasal Secretions?

Do nasal secretions have antibacterial effects?

A study in 1999 found that nasal fluid itself has the ability to kill bacteria. But the antibacterial strength varies between people, and depends on the type of bacteria. Some people's nasal fluid can gradually kill the bacteria already present in the nasal fluid, while other people's nasal fluid allows bacterial growth. Against added external bacteria, the nasal fluid is strongly antibacterial towards some mutant strains, but weaker against wild type strains. Staphylococcus aureus gets eliminated within 24 hours in nasal fluid. Diluting the nasal fluid reduces the antibacterial effects, indicating that concentration is key.

What proteins and peptides with antibacterial effects are present in nasal fluid?

The study found multiple proteins and peptides in nasal fluid that have antibacterial functions, such as lysozyme, lactoferrin, phospholipase A2, SLPI, defensins and statherin. Lysozyme and lactoferrin are the most abundant. Different people have varying types and amounts of these proteins, leading to differences in antibacterial activity of nasal fluid.

Is Staphylococcus aureus colonization related to nasal fluid antibacterial effects?

Among 24 subjects, 3 people's nasal fluid was permissive for Staphylococcus aureus growth, confirming them as S. aureus carriers. Their nasal fluid had insufficient antibacterial activity against their own strains. Adding nasal fluid from non-carriers restored the antibacterial effects against the indigenous bacteria. This suggests carriers lack certain active substances present in non-carriers. Insufficient antimicrobial activity of nasal fluid may be one of the reasons for S. aureus colonization.

Can lysozyme and lactoferrin reconstitute the antibacterial activity in heat-inactivated nasal fluid?

Although these two proteins are the major antibacterial proteins in nasal fluid, adding them to heat-inactivated nasal fluid did not restore antibacterial effects against Pseudomonas aeruginosa. This suggests that the antibacterial effects of nasal fluid result from the combined actions of multiple components, and even abundant lysozyme and lactoferrin are not the sole determining factors.

What does this mean for cystic fibrosis and other respiratory diseases?

The variability and instability of nasal fluid antibacterial activity, and the involvement of multiple proteins, allows us to better understand respiratory tract infections. Slowed clearance in cystic fibrosis patients gives bacteria time to adapt. Reduced fluid volume also decreases concentrations of antibacterial substances. Studying the immune mechanisms of nasal fluid can identify deficiencies leading to respiratory infections. Nasal fluid could serve as a model for the lower respiratory tract.

How to improve the protective antibacterial effects of nasal fluid?

Maintaining optimal protein concentrations and fluid volume may enhance antibacterial effects. Complementary effects between different people's nasal fluid may compensate for individual variability. Identifying key antibacterial proteins can provide ideas for targeted local therapies. Further illuminating nasal fluid's protective mechanisms can aid respiratory health.

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Reference

Cole AM, Dewan P, Ganz T. Innate antimicrobial activity of nasal secretions. Infect Immun. 1999 Jul;67(7):3267-75. doi: 10.1128/IAI.67.7.3267-3275.1999. PMID: 10377100; PMCID: PMC116505.