Antimicrobial Peptides (AMPs) Are Not Increased in Asymptomatic Bacteriuria in Healthy Older Adult Patients

Antimicrobial peptides have demonstrated promise as biomarkers for urinary tract infection (UTI) in older adults (age ≥ 65 years). However, it is unknown if urinary AMP levels also increase in asymptomatic bacteriuria. Our objective was to determine if AMP levels vary between older adult patients with and without asymptomatic bacteriuria.

This was a preplanned secondary analysis of older adults enrolled in a cross-sectional study of patients presenting to a family medicine clinic for a non-acute visit and without urinary symptoms. Asymptomatic bacteriuria was considered present if a patient had a positive culture defined as (> 10,000) colony-forming units (CFUs) of a single organism. All other culture results were considered negative. Urinalysis results are presented based on the presence/absence of asymptomatic bacteriuria. Urinary levels of 4 AMPs (human neutrophil peptides 1-3 (HNP 1-3), human alpha-defensin-5 (HD-5), human beta-defensin-2 (hBD-2), and cathelicidin (LL-37)) are reported as median and interquartile range. The Wilcoxon Rank Sum test was used to compare the log-transformed AMP values between the groups.

The analytic cohort included 162 older adult patients; 18 (11%) had asymptomatic bacteriuria. Urinalysis results varied between asymptomatic older adult patients with positive asymptomatic bacteriuria and negative cultures, but AMP values did not differ (p > 0.2 for all four AMPs).

AMPs did not differ between asymptomatic older adult patients with positive and negative cultures in this secondary analysis. AMPs should be further studied as if they increase in older adults with symptomatic UTI, they may then be able to distinguish negative culture/asymptomatic bacteriuria from true infection where urinalysis cannot.