The antimicrobial effect of heparin on common respiratory pathogens

AIM: The mucolytic, anticoagulative, anti-inflammatory and neo-angiogenic properties of inhaled heparin may benefit patients with burns and cystic fibrosis. We assessed the antibacterial effects of unfractionated heparin. METHODS: Stored clinical isolates of Acinetobacter baumannii (n =4), Candida albicans (n = 5), Haemophilus influenzae (n =5), Klebsiella pneumoniae (n =4), methicillin-resistant Staphylococcus aureus (n=3), Pseudomonas aeruginosa (n = 2), and Streptococcus pneumoniae (n = 7) were subcultured on horse blood agar, incubated at 35 degrees C overnight, then inoculated into trypticase soy broth to a density of 1 McFarland standard. Dilutions of unfractionated heparin (containing 250- 7500 U) and 100 microL of the 1.0 McFarland standard broth were incubated at 35 degrees C overnight in microtitre plates and then subcultured on horse blood agar using 1 microL standard loops. Colonies (representing viable organisms) were counted. RESULTS: Heparin produced dose-dependent growth inhibition of three of seven S. pneumoniae isolates (complete inhibition at 2500U dose per 200 microL) and one of five H. influenzae isolates (complete inhibition at 7500 U dose per 200 microL), but no inhibition of other isolates. CONCLUSIONS: Unfractionated heparin is unlikely to have antibacterial effects because of its unpredictable inhibition of growth of common respiratory pathogens.