EFFECT OF THERAPEUTIC CONCENTRATIONS OF NITRIC-OXIDE ON BACTERIAL-GROWTH IN-VITRO

Objectives: Besides its vasodilative actions, nitric oxide (NO) is als o involved in host defense on a cellular level. We studied the antimic robial properties of NO in concentrations used with inhaled NO therapy for the treatment of pulmonary hypertension in neonates. Design: In v itro study of bacterial growth of five species, with and without NO ex posure. Setting: Level IV neonatal intensive care unit at a university children's hospital. Subjects: in vitro bacterial cultures. Intervent ions: We tested ten different strains of five bacterial species (Staph ylococcus aureus, Staphylococcus epidermidis, group B streptococcus [G BS/Streptococcus agalactiae], Escherichia coil, and Pseudomonas aerugi nosa), derived from the tracheal isolates of ventilated premature and term infants. Cultures were exposed to three different concentrations of NO (40, 80, and 120 parts per million [ppm]) and bacterial growth w as compared with the same strains incubated in ambient air for 24 hrs. After incubation (with or without NO), colony-forming units were coun ted. Measurements and Main Results: Bacterial growth of S. aureus, E. coil, and P. aeruginosa was not reduced with the NO concentrations app lied. The number of colony-forming units of S aureus increased at 80 p pm of NO. Growth of S. epidermidis and GBS was significantly affected at 120 ppm, resulting in decreased numbers of colony-forming units as compared with controls exposed to ambient air. Conclusions: We conclud e that NO has a selective bacteriostatic effect on some of those bacte ria most commonly cultured in tracheal specimens of premature infants and neonates. This effect appears to be dose-dependent and occurs in t he upper range of dosages used with inhaled NO therapy. However, in th e range of dosages applied in ongoing controlled trials of inhaled NO in neonates and premature infants (1 to 80 ppm), a bacteriostatic effe ct of NO is not to be expected.