The Science Journal of the American Association for Respiratory Care

2003 OPEN FORUM Abstracts

THE ANTIMICROBIAL EFFECT OF NITRIC OXIDE ON BACTERIAL PATHOGENS CAUSING PNEUMONIA IN THE ICU: A Pilot Study

McMullin B. RRT1, Miller C. RRT BA PhD(c)2, Roscoe D. MD2,3
1. Vancouver Hospital -UBC site, Vancouver, British Columbia, Canada
2. University of British Columbia, Vancouver, British Columbia, Canada
3. Vancouver Hospital-VGH site, Vancouver, British Columbia, Canada

BACKGROUND: Nosocomial pneumonia is the second most frequent nosocomial infection and the leading cause of death from infections acquired in the hospital.1 Recent studies have demonstrated that gaseous nitric oxide (gNO) is cidal to bacteria and that inhaled NO is beneficial to bacterial clearance.2,3

OBJECTIVE: Determine the antimicrobial effect of exogenous gNO in vitro against organisms from culture collections and ultimately pathogens derived from tracheal aspirates of mechanically ventilated (MV) patients suspected of having pneumonia in an intensive care unit (ICU).

METHOD: Prior to the testing of ICU patient isolates a pilot study was conducted using Pseudomonas aeruginosa (ATCC 27853) and Staphylococcus aureus (ATCC 25923). Using pure cultures, a 0.5 McFarland standard with 108 colony forming units (CFU) per ml was prepared and further diluted l:1000 with saline to 105 CFU per ml. Three mL was pipetted into each well of a six well plate, and placed in a specially designed incubator. The incubator had both a control chamber, in which the organism suspension was exposed to a constant flow of heated (37.4 ? 0.2o C) and humidified air (RH= 74.1 ? 5.1), and a test chamber, in which a constant flow of gNO at 200 parts per million (ppm) in air was added to the same temperature and humidified air as in the control chamber. Samples (0.1ml, 0.01ml, and 0.001ml) were drawn off at time intervals of 6, 12, 24, 48, 72 and 96 hours, were plated onto 5% sheep blood agar plates, and placed in a traditional incubator at 35o C for 24 hours. All tests were performed in duplicate. CFU per ml were visually counted to determine % kill. Clinical isolates were obtained from sputum samples from MV patients with suspected pneumonia in a multi-disciplinary ICU collected for diagnostic purposes. Pathogens were cultured and identified by routine laboratory methods and tested according to the above protocol.

RESULTS: Total kill (100%) of Staphylococcus aureus (ATCC 25923) and Pseudomonas aeruginosa (ATCC 27853) CFUs was noted between 6-12 hours of exposure to 200 ppm gNO as compared to the control arm. The control arm had 100% survival during the study interval when compared to the original inoculum.

CONCLUSION:
Gaseous NO is bactericidal on ATCC strains of Staphylococcus aureus and Pseudomonas aeruginosa suspended in saline. Testing of isolates from ICU patients is on-going. 1. Höffken G. Nosocomial pneumonia: the importance of a de-escalating strategy for antibiotic treatment of pneumonia in the ICU. Chest 2002: 122(6);2183-96. 2. Jean D. Beneficial effects of nitric oxide inhalation on pulmonary bacterial clearance. Crit Care Med 2002: 30(2): 442-7. 3. Webert KE. Effects of inhaled nitric oxide in a rat model of Pseudomonas aeruginosa pneumonia. Crit Care Med 2000: 28(7);2397-405. This study was sponsored in part by PulmoNOx Medical Inc.

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