Laboratory Research
Wounds are colonized frequently by heterogeneous microflora. 1,2 Pseudomonas aeruginosa (PA) and Staphylococcus aureus (SA) are two of the most isolated bacterial species from wounds, and both typically form highly organized biofilms.3 Nitric oxide (NO) is a short-lived, diatomic, lipophilic gas with antimicrobial activity. 4 Recently, NO and its derivatives have been shown to exhibit broad-spectrum antimicrobial activity against bacteria, viruses, and parasites. 5,6 Using Pseudomonas aeruginosa (military isolate PA09-010 and ATCC 27312) were combined with Methicillin Resistant Staphylococcus aureus MRSA USA300 to demonstrate the efficacy of the NO to reduce polymicrobial infected wounds.
Methods: Fifty-nine (59) deep partial-thickness wounds (10mm x 7mm x 0.5mm) were made with a specialized electrokeratome. Wounds were inoculated with MRSA USA300 in one animal combined with PA09-010 and with PA27312 in the other, then wounds were covered with polyurethane film dressings. After 48hours three wounds were recovered for baseline enumeration. The remaining wounds were randomly assigned to the following treatment: 1)Negative Control: Vehicle, 2)NO Formulation: High, 3)NO Formulation: Mid/Fast, 4)NO Formulation: Mid/Slow, 5)NO Formulation: Low/Fast and 6)NO Formulation: Low/Slow. Wounds were recovered for bacterial bioburden on day 7.
Results: All treatments reduced MRSA bacterial counts compared to baseline counts, however the bacterial counts either for PA09-010 and PA27312 were lowest compared to baseline counts. The largest difference in efficacy against two strains of bacteria was the NO Formulation: Low/Fast. This treatment reduced the MRSA USA300 bacteria down to 4.47±0.28 Log CFU/ml but only reduced the PA 09-010 bacteria down to 8.87±0.56 Log CFU/ml. Results showed that the same formulation NO Low/Fast, reduced less MRSA USA300 when was combined with PA27312. These studies demonstrate that NO formulations reduce the mixed microbial burden of multiple microorganisms. Interesting studies have been demonstrated that NO formulations have better efficacy against PA than MRSA.7 We have previously shown MRSA was significantly reduced when was inoculated together with PA09-10.8
Discussion: Simultaneous presence of mixed populations of bacteria in wounds may favor one species survival over the other.9 A better understanding of mechanisms of host-bacteria interactions, in single or mixed species biofilms, may lead to development of novel therapeutic approaches to treat wound infections.