Bactericidal effects of silver plus titanium dioxide-coated endotracheal tubes on Pseudomonas aeruginosa and Staphylococcus aureus

Abstract

Purpose: Ventilator-associated pneumonia (VAP) is a nosocomial infection resulting in significant morbidity and mortality. Pseudomonas aeruginosa (P. aeruginosa) and Staphylococcus aureus (S. aureus) are pathogens associated with VAP. Silver (Ag) coating of endotracheal tubes (ETTs) reduces bacterial colonization, however titanium dioxide (TiO(2)) coating has not been studied.

Methods: Five types of ETT coatings were applied over silica layer: Ag, solgel TiO(2), solgel TiO(2) with Ag, Degussa P25 TiO(2) (Degussa TiO(2)), and Degussa TiO(2) with Ag. After ETTs were incubated with P. aeruginosa or S. aureus; colonization was determined quantitatively.

Results: Pseudomonas aeruginosa and S. aureus grew for 5 days on standard ETTs. Compared to standard ETTs, P. aeruginosa growth was significantly inhibited by solgel TiO(2) with Ag at 24 hours, and by Degussa TiO(2) with Ag at 24 and 48 hours after inoculation. No significant difference in S. aureus growth was observed between the control and any of the five coatings for 5 days.

Conclusion: In vitro, solgel TiO(2) with Ag and Degussa TiO(2) with Ag both attenuated P. aeruginosa growth, but demonstrated no effect on S. aureus colonization. Further studies using alternative coating and incorporating UV light exposure are needed to identify their potential utility in reducing VAP.

Keywords: Degussa titanium dioxide; quantitative culture; solgel titanium dioxide; ventilator-associated pneumonia.

Figure 1

Standard endotracheal tubes were coated with a passivating layer of colloidal silica and served as controls. Five types of coatings were applied over a silica layer; 1. solgel titanium dioxide without silver, 2. solgel titanium dioxide with silver, 3. Degussa titanium dioxide without silver, 4. Degussa titanium dioxide with silver and 5. silver only (not shown).

Figure 2

Characterization of P. aeruginosa growth on polyvinyl chloride endotracheal tubes over a 144-hour period. Comparison of standard and silver only coated endotracheal tubes. There was less P. aeruginosa growth on silver-coated endotracheal tubes at 24 hours (P < 0.01), but more growth at 120 hours (P = 0.04) and 144 hours (P = 0.06) compared to standard endotracheal tubes. Notes: Mean ± standard error of mean, *P < 0.05 compared to standard endotracheal tube. N = 4. Abbreviation: CFU, colony-forming units.

Figure 3

Characterization of P. aeruginosa growth on polyvinyl chloride endotracheal tubes coated with titanium dioxide over 144 hour period. Comparison of standard, solgel titanium dioxide and Degussa titanium dioxide endotracheal tubes. P. aeruginosa growth was not statistically significant at all time points. Notes: Mean ± standard error of mean, N = 4. Abbreviation: CFU, colony-forming units.

Figure 4

Characterization of P. aeruginosa growth on polyvinyl chloride endotracheal tubes coated with titanium dioxide with silver over a 144-hour period. Comparison of standard, solgel titanium dioxide with silver, and Degussa titanium dioxide with silver endotracheal tubes. P. aeruginosa growth was inhibited significantly by solgel titanium dioxide with silver at 24 hours and by Degussa titanium dioxide with silver at 24 and 48 hours, respectively. Notes: Mean ± standard error of mean; *P < 0.05 compared to standard endotracheal tube, # P < 0.05 compared to standard endotracheal tube. N = 4. Abbreviation: CFU, colony-forming units.

Figure 5

Characterization of S. aureus growth on polyvinyl chloride endotracheal tubes coated with silver only over a 144-hour period. Comparison of standard and silver only coated endotracheal tubes. There was no difference in S. aureus growth between standard and silver coated endotracheal tubes at any time point over 144 hours compared with standard endotracheal tubes. Note: N = 4. Abbreviation: CFU, colony-forming units.

Figure 6

Characterization of S. aureus growth on polyvinyl chloride endotracheal tubes coated with titanium dioxide only over a 144-hour period. Comparison of standard, solgel titanium dioxide and Degussa titanium dioxide endotracheal tubes. There was no difference in S. aureus growth in the titanium dioxide-coated groups compared to standard endotracheal tubes at any time point. Note: N = 4. Abbreviation: CFU, colony-forming units.

Figure 7

Characterization of S. aureus growth on polyvinyl chloride endotracheal tubes coated with titanium dioxide with silver over a 144-hour period. Comparison of standard, solgel titanium dioxide with silver and Degussa titanium dioxide with silver endotracheal tubes. There was no difference in S. aureus growth in the titanium dioxide with silver-coated groups compared to standard endotracheal tubes except at 144 hours with solgel titanium dioxide with silver endotracheal tubes. Note: N = 4. Abbreviation: CFU, colony-forming units.